Antigen Antibody Reaction Questions and Answers

Q: All of the following are true EXCEPT

Correct answer: an antigenic determinant is a paratopeThis is the false statement. An antigenic determinant is an epitope, on the antigen; a paratope is the binding site on the antibody. The two are complementary partners, not synonyms. The other three statements are correct: an epitope is a small part of a macromolecule, the variable domains form the binding site, and the heavy chain determines the class.

Q: Transplanted graft may be rejected due to

Correct answer: cell-mediated immune responseAcute graft rejection is driven principally by T cells recognising foreign major histocompatibility complex molecules on the graft, and it is T-cell activity that immunosuppressive regimens are designed to blunt. Antibody does contribute, notably in hyperacute rejection where preformed antibody attacks the graft vasculature within minutes, but the cell-mediated response is the main mechanism.

Q: Counter-immunoelectrophoresis is used for the detection of

Correct answer: All of theseCounter-immunoelectrophoresis drives antigen and antibody towards each other electrophoretically, so a precipitin line forms in minutes instead of the many hours diffusion alone would take. That speed is why it was adopted for urgent diagnoses: meningococcal antigen in cerebrospinal fluid, hepatitis B surface antigen, and alpha-fetoprotein are all standard applications.

Q: Ring test is used for

Correct answer: all of the aboveThe ring test simply layers antigen over antiserum in a narrow tube so that a ring of precipitate forms at the interface. All three named applications use it: the C-reactive protein test, Ascoli’s thermoprecipitin test for anthrax in tissue extracts, and the grouping of streptococci and pneumococci by their capsular or cell wall antigens.

Q: Which of the following immunoglobulins is present normally in plasma at the highest concentration?

Correct answer: IgGIgG accounts for about three quarters of the serum immunoglobulin, at roughly 8 to 16 g per litre, well ahead of IgA and IgM. Its long half-life of about three weeks, longer than any other class, is maintained by the neonatal Fc receptor, which recycles it rather than letting it be degraded.

Q: Type I hypersensitivity involves

Correct answer: IgEType I hypersensitivity is IgE-mediated. IgE binds through its Fc to high affinity receptors on mast cells and basophils, and when antigen cross-links two adjacent molecules the cell degranulates, releasing histamine and other mediators within minutes. This is the mechanism of hay fever, allergic asthma and anaphylaxis.

Q: Which immunoglobulin is the principal one found in secretions such as milk?

Correct answer: IgASecretory IgA predominates in milk, as in all external secretions. In colostrum the concentration is especially high, and because the antibody is not absorbed it works locally in the infant’s gut, coating organisms and blocking their attachment to the mucosa - protection at the surface where the newborn is most exposed.

21.

Antibody molecules

A.Are globular proteins found predominantly in the gamma region during electrophoresis
B.Recognise carbohydrates via a lectin head
C.Are produced by T cells
D.Use the Fc region to bind antigen

Answer: A

Correct answer: Are globular proteins found predominantly in the gamma region during electrophoresis

Antibodies are globular glycoproteins that migrate mainly in the gamma fraction on serum electrophoresis, which is the origin of the name gamma globulin. The other options each misplace a fact: lectin heads belong to collectins such as mannose-binding lectin, plasma cells derived from B cells produce antibody, and it is the Fab region rather than the Fc that binds antigen.

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22.

The immunoglobulin Joining chain (J-chain) is

A.only produced by T-Cells
B.only produced by neutrophils
C.associated with only multimeric forms of lgM and IgA
D.associated with IgE for histamine release

Answer: C

Correct answer: associated with only multimeric forms of lgM and IgA

The J chain is a small polypeptide that joins the monomer units of polymeric immunoglobulins - pentameric IgM and dimeric secretory IgA. Monomeric IgG, IgD and IgE have no J chain. It is made by the same plasma cell as the immunoglobulin, and it is also required for transport of IgA across the epithelium.

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23.

All of the following are true EXCEPT

A.An epitope is a small portion of a macromolecule
B. the variable region domains contain the antigen recognition site
C. an antigenic determinant is a paratope
D.The class of an immunoglobulin is determined by its heavy chain

Answer: C

Correct answer: an antigenic determinant is a paratope

This is the false statement. An antigenic determinant is an epitope, on the antigen; a paratope is the binding site on the antibody. The two are complementary partners, not synonyms. The other three statements are correct: an epitope is a small part of a macromolecule, the variable domains form the binding site, and the heavy chain determines the class.

Discuss in Forum

24.

Transplanted graft may be rejected due to

A.cell-mediated immune response
B.humoral immune response
C.innate immune response
D.passive response

Answer: A

Correct answer: cell-mediated immune response

Acute graft rejection is driven principally by T cells recognising foreign major histocompatibility complex molecules on the graft, and it is T-cell activity that immunosuppressive regimens are designed to blunt. Antibody does contribute, notably in hyperacute rejection where preformed antibody attacks the graft vasculature within minutes, but the cell-mediated response is the main mechanism.

Discuss in Forum

25.

A primary role for antibodies in resistance to bacterial infection is

A.Antibody dependent cell mediated cytotoxicity
B.Lysis of infected host cells
C.Activation of the alternative complement pathway
D.Opsonisation for increased uptake by phagocytic cells

Answer: D

Correct answer: Opsonisation for increased uptake by phagocytic cells

Antibody bound to a bacterial surface is recognised by Fc receptors on neutrophils and macrophages, so the organism is taken up far more readily than it would be unopsonised. Complement fixed by the same antibody adds C3b, a second opsonin. Cell-mediated cytotoxicity and lysis of infected host cells matter chiefly against viruses and parasites rather than against extracellular bacteria.

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26.

Counter-immunoelectrophoresis is used for the detection of

A.Meningococcal antigen
B.Hepatitis B surface antigen
C.Alpha-fetoprotein
D.All of these

Answer: D

Correct answer: All of these

Counter-immunoelectrophoresis drives antigen and antibody towards each other electrophoretically, so a precipitin line forms in minutes instead of the many hours diffusion alone would take. That speed is why it was adopted for urgent diagnoses: meningococcal antigen in cerebrospinal fluid, hepatitis B surface antigen, and alpha-fetoprotein are all standard applications.

Discuss in Forum

27.

Ring test is used for

A.C-reactive protein test
B.Ascoli's thermoprecipitation test
C.typing of streptococci and pneumococci
D.all of the above

Answer: D

Correct answer: all of the above

The ring test simply layers antigen over antiserum in a narrow tube so that a ring of precipitate forms at the interface. All three named applications use it: the C-reactive protein test, Ascoli’s thermoprecipitin test for anthrax in tissue extracts, and the grouping of streptococci and pneumococci by their capsular or cell wall antigens.

Discuss in Forum

28.

Which of the following immunoglobulins is present normally in plasma at the highest concentration?

A.IgG
B.IgM
C.IgA
D.IgD

Answer: A

Correct answer: IgG

IgG accounts for about three quarters of the serum immunoglobulin, at roughly 8 to 16 g per litre, well ahead of IgA and IgM. Its long half-life of about three weeks, longer than any other class, is maintained by the neonatal Fc receptor, which recycles it rather than letting it be degraded.

Discuss in Forum

29.

Type I hypersensitivity involves

A.IgD
B.IgM
C.IgE
D.IgG

Answer: C

Correct answer: IgE

Type I hypersensitivity is IgE-mediated. IgE binds through its Fc to high affinity receptors on mast cells and basophils, and when antigen cross-links two adjacent molecules the cell degranulates, releasing histamine and other mediators within minutes. This is the mechanism of hay fever, allergic asthma and anaphylaxis.

Discuss in Forum

30.

Which immunoglobulin is the principal one found in secretions such as milk?

A.IgG
B.IgM
C.IgA
D.IgD

Answer: C

Correct answer: IgA

Secretory IgA predominates in milk, as in all external secretions. In colostrum the concentration is especially high, and because the antibody is not absorbed it works locally in the infant’s gut, coating organisms and blocking their attachment to the mucosa - protection at the surface where the newborn is most exposed.

Discuss in Forum

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