Immune System and Page Ref

Essentials of Anatomy and Physiology, 9e (Marieb)

Chapter 12 The Lymphatic System and Body Defenses Short Answer Figure 12. 1

Using Figure 12. 1, identify the following:

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2) A lymph node is indicated by letter __________. Answer: B Diff: 2 Page Ref: 404

3) The lymph duct is indicated by lettter __________. Answer: A Diff: 2 Page Ref: 404

4) Blood capillaries are indicated by letter __________. Answer: E Diff: 2 Page Ref: 404

5) Lymphatic collecting vessels are indicated by letter __________. Answer: C Diff: 2 Page Ref: 404 1 Figure 12. Using Figure 12. 2, identify the following:

6) The spleen is indicated by letter __________. Answer: C Diff: 1 Page Ref: 407

7) The tonsils are indicated by letter __________. Answer: A Diff: 1 Page Ref: 407

8) The thymus gland is indicated by letter __________. Answer: B Diff: 1 Page Ref: 407

9) The Peyer’s patches are indicated by letter __________. Answer: D Diff: 1 Page Ref: 407

10) The lymphoid organ that destroys worn-out blood cells is indicated by letter __________. Answer: C Diff: 2 Page Ref: 407 2

11) The lymphoid tissues that trap and remove bacteria that enter the throat are indicated by letter __________.

Answer: A Diff: 2 Page Ref: 407-408 Fill in the blank or provide a short answer:

12) Lymph fluid and some plasma proteins originate (escape) from the _________ _. Answer: blood plasma Diff: 2 Page Ref: 403-404

13) Excess accumulations of fluid, which impair the exchange of materials within the tissues, is called __________. Answer: edema Diff: 2 Page Ref: 403

14) The fibrous capsule of lymph nodes contains strands called __________ that divide the node into compartments. Answer: trabeculae Diff: 3 Page Ref: 406

15) Lymph exits the lymph node via the __________ vessels. Answer: efferent lymphatic Diff: 2Page Ref: 406

16) The role of the __________ in the lymphatic system is to remove worn -out blood cells and return some of the products to the liver. Answer: spleen Diff: 2 Page Ref: 407

17) Peyer’s patches and the tonsils are part of the collection of small lymphoid tissues that protect the upper respiratory and digestive tracts from infection and are referred to as __________. Answer: MALT (mucosa-associated lymphatic tissue) Diff: 3 Page Ref: 408

18) Harmful or disease-causing microorganisms from which nonspecific defenses protect the body are called __________. Answer: pathogens Diff: 1 Page Ref: 409

19) The process by which WBCs and phagocytes migrate to an area experiencing acute inflammation is called __________. Answer: chemotaxis Diff: 3 Page Ref: 411

20) The process by which neutrophils squeeze through capillary walls is called __________. Answer: diapedesis Diff: 2 Page Ref: 412 3

21) The binding of complement proteins to certain sugar or proteins on a foreign cell’s surf ace is called __________. Answer: complement fixation Diff: 3 Page Ref: 413

22) One effect of complement fixation that causes the cell membranes of foreign cells to become sticky so that they are easier to phagocytize is called __________.

Answer: opsonization Diff: 3 Page Ref: 413

23) Cells studded with protein molecules found on our own cells that do not trigger an immune response within us (but may within others) are called __________. Answer: self-antigens (autoantigens) Diff: 1 Page Ref: 416

24) Troublesome small molecules or incomplete antigens that may mount an attack that is harmful rather than protective are called __________. Answer: haptens Diff: 3 Page Ref: 416

25) When an antigen binds to B cell surface receptors, it becomes sensitized (activated) and undergoes __________. Answer: clonal selection Diff: 3 Page Ref: 418

26) When B cells encounter antigens and produce antibodies against them, we exhibit __________. Answer: active immunity Diff: 2 Page Ref: 420

27) Antibodies constitute an important part of blood proteins and are also referred to as __________. Answer: immunoglobulins Diff: 2 Page Ref: 421

28) The five major immunoglobulin classes are __________. Answer: IgM, IgA, IdD, IgG, IgE Diff: 1 Page Ref: 422

29) The binding of antibodies to specific sites on bacterial exotoxins or viruses is called __________. Answer: neutralization Diff: 2 Page Ref: 424

30) The clumping of foreign cells, a type of antigen-antibody reaction, is called __________.

Answer: agglutination Diff: 2 Page Ref: 424

31) Killer T cells, which kill virus-invaded body cells, are also called __________. Answer: cytotoxic T cells Diff: 3 Page Ref: 425 4

32) Antigens that produce abnormally vigorous immune responses whereby the immune system causes tissue damage as it fights off a perceived threat that would otherwise be harmless are called __________. Answer: allergens or hypersensitivities Diff: 2 Page Ref: 430

33) Systemic (bodywide) acute allergic response caused by allergens that directly enter the blood, as with certain bee stings or spider bites, is called __________.

Answer: anaphylactic shock Diff: 2 Page Ref: 430

34) AIDS cripples the immune system by interfering with the activity of cells called __________. Answer: helper T cells Diff: 2 Page Ref: 431

35) A tropical disease that results when parasitic worms clog the lymphatic vessels is called __________. Answer: elephantiasis Diff: 2 Page Ref: 431

Multiple Choice

1) The fluid that is forced out of the capillary beds by hydrostatic and osmotic pressures and into the tissue spaces is called: A) arterial blood B) venous blood C) plasma D) interstitial fluid E) lymph Answer: E Diff: 1 Page Ref: 403-404

2) Lymph flows: A) in a circular pattern within the tissues B) away from the heart only C) toward the heart only D) both toward and away from the heart E) into the capillaries Answer: C Diff: 1 Page Ref: 404

3) Lymph from the left arm would return to the heart through the: A) inferior vena cava B) thoracic duct C) right lymphatic duct D) left subclavian artery E) aorta Answer: B Diff: 3 Page Ref: 404; 406 5

4) Which one of the following is NOT a mechanism that aids lymph return: A) milking action of skeletal muscles B) pressure changes within the thorax C) the pumping action of the heart D) smooth muscle contractions within the lymphatic vessels E) presence of valves within the larger lymph vessels Answer: C Diff: 1 Page Ref: 404

5) Which one of the following is NOT true of lymph nodes: A) they remove foreign materials from the lymph fluid B) they have valves similar to those found in veins C) they contain lymphocytes D) they act as filters along the lymphatic vessels E) they contain macrophages Answer: B Diff: 2 Page Ref: 405-406

6) Which lymphatic organ’s major job is to destroy worn-out red blood cells and return some of the products to the liver: A) tonsils B) spleen C) thymus gland D) tonsils E) Peyer’s patches Answer: B Diff: 2 Page Ref: 40

7 ) Which lymphoid tissues trap and remove bacteria entering the throat: A) axillary lymph nodes B) cervical lymph nodes C) tonsils D) Peyer’s patches E) thymus gland Answer: C Diff: 2 Page Ref: 408

8) Which one of the following is NOT a type of lymphoid organ: A) spleen B) thymus gland C) tonsils D) appendix E) Peyer’s patches Answer: D Diff: 2 Page Ref: 407-408 6

9) The lymph organ that programs T cells and functions at peak levels only during youth is the: A) thymus B) spleen C) appendix D) tonsils E) Peyer’s patches Answer: A Diff: 2 Page Ref: 408

10) The lymph tissues found within the walls of the small intestine are called: A) tonsils B) appendix C) Peyer’s patches D) thymus tissues E) intestinal nodes Answer: C Diff: 2 Page Ref: 408

11) Which of these lymphoid organs is found along the left side of the abdominal cavity: A) spleen B) Peyer’s patches C) thymus gland D) tonsils E) axillary lymph nodes Answer: A Diff: 1 Page Ref: 407

12) Musoca-associated lymphatic tissue (MALT) includes: A) spleen B) thymus gland C) tonsils only D) tonsils and Peyer’s patches E) tonsils and spleen Answer: D Diff: 3 Page Ref: 408

13) The body’s first line of defense against the invasion of disease -causing microorganisms is: A) phagocytes B) natural killer cells C) skin and mucous membranes D) inflammatory response E) fever Answer: C Diff: 2 Page Ref: 409 7

14) Compared to the nonspecific chemicals that cover body surfaces and mucous membranes, the specific body defense system is: A) faster B) slower C) the same speed D) sometimes faster and sometimes slower E) not comparable in speed Answer: B Diff: 2 Page Ref: 409

15) Which one of the following is NOT one of the nonspecific body defenses: A) intact skin B) antibody production C) the inflammatory response D) fever E) natural killer cells Answer: B Diff: 2 Page Ref: 409-415

16) The process by which neutrophils are squeezed through the capillary wall s during the inflammatory process is called: A) agglutination B) chemotaxis C) diapedesis D) coagulation E) antibody production Answer: C Diff: 2 Page Ref: 412

17) Which one of the following is NOT one of the four most common indic ators of the inflammatory response: A) redness B) heat C) swelling D) fever E) pain Answer: D Diff: 1 Page Ref: 410-412

18) The migration of phagocytes and white blood cells to an inflamed area along a chemical gradient is called: A) diapedesis B) chemotaxis C) immunity D) perforins E) complement fixation

Answer: B Diff: 2 Page Ref: 411 8

19) The inflammatory process begins with release of chemicals, which do all of the following EXCEPT: A) dilate blood vessels B) attract phagocytes to the area C) stimulate release of lysozyme D) cause capillaries to become leaky E) activate pain receptors Answer: C Diff: 2 Page Ref: 411-412

20) Tissues invaded by viruses, which attempt to replicate themselves by taking over cellular machinery, secrete small proteins called __________ to protect nearby cells and hinder further multiplication of the viruses. A) histamine B) interferon C) kinins D) interleukins E) pyrogens Answer: B Diff: 2 Page Ref: 413; 415

21) The body’s temperature-regulating “thermostat” that can be reset upward in response to pyrogens is located in the: A) hypothalamus B) thalamus C) pineal gland D) cerebellum E) medulla oblongata Answer: A Diff: 1 Page Ref: 415

22) Fever has the effect of doing all of the following EXCEPT: A) denaturing (scrambling) proteins B) stimulating the liver and spleen to gather up iron and zinc C) increasing metabolic rate of tissue cells D) stimulating complement fixation E) speeding up repair processes Answer: D Diff: 3 Page Ref: 415

23) The study of immunity is called: A) histology B) anatomy C) pathology D) immunology E) microbiology Answer: D Diff: 1 Page Ref: 415 9

24) Which of the following substances is NOT typically perceived as an antigen: A) pollen grains B) bacteria C) self-antigens D) fungi E) virus particles Answer: C Diff: 2 Page Ref: 416

25) Which one of the following CANNOT be said about the history of immunity: A) the ancient Greeks knew something existed within the body to protect it from infectious disease B) scientists of the 1800s discovered “factors” now called antibodies C) scientists of the 1800s demonstrated that immune serum could protect another animal from disease

D) scientists of the mid-1900s discovered the viral origin of AIDS E) scientists of the mid-1900s discovered that injection of serum containing antibodies did NOT always protect a recipient from disease Answer: D Diff: 2 Page Ref: 415

26) Regardless of whether it matures into a B cell or a T cell, a lymphocyte that is capable of responding to a specific antigen by binding to it is said to be: A) clonal B) incompetent C) immune D) immunocompetent E) complemented Answer: D Diff: 3 Page Ref: 416

27) The specific foreign substances that an individual’s immune system has the ability to recognize and resist is determined by: A) individual exposure to the specific foreign substance B) individual genetic makeup C) the total number of lymphocytes present at a given time D) the total number of macrophages at a given time E) the total number of self-antigens at a given time Answer: B Diff: 3 Page Ref: 417

28) Which one of the following is NOT true of macrophages: A) they are considered the “big eaters” of the immune system B) they engulf foreign particles C) they circulate continuously throughout the body D) they act as antigen presenters E) they secrete monokines Answer: C Diff: 2 Page Ref: 418 10

29) B cells develop immunocompetence in the: A) thymus gland B) bone marrow C) spleen D) thyroid gland E) lymph nodes Answer: B Diff: 2 Page Ref: 417

30) The specific type of acquired immunity that a fetus obtains from maternal antibodies that cross the placenta is called: A) naturally acquired active immunity B) naturally acquired passive immunity C) artificially acquired active immunity D) artificially acquired passive immunity E) artificially acquired natural immunity Answer: B Diff: 1 Page Ref: 420

31) What specific type of acquired immunity do vaccines provide: A) naturally acquired active immunity B) naturally acquired passive immunity C) artificially acquired active immunity D) artificially acquired passive immunity E) naturally acquired artificial immunity Answer: C Diff: 1 Page Ref: 420

32) Vaccines are NOT for: A) pneumonia B) tetanus C) measles D) snake bites E) polio Answer: D Diff: 2 Page Ref: 420

33) Immune sera are used for all of the following EXCEPT: A) tuberculosis B) rabies C) snake bites D) botulism E) tetanus Answer: A Diff: 2 Page Ref: 421 11

34) Which one of the following is NOT true of basic antibody structure: A) they consist of four amino acid chains B) they are linked together by disulfide bonds C) the heavy chains are identicalD) the heavy chains are about 400 amino acids long E) the light chains are often of differing lengths Answer: E Diff: 3 Page Ref: 421-422

35) Which one of the following is NOT true of the constant (C) regions of antibodies: A) they are the same or nearly the same B) they form the “stem” of an antibody C) they determine the specific type of antibody class formed D) they form an antigen-binding site E) they determine how an antibody class will carry out its immune role Answer: D Diff: 3 Page Ref: 422

36) Which one of the following is NOT one of the antibody classes: A) IgA B) IgB C) IgD D) IgG E) IgE Answer: B Diff: 1 Page Ref: 422

37) IgA: A) is mainly found in mucus and secretions such as tears and saliva B) is passed from mother to fetus during pregnancy C) is the most abundant antibody in blood plasma D) can fix complement E) is involved in allergies Answer: A Diff: 3 Page Ref: 423

38) Which one of the following is NOT a method by which antibodies inactivate antigen s: A) agglutination B) chemotaxis C) complement fixation D) neutralization E) precipitation Answer: B Diff: 2 Page Ref: 423-424 12

39) The specific antibody class that has the ability to cross the placental barrier and provide immunity to the fetus is: A) IgM B) IgA C) IgD D) IgG E) IgE Answer: D Diff: 2 Page Ref: 422-423

40) The process by which antibodies bind to specific sites on bacterial exotoxins (toxic chemicals secreted by bacteria) to block their harmful effects is called: A) agglutination B) chemotaxis C) complement fixation D) neutralization E) precipitation Answer: D Diff: 2 Page Ref: 424

41) Antigen presentation is essential for the activation and clonal selection of: A) T cells B) B cells C) plasma cell D) antigen-presenting cells E) antibodies Answer: A Diff: 2 Page Ref: 425

42) An isograft is a tissue graft donated by: A) an unrelated person B) a parent C) a different animal species D) the same person E) an identical twin Answer: E Diff: 2 Page Ref: 427

43) Which one of the following is NOT a type of immunosuppressive therapy given after surgery to prevent rejection of a graft: A) corticosteroids B) radiation C) antiproliferative drugs D) gamma globulin E) immunosuppressive drugs Answer: D Diff: 2 Page Ref: 429 13

44) With immediate hypersensitivy, the antibody class that binds to mast cells and basophils that trigger the release of histamine and other chemicals is: A) IgM B) IgA C) IgD D) IgG E) IgE Answer: E Diff: 2 Page Ref: 422-423

45) Allergic contact dermatitis following skin contact with poison ivy would normally lead to: A) immediate hypersensitivity B) acute hypersensitivity C) delayed hypersensitivity D) anaphylactic shock E) immunodeficiency Answer: C Diff: 2 Page Ref: 431

46) The relatively common autoimmune disease in which the thyroid gland produces excessive amounts of thyroxine is called: A) multiple sclerosis B) Graves’ disease C) myasthenia gravis D) glomerulonephritis E) systemic lupus erythematosis Answer: B Diff: 2 Page Ref: 429

47) Which one of the following is NOT an autoimmune disease: A) AIDS B) multiple sclerosisтC) Graves’ disease D) type I diabetes mellitus E) rheumatoid arthritis Answer: A Diff: 2 Page Ref: 429

True/False

1) The flaplike minivalves of the lymph capillaries act like one -way swinging doors that allow lymph fluid to enter the lymph capillaries but not exit. Answer: TRUE Diff: 2 Page Ref: 404

2) The daughter cells of B cells, called plasma cells, release antibodies. Answer: TRUE Diff: 2 Page Ref: 418 14

3) Lymph in the right arm is returned to the heart via the right lymphatic duct. Answer: TRUE Diff: 2 Page Ref: 404

4) The thymus gland, found around the trachea, programs certain lymphocytes. Answer: FALSE Diff: 2 Page Ref: 408

5) The tonsils, spleen, thymus gland, and Peyer’s patches are referred to as mucosa-associated lymphatic tissue (MALT). Answer: FALSE Diff: 2 Page Ref: 408

6) Natural killers are unique phagocytic defense cells that can kill cancer cells and virus infected body cells well before the immune system i s activated. Answer: FALSE Diff: 2 Page Ref: 410

7) Some pathologists consider limitation of joint movement to be an additional fifth cardinal sign of inflammation. Answer: TRUE Diff: 1 Page Ref: 412

8) The final disposal of cell debris as inflammation subsides is performed by neutrophils. Answer: FALSE Diff: 3 Page Ref: 412

9) The nonspecific defense by which complement proteins attach to sugars or proteins on the surface of foreign cells is called complement fixation. Answer: TRUE Diff: 1 Page Ref: 413

10) Chemicals secreted by white blood cells and macrophages exposed to foreign substances that can increase body temperature are called pyrogens. Answer: TRUE Diff: 1 Page Ref: 415

11) Fever is a systemic response triggered by pyrogens. Answer: TRUE Diff: 2 Page Ref: 415

12) Like all blood cells, lymphocytes originate from hemocytoblasts contained within red bone marrow. Answer: TRUE Diff: 3 Page Ref: 416

13) Macrophages arise from monoctyes formed within the bone marrow. Answer: TRUE Diff: 2 Page Ref: 418 15

14) Extremely weakened pathogens that are still alive are attenuated. Answer: TRUE Diff: 2 Page Ref: 420

15) Artificially acquired passive immunity is conferred when o ne receives immune serum for poisonous snake bites. Answer: TRUE Diff: 3 Page Ref: 421

16) Antibodies are also referred to as immunoglobulins. Answer: TRUE Diff: 1 Page Ref: 421

17) There are three major immunoglobulin classes: IgM, IgA , and IgD. Answer: FALSE Diff: 2 Page Ref: 422

18) The antibody a mother passes to her fetus is IgM. Answer: FALSE Diff: 3 Page Ref: 422-423

19) The process that occurs when antibodies clump foreign cells is called agglutination. Answer: TRUE Diff: 2 Page Ref: 424

20) Memory cells are descendants of an activated B or T cell. Answer: TRUE Diff: 3 Page Ref: 427

21) An antibody is a substance capable of provoking an immune response. Answer: FALSE Diff: 2 Page Ref: 416

22) Tissue grafts harvested from an unrelated person are called xenografts. Answer: FALSE Diff: 1 Page Ref: 427

23) Allografts are tissue grafts taken from an unrelated person. Answer: TRUE Diff: 2 Page Ref: 427

24) Allergies, or hypersensitivities, are normal immune responses. Answer: FALSE Diff: 2 Page Ref: 430

25) Autoimmune diseases occur when the immune system loses its ability to tolerate self antigens while still recognizing and attaching foreign antigens. Answer: TRUE Diff: 3 Page Ref: 429 16

26) Our immune system can be affected by severe stress. Answer: TRUE Diff: 1 Page Ref: 435 Matching Match the following descriptions with the appropriate lymphoid organ or tissue:

1) Located on the left side of the A) thymus gland abdominal cavity Diff: 1 Page Ref: 407 B) spleen

2) Trap and remove bacteria and pathogens entering the throat Diff: 2 Page Ref: 408 C) Peyer’s patches D) tonsils

3) Located overlying the heart Diff: 1 Page Ref: 408

4) Filters and cleanses the blood of bacteria, viruses, and other debris Diff: 2 Page Ref: 407-408

5) Located in the wall of the small intestines Diff: 1 Page Ref: 408

6) Located in the pharynx (throat) Diff: 1 1) B Page Ref: 408 2) D 3) A 4) B 17 5) C 6) D Match the following protective mechanism with its associated element:

7) Traps microorganisms in A) nasal hairs respiratory and digestive tracts Diff: 1 Page Ref: 409 B) mucus C) acid mantle

8) Inhibits growth of bacteria and fungi in female reproductive tract Diff: 1 Page Ref: 409 E) keratin ) Contains lysozyme Diff: 2 D) lacrimal secretions F) cilia Page Ref: 409 G) gastric juice

10) Provides resistance against acids, alkalis, and bacterial enzymes Diff: 1 Page Ref: 409

11) Filters and traps microorganisms within inhaled air Diff: 1 Page Ref: 409

12) Contains concentrated hydrochloric acid and protein-digested enzymes that destroy pathogens within the stomach Diff: 1 Page Ref: 409

13) Propels debris-laden mucus away from lower respiratory passages Diff: 1 7) B 13) F Page Ref: 409 8) C 9) D 10) E 18 11) A 12) G Match the following biological function with its antibody class:

14) Believed to be cell surface A) IgD receptor of immunocompetent B cell Diff: 3 Page Ref: 422-423 B) IgG C) IgA

15) First immunoglobulin class released to plasma by plasma cells during primary response Diff: 3 Page Ref: 422-423 D) IgM E) IgE

16) Main antibody of primary and secondary responses Diff: 3 Page Ref: 422-423

17) Bathes and protects mucosal surfaces from attachment of pathogens Diff: 3 Page Ref: 422-423

18) Triggers the release of histamine Diff: 3 Page Ref: 422-423

19) Potent agglutinating agent Diff: 3 Page Ref: 422-423

20) Crosses placenta and provides passive immunity to fetus Diff: 3 14) A 20) B Page Ref: 422-423 15) D 6) B 17) C 18) E 19) D

Essay

1) Explain the origin and pathway of lymph. Answer: Lymph fluid arises from blood plasma that has been forced out of the capillary beds by osmotic and hydrostatic pressures. The fluid left behind is called interstitial fluid. The interstitial fluid is then picked up by lymph capillaries, after which it is called lymph. Lymph is routed up the lymphatic vessels until it is finally returned to the venous system through either the right lymphatic duct or the thoracic duct. Diff: 2 Page Ref: 403-404 19

2) Describe the methods the body uses to help return lymph to the heart.

Answer: The return of lymph to the heart is aided by: 1. the milking action of the skeletal muscles, 2. pressure changes in the thorax during brea thing, 3. smooth muscles in the walls of the larger lymphatics contract rhythmically. Diff: 1 Page Ref: 404-405

3) Describe several of the protective chemicals produced by the skin and mucous membranes. Answer: Skin produces acid secretions that inhibit bacterial growth, and sebum contains chemicals that are toxic to bacteria. Vaginal secretions are highly acidic. The stomach mucosa secretes hydrochloric acid and protein-digesting enzymes, both of which can kill pathogens. Saliva and tears contain lysozyme, an enzyme that destroys bacteria. Mucus is a sticky mucous membrane secretion that traps microorganisms. Diff: 2 Page Ref: 409

4) Identify the four most common indicators and major symptoms of an acute inflammatory response and explain their origins. Answer: The four most common indicators of the inflammatory response are redness, heat, swelling, and pain. Redness and heat are a result of dilation of blood vessels that increase blood flow to the injured area. Swelling occurs when increa sed permeability of the capillaries allows plasma to leak from the bloodstream into the tissue spaces. The excess fluid, or edema, triggers the activation of pain receptors in the area, accounting for the pain associated with an injury. Diff: 2 Page Ref: 410-412

5) List and describe the cells and chemicals the body uses as its second line of defense. Answer: 1. Phagocytes, such as neutrophils or macrophages, engulf foreign particles. These cells are in nearly every body organ and confront pathoge ns that make it through the surface membrane barriers. 2. Natural killer cells, found in blood and lymph, are lymphocytes. They can lyse and kill cancer cells and virus-infected body cells. 3. The inflammatory response is a nonspecific response that occurs when body tissues are injured. Diff: 2 Page Ref: 409-411

6) Describe the four major types of transplant grafts. Answer: Autografts are tissue grafts transplanted from one site to another within the same person. Isografts are tissue grafts harves ted from a genetically identical person (identical twin). Allografts are tissue grafts harvested from an unrelated person. Xenografts are tissue grafts harvested from different animal species. Diff: 2 Page Ref: 427

7) Explain three current theories that attempt to explain why self-tolerance breaks down in autoimmune disorders.

Answer: Inefficient lymphocyte programming is one theory that suggests self-reactive B or T cells escape to the rest of the body. Another theory is that self -proteins appear within the circulation that were not previously exposed to the immune system, thus initiating an immune response. These “hidden” antigens are found in sperm cells, the eye lens, and thyroid proteins. Another theory is that antibodies produced against fore ign antigens cross-react with self-antigens such as when streptococcal bacteria crossreact with heart antigens causing rheumatic fever. Diff: 3 Page Ref: 429 20

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