What is the outcome of clonal selection after a lymphocyte is activated?

Correct Answer: B

Rationale: The correct answer is B because clonal selection during lymphocyte activation leads to the formation of memory and effector cells. This process involves the proliferation and differentiation of the activated lymphocyte into these specialized cells, which play crucial roles in immune responses upon encountering the same antigen in the future. Cytokine suppression (choice A) is not the direct outcome of clonal selection but may be a regulatory mechanism during immune responses. Antigen elimination without cellular proliferation (choice C) is not accurate as clonal selection involves the expansion of specific lymphocyte clones. Destruction of the lymphocyte (choice D) is not the outcome of clonal selection, as activated lymphocytes undergo proliferation and differentiation rather than destruction.

Correct Answer: B

Rationale: The correct answer is B: Differentiation into effector and memory cells. During clonal selection, activated lymphocytes undergo differentiation into effector cells that combat the current infection and memory cells that provide long-lasting immunity. Effector cells directly eliminate pathogens, while memory cells remember the specific pathogen for future encounters. Choices A, C, and D are incorrect as they do not accurately represent the main outcomes of clonal selection. T cell activation and cytokine suppression (A) are processes involved in immune response regulation rather than the direct outcomes of clonal selection. Pathogen destruction and tissue repair (C) are broader immune responses that occur after clonal selection. Phagocytosis and complement activation (D) involve innate immune responses, not the adaptive immune responses seen in clonal selection.

Correct Answer: C

Rationale: Isotype switching in B cells involves changing the constant region to produce different antibody isotypes, such as IgG, IgA, or IgE. This is important for diversifying the functions of antibodies without altering antigen specificity. It allows for different effector functions, such as opsonization, neutralization, or complement activation. This process does not eliminate antigen-specific B cells, as it maintains the immunological memory. Isotype switching does not directly affect antibody affinity for antigens, which is primarily determined by somatic hypermutation and affinity maturation. It is not limited to producing IgM only, as B cells can switch to other isotypes based on the cytokine microenvironment.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Atopy is a genetic predisposition to produce IgE antibodies in response to allergens. 2. IgE antibodies play a crucial role in allergic reactions. 3. Individuals with atopy have an exaggerated immune response to allergens. 4. Excess production of IgA antibodies (B) and suppressed immune response to allergens (C) are not characteristic features of atopy. 5. Delayed hypersensitivity reactions (D) involve a different immune mechanism compared to the immediate IgE-mediated response in atopy.

Correct Answer: B

Rationale: The correct answer is B because sensitization in contact hypersensitivity requires T cell presentation of a hapten-modified antigen. This process activates T cells, leading to immune response. Antigen-antibody complex formation (A) is more related to immune responses in humoral immunity. Mast cell degranulation (C) is associated with allergic reactions, not contact hypersensitivity. Cytokine suppression (D) would hinder, not promote, the immune response needed for sensitization in contact hypersensitivity.