Abbas: Basic Immunology, 3rd Updated Edition Chapter 01: Introduction to the Immune System est Ban! "U#I$#E C%&ICE
1. The princi principal pal functio function n of the immu immune ne system system is: is: A. Defe Defens nsee agains againstt cancer cancer B. Repair Repair of injur injured ed tissues tissues C. Defense Defense against microbial microbial infections infections D. Preention of inflam inflammatory matory diseases diseases !. Protection Protection against against eniro enironme nmental ntal to"ins to"ins A'S: C The immune system has eoled in the setting of selectie pressures imposed by microbial infections. Although immune responses to cancer may occur# the concept that $immunosureillance% against cancer is a principal function of the immune system is controersial. Repair of injured tissues may be a secondary conse&uence of the immune responses and inflammation. Although the immune system has regulatory features that are needed to preent e"cessie inflammation# preention of inflammatory diseases is not a primary primary function. function. The imm immune une system system can protect against microbi microbial al to"ins# to"ins# but it generally generally does not offer protection against to"ins of nonbiologic origin.
'. (hich (hich of the follo)i follo)ing ng infectio infectious us diseases diseases )as preented by the first first successful successful accination* A. Polio B. Tube Tuberc rcul ulos osis is C. +mallpo" po" D. Tetanu tanuss !. Rubella A'S: C ,n 1-/# !d)ard 0enner reported the first intentional successful accination# )hich )as against smallpo" in a boy# using material from the co)po" pustules of a milmaid. ,n 1/2# smallpo" smallpo" )as reported to be eradicated )orld)ide by a accination accination program. !ffectie accines against tetanus to"in# rubella irus# and polioirus )ere deeloped in the '2th century and are )idely used. There is no effectie accine against Mycobacterium against Mycobacterium tuberculosis.
3. A preiously preiously healthy healthy /4year4old /4year4old boy is infected infected )ith an upper respiratory respiratory tract irus for the first time. During the first fe) hours of infection# )hich one of the follo)ing eents occurs* A. The adaptie immune immune system system responds rapidly rapidly to the irus and eeps the iral iral infection under control.
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B. The innate immune system responds rapidly to the iral infection and eeps the iral infection under control. C. Passie immunity mediated by maternal antibodies limits the spread of infection. D. B and T lymphocytes recogni5e the irus and stimulate the innate immune response. !. The irus causes malignant transformation of respiratory mucosal epithelial cells# and the malignant cells are recogni5ed by the adaptie immune system. A'S: B The innate immune response to microbes deelops )ithin hours of infection# )ell before the adaptie immune response. B and T lymphocytes are components of the adaptie immune response# and they )ould not be able to respond to a ne)ly encountered irus before the innate immune response. An /4year4old boy )ould no longer hae maternal antibodies from transplacental passie transfer and is unliely to be breast4feeding# )hich is another potential source of maternal antibodies. 6alignant transformation taes months or years to deelop.
7. (hich of the follo)ing is a uni&ue property of the adaptie immune system* A. 8ighly dierse repertoire of specificities for antigens B. +elf4nonself discrimination C. Recognition of microbial structures by both cell4associated and soluble receptors D. Protection against iral infections !. Responses that hae the same inetics and magnitude on repeated e"posure to the same microbe A'S: A 8ighly dierse repertoires of specificities for antigens are found only in T and B lymphocytes# )hich are the central cellular components of the adaptie immune system. Both the innate and the adaptie immune systems use cell4associated and soluble receptors to recogni5e microbes# display some degree of self4nonself discrimination# and protect against iruses. 9n repeated e"posure to the same microbe# the adaptie immune response becomes more rapid and of greater magnitude this is the manifestation of memory.
;. Antibodies and T lymphocytes are the respectie mediators of )hich t)o types of immunity* A. ,nnate and adaptie B. Passie and actie C. +pecific and nonspecific D. 8umoral and cell4mediated !. Adult and neonatal A'S: ( Both B and T lymphocytes are principal components of adaptie immunity. B lymphocytes produce antibodies# )hich are the recognition and effector molecules of humoral immune responses to e"tracellular pathogens. T cells recogni5e and promote eradication of intracellular pathogens in cell4mediated immunity. Passie and actie immunity both can be mediated by either B or T lymphocytes. Specific immunity is another term for adaptie
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immunity. Both B and T lymphocytes participate in adult adaptie immunity but are still deeloping in the neonatal period. <. A standard treatment of animal bite ictims# )hen there is a possibility that the animal )as infected )ith the rabies irus# is administration of human immunoglobulin preparations containing anti=rabies irus antibodies. (hich type of immunity )ould be established by this treatment* A. Actie humoral immunity B. Passie humoral immunity C. Actie cell4mediated immunity D. Passie cell4mediated immunity !. ,nnate immunity A'S: B 8umoral immunity is mediated by antibodies. The transfer of protectie antibodies made by one or more indiiduals into another indiidual is a form of passie humoral immunity. Actie immunity to an infection deelops )hen an indiidual>s o)n immune system responds to the microbe. Cell4mediated immunity is mediated by T lymphocytes# not antibodies# and innate immunity is not mediated by either antibodies or T lymphocytes.
-. At 1; months of age# a child receied a measles4mumps4rubella accine ?66R@. At age ''# she is liing )ith a family in 6e"ico that has not been accinated and she is e"posed to measles. Despite the e"posure# she does not become infected. (hich of the follo)ing properties of the adaptie immune system is best illustrated by this scenario* A. +pecificity B. Diersity C. +peciali5ation D. 6emory !. onreactiity to self A'S: ( Protection against infections after accination is due to immunologic memory of the adaptie immune system. 6emory is manifested as a more rapidly deeloping and igorous response on repeat e"posure to an antigen compared )ith the first e"posure. +pecificity and diersity are properties related to the range of antigenic structures recogni5ed by the immune system# and speciali5ation is the ability of the adaptie immune system to use distinct effector mechanisms for distinct infections.
/. A accine administered in the autumn of one year may protect against the prealent strain of influen5a irus that originated in 8ong ong that same year# but it )ill not protect against another strain of influen5a irus that originated in Russia. This phenomenon illustrates )hich property of the adaptie immune system* A. +pecificity B. Amnesia C. +peciali5ation D. Cultural diersity !. +elf4tolerance
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A'S: A Adaptie immune responses are highly specific for distinct molecular structures# )hich may be present in a accine and be produced by one strain of irus but not by a closely related strain. Amnesia# although generally not used in immunology# implies lac of memory# but the efficacy of the accine against the 8ong ong strain implies it has induced memory. The same effector mechanisms )ould be re&uired to combat different strains of influen5a# and therefore failure of a accine to protect against t)o different strains of irus is not related to speciali5ation of effector functions.
. The t)o major functional classes of effector T lymphocytes are: A. 8elper T lymphocytes and cytoto"ic T lymphocytes B. atural iller cells and cytoto"ic T lymphocytes C. 6emory T cells and effector T cells D. 8elper cells and antigen4presenting cells !. Cytoto"ic T lymphocytes and target cells A'S: A T cells can be classified into effector subsets that perform different effector functions. 6ost effector T cells are either helper T lymphocytes# )hich promote macrophage and B cell responses to infections# or cytoto"ic T lymphocytes# )hich directly ill infected cells. atural iller cells are not T lymphocytes. Antigen4presenting cells usually are not T cells. 6emory T cells are not effector T cells.
12. (hich of the follo)ing cell types is re&uired for all humoral immune responses* A. atural iller cells B. Dendritic cells C. Cytolytic T lymphocytes D. B lymphocytes !. 8elper T lymphocytes A'S: ( 8umoral immune responses are antibody4mediated immune responses# and all antibodies are made by B lymphocytes and by no other cell type.
11. During a humoral immune response to a ne)ly encountered bacterial infection# B cells are first stimulated to proliferate and then secrete antibodies specific for the bacterium. The antibodies may then bind to the bacteria and facilitate ingestion of the microbes by phagocytic cells. ,n )hat phase of the humoral immune response does the binding of secreted antibodies to bacteria occur* A. Recognition phase B. Actiation phase C. !ffector phase D. 8omeostatic phase !. 6emory phase A'S: C The effector phase of an immune response occurs )hen cells or molecules eliminate the microbe or microbial to"in. ,n a humoral immune response# the effector phase includes
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secretion of antibody# binding of the antibody to the microbe or to"in# and subse&uent antibody4dependent elimination of the microbe or to"in. The recognition phase is the initial binding of the antigen by the naie lymphocyte. The actiation phase includes proliferation and differentiation of lymphocytes in response to antigen recognition. The homeostatic phase follo)s the effector phase# during )hich the response )anes. ,n the memory phase# memory B cells and antibodies secreted by long4lied antibody4secreting cells are $)aiting% for a repeat e"posure to the microbe. 1'. (hich of the follo)ing statements is consistent )ith the process of clonal selection* A. The specificity of a lymphocyte antigen receptor changes to accommodate the structure of an antigen that binds to it. B. 6any different antigen receptors )ith different specificities are e"pressed on each lymphocyte. C. ymphocytes do not e"press antigen receptors on their cell surfaces until after e"posure to antigen. D. The diersity of the lymphocyte repertoire for antigens is ery small before e"posure to antigen but increases significantly after antigen e"posure. !. The diersity of the lymphocyte repertoire for antigens is ery large before e"posure to antigen# )ith millions of different clones of lymphocytes# each haing a different specificity. A'S: E The clonal selection hypothesis accurately predicted that indiiduals possess large numbers of different clones of lymphocytes before antigen e"posure# )ith cells in each clone e"pressing antigen receptors )ith a single identical specificity# but )ith different specificities from other clones. Thus# the diersity of the lymphocyte repertoire is ery large een before antigen e"posure. These receptors are e"pressed before antigen e"posure# and their specificities generally do not change in response to antigen.
13. (hich of the follo)ing best describes clonal e"pansion in adaptie immune responses* A. ,ncreased number of different lymphocyte clones# each clone specific for a different antigen during the course of an infection B. ,ncreased number of different lymphocyte clones# each clone specific for a different antigen during deelopment of the immune system# before e"posure to antigen C. ,ncreased number of lymphocytes )ith identical specificities# all deried from a single lymphocyte due to nonspecific stimuli from the innate immune system D. ,ncreased number of lymphocytes )ith identical specificities# all deried from a single lymphocyte stimulated by a single antigen !. ,ncreased si5e of the lymphocytes of a single clone due to antigen4induced actiation of the cells A'S: ( Clonal e"pansion occurs during the actiation phase of an adaptie immune response. A single lymphocyte is stimulated to diide by antigen# and the progeny go through seeral rounds of diision until there are many lymphocytes# all )ith identical specificities# all deried from one cell. The number of different clones is not influenced by antigen e"posure. !"pansion does not refer to the si5e of the cells# although actiated lymphocytes are larger than their naie precursors.
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17. The estimated number of distinct structures that can be recogni5ed by the mammalian adaptie immune system is A. 1412 B. 12'4123 C. 123412; D. 12-412 !. A'S: ( Although the theoretical number of antigen specificities of the adaptie immune system is higher# estimates of the actual number of different antibody and T cell antigen receptor specificities are in the range of 12-412. This number is large enough to accommodate
most of the diersity in molecular structures that the microbial )orld is capable of producing. 1;. (hich of the follo)ing statements best describes the $t)o4signal re&uirement% for naie lymphocyte actiation* A. ymphocytes must recogni5e t)o different antigens to become actiated. B. ymphocytes must recogni5e the same antigen at t)o se&uential times to become actiated. C. ymphocytes must recogni5e antigen and respond to another signal generated by microbial infection to become actiated. D. Both naie B and naie T lymphocytes must simultaneously recogni5e antigen for either to be actiated. !. (hen lymphocytes recogni5e antigen# the antigen receptors must actiate t)o4 signal transduction path)ays to become actiated. A'S: C aie lymphocytes )ill not become actiated by antigen alone ?signal 1@. ,n addition# they re&uire $costimulatory% signals ?signal '@# )hich are either microbial products or molecules on host cells induced by microbial infection. The molecules that proide signal ' bind to receptors on the lymphocytes that are distinct from the clonally distributed antigen receptors. !ach lymphocyte cannot generally recogni5e more than one antigen. Although lymphocyte actiation may re&uire recognition of antigen molecules by more than one antigen receptor# the t)o4signal re&uirement does not refer to this. There is no general re&uirement for both T and B cells to recogni5e the same antigen for actiation of either to occur. The t)o4signal re&uirement does not refer to antigen receptor=associated signal transduction path)ays.
1<. ,n addition to T cells# )hich cell type is re&uired for initiation of all T cell=mediated immune responses* A. !ffector cells B. 6emory cells C. atural iller cells D. Antigen4presenting cells !. B lymphocytes
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A'S: ( T cell=mediated immune responses are initiated )hen naie T cells are actiated. Antigen4 presenting cells# such as dendritic cells# are re&uired to display antigens ?peptide468C molecule comple"es@ for naie T cell recognition and to e"press costimulatory molecules also needed for T cell actiation. 6emory cells# cytoto"ic T cells# and B lymphocytes are not inoled in the initial actiation of naie T lymphocytes.
