What is the chance of their child having sickle cell anaemia? (Parents are both sickle cell trait carriers)

Correct Answer: B

Rationale: The correct answer is B (25%). When both parents are carriers of the sickle cell trait, they each pass down the gene for sickle cell or normal hemoglobin with a 50% chance. The possible combinations are SS (normal), SS (sickle cell disease), AS (sickle cell trait), or AS (sickle cell trait). Therefore, there is a 25% chance (1 out of 4) that their child will inherit two sickle cell genes and have sickle cell anaemia. Choices A, C, and D are incorrect as they do not accurately reflect the genetic probability based on Mendelian inheritance principles.

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: C

Rationale: Neutrophils are attracted to an infected area by phagocytosis of IgE-coated bacteria. This is because IgE antibodies bind to pathogens, activating neutrophils through Fc receptors for phagocytosis. IgM (A) is not directly involved in neutrophil attraction. Vascular permeability (B) is a response to inflammation but does not directly attract neutrophils. Aggregation of C4 and C2 (D) is part of the complement system and does not specifically attract neutrophils.

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.