A recipient of a 2-haplotype MHC-matched kidney from a relative still needs immunosuppression to prevent graft rejection because

Correct Answer: C

Rationale: The correct answer is C because minor histocompatibility antigens, which are not matched in a 2-haplotype MHC-matched kidney transplant from a relative, can still trigger an immune response leading to graft rejection. This is why immunosuppression is still necessary. A: Graft-versus-host disease would not be a problem in this scenario as the recipient is receiving a kidney transplant, not bone marrow. B: This choice is redundant with the correct answer. Matching minor histocompatibility antigens is crucial for reducing the risk of rejection. D: Complement components do not play a significant role in graft rejection in this context.

Correct Answer: D

Rationale: The correct answer is D because the genes for the gamma chain and alpha chain are located on the same chromosome, making them linked genes. This is known as genetic linkage. The other choices (A, B, C) involve genes from different chromosomes or gene segments, so they are not linked genes. Genes that are physically close together on the same chromosome tend to be inherited together, which is the basis of genetic linkage analysis.

Correct Answer: A

Rationale: Activated helper T cells release various cytokines to regulate the immune response. Interleukin-1 is primarily produced by macrophages and monocytes, not helper T cells. It plays a role in inflammation and fever. Interleukin-2, interleukin-4, and gamma interferon are indeed released by activated helper T cells to stimulate immune responses. Therefore, choice A, interleukin-1, is the correct answer as it is not typically released by activated helper T cells.

Correct Answer: B

Rationale: The correct answer is B because the antibody-binding site is primarily formed by the hypervariable regions of both the heavy (H) and light (L) chains. These regions contain the most sequence diversity and directly interact with antigens. Choice A is incorrect because the constant regions do not directly participate in antigen binding. Choice C is incorrect as it only mentions H chains, disregarding the contribution of L chains. Choice D is incorrect as it focuses solely on the variable regions of H chains, neglecting the importance of the L chains in forming the binding site.

Correct Answer: D

Rationale: The correct answer is D. The affinity for antigen is determined by the variable region of the antibody, specifically the antigen-binding site. The heavy-chain constant region influences the other properties listed. A: The ability to cross the placenta is determined by the structure of the heavy-chain constant region, particularly the Fc region. B: Isotype (class) is determined by the type of heavy-chain constant region present in the antibody. C: The ability to fix complement is also influenced by the heavy-chain constant region, particularly the Fc region. Therefore, D is the only property that is not dependent on the structure of the heavy-chain constant region.