If adult AB spleen cells are injected into a newborn B mouse, which one of the following is MOST likely to occur?

Correct Answer: D

Rationale: The correct answer is D because when adult AB spleen cells are injected into a newborn B mouse, the recipient's immune system is still developing. This allows the injected cells to establish tolerance towards strain A antigens. This process is known as neonatal tolerance induction. Option A is incorrect because the immune system of the recipient is not mature enough to mount a strong response to destroy the injected cells. Option B is unlikely as the injected cells would likely interact with the recipient's immune system. Option C is less likely as the immune system of the newborn mouse is not fully developed to initiate a graft-versus-host reaction efficiently.

Correct Answer: C

Rationale: The correct answer is C because the purified protein derivative (PPD) is used to test for tuberculosis, which elicits a delayed-type hypersensitivity reaction. Helper T cells and macrophages are key players in this response, as they release cytokines and activate macrophages to combat the antigen. Eosinophils (A) are more commonly seen in allergic reactions, neutrophils (B) are prominent in acute bacterial infections, and B cells (D) are involved in antibody production, not the primary response to PPD.

Correct Answer: B

Rationale: The correct answer is B: it provides antibody more rapidly. Passive immunization involves giving pre-formed antibodies directly to an individual, providing immediate protection. This is advantageous over active immunization, where the body needs time to produce antibodies after exposure to an antigen. Choice A is incorrect because passive immunization is typically administered through injection, not orally. Choice C is incorrect as the duration of antibody persistence is usually shorter in passive immunization compared to active immunization. Choice D is incorrect because passive immunization can contain various types of antibodies, not just IgM.

Correct Answer: D

Rationale: Rationale for Correct Answer (D): Haptens are small molecules that can bind to antibodies without inducing an immune response on their own. They require a carrier protein to become immunogenic and induce an antibody response. However, haptens do not need to be processed by CD8+ cells to become immunogenic, as they primarily induce responses from B cells. CD8+ cells are involved in processing antigens for presentation to T cells. Therefore, statement D is incorrect. Summary of Incorrect Choices: A: True - haptens can bind to antibodies. B: True - haptens require a carrier protein to induce antibody response. C: True - both penicillin and poison ivy allergens are haptens.