Sloma.Immune System I And Ii_practice Questions

1.

Which of the following is not a direct consequence of antibody binding to antigen?

A.

Activation of B cells
B.

Neturalization of the antigen
C.

Activation of complement
D.

Phagocytosis of the antigen
E.

Activation of T cells

Correct Answer
E. Activation of T cells

Explanation
E : Antibody binding to antigen can trigger all of the events described in A‐D. Recall that T cells are
activated when they encounter their specific antigen presented in MHC class I or II by antigenpresenting
cells. While the B cell may become activated when surface‐bound antibody binds its specific
antigen and then go on to present the antigen to the T cell, the activation of the T cell is a consequence
of presentation of the antigen by the B cell, not a direct consequence antigen binding to antigen.

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2.

Immunodeficienies can be caused by defects in expression of many different molecules that contribute to both adaptive and innate immune responses. Failure to express which molecule would have no effect on the immune system’s ability to eliminate an extracellular bacterium?

A.

MHC class I
B.

MHC class II
C.

Surface‐bound antibody molecules
D.

Toll‐like receptors
E.

Complement components

Correct Answer
A. MHC class I

Explanation
A : Without MHC class II, antigen presenting cells cannot present exogenously‐derived antigen to CD4
T cells, thus preventing a CD4 T cell response against the extracellular bacterium. Without surfacebound
antibody molecules, B cells cannot get activated and there would be no antibody production
against the antigen. Without antibody production, there would be diminished phagocytosis of the
antigen by phagocytes and no classical complement activation to eliminate the pathogen. Without Tolllike
receptors, macrophages and dendritic cells would have decreased recognition of the antigen;
consequently, there would be no killing by the macrophage and very little antigen presentation of the
antigen to CD4 T cells. Without the complement components, there would be reduced inflammation at
the site of infection, no direct killing of the pathogen via the complement pathway, and no opsonization
of the pathogen by complement components (reduced pathogen uptake by phagocytes).

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3.

Your patient, a 7 month‐old boy, is suffering from repeated ear infections. In the lab, you determine that he has a defect in B cell function. What is the most likely defect?

A.

Inability to synthesize toxic nitric oxides
B.

Failure to produce complement components
C.

Failure to express toll‐like receptors
D.

Failure to express MHC class I molecules
E.

Failure to express surface‐bound antibody molecules

Correct Answer
E. Failure to express surface‐bound antibody molecules

Explanation
E: Without surface‐bound antibody expression, a B cell cannot become activated. Surface‐bound
antibody molecules serve as the antigen‐recognition receptor for B cells.

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4.

How do macrophages play an important role in the elimination of pathogens?

A.

Produce complement proteins that can eliminate the pathogen
B.

Phagocytosis of pathogens followed by presentation of antigens to B cells
C.

Phagocytosis of pathogens followed by oxygen‐dependent and oxygen‐independent killing of the pathogen
D.

Produce antibody molecules that can mark the pathogen for destruction
E.

Phagocytosis of pathogens followed by formation of the membrane‐attack complex that causes lysis of pathogens

Correct Answer
C. Phagocytosis of pathogens followed by oxygen‐dependent and oxygen‐independent killing of the pathogen

Explanation
C NOTE: The membrane attack complex is formed by the activation of complement…this is a detail
about complement activation that I don’t expect you to know for now…

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5.

Antigen presenting cells are essential in contributing to the activation of T cells. How do they accomplish this?

A.

They use MHC class I and class II molecules to present peptide antigens to T cells
B.

They use MHC class I and class II molecules to present carbohydrate antigens to T cells
C.

They secrete complement proteins that activate T cells
D.

They present antigen:antibody complexes to T cells
E.

They trigger activation of T cells through Toll‐like receptors

Correct Answer
A. They use MHC class I and class II molecules to present peptide antigens to T cells

Explanation
A : This question is simply asking about how T cells recognize antigen and what type of antigens they
can recognize.

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6.

What type of pathogen would be processed and loaded into MHC class II molecules?

A.

Antigens from a parasite that infects endothelial cells
B.

Antigens from a virus infecting endothelial cells
C.

Antigens from a bacterium infecting endothelial cells
D.

Antigens from extracellular bacteria
E.

Antigens from bacteria that infects endothelial cells

Correct Answer
D. Antigens from extracellular bacteria

Explanation
D : This question relies on the recognition that MHC class II molecules present exogenously‐derived
antigens. In all answer choices except D the cell is infecting a cell that does not express MHC class II.

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