Neutrophils are attracted to an infected area by

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: 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.

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.