Which of the following statements is characteristic of isotype switching?

Correct Answer: C

Rationale: Isotype switching in germinal centers, driven by CD40 and cytokines, is irreversible and not required for IgM.

Correct Answer: A

Rationale: IgA dominates secretions like milk; IgD , IgE , and IgG are less prevalent there.

Correct Answer: D

Rationale: Variable regions determine specificity; valence is binding capacity, Fc is effector.

Correct Answer: D

Rationale: Pasteur developed vaccines for all : rabies, anthrax, and cholera.

Correct Answer: B

Rationale: A hallmark of the adaptive immune system is that it progressively alters its response upon reexposure to an antigenic stimulus, and in doing so, it must recall the previous exposure, a process known as memory. Although they are members of the innate immune system and do not possess immunologic memory, phagocytes may be influenced by the adaptive immune system. Consistency in immune response from initial to subsequent encounters is a hallmark of the innate immune response. Immunologic memory of the adaptive immune system is not passed genetically from one generation of individuals to the next. Detection of diminished MHC class I expression is a function of natural killer cells, members of the innate immune system.