A delayed hypersensitivity reaction is characterized by

Correct Answer: C

Rationale: A delayed hypersensitivity reaction involves helper T cells and macrophages, causing inflammation and tissue damage over time. Helper T cells release cytokines, activating macrophages to mediate the immune response. This process leads to the formation of granulomas, which are characteristic of delayed hypersensitivity reactions. Choices A, B, and D do not align with the pathophysiology of delayed hypersensitivity reactions and are incorrect. Edema without a cellular infiltrate (Choice A) is not specific to delayed hypersensitivity reactions. An infiltrate composed of neutrophils (Choice B) is indicative of acute inflammation, not delayed hypersensitivity. Eosinophils (Choice D) are typically involved in allergic reactions and parasitic infections, not delayed hypersensitivity reactions.

Correct Answer: C

Rationale: The correct answer is C because the recipient is X-irradiated, which impairs their immune system, making them more susceptible to graft-versus-host reaction when receiving cells from a different strain. In this scenario, the adult strain A spleen cells injected into an X-irradiated strain AB adult, the immune system of the recipient is compromised, increasing the likelihood of the reaction. Choice A is less likely as newborns have an immature immune system. Choice B is less likely because x-irradiation of the donor reduces the likelihood of a reaction. Choice D is less likely because the recipient is a newborn, having an immature immune system.

Correct Answer: A

Rationale: The correct answer is A: a single terminal sugar residue. Blood group A and B antigens are determined by the presence of specific sugar molecules at the terminal end of glycoproteins on red blood cells. The specificity is based on the addition of a single sugar residue - either N-acetylgalactosamine (A antigen) or galactose (B antigen) to the H antigen precursor. This single terminal sugar residue determines the blood group specificity. Choice B is incorrect because amino acids are not involved in determining blood group antigens. Choice C is incorrect as blood group antigens are determined by single sugar residues, not multiple differences in the carbohydrate portion. Choice D is incorrect as blood group antigens are based on sugar residues, not protein differences.

Correct Answer: A

Rationale: Rationale for Correct Answer (A): A: The statement is incorrect. Tolerance is antigen-specific, meaning the immune system can distinguish between self and non-self antigens. Paralysis of immune cells leads to a lack of response against specific antigens, not many. Therefore, this statement is incorrect. Summary of Incorrect Choices: B: Tolerance is actually more easily induced in B cells than in T cells due to their inherent self-tolerance mechanisms. C: Tolerance is actually more easily induced in neonates due to their developing immune system, but it can be induced in adults as well. D: Tolerance can be induced by both simple and complex molecules, but the level of ease may vary depending on the specific context.