What is the key characteristic of adaptive immunity compared to innate immunity?

Correct Answer: B

Rationale: The correct answer is B because adaptive immunity is characterized by antigen-specific responses and memory. This means that it can recognize and target specific antigens upon exposure and develop long-lasting immunological memory. Choice A is incorrect because physical barriers like skin are part of innate immunity, not adaptive immunity. Choice C is incorrect as adaptive immunity responds to specific antigens, not all antigens non-specifically. Choice D is incorrect because adaptive immunity typically takes longer to respond compared to innate immunity due to the need for activation and clonal expansion of specific immune cells.

Correct Answer: B

Rationale: The correct answer is B: Type I, II, III, and V. - Type I hypersensitivity involves IgE antibodies and immediate allergic reactions. - Type II hypersensitivity involves IgG and IgM antibodies attacking self-antigens on cells. - Type III hypersensitivity involves immune complex deposition. - Type V hypersensitivity involves autoantibodies stimulating receptors. Choices A, C, and D are incorrect because they do not include all types of hypersensitivity mediated by antibodies as specified in the question.

Correct Answer: B

Rationale: The correct answer is B because when immune complexes are not cleared in Type III hypersensitivity, they deposit in tissues, activating complement cascades and causing inflammation. This leads to tissue damage and the recruitment of inflammatory cells. A: Immune complexes do not directly activate T cells in Type III hypersensitivity. C: Phagocytosis of immune complexes can lead to cell activation and inflammation. D: Immune complexes do not suppress antibody production in Type III hypersensitivity.

Correct Answer: A

Rationale: The correct answer is A. Cross-linking of IgE molecules on the mast cell surface triggers the release of mediators during Type I hypersensitivity. When allergens bind to IgE antibodies on mast cells, it leads to cross-linking of IgE molecules, causing the mast cell to release histamine and other inflammatory mediators. This process initiates the allergic response. Explanation for incorrect choices: B: Activation of complement proteins does not directly trigger mast cell degranulation in Type I hypersensitivity. C: Binding of IgG to antigen is characteristic of Type II and Type III hypersensitivity reactions, not Type I. D: Phagocytosis of allergens does not directly stimulate mast cells to release mediators in Type I hypersensitivity.

Correct Answer: C

Rationale: The correct answer is C (24-72 hours) for Type IV hypersensitivity reactions to develop. This type of reaction involves T cell-mediated immune responses, which take time to develop. Initially, sensitization occurs, followed by activation of memory T cells upon re-exposure to the antigen. This process typically takes 24-72 hours to manifest clinically. Choices A (Within minutes), B (1-3 hours), and D (5-7 days) are incorrect because Type IV reactions do not exhibit immediate responses like Type I hypersensitivity reactions (Choice A), nor do they typically take as long as 5-7 days to develop (Choice D). The time frame of 1-3 hours (Choice B) is too short for the characteristic delayed hypersensitivity reaction seen in Type IV responses.