BAB AKHIR KELAS XI IMMUN

Suatu sistem dalam tubuh yang memiliki peran utama dalam pertahanan diri ini disebut sistem pertahanan tubuh atau sistem imun.

Sistem ini terdiri atas struktur dan sel yang didistribusikan ke seluruh jaringan tubuh.
Fungsi utamanya adalah se-bagai pelindung dari serangan benda-benda asing yang masuk ke dalam tubuh.
Sementara ilmu yang mempelajari sistem imun atau kekebalan tubuh disebut immunologi.
Apabila sistem imun di dalam tubuh kita baik, tentu serangan penyakit dapat ditangkal sedini mungkin.

Sebaliknya, bila sistem imun tubuh kita lemah, kemungkinan terserang penyakit pun menjadi besar

Di dalam tubuh, sistem imun melawan berbagai penyerang asing atau antigen dengan garis pertahanan yang bertahap
Tahapan-nya dimulai dari garis pertahanan pertama seperti kulit, membran mukosa, sekresi dari kulit dan mukosa.
Garis pertahanan kedua de-ngan fagositosis oleh sel darah putih, protein antimikroba, dan respon peradangan.
Sementara garis pertahanan ketiga melalui limfosit yang menghasilkan antibodi.

Pengertian Antigen dan Antibodi

Tanpa kita sadari, sebenarnya di lingkungan sekitar terdapat banyak bibit penyakit yang dapat mengancam tubuh.
Ketika perta hanan tubuh lemah, dengan segera bibit penyakit akan menyerang.
Berbagai bibit penyakit tersebut dapat melayang di udara, larut dalam air, menempel pada tanah, meja, kursi bahkan buku dan pensil.
Bakteri, virus dan organisme sejenisnya adalah contoh bibit penyakit yang dapat menye-rang tubuh

Berbagai organisme dan substansi asing yang masuk ke dalam tubuh dinamakan antigen.

Antigen meliputi molekul yang dimiliki virus, bakteri, fungi, protozoa, dan cacing parasit.
Apabila antigen tersebut masuk ke dalam tubuh, secara otomatis tubuh meningkatkan sistem pertahanannya.
Peningkatan sistem pertahanan dilakukan untuk mela-wan serangan-serangan dari organisme dan substansi asing tersebut.
Caranya yakni dengan memproduksi suatu zat sejenis protein atau polisakarida.
Zat yang demikian dinamakan antibodi.
Pada umumnya, antibodi terletak dan melekat pada permukaan sel.
Namun, apabila tidak melekat, antibodi berada dalam darah dan dalam sekresi jaringan eksokrin
Awalnya, antibodi ditemukan pada serum darah, yakni cairan darah yang dipisahkan dari sel-selnya
Oleh karena itu, banyak penyakit yang dapat didiagnosis dengan keberadaan antibodi khusus dalam serum.
Ilmu yang mempelajari cara seperti ini dinamakan serologiyang merupakan cabang immunologi

Sistem imun

Sistem imun merupakan suatu sistem pertahanan atau kekebalan tubuh terhadap berbagai organisme merugikan yang masuk ke dalam tubuh.

· Sistem kekebalan tubuh manusia akan menyerang organisme merugikan seperti virus, bakteri, jamur, dan parasit yang masuk ke dalam organ tubuh.

· Selain itu, sistem kekebalan juga akan menyerang sel-sel kanker atau sel-sel abnormal yang berkembang di dalam tubuh.

· Sistem imun terdiri atas: sel-sel darah putih, sumsum tulang, limpa, timus, hati, kelenjar getah bening, dan pertahanan tubuh lainnya (seperti air mata, air liur, kulit, asam lambung, serta mukosa pada organ pernafasan).

Sel darah putih (leukosit) merupakan sel yang berfungsi untuk menghancurkan organisme berbahaya yang masuk ke dalam tubuh.

· Leukosit bersifat amuboid (dapat berubah bentuk), fagositosis (memakan), serta dapat keluar masuk jaringan. Leukosit terbagi menjadi granulosit (mengandung butir-butir pada sitoplasma) dan agranulosit (tidak mengandung butir-butir pada sitoplasma).

· Granulosit terdiri dari neutrofil, basofil, dan eusinofil.

· Agranulosit terdiri atas monosit dan limfosit.

Beberapa contoh sel darah putih antara lain:

Description: Macam-macam sel darah putih

1. Sel-T.

T berasal dari kata tymus.

· Sel-T termasuk dalam limfosit. Sel-T diproduksi oleh sel stem dalam sumsum tulang dan mengalami pematangan di timus.

· Sel-T berperan dalam imunitas seluler, yaitu pembentukan sel-sel kekebalan dalam jumlah besar untuk menghancurkan organisme berbahaya.

Sel-B.

B berasal dari kata bone marrow.

· Sel-B juga termasuk dalam limfosit. Sel-B diproduksi oleh sel stem dalam sumsum tulang.

· Sel-B berperan dalam imunitas humoral, yaitu dengan mengeluarkan antibodi.

· Sel-B yang matang ketika mendeteksi adanya organisme yang berbahaya bagi tubuh akan berubah menjadi sel plasma untuk mengeluarkan antibodi.

· Antibodi merupakan molekul kompleks yang berperan sebagai penanda organisme asing untuk segera dibasmi oleh sel-sel kekebalan.

Monosit.

· Monosit merupakan sel darah putih yang dapat berkembang menjadi makrofag sehingga dapat memakan antigen (organisme/benda yang dapat memacu terbentuknya antibodi).

· Makrofag dapat bergerak bebas dan sebagian lagi terkumpul dalam limpa, kelenjar getah bening, sumsum tulang belakang, paru-paru dan hati.

Neutrofil.

· Selnya memiliki inti lebih dari dua granul (butir). Neutrofil dapat mendeteksi antigen yang ada di dalam tubuh.

Eosinofil.

· Selnya memiliki inti berjumlah dua granul. Eosinofil juga berperan dalam menghancurkan parasit penginfeksi tubuh

Basofil.

· Selnya memiliki granul yang bervariasi. Basofil berperan membawa zat kimia seperti histamin dalam gejala alergi dan penarikan sel sel kekebalan ke daerah reaksi alergi.

· Sumsum tulang, limpa, timus, hati, kelenjar getah bening berfungsi membersihkan darah dan jaringan dari organisme berbahaya dan menyediakan lokasi dimana sel-sel kekebalan tubuh dapat diaktifkan

· Pertahanan lain seperti air mata, air liur, mukosa pada organ pernafasan, dan asam lambung memiliki zat antibiotik untuk membunuh organisme berbahaya.

· Kulit dapat mengeluarkan zat antibakteri untuk melindungi tubuh dari organisme asing yang menempel pada tubuh.

Alergi

· Alergi merupakan suatu reaksi berlebih dari sistem kekebalan tubuh seseorang terhadap zat asing yang tidak berbahaya seperti debu, bulu binatang, tepung sari, makanan, obat-obat tertentu, dan sebagainya.

· Zat asing penyebab alergi disebut alergen.

· Reaksi alergi dapat bermacam-macam mulai dari gatal-gatal, pembengkakan, pilek, dan penyempitan saluran pernafasan

Imunisasi

· Imunisasi merupakan pengebalan tubuh terhadap racun atau organisme penyebab penyakit.

· Salah satu bentuk imunisasi adalah pemberian vaksin.

· Vaksin adalah virus atau bakteri yang telah mati atau masih hidup namun telah dilemahkan.

· Tujuan pemberian vaksin yaitu supaya tubuh membentuk kekebalan terhadap virus atau bakteri penyebab penyakit tanpa menyebabkan terjangkitnya penyakit itu terlebih dahulu.

· Sistem kekebalan tubuh sangat penting untuk dalam menjaga tubuh kita dari serangan penyakit.

Untuk menjaga sistem kekebalan tubuh tetap dalam kondisi baik, kita perlu menerapkan gaya hidup sehat, berolah raga dengan teratur dan menyantap makanan yang bergizi, serta minum multivitamin jika perlu.

PILIHAN GANDA

1. Monosit dalam perkembangannya dapat berubah menjadi....
a. basofil
b. makrofag
c. antigen
d. eosinofil

2. Zat penyebab alergi disebut ...
a. alergen
b. antigen
c. antibodi
d. makrofag

3. Sel-T mengalami pematangan di ...
a. bursa
b. timus
c. sumsum tulang
d. hati

4. Sel-B berperan dalam imunitas ...
a. seluler
b. humoral
c. buatan
d. alami

5. Sel-T berperan dalam imunitas ...
a. seluler
b. humoral
c. buatan
d. alam

6. What are antigens?
A) proteins found in the blood that cause foreign blood cells to clump
B) proteins embedded in B cell membranes
C) proteins that consist of two light and two heavy polypeptide chains
D) foreign molecules that trigger the generation of antibodies
E) proteins released during an inflammatory response

7) Clonal selection implies that
A) brothers and sisters have similar immune responses.
B) antigens increase mitosis in specific lymphocytes.
C) only certain cells can produce interferon.
D) a B cell has multiple types of antigen receptors.
E) the body selects which antigens it will respond to.

8) In which of the following situations will helper T cells be activated?
A) when an antigen is displayed by a dendritic cell
B) when a cytotoxic T cell releases cytokines
C) when natural killer (NK) cells come in contact with a tumor cell
D) in the bone marrow during the self-tolerance test

9) A nonfunctional CD4 protein on a helper T cell would result in the helper T cell being unable to
A) respond to T-independent antigens.
B) lyse tumor cells.
C) stimulate a cytotoxic T cell.
D) interact with a class I MHC-antigen complex.
E) interact with a class II MHC-antigen complex.

10) Which of the following is a false statement about innate immunity?
A) They include inflammatory responses.
B) They include physical and chemical barriers.
C) They must be primed by the presence of antigen.
D) They may involve the formation of membrane attack complexes.
E) Macrophages and natural killer cells are participants in the process.

11) The clonal selection theory implies that
A) brothers and sisters have similar immune responses.
B) antigens activate specific lymphocytes.
C) only certain cells can produce interferon.
D) a B cell has multiple types of antigen receptors.
E) the body selects which antigens it will respond to.

12) The clonal selection theory is an explanation for how
A) a single type of stem cell can produce both red blood cells and white blood cells.
B) V gene and J gene segments are rearranged.
C) an antigen can provoke development of very few cells to result in production of high levels of specific antibodies.
D) HIV can disrupt the immune system.
E) macrophages can recognize specific T cells and B cells.

13) These cells are involved in cell-mediated immunity, and they respond to class I MHC molecule-antigen complexes.

A. cytotoxic T cells

14) Which of the following is (are) not involved in the activation and functioning of cytotoxic T cells?
A) interleukins
B) antigen-presenting cells
C) class I MHC molecules
D) T cell surface protein CD8
E) perforin

15) Which of the following is a pathway that would lead to the activation of cytotoxic T cells?
A) B cell contact antigen → helper T cell is activated → clonal selection occurs
B) body cell becomes infected with a virus → synthesis of new viral proteins → class I MHC molecule-antigen complex displayed on cell surface
C) self-tolerance of immune cells → B cells contact antigen → cytokines released
D) complement cells → B cell contacts antigen → helper T cell activated → cytokines released
E) cytotoxic T cells → class II MHC molecule-antigen complex displayed → cytokines released → cell lysis

16) Some viruses can undergo latency, the ability to remain inactive for some period of time. Which of the following is an example?
A) influenza, a particular strain of which returns every 10-20 years
B) herpes simplex viruses (oral or genital) whose reproduction is triggered by physiological or emotional stress in the host
C) Kaposiʹs sarcoma, which causes a skin cancer in people with AIDS, but rarely in those not infected by HIV
D) the virus that causes a form of the common cold, which recurs in patients many times in their lives
E) myasthenia gravis, an autoimmune disease that blocks muscle contraction from time to time

17) Major innate mechanism that mediates destruction of foreign substances in the body.

D) Complement

18) The mechanism of the "lethal hit" of cytotoxic T cells and NK cells involves a protein called
perforin.

19) Select the correct statement about the function of antibodies.

A) Complement fixation is the main mechanism by which antibodies provide protection.
B) Neutralization is the process by which antibodies cause invading cells to clump together.
C) The most potent agglutinating agent is IgG.
D) Antibodies may directly destroy "invaders."

20) Which of the following is not a mechanism for the development of autoimmune disorders?
A) mutation followed by the appearance of membrane proteins not previously present
B) a second exposure to an allergen
C) exposure of previously "hidden" self-antigens to the adaptive immune system
D) cross-reaction of antibodies formed against foreign antigens with self-antigens

21) Select the correct statement about complement.
A) An adaptive immune mechanism is often involved in directing complement to its target.
B) Complement can be activated through three pathways: classical, secondary, and alternate.
C) Complement proteins C1 through C9 act exclusively in the classical pathway.
D) The membrane attack complex consists of complement proteins C3a through C5.

22) What is the role of interferon in defense against disease?
A) protects cells that have not yet been infected by bacteria
B) activates the inflammatory process
C) protects cells that have not yet been infected by viruses
D) activates the complement mechanism

23) Which of the following is a characteristic of the early stages of local inflammation?
A) anaphylactic shock
B) fever
C) attack by cytotoxic T cells
D) release of histamine
E) antibody- and complement-mediated lysis of microbes

24) Which cells and which signaling molecules are responsible for initiating an inflammatory response?
A) phagocytes: lysozymes
B) phagocytes: chemokines
C) dendritic cells: interferons
D) mast cells: histamines
E) lymphocytes: interferons

25) Inflammatory responses may include which of the following?
A) clotting proteins migrating away from the site of infection
B) increased activity of phagocytes in an inflamed area
C) reduced permeability of blood vessels to conserve plasma
D) release of substances to decrease the blood supply to an inflamed area
E) inhibiting the release of white blood cells from bone marrow

26) Which of the following are symptoms of inflammation that might appear in such art?
A) heat, pain, and redness
B) pain and whitening of the surrounding tissue
C) swelling and pain
D) antibody producing cells
E) swelling, heat, redness, and pain

27) Inflammatory responses may include all of the following except
A) clotting proteins sealing off a localized area.
B) increased activity of phagocytes in an inflamed area.
C) reduced permeability of blood vessels to conserve plasma.
D) release of substances to increase the blood supply to an inflamed area.
E) increased release of white blood cells from bone marrow.

28) Each indication below is a clinical characteristic of inflammation except
A) decreased temperature.
B) edema.
C) redness.
D) pain.
E) increased blood flow.

29) Anaphylactic shock can result from an immediate hypersensitivity where the allergen enters the
blood.

TRUE

30) Which of the following would be classified as a delayed hypersensitivity reaction?
A) anaphylaxis
B) allergic contact dermatitis
C) cytotoxic hypersensitivity
D) immune complex hypersensitivity

31) Which of the following is true of immediate hypersensitivities?
A) They are are adaptive immune responses to disease organisms.
B) They include allergic contact dermatitis.
C) They are also called type IV hypersensitivities.
D) They involve IgE antibodies and the release of histamine from mast cells and basophils.

32) Which of the following is not a mechanism for the development of autoimmune disorders?
A) mutation followed by the appearance of membrane proteins not previously present
B) a second exposure to an allergen
C) exposure of previously "hidden" self-antigens to the adaptive immune system
D) cross-reaction of antibodies formed against foreign antigens with self-antigens

33) ________ is the most common type of immediate hypersensitivity.

Allergy

34) Which of the following is not a part of an antibody molecule?
A) the epitope
B) the constant or C regions
C) the variable or V regions
D) the light chains
E) the heavy chains

35) Why can normal immune responses be described as polyclonal?
A) Blood contains many different antibodies to many different antigens.
B) Construction of a hybridoma requires multiple types of cells.
C) Multiple immunoglobulins are produced from descendants of a single B cell.
D) Diverse antibodies are produced for different epitopes of a specific antigen.
E) Macrophages, T cells, and B cells all are involved in normal immune response.

36) An epitope associates with which part of an antibody?
A) the antibody-binding site
B) the heavy-chain constant regions only
C) the variable regions of a heavy chain and light chain combined
D) the light-chain constant regions only
E) the antibody tail

37) Which of the following could prevent the appearance of the symptoms of an allergy attack?
A) blocking the attachment of the IgE antibodies to the mast cells
B) blocking the antigenic determinants of the IgM antibodies
C) reducing the number of helper T cells in the body
D) A and B only
E) B and C only

39) What aspect of the immune response would a patient who has a parasitic worm infection and another patient responding to an allergen such as ragweed pollen have in common?
A) Both patients would have an increase in cytotoxic T cell number.
B) Both patients would suffer from anaphylactic shock.
C) Both patients would risk development of an autoimmune disease.
D) Both patients would be suffering from a decreased level of innate immunity.
E) Both patients would have increased levels of IgE.

40) What happens to people who receive flu vaccinations?
A) They develop active immunity to the flu.
B) They develop passive immunity to the flu.
C) They have immunity to smallpox infection.
D) They have an increased number of natural killer (NK) cells.
E) They develop a hypersensitive humoral immune response.

41) Naturally acquired passive immunity would involve the
A) injection of vaccine.
B) ingestion of interferon.
C) placental transfer of antibodies.
D) absorption of pathogens through mucous membranes.
E) injection of antibodies.

42) A major difference between active and passive immunity is that active immunity requires
A) acquisition and activation of antibodies.
B) proliferation of lymphocytes in bone marrow.
C) transfer of antibodies from the mother across the placenta.
D) direct exposure to a living or simulated pathogen.
E) secretion of interleukins from macrophages.

43) What would be the major concern for an individual with type A blood who receives a transfusion of type B blood?
A) the antibodies in the serum of the donor
B) the antibodies in the serum of the recipient
C) the anti-A antibodies produced by the donor
D) the production of memory cells that will occur in the recipient
E) antibodies in both the donor's and recipient's serum

44) A transfusion of type A blood given to a person who has type O blood would result in which of the following?
A) the recipient's B antigens reacting with the donated anti-B antibodies
B) the recipient's anti-A antibodies clumping the donated red blood cells
C) the recipient's anti-A and anti-O antibodies reacting with the donated red blood cells if the donor was a heterozygote (Ai) for blood type
D) no reaction because type O is a universal donor
E) no reaction because the O-type individual does not have antibodies

45) If a newborn were accidentally given a drug that destroyed the thymus, what would most likely happen?
A) His cells would lack class I MHC molecules on their surface.
B) His immune system would not function.
C) Genetic rearrangement of antigen receptors would not occur.
D) His T cells would not undergo the test of self-tolerance.
E) His B cells would be reduced in number.

46) Select the correct statement about the prevention of immune attack on "self."
A) Neutrophils capable of binding to self-antigens are chemically inactivated.
B) The development of tolerance is specific to B cells only.
C) Tolerance is developed during fetal life.
D) Tolerance to self is due to the action of foreign antigens that inactivate the immune response
to one's own tissues.

47) The clonal selection theory is an explanation for how
A) a single type of stem cell can produce both red blood cells and white blood cells.
B) V gene and J gene segments are rearranged.
C) an antigen can provoke development of very few cells to result in production of high levels of specific antibodies.
D) HIV can disrupt the immune system.
E) macrophages can recognize specific T cells and B cells.

48) Which choice could be used as an analogy to describe how HIV affects the body?
A) bypassing a light switch so that electricity is constantly flowing to a light
B) rebooting a computer after getting a program error message
C) snipping the wires coming from a car battery so that no electricity flows to the car components
D) an elevator stopping at the floor for which the button has been pushed
E) changing the color of your house to match the color of your car

49) The genetic material of HIV consists of
A) single-stranded DNA.
B) single-stranded RNA.
C) double-stranded DNA.
D) double-stranded RNA.
E) none of the above

50) Double-stranded viral DNA is incorporated into a host cell as a
A) promoter.
B) provirus.
C) transposon.
D) lac.
E) homeobox.

51) HIV targets include all of the following except
A) macrophages.
B) cytotoxic T cells.
C) helper T cells.
D) cells bearing CD4 and fusin.
E) brain cells.

52) Which of the following molecules is incorrectly paired with a source?
A) lysozyme—tears
B) interferons—virus-infected cells
C) antibodies—B cells
D) chemokines—cytotoxic T cells
E) cytokines—helper T cells

53) The MHC is important in
A) distinguishing self from nonself.
B) recognizing parasitic pathogens.
C) identifying bacterial pathogens.
D) identifying cancer cells.
E) both A and D

54) A person with AIDS would be unlikely to suffer from which of the following diseases?
A) cancer
B) rheumatoid arthritis
C) hepatitis
D) tuberculosis
E) influenza

55) A person exposed to a new cold virus would not feel better for one to two weeks because
A) specific B cells and T cells must be selected prior to a protective response.
B) it takes up to two weeks to stimulate immunologic memory cells.
C) phagocytic cells must first be activated by the complement system.
D) antigen receptors are not the same.
E) V-J gene rearrangement must occur prior to a response.

56) The process whereby neutrophils and other white blood cells are attracted to an inflammatory site
is called ________.
A) margination
B) chemotaxis
C) diapedesis
D) phagocytosis

57) Which of the following is the correct sequence of events in phagocytosis?
A) chemotaxis, ingestion, digestion, adherence, killing
B) adherence, digestion, killing, ingestion, chemotaxis
C) chemotaxis, adherence, ingestion, digestion, killing
D) ingestion, adherence, chemotaxis, digestion, killing

58) Which of the following is a part of the second line of defense against microorganisms?
A) phagocytes
B) gastric juice
C) keratin
D) cilia

59) Complement proteins and antibodies coat a microorganism and provide binding sites, enabling
macrophages and neutrophils to phagocytize the organism. This phenomenon is termed ________.
A) diapedesis
B) opsonization
C) agglutination
D) chemotaxis

60) Innate immune system defenses include ________.
A) plasma cells
B) B cells
C) T cells
D) phagocytosis

61) Phagocyte mobilization involves ________.
A) diapedesis, during which cells line up against the capillary wall
B) monocytes as the most active phagocyte
C) mainly neutrophil and macrophage migration into inflamed areas
D) margination, which is the process of white cell movement through the walls of capillaries into
injured tissues

62 Natural killer (NK) cells ________.
A) can kill cancer cells before the immune system is activated
B) are also called cytotoxic T cells
C) are cells of the adaptive immune system
D) are a type of phagocyte

63) Which of the following is not a method by which antibodies work?
A) agglutinating and precipitating antigen B) neutralizing antigen
C) activating cytokines D) enhancing phagocytosis

64) Cellular ingestion and destruction of particulate matter is called phagocytosis.

TRUE

65) Fever ________.
A) production is regulated by chemicals that reset the body's thermostat to a higher setting
B) causes the liver to release large amounts of iron, which seems to inhibit bacterial replication
C) decreases the metabolic rate of the body to conserve energy
D) is a higher-than-normal body temperature that is always dangerous

66) Fever is seldom beneficial because it speeds up the cellular metabolic rate and will not allow
antigen-antibody reactions to occur.

FALSE

14) What is the single most important event establishing a primary immune response?
A) the presentation of viral protein complexed to class I MHC
B) the lyses of virally infected cells by cytotoxic T cells
C) the phagocytosis of microbes by antigen-presenting cells
D) the recognition of self versus foreign
E) apoptosis of virally infected cells

24) Which of the following cell types are responsible for initiating a secondary immune response?
A) memory cells
B) macrophages
C) stem cells
D) B cells
E) T cells

89) The primary immune response ________.
A) occurs when memory cells are stimulated
B) has a lag period while B cells proliferate and differentiate into plasma cells
C) is another name for immunological memory
D) occurs more rapidly and is stronger than the secondary response

94) Select the correct statement about complement.
A) An adaptive immune mechanism is often involved in directing complement to its target.
B) Complement can be activated through three pathways: classical, secondary, and alternate.
C) Complement proteins C1 through C9 act exclusively in the classical pathway.
D) The membrane attack complex consists of complement proteins C3a through C5.

21) Main antibody of both primary and
secondary immune response.

IgG

14) Innate defense system.

Inflammatory response and skin and
mucous membranes

Major innate mechanism that mediates
destruction of foreign substances in
the body.

Complement

74) Innate immune system defenses include ________.
A) plasma cells B) B cells C) T cells D) phagocytosis

80) Select the correct statement about active and passive immunity.
A) Immunological memory is established by passive immunization.
B) Active and passive humoral immunity are both mechanisms of adaptive immunity that use
antibodies.
C) A vaccination is an example of the introduction of passive immunity into the body.
D) The antibodies utilized in active immunity are acquired from another organism.

39) Which cell type interacts with both the humoral and cell-mediated immune pathways?
A) plasma cells
B) cytotoxic T cells
C) natural killer cells
D) CD8 cells
E) helper T cells

51) Which of the following statements about humoral immunity is correct?
A) It primarily defends against fungi and protozoa.
B) It is responsible for transplant tissue rejection.
C) It protects the body against cells that become cancerous.
D) It is mounted by lymphocytes that have matured in the bone marrow.
E) It primarily defends against bacteria and viruses that have already infected cells.

81) Which of the following is not true about helper T cells?
A) They function in both cell-mediated and humoral immune responses.
B) They recognize polysaccharide fragments presented by class II MHC molecules.
C) They bear surface CD4 molecules.
D) They are subject to infection by HIV.
E) When activated, they secrete cytokines.

33) A given pathogen will provoke either a cell-mediated response or an antibody-mediated response
but not both.

FALSE

57) Which of the following does not respond to cell-mediated immunity?
A) foreign tissue transplants
B) some cancer cells
C) pathogens in the CNS
D) intracellular pathogens that reside within host cells

54) Small molecules that bind with self-proteins to produce antigenic substances are called ________.
A) reagins B) antibodies C) haptens D) ions

61) Regulatory T cells ________.
A) may function in preventing autoimmune reactions
B) decrease their activity as antigenic stimulus decreases
C) release cytokines that increase the activity of cytotoxic T cells and activated B cells
D) are the most thoroughly understood T cells

63) Which of the statements below does not describe antigens?
A) Antigens can include proteins, nucleic acids, lipoproteins, glycoproteins, and certain large
polysaccharides.
B) Antigens exhibit immunogenicity and reactivity.
C) The parts of antigen molecules that initiate immune responses are called epitopes or antigenic
determinants.
D) Antigens only come from microbes.

87) Select the correct statement about antigens.
A) One antigen may have many different antigenic determinants and may therefore cause the
formation of more than one antibody.
B) "Self-antigens" is another name for incomplete antigens.
C) Only small antigens exhibit reactivity.
D) The largest type of antigen is called a hapten.

35) Monoclonal antibodies can be specific for several antigenic determinants.

FALSE

46) Which of the following is not a type of T cell?
A) regulatory B) cytotoxic C) antigenic D) helper

47) Antibodies of the different classes IgM, IgG, IgA, IgD, and IgE differ from each other in the
A) way they are produced.
B) way they interact with the antigen.
C) type of cell that produces them.
D) antigenic determinants that they recognize.
E) number of carbohydrate subunits they have.

55) Jenner successfully used cowpox virus as a vaccine against the virus that causes smallpox. Why was he successful even though he used viruses of different kinds?
A) The immune system responds nonspecifically to antigens.
B) The cowpox virus made antibodies in response to the presence of smallpox.
C) Cowpox and smallpox are antibodies with similar immunizing properties.
D) There are some antigenic determinants common to both pox viruses.
E) All of the above are true.

38) The following events occur when a mammalian immune system first encounters a pathogen. Place them in correct sequence and then choose the answer that indicates that sequence.
I. Pathogen is destroyed.
II. Lymphocytes secrete antibodies.
III. Antigenic determinants from pathogen bind to antigen receptors on lymphocytes.
IV. Lymphocytes specific to antigenic determinants from pathogen become numerous.
V. Only memory cells remain.
A) I, III, II, IV, V
B) III, II, I, V, IV
C) II, I, IV, III, V
D) IV, II, III, I, V
E) III, IV, II, I, V

71) Some pathogens can undergo rapid changes resulting in antigenic variation. Which of the following is such a
pathogen?
A) the influenza virus, which expresses alternative envelope proteins
B) the strep bacteria, which can be communicated from patient to patient with high efficiency
C) human papilloma virus, that can remain latent for several years
D) the causative agent of an autoimmune disease such as rheumatoid arthritis
E) multiple sclerosis, that attacks the myelinated cells of the nervous system

50) What is the primary function of humoral immunity?
A) It primarily defends against fungi and protozoa.
B) It is responsible for transplant tissue rejection.
C) It protects the body against cells that become cancerous.
D) It produces antibodies that circulate in body fluids.
E) It primarily defends against bacteria and viruses that have already infected cells.

17) If a newborn were accidentally given a drug that destroyed the thymus, what would most likely happen?
A) His cells would lack class I MHC molecules on their surface.
B) His humoral immunity would be missing.
C) Genetic rearrangement of antigen receptors would not occur.
D) His T cells would not mature and differentiate appropriately.
E) His B cells would be reduced in number and antibodies would not form.

58) The number of MHC protein combinations possible in a given population is enormous. However, an individual
in that population has only a couple of MHC possibilities. Why?
A) The MHC proteins are made from several different gene regions that are capable of rearranging in a
number of ways.
B) MHC proteins from one individual can only be of class I or class II.
C) Each of the MHC genes has a large number of alleles, but each individual only inherits 2 for each gene.
D) Once a B cell has matured in the bone marrow, it is limited to two MHC response categories.
E) Once a T cell has matured in the thymus, it can only respond to two MHC categories.

59) A bone marrow transplant may not be appropriate from a given donor (Jane) to a given recipient (Janeʹs cousin
Bob), even though Jane has previously given blood for one of Bobʹs needed transfusions. Which of the
following might account for this?
A) Janeʹs blood type is a match to Bobʹs but her MHC proteins are not.
B) A blood type match is less stringent than a match required for transplant because blood is more tolerant
of change.
C) For each gene, there is only one blood allele but many tissue alleles.
D) Janeʹs class II genes are not expressed in bone marrow.
E) Bobʹs immune response has been made inadequate before he receives the transplant.

64) An immune response to a tissue graft will differ from an immune response to a bacterium because
A) MHC molecules of the donor may stimulate rejection of the graft tissue.
B) the tissue graft, unlike the bacterium, is isolated from the circulation and will not enter into an immune
response.
C) a response to the graft will involve T cells and a response to the bacterium will not.
D) a bacterium cannot escape the immune system by replicating inside normal body cells.
E) the graft will stimulate an autoimmune response in the recipient.

4) Which of the following is not true about helper T cells?
A) They function in cell-mediated and humoral responses.
B) They recognize polysaccharide fragments presented by class II MHC molecules.
C) They bear surface CD4 molecules.
D) They are subject to infection by HIV.
E) When activated, they secrete cytokines.

26) The MHC is important in a T cellʹs ability to
A) distinguish self from nonself.
B) recognize specific parasitic pathogens.
C) identify specific bacterial pathogens.
D) identify specific viruses.
E) recognize differences among types of cancer.

33) The EBV antigen fragments will be presented by the virus-infected cells along with which of the following?
A) complement
B) antibodies
C) class I MHC molecules
D) class II MHC molecules
E) Dendritic cells

35) These cells are involved in cell-mediated immunity, and they respond to class I MHC molecule-antigen
complexes:
A) cytotoxic T cells
B) natural killer cells
C) helper T cells
D) macrophages
E) B cells

37) Which of the following is a pathway that would lead to the activation of cytotoxic T cells?
A) B cell contact antigen → helper T cell is activated → clonal selection occurs
B) body cell becomes infected with a virus → new viral proteins appear → class I MHC molecule-antigen
complex displayed on cell surface
C) self-tolerance of immune cells → B cells contact antigen → cytokines released
D) complement is secreted → B cell contacts antigen → helper T cell activated → cytokines released
E) cytotoxic T cells → class II MHC molecule-antigen complex displayed → cytokines released → cell lysis

42) A nonfunctional CD4 protein on a helper T cell would result in the helper T cell being unable to
A) respond to T-independent antigens.
B) lyse tumor cells.
C) stimulate a cytotoxic T cell.
D) interact with a class I MHC-antigen complex.
E) interact with a class II MHC-antigen complex.

48) When antibodies attack antigens, clumping of the affected cells generally occurs. This is best explained by
A) the shape of the antibody with at least two binding regions.
B) disulfide bridges between the antigens.
C) complement that makes the affected cells sticky.
D) bonds between class I and class II MHC molecules.
E) denaturation of the antibodies.

52) Which of the following statements regarding NK cells is a false or incorrect statement?
A) NK cells attack cancer cells and virus-infected body cells.
B) NK cells attack cells that display abnormal MHC antigens.
C) NK cells are a type of neutrophil.
D) NK cells are present in the blood, spleen, lymph nodes, and red bone marrow.

75) Which of the following statements is incorrect or false?
A) MHC proteins are the cell's identity markers.
B) Class II MHC molecules appear only on the surface of antigen-presenting cells, thymic cells,
and T cells that have been activated by exposure to antigens.
C) Haptens lack immunogenicity unless attached to protein carriers.
D) Class 1 MHC molecules are built into the plasma membranes of all body cells.

81) Cytotoxic T cells ________.
A) function mainly to stimulate the proliferation of other T cell populations
B) self-destruct once the antigen has been neutralized
C) require the double recognition signal of I MHC plus II MHC on the target cell in order to
function
D) are the only T cells that can directly attack and kill other cells

97) Which statement is true about T cells?
A) Once activated, they cannot secrete cytokines.
B) They usually directly recognize antigens, which then activates a subpopulation of killer cells.
C) They will develop into cytotoxic T cells if antigen is complexed with class II MHC proteins.
D) Their proliferation is enhanced by interleukins 1 and 2.

68) Graft rejection may be caused by ________.
A) total body irradiation B) use of immunosuppressive drugs
C) using a xenograft D) treatment with antilymphocyte serum

7) All of the following represent adaptations by terrestrial animals to drying conditions except
A) anhydrobiosis.
B) salt glands.
C) efficient kidneys.
D) impervious surfaces.
E) increased thirst.

29) The osmoregulatory/excretory system of a freshwater flatworm is based on the operation of
A) protonephridia.
B) metanephridia.
C) Malpighian tubules.
D) nephrons.
E) ananephredia.

31) The osmoregulatory process called secretion refers to the
A) formation of filtrate at an excretory structure.
B) reabsorption of nutrients from a filtrate.
C) selective elimination of excess ions and toxins from body fluids.
D) formation of an osmotic gradient along an excretory structure.
E) expulsion of urine from the body.

33) The osmoregulatory/excretory system of an insect is based on the operation of
A) protonephridia.
B) metanephridia.
C) Malpighian tubules.
D) nephrons.
E) ananephredia.

57) Osmoregulatory adjustment via the renin-angiotensin-aldosterone system can be triggered by
A) sleeping for one hour.
B) severe sweating on a hot day.
C) eating a bag of potato chips.
D) eating a pizza with olives and pepperoni.
E) drinking several glasses of water.

59) ADH and RAAS work together in maintaining osmoregulatory homeostasis through which of the following ways?
A) ADH regulates the osmolarity of the blood and RAAS regulates the volume of the blood.
B) ADH regulates the osmolarity of the blood by altering renal reabsorption of water, and RAAS maintains the osmolarity of the blood by stimulating Na+ reabsorption.
C) ADH and RAAS work antagonistically; ADH stimulates water reabsorption during dehydration and RAAS causes increased excretion of water when it is in excess in body fluids.
D) both stimulate the adrenal gland to secrete aldosterone, which increases both blood volume and pressure via its receptors in the urinary bladder.
E) by combining at the receptor sites of proximal tubule cells, where reabsorption of essential nutrients takes place.

32) The osmoregulatory/excretory system of an earthworm is based on the operation of
A) protonephridia.
B) metanephridia.
C) Malpighian tubules.
D) nephrons.
E) ananephredia.

84) The regulation of sodium ________.
A) is due to specific sodium receptors in the hypothalamus
B) involves aldosterone, a hormone that increases sodium excretion in the kidneys
C) is linked to blood pressure
D) involves hypothalamic osmoreceptor detection of ion concentration

67) The high osmolarity of the renal medulla is maintained by all of the following except
A) diffusion of salt from the thin segment of the ascending limb of the loop of Henle.
B) active transport of salt from the upper region of the ascending limb.
C) the spatial arrangement of juxtamedullary nephrons.
D) diffusion of urea from the collecting duct.
E) diffusion of salt from the descending limb of the loop of Henle.

5) The fluid with the highest osmolarity is
A) distilled water.
B) plasma in birds.
C) plasma in mammals.
D) seawater in a tidal pool.
E) estuarine water.

10) Unlike most bony fishes, sharks maintain body fluids that are isoosmotic to seawater, so they are considered by many to be osmoconformers. Nonetheless, these sharks osmoregulate at least partially by
A) using their gills and kidneys to rid themselves of sea salts.
B) monitoring dehydration at the cellular level with special gated aquaporins.
C) tolerating high urea concentrations that balance internal salt concentrations to seawater osmolarity.
D) synthesizing trimethylamine oxide, a chemical that binds and precipitates salts inside cells.
E) possessing a special adaptation that allows their cells to operate at an extraordinarily high salt concentration.

44) The osmolarity of human urine
A) can be four times as great as normal osmolarity of human plasma.
B) is always exactly equal to plasma osmolarity.
C) is always less than plasma osmolarity.
D) is always greater than plasma osmolarity.
E) is determined primarily by the concentration of glucose.

46) Low selectivity of solute movement is a characteristic of
A) salt pumping to control osmolarity.
B) H+ pumping to control pH.
C) reabsorption mechanisms along the proximal tubule.
D) filtration from the glomerular capillaries.
E) secretion along the distal tubule.

51) The typical osmolarity of human blood is
A) 30 mosm/L.
B) 100 mosm/L.
C) 200 mosm/L.
D) 300 mosm/L.
E) 500 mosm/L.

54) Increased ADH secretion is likely after
A) drinking lots of pure water.
B) sweating-induced dehydration increases plasma osmolarity.
C) ingestion of ethanol (drinking alcoholic drinks).
D) eating a small sugary snack.
E) blood pressure is abnormally high.

38) Which of the following processes of osmoregulation by the kidney is the least selective?
A) salt pumping to control osmolarity
B) H+ pumping to control pH
C) reabsorption
D) filtration
E) secretion

42) A toxin that specifically blocks active transport in the loop of Henle might result in which of the following?
A) a decrease in the interstitial concentration of NaCl
B) a decrease in the filtrate concentration ability of the kidney
C) an increase in the amount of interstitial urea to maintain interstitial osmolarity
D) A and C only
E) A, B and C

56) Which of the following is not a normal response to increased blood osmolarity in humans?
A) increased permeability of the collecting duct to water
B) increased thirst
C) release of ADH by the pituitary gland
D) production of more dilute urine
E) reduced urine production

57) The high osmolarity of the renal medulla is maintained by all of the following except
A) diffusion of salt from the ascending limb of the loop of Henle.
B) active transport of salt from the upper region of the ascending limb.
C) the spatial arrangement of juxtamedullary nephrons.
D) diffusion of urea from the collecting duct.
E) diffusion of salt from the descending limb of the loop of Henle.

59) The body fluids of freshwater crustaceans generally have a lower osmolarity than the body fluids of their nearest marine crustacean relatives. Which of the following is a benefit of reduced osmolarity of body fluids in freshwater crustaceans?
A) an increase in the rate of water flow into the body fluids
B) a decrease in the rate of water loss to the surrounding environment
C) a reduction in energy expenditures for osmoregulation
D) an increase in the rate of salt loss to the surrounding environment
E) a decrease in the rate of salt gain from the environment

58) Select the pair in which the nitrogenous waste is incorrectly matched with the benefit of its excretion.
A) urea—low toxicity relative to ammonia
B) uric acid—can be stored as a precipitate
C) ammonia—very soluble in water
D) uric acid—minimal loss of water when excreted
E) urea—very insoluble in water

62) African lungfish, which are often found in small stagnant pools of fresh water, produce urea as a nitrogenous waste. What is the advantage of this adaptation?
A) Urea takes less energy to synthesize then ammonia.
B) Small stagnant pools do not provide enough water to dilute the toxic ammonia.
C) The highly toxic urea makes the pool uninhabitable to potential competitors.
D) Urea forms a precipitate and does not accumulate in the surrounding water.
E) A buildup of urea in the blood makes a lungfish hypoosmotic to its environment.

11) Which of the following is true of urea? It is
A) insoluble in water.
B) more toxic to human cells than ammonia.
C) the primary nitrogenous waste product of humans.
D) the primary nitrogenous waste product of most birds.
E) the primary nitrogenous waste product of most aquatic invertebrates.

12) Which of the following is true of ammonia?
A) It is soluble in water.
B) It can be stored as a precipitate.
C) It has low toxicity relative to urea.
D) Only A and C are true.
E) A, B, and C are true.

14) The advantage of excreting wastes as urea rather than as ammonia is that
A) urea can be exchanged for Na+.
B) urea is less toxic than ammonia.
C) urea requires more water for excretion than ammonia.
D) urea does not affect the osmolar gradient.
E) less nitrogen is removed from the body.

30) What substance is secreted by the proximal-tubule cells and prevents the pH of urine from becoming too acidic?
A) bicarbonate
B) salt
C) glucose
D) ammonia
E) HCl

15) Ammonia is likely to be the primary nitrogenous waste in living conditions that include
A) lots of fresh water flowing across the gills of a fish.
B) lots of seawater, such as a bird living in a marine environment.
C) lots of seawater, such as a marine mammal (e.g., a polar bear).
D) a terrestrial environment, such as that supporting crickets.
E) a moist system of burrows, such as those of naked mole rats.

16) Among vertebrate animals, urea
A) is made in the kidneys and immediately excreted.
B) is added to the air in the lungs to be exhaled, along with carbon dioxide.
C) is made in the liver by combining two ammonia molecules with one carbon dioxide.
D) is made in the pancreas and added to the intestinal contents, along with bile salts, for excretion.
E) is rarely the nitrogenous waste of choice.

39) A person with alkalosis will likely excrete urine that has abnormally high levels of
A) bicarbonate ions.
B) sodium ions.
C) glucose.
D) ammonia.
E) NaOH.

49) Processing of filtrate in the proximal and distal tubules
A) achieves the sorting of plasma proteins according to size.
B) achieves the conversion of toxic ammonia to less toxic urea.
C) maintains homeostasis of pH in body fluids.
D) regulates the speed of blood flow through the nephrons.
E) reabsorbs urea to maintain osmotic balance.

63) The juxtaglomerular apparatus is responsible for ________.
A) regulating the rate of filtrate formation and controlling systemic blood pressure
B) the secretion of drugs
C) the secretion of acids and ammonia
D) reabsorption of organic molecules, vitamins, and water

95) Which of the choices below does not describe the importance of tubular secretion?
A) disposing of substances not already in the filtrate, such as certain drugs
B) eliminating undesirable substances such as urea and uric acid that have been reabsorbed by
passive processes
C) ridding the body of excessive potassium ions
D) ridding the body of bicarbonate ions

97) What is the function of the juxtaglomerular apparatus?
A) help regulate urea absorption by the kidneys
B) help regulate blood pressure and the rate of blood filtration by the kidneys
C) help regulate water and electrolyte excretion by the kidneys
D) help regulate blood pressure and the rate of excretion by the kidneys

37) Urea is reabsorbed in the loop of Henle.

FALSE

44) The macula densa cells are chemoreceptors that respond to changes in the urea content of the
filtrate.

FALSE

58) The descending limb of the loop of Henle ________.
A) is freely permeable to sodium and urea
B) is not permeable to water
C) pulls water by osmosis into the lumen of the tubule
D) contains fluid that becomes more concentrated as it moves down into the medulla

14) Which nitrogenous waste has the greatest number of nitrogen atoms?
A) ammonia
B) ammonium ions
C) urea
D) uric acid

17) The nitrogenous waste that requires the most energy to produce is
A) ammonia.
B) ammonium.
C) urea.
D) uric acid.

18) Excessive formation of uric acid crystals in humans leads to
A) a condition called diabetes, where excessive urine formation occurs.
B) a condition of insatiable thirst and excessive urine formation.
C) gout, a painful inflammatory disease that primarily affects the joints.
D) the absence of urea in the urine.
E) osteoarthritis, an inevitable consequence of aging

21) The primary nitrogenous waste excreted by birds is
A) ammonia.
B) nitrate.
C) nitrite.
D) urea.
E) uric acid.

22) Which nitrogenous waste requires hardly any water for its excretion?
A) amino acids
B) urea
C) uric acid
D) ammonia
E) nitrogen gas

35) All of the following are functions of the mammalian kidney except
A) water reabsorption.
B) filtration of blood.
C) excretion of nitrogenous waste.
D) regulation of salt balance in the blood.
E) production of urea as a waste product of protein catabolism.

53) The most abundant solute in urine is
A) glucose.
B) water.
C) plasma proteins.
D) sodium chloride.
E) urea (and other nitrogenous wastes).

10) Where and from what compound(s) is urea produced?
A) liver from NH3 and CO2
B) liver from glycogen
C) kidneys from glucose
D) kidneys from glycerol and fatty acids
E) bladder from uric acid and H2O

13) Which of the following is not a function of the liver?
A) storage of glycogen
B) secretion of urea
C) production of plasma proteins
D) removal of glucose from the blood
E) detoxification of chemical poisons in the blood

THEORI

Struktur dan Fungsi Antibodi

· Antigen merupakan protein dan permukaan polisakarida berbagai mikroba, jaringan cangkokan yang tidak cocok, ataupun sel-sel darah yang ditransfusikan.

· Selain itu, antigen dapat pula berwujud protein asing seperti racun lebah atau serbuk sari yang dapat menyebabkan alergi atau hipersensitivitas.

· Sebuah antigen mempunyai bagian pada permukaan suatu or-ganisme atau substansi tertentu yang dapat berikatan dengan antibodi.

· Bagian tersebut dinamakan epitopatau determinan antigenik. Semua epitop tentu akan berikatan dengan antibodi yang sesuai.

· Sehingga per-mukaan bakteri, misalnya, yang berperan sebagai antigen seluruhnya dapat ditutupi oleh banyak jenis antibodi.

· Antibodi merupakan protein terdiri atas satu atau lebih molekul yang berbentuk huruf Y. Empat rantai proteinnya disusun oleh ikatan sulfida.

· Dua rantai berat yang identik merupakan batang dan sebagian lengan Y.

· Sedangkan dua rantai ringan yang identik berada pada bagian lainnya.

· Pada kedua molekul berbentuk Y terdapat daerah variable (V) rantai berat dan rantai ringan.

· Dinamakan seperti itu karena pada ba-gian V memiliki urutan asam amino yang bervariasi dari satu antibodi ke antibodi lainnya.

· Umumnya antibodi terdiri atas sekelompok protein yang berada pada fraksi-fraksi globulin serum.

· Fraksi-fraksi globulin serum ini dinamakan imunoglobulin atau disingkat Ig.

· Imunoglobulin ini ber-manfaat apabila di dalam tubuh terjadi reaksi imun.

· Manusia memiliki beberapa tipe imunoglobulin dengan berbagai struktur.

Adapun tipe-tipe imunoglobulin tersebut meliputi imunoglobin

· M (IgM), imunoglobulin G (IgG), imunoglobulin A (IgA), imunoglobulin D (IgD), dan imunoglobulin E (IgE).

· Pembentukan Antigen dan Antibodi

· Di dalam tubuh manusia, antibodi dihasilkan oleh organ limfoid sentral yang terdiri atas sumsum tulang dan kelenjar timus, terutama oleh sel-sel limfosit.

· Ada dua macam sel limfo sit, yaitu sel limfosit B dan sel limfosit T.

· Kedua sel ini bekerja sama untuk menghasilkan antibodi dalam tubuh.

· Baik antibodi maupun antigen keduanya mempunyai hubungan spesifik yang sangat khas.

· Keadaan ini terlihat sewaktu antigen masuk ke dalam tubuh.

· Saat itu, dengan seketika sel limfosit T mendeteksi karakteristik dan jenis antigen.

· Ke-mudian sel limfosit T bereaksi cepat dengan cara mengikat antigen tersebut melalui permukaan reseptornya.

· Setelah itu, sel limfosit T membelah dan membentuk klon.

· Sementara pada permukaan membrannya menghasilkan immunoglobu-lin monomerik.

· Berikutnya, molekul antigen dan molekul an-tibodi saling berikat an dan ikatan kedua molekul ini ditempatkan pada makrofaga.

· Secara beruru-tan, makrofaga menghadirkan antigen pada sel limfosit B. Lantas, sel limfosit B berpoliferasi dan menjadi dewasa, sehingga mampu membentuk

Sementara itu, pembuangan antigen setelah diikat antibodi dapat menggunakan berbagai cara, yakni

1. Netralisasi

2. Aglutinasi

3. Presipitasi

4. Fiksasi komplemen

Netralisasi

· Netralisasi merupakan cara yang digunakan antibodi untuk berikatan dengan antigen supaya aktivitasnya terhambat.

· Sebagai contoh, antibodi melekat pada molekul yang akan digunakan virus untuk menginfeksi inangnya.

· Pada proses ini, antibodi dan antigen dapat mengalami proses opsonisasi, yakni proses pelenyapan bakteri yang diikat antibodi oleh makrofaga melalui fagositosis.

Aglutinasi

· Aglutinasi atau penggumpalan merupakan proses pengikatan antibodi terhadap bakteri atau virus sehingga mudah dinetralkan dan diopsonisasi.

· Misalnya, IgG yang berikatan dengan dua sel bakteri atau virus secara bersama-sama.

· Presi pitasi.

· Presipitasi atau pengendapan merupakan pengikatan silang molekul-molekul antigen yang terlarut dalam cairan tubuh.

· Setelah di-endapkan, antigen tersebut dikeluarkan dan dibuang melalui fagositosis.

Selain berbagai cara tersebut, pembuangan antigen dapat melalui fiksasi komplemen.

Fiksasi komplemen

· Fiksasi komplemen merupakan pengaktifan rentetan molekul protein komplemen karena adanya infeksi.

· Prosesnya menyebabkan virus dan sel-sel patogen yang menginfeksi bagian tubuh menjadi lisis

Mekanisme Pertahanan Tubuh

· Adanya sistem pertahanan tubuh membuat tubuh kita aman dari serangan penyakit.

· Diibaratkan sebuah senjata, sistem pertahan-an tubuh membunuh semua bibit penyakit yang menyerang tubuh.

· Mekanisme yang dilakukan pun amat beragam. Berikut kita bahas ragam mekanisme sistem pertahanan tubuh pada manusia.

Ragam Mekanisme Pertahanan Tubuh

Di dalam tubuh, sistem imun yang kita miliki dapat melakukan mekanisme pertahanan dari berbagai jenis antigen, seperti bakteri, virus maupun kuman tertentu.
Mekanisme pertahanan tersebut dapat dilaku-kan dengan cara membentuk kekebalan aktif dan kekebalan pasif

Kekebalan Aktif

Kekebalan aktifmerupakan kekebalan tubuh yang diperoleh dari dalam tubuh, karena tubuh membuat antibodi sendiri. Jenis kekebalan ini dapat terbentuk baik secara alami ataupun buatan.
Kekebalan aktif alami(natural immunity) adalah kekebalan tu-buh yang diperoleh tubuh setelah seseorang sembuh dari serangan suatu penyakit.
Sebagai contoh, orang yang pernah terserang penyakit seperti cacar air, campak, dan gondongan tidak akan terserang penyakit yang sama untuk kedua kalinya.
Sebab, tubuh yang terserang sudah begitu kenal atau tidak asing dengan antigen yang menyerang.
Akibat-nya, darah membentuk antibodi untuk melawan antigen tersebut.
Selain secara alami, kekebalan aktif dapat diperoleh secara buat an.
Kekebalan aktif buatan(induced immunity) diperoleh dari luar tubuh, yakni setelah tubuh mendapatkan vaksinasi.
Vaksinasi merupa kan proses memasukkan vaksin ke dalam tubuh supaya tubuh membentuk antibodi sehingga kebal terhadap suatu penyakit.
Sementara vaksini alah kuman penyakit yang sudah dilemahkan atau dijinakkan sehingga tidak berbahaya bagi tubuh.
Tindakan membentuk kekebalan dalam tubuh seseorang de ngan memberikan vaksin disebut imunisasi.
Orang yang mengembangkan Imunisasi pertama kali adalah dr. Edward Jenner, seorang dokter berkebangsaan Inggris.
Teknik ini seringkali diberikan kepada semua umur supaya kebal terhadap antigen tertentu.
Ada beberapa penyakit yng dapat dilawan dengan vaksin, misalnya vaksin BCG yang mela-wan antigen penyakit TBC.
Imunisasi mempunyai beberapa tipe. Imunisasi yang diberikan kepada individu dari spesies yang sama disebut isoimun.
Sedangkan imunisasi yang diberikan pada individu yang berbeda dan dari spesies yang berbeda pula disebut heteroimu

Kekebalan Pasif

Kekebalan pasifmerupakan kekebalan yang diperoleh bukan dari antibodi yang disintesis dalam tubuh, melainkan tinggal memakainya saja.
Seperti halnya kekebalan aktif, kekebalan pasif juga terjadi secara alami dan buatan.
Kekebalan pasif alamiadalah kekebalan yang diperoleh bukan dari tubuhnya sendiri, melainkan dari tubuh orang lain.
Misalnya kekebalan bayi yang diperoleh dari ibunya. Ketika masih dalam kan-dungan, bayi mendapatkan antibodi dari ibunya melalui plasenta dan tali pusat.
Kemudian setelah lahir, bayi mendapatkan antibodi dari ASI eksklusif melalui proses menyusui.
Sedangkan kekebalan pasif buatan adalah kekebalan yang di-peroleh dari antibodi yang sudah jadi dan terlarut dalam serum.
Sepintas antibodi ini mirip dengan vaksin.
Perbedaannya yakni vaksin bersifat sementara, sedangkan serum dapat digunakan dalam jangka waktu yang relatif lebih lama.
Bahkan dapat digunakan seumur hidup. Seba-gai contoh adalah suntikan ATS (Anti Tetanus Serum) dan sun tikan IG (Globulin Imun).
Sistem pertahanan tubuh ibarat benteng yang melindungi tubuh dari serangan berbagai macam antigen. Akan tetapi, adakalanya sistem pertahanan tubuh justru menyerang dan merusak tubuh itu sendiri. Keadaan semacam ini disebut dengan autoimun.
Menurut beberapa penelitian, penyakit autoimun lebih banyak menyerang wanita daripada pria, khususnya wanita usia produktif.
Penyakit ini tidak menular, namun memiliki kecenderungan bersifat menurun. Seseorang dikatakan menderita autoimun apabila sistem pertahanan tubuhnya mengalami kesalahan.
Kesalahan ini ditandai dengan penyerangan antibodi hasil sintesis tubuh terhadap sel, jaring-an dan organ di dalam tubuh yang sama.
Akibatnya, sistem kekebalan tubuh mengalami peradangan.
Autoimun pada manusia kebanyakan menyebabkan timbulnya penyakit.
Hasil publikasi dari Lembaga Penyakit Infeksi dan Alergi Nasional (NIAID) Amerika Serikat, menyatakan bahwa penyakit yang disebabkan oleh autoimun menyerang tubuh dengan cara berlainan.
Misalnya, apabila autoimun terjadi di otak, maka akan menyebabkan penyakit multiple sclerosis.
Kemudian, apabila autoimun terjadi di usus dapat menyebabkan penyakit crohn.
Beberapa jenis penyakit autoimun semakin parah apabila mengalami infeksi oleh virus, paparan sinar matahari, faktor usia, stres kronis, gangguan hormon, dan kehamilan.
Hingga saat ini, penyakit-penyakit autoimun masih sulit untuk didiagnosis, terutama pada stadium dini yang gejalanya tidak spesi-fik.
Meski tergolong penyakit kronis, kebanyakan dokter tidak bisa meramalkan kondisi pasien penderita penyakit autoimun pada suatu waktu.
Dokter hanya memberikan obat-obatan tertentu dan memoni-tor kondisi pasien tersebut.

Sistem pertahanan tubuh dapat pula disebut sistem kekebalan atau sistem imun. Sistem imun tubuh terdiri dari banyak komponen. Semua komponen tersebut akan bekerja secara serentak manakala tubuh mendapatkan serangan dari penyakit yang berasal dari luar tubuh maupun dari dalam tubuh kita sendiri.
Kerja sistem imun tubuh kita secara sederhana terbagi dalam 3 kelompok :

Sistem pertahan tubuh awal : contohnya, kulit, rambut di kulit, air mata
Sistem pertahanan tubuh non spesifik (alamiah) : adalah sistem yang paling cepat bereaksi ketika ada serangan virus, bakteri atau mikroba dari luar.
Sistem pertahanan spesifik (dapatan) : sistem ini baru bekerja ketika perlawanan sistem imun alami kita tidak cukup dan bekerja menurut jeniis serangan virus atau bakteri yang terjadi. Yang bekerja pada sistem ini adalah Limfosit T & B. Hasil kerja sistem inilah yang berbentuk antibodi (IgG dan IgM).

Sistem imun berkembang sesuai dengan perkembangan tubuh kita, pada waktu bayi umumya sistem imun masih belum banyak berkembang, beberapa komponen masih belum dapat bekerja optimal. Dengan bertambahnya usia dari anak-nak menuju remaja hingga dewasa, sistem imun berkembang untuk bekerja lebih optimal. Tetapi memasuki usia tua, sistem imun menurun kemballi. Oleh karena itu, anak-anak dan lansia mudah sekali terkena penyakit.

Pada prinsipnya, orang dengan kondisi sistem imun dalam keadaan prima, tidak mudah terkena infeksi, akan tetapi jika pada saat tertentu sistem imunterganggu atau tidak bekerja dengan baik, maka infeksi oleh bakteri, virus atau jamur mudah masuk ke dalam tubuh.

Banyak faktor yang dapat mengakibatkan sistem imun terganggu, di antaranya: stress, kurang gizi, terlalu lelah, dsb. Untuk mengatsinya diperlukan pola hidup sehat, antara lain : cukup istirahat, makan bergizi seimbang, tidak stress, menghindari lingkungan yang dapat mengakibatkan sakit dan bila perlu mengkonsusmsi obat atau suplementasi yang dapat menguatkan sistem imun (daya tahan) tubuh.

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