Bone marrow transplantation in immunocompromised patients presents which major problem?

Correct Answer: A

Rationale: The correct answer is A: potentially lethal graft-versus-host disease. Bone marrow transplantation in immunocompromised patients can lead to graft-versus-host disease, where the donor's immune cells attack the recipient's tissues, potentially leading to severe complications or death. This occurs due to the recognition of the recipient's tissues as foreign by the donor's immune system. The other choices are incorrect because B (high risk of T cell leukemia) is not a major problem associated with bone marrow transplantation, C (inability to use a live donor) is not a major problem but a limitation, and D (delayed hypersensitivity) is not a major concern in this context.

Correct Answer: A

Rationale: The idiotypic determinants are unique antigenic determinants located within the hypervariable regions of heavy and light chains. These regions are highly variable and contribute to the diversity of antibodies. The correct answer is A because idiotypic determinants are specific to the variable regions of antibodies, not the constant regions. Choices B, C, and D are incorrect because idiotypic determinants are not found in the constant regions or hinge region of antibodies. The variability in the hypervariable regions allows antibodies to recognize and bind to a wide range of antigens, making them crucial for the specificity of the immune response.

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: A

Rationale: The correct answer is A: IgG. IgG is the class of immunoglobulins that crosses the placenta from the mother to the fetus, leading to high concentrations in newborns. IgM is the first class produced in response to infection but is not present in high levels in newborns. IgA is primarily found in mucosal areas and secretions, not in high concentrations in the blood. IgD is mainly present on the surface of B cells and has limited presence in the bloodstream. Therefore, IgG is the most abundant immunoglobulin in the blood of a human newborn due to passive transfer from the mother.

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.