What happens to B cells after clonal selection and expansion?

Correct Answer: B

Rationale: After clonal selection and expansion, B cells differentiate into plasma cells to produce antibodies. This is crucial for the immune response as plasma cells are specialized in antibody production. B cells do not produce cytokines (choice A), initiate phagocytosis (choice C), or present antigens to T cells (choice D) post-clonal selection. Plasma cell differentiation is the key outcome of the B cell activation process, enabling the body to mount an effective immune response against pathogens.

Correct Answer: C

Rationale: The correct answer is C: Mucosal immunity. IgA plays a crucial role in protecting mucosal surfaces, such as the lining of the gut and respiratory tract, from pathogens. It helps prevent infections by neutralizing and blocking the entry of harmful substances. IgA is not involved in allergy mediation (choice A), placental transfer (choice B), or primary response (choice D), as those functions are typically associated with other types of antibodies. IgA's specificity for mucosal surfaces makes it uniquely suited for providing defense at these vulnerable sites.

Correct Answer: B

Rationale: The correct answer is B: Type I, II, III, and V. - Type I hypersensitivity involves IgE antibodies and immediate allergic reactions. - Type II hypersensitivity involves IgG and IgM antibodies attacking self-antigens on cells. - Type III hypersensitivity involves immune complex deposition. - Type V hypersensitivity involves autoantibodies stimulating receptors. Choices A, C, and D are incorrect because they do not include all types of hypersensitivity mediated by antibodies as specified in the question.

Correct Answer: B

Rationale: The correct answer is B because when immune complexes are not cleared in Type III hypersensitivity, they deposit in tissues, activating complement cascades and causing inflammation. This leads to tissue damage and the recruitment of inflammatory cells. A: Immune complexes do not directly activate T cells in Type III hypersensitivity. C: Phagocytosis of immune complexes can lead to cell activation and inflammation. D: Immune complexes do not suppress antibody production in Type III hypersensitivity.

Correct Answer: A

Rationale: The correct answer is A. Cross-linking of IgE molecules on the mast cell surface triggers the release of mediators during Type I hypersensitivity. When allergens bind to IgE antibodies on mast cells, it leads to cross-linking of IgE molecules, causing the mast cell to release histamine and other inflammatory mediators. This process initiates the allergic response. Explanation for incorrect choices: B: Activation of complement proteins does not directly trigger mast cell degranulation in Type I hypersensitivity. C: Binding of IgG to antigen is characteristic of Type II and Type III hypersensitivity reactions, not Type I. D: Phagocytosis of allergens does not directly stimulate mast cells to release mediators in Type I hypersensitivity.