What is the function of IgA?

Correct Answer: C

Rationale: The correct answer is C: Mucosal immunity. IgA plays a crucial role in protecting mucosal surfaces, such as the lining of the gut and respiratory tract, from pathogens. It helps prevent infections by neutralizing and blocking the entry of harmful substances. IgA is not involved in allergy mediation (choice A), placental transfer (choice B), or primary response (choice D), as those functions are typically associated with other types of antibodies. IgA's specificity for mucosal surfaces makes it uniquely suited for providing defense at these vulnerable sites.

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.

Correct Answer: B

Rationale: The correct answer is B because correctly identifying the client prior to a blood transfusion helps prevent a type II hypersensitivity reaction, which occurs when the body attacks its own cells due to mismatched blood types. This action ensures that the client receives compatible blood, reducing the risk of a transfusion reaction. Administering steroids for a positive TB test (A) is unrelated to preventing a type II hypersensitivity reaction. Keeping the client free of the offending agent (C) is more relevant to preventing a type IV hypersensitivity reaction. Providing a latex-free environment for the client (D) is important for preventing a type I hypersensitivity reaction in latex-sensitive individuals, not type II reactions related to blood transfusions.