What term describes the increased affinity of antibodies during a secondary response?

Correct Answer: B

Rationale: The correct answer is B: Affinity maturation. During a secondary immune response, B cells undergo somatic hypermutation, leading to the production of antibodies with higher affinity for the antigen. This process occurs in germinal centers within secondary lymphoid organs. Isotype switching (A) refers to the change in antibody class but not affinity. Somatic recombination (C) is the process of creating diverse antibody repertoires. Clonal expansion (D) involves the proliferation of antigen-specific B cells but does not directly address affinity enhancement.

Correct Answer: C

Rationale: Regulatory T cells (Tregs) maintain immune homeostasis by suppressing immune responses using IL-10. Tregs release IL-10, which inhibits the activity of effector T cells and other immune cells, preventing excessive immune responses and maintaining balance. This mechanism helps prevent autoimmune diseases and chronic inflammation. Choices A, B, and D are incorrect because Tregs do not kill infected cells, produce pro-inflammatory cytokines, or activate macrophages. Instead, Tregs focus on regulating and dampening immune responses to maintain overall immune balance.

Correct Answer: B

Rationale: The correct answer is B: Goodpasture's syndrome. This disease is specifically associated with autoantibodies targeting type IV collagen in the basement membranes of the kidneys and lungs, leading to glomerulonephritis and pulmonary hemorrhage. Sarcoidosis (A) involves non-caseating granulomas, not collagen autoantibodies. Systemic lupus erythematosus (SLE) (C) is associated with various autoantibodies but not specifically targeting type IV collagen. Rheumatoid arthritis (D) is characterized by autoantibodies against citrullinated peptides and synovial tissue, not type IV collagen.

Correct Answer: B

Rationale: The correct answer is B: Macrophages. Macrophages are key immune cells involved in granuloma formation. They play a crucial role in engulfing and processing pathogens or foreign particles, leading to the formation of granulomas as part of the body's immune response. Mast cells (A) are primarily involved in allergic reactions. Neutrophils (C) are important in the initial immune response to infections but are not typically associated with granuloma formation. Dendritic cells (D) are important in antigen presentation and activation of T cells, but they are not the primary immune cells involved in granuloma formation.

Correct Answer: B

Rationale: The correct answer is B: C3a and C5a. In Type III hypersensitivity reactions, immune complexes form and deposit in tissues, leading to complement activation. C3a and C5a are anaphylatoxins released during complement activation, causing inflammation and tissue damage in Type III hypersensitivity. Rationale: A: C1 and C4 are primarily involved in Type I hypersensitivity reactions. C: C5b and C6 are part of the membrane attack complex in the classical pathway of complement activation, not specific to Type III hypersensitivity. D: C2 and C7 are involved in the classical pathway of complement activation but not directly implicated in Type III hypersensitivity reactions.