Penicillin is a hapten... which one will induce a secondary response to penicillin when injected into the mouse 1 month later?

Correct Answer: D

Rationale: The correct answer is D (bovine serum albumin). Bovine serum albumin can act as a carrier protein, allowing hapten (penicillin) to bind and form a complex, triggering an immune response. This complex induces memory B cells, leading to a secondary response upon re-exposure to penicillin. Penicillin alone (choice A) is a hapten and cannot induce a secondary response without a carrier protein. Penicillin bound to egg albumin (choice B) is specific to egg albumin, not penicillin, and would not generate a response to penicillin. Egg albumin (choice C) is a protein unrelated to penicillin. Bovine serum albumin (choice D) is the correct carrier protein for penicillin in this context.

Correct Answer: A

Rationale: The correct answer is A: Mu chain. During B lymphocyte maturation, the first immunoglobulin heavy chain synthesized is the Mu chain. This is because the Mu chain is the first heavy chain isotype expressed during early B cell development. The Mu chain combines with the surrogate light chain to form the pre-B cell receptor, which is essential for signaling in pre-B cells. The Mu chain is later replaced by other heavy chain isotypes such as gamma, epsilon, and alpha during B cell differentiation. Therefore, the Mu chain is the correct answer as it is the initial heavy chain produced in B cell maturation. Choices B, C, and D are incorrect because they represent heavy chain isotypes that are expressed at later stages of B cell development and differentiation.

Correct Answer: D

Rationale: The correct answer is D because minor histocompatibility antigens can induce immune reactions leading to rejection in transplantation. These antigens are derived from genetic variations, not detected by antibodies and complement (A), controlled by genes outside the major histocompatibility complex (B), and are important in transplantation as they contribute to rejection responses (C).

Correct Answer: D

Rationale: The correct answer is D: class II MHC antigens. Antigen-presenting cells activate helper T cells by presenting antigens on their surfaces via class II MHC molecules. These molecules bind to the T cell receptor, triggering the immune response. IgE (choice A) is not involved in activating helper T cells. Gamma interferon (choice B) is a cytokine produced by T cells but is not directly involved in antigen presentation. Class I MHC antigens (choice C) present antigens to cytotoxic T cells, not helper T cells.

Correct Answer: B

Rationale: The correct answer is B: IgG antibody. In hemolytic disease of the newborn, maternal IgG antibodies against fetal Rh-positive red blood cells can cross the placenta and attack the fetal RBCs, leading to hemolysis. IgE is primarily involved in allergic reactions, not hemolytic disease. IgM antibodies are too large to cross the placenta efficiently. IgA is not typically involved in hemolytic diseases. Therefore, IgG is the most likely mediator of hemolytic disease of the newborn in cases of Rh blood group incompatibility.