AIDS is caused by a human retrovirus that kills

Correct Answer: C

Rationale: The correct answer is C because AIDS is caused by the human immunodeficiency virus (HIV), which specifically targets and kills CD4-positive T lymphocytes. These cells are crucial for coordinating the immune response. A, B, and D are incorrect because HIV primarily affects CD4-positive T cells, not B lymphocytes, lymphocyte stem cells, or CD8-positive T cells. This leads to a weakened immune system, making individuals more susceptible to infections and other complications associated with AIDS.

Correct Answer: B

Rationale: The correct answer is B because helper T cells play a crucial role in activating B cells to produce antibodies. In this scenario, the protein component of the hapten-protein conjugate must be recognized by helper T cells to initiate the immune response. This recognition leads to the activation and differentiation of B cells into plasma cells that secrete anti-hapten antibodies. Choices A, C, and D are incorrect because the focus should be on the protein component, not the hapten or suppressor T cells, for the production of anti-hapten antibodies.

Correct Answer: D

Rationale: The correct answer, D, is not true because class I MHC antigens are primarily found on all nucleated cells, not just B cells, macrophages, and activated T cells. These antigens present endogenous antigens to CD8+ T cells. Choice A is incorrect because class I MHC antigens are not typically assayed using antibody and complement; instead, they are recognized by CD8+ T cells. Choice B is incorrect because identifying class I MHC antigens in the lab usually requires more than a few hours due to the complexity of the process. Choice C is incorrect because class I MHC antigens are controlled by a single gene locus in the major histocompatibility complex.

Correct Answer: C

Rationale: The correct answer is C because classic-pathway C3 convertase does not contain C3b. In the classical pathway, C3 convertase is formed by the cleavage of C4bC2a, which does not involve C3b. A: classic-pathway C5 convertase contains C3b as it is formed by the binding of C4b2a3b complex to C5. B: alternative-pathway C5 convertase contains C3b as it is formed by the binding of C3bBb3b complex to C5. D: alternative-pathway C3 convertase contains C3b as it is formed by the binding of C3bBb complex to C3.

Correct Answer: C

Rationale: Certainly! The Rh factor follows Mendelian inheritance. The Rh-negative woman is homozygous Rh-negative (rr) and the Rh-positive man is heterozygous (Rr). The Punnett square for their offspring shows a 1/2 chance of each child being Rh-positive (Rr). Therefore, the probability of all three children being Rh-positive is (1/2)^3 = 1/8, making choice C the correct answer. Choices A, B, and D are incorrect because they do not consider the specific genetic inheritance pattern of the Rh factor in this scenario.