AP-Micro Immunology and Host Defense 2

Question 1

Which cells present exogenous antigens via MHC class II molecules to activate CD4+ helper T cells?

Accepted Answer

Professional antigen-presenting cells (APCs)

Answer

Dendritic cells, macrophages, and B cells process exogenous antigens and present peptides on MHC class II to CD4+ T helper cells.

Question 2

Which immunoglobulin class is the most abundant in serum and the predominant antibody in secondary (anamnestic) immune responses?

Accepted Answer

IgG

Answer

IgG constitutes ~75% of serum immunoglobulin and is the major antibody produced during secondary immune responses due to memory B cell activation.

Question 3

The first antibody class produced during a primary immune response, existing as a pentamer in serum, is:

Accepted Answer

IgM

Answer

IgM is the earliest antibody produced in a primary response; its pentameric structure makes it highly effective at agglutination and complement activation.

Question 4

Which T cell subset directly kills virus-infected cells by recognizing antigens presented on MHC class I molecules?

Accepted Answer

CD8+ cytotoxic T lymphocytes (CTLs)

Answer

CD8+ CTLs recognize viral peptides on MHC class I (expressed on all nucleated cells) and kill infected cells via perforin/granzyme and Fas-FasL pathways.

Question 5

Secretory IgA (sIgA) protects mucosal surfaces primarily by:

Accepted Answer

Neutralizing pathogens and preventing epithelial attachment

Answer

sIgA neutralizes pathogens and blocks their attachment to mucosal epithelium without activating inflammation, providing non-inflammatory first-line mucosal defense.

AP Practice Test

AP Practice Test

AP-Micro Immunology and Host Defense 2