Which of the following statements is incorrect about allergic reactions?

Correct Answer: D

Rationale: The correct answer is D because current guidelines actually recommend early introduction of peanuts to prevent peanut allergies, not complete avoidance. This is based on research showing early introduction can reduce the risk of developing peanut allergies. Choice A is correct as sensitization is a key step in allergic reactions. Choice B is correct as inhaled allergens can cause hay fever. Choice C is correct as food allergies can indeed manifest as hives.

Correct Answer: C

Rationale: Rationale: 1. Class switching in B cells involves changing the class of antibody produced. 2. This allows the B cell to stop making one class of antibody and start making another. 3. This process enhances the immune response by generating antibodies with different functions. 4. Differentiating into a memory cell (choice A) is a separate process from class switching. 5. Making two or more antibody classes simultaneously (choice B) is not a characteristic of class switching. 6. Costimulatory signals from T helper cells (choice D) are important for B cell activation but not directly related to class switching.

Correct Answer: B

Rationale: The correct answer is B: Response that activates macrophages. Macrophages play a crucial role in controlling Leishmania infection by phagocytizing the parasites. Activating macrophages enhances their ability to kill the intracellular parasites, leading to effective immunity. Antibodies (choice A) are not as effective against intracellular pathogens like Leishmania. Mast cells (choice C) are primarily involved in allergic reactions, not protective immunity against parasites. Anti-bacterial response (choice D) is not directly relevant to combating Leishmania, an intracellular parasite.

Correct Answer: C

Rationale: The correct answer is C: Phagocytosis of microbes. Epithelial cells primarily act as a physical barrier to prevent the entry of microbes. Phagocytosis is a function of immune cells, not epithelial cells. A: Secretion of mucins helps trap pathogens. B: Secretion of antimicrobial peptides aids in defense. D: Tight junctions form a physical barrier between cells. Therefore, phagocytosis is not a direct mechanism exerted by epithelial cells at mucosal sites.

Correct Answer: D

Rationale: The correct answer is D because the binding of allergen-specific IgE to mast cells is actually a key event in anaphylactic shock, leading to the release of inflammatory mediators. Constriction of airways (A), loss of blood pressure (B), and hives (C) are all consequences of anaphylactic shock due to the systemic release of histamine and other mediators. IgE binding to mast cells triggers the release of these mediators, causing the symptoms associated with anaphylaxis. Therefore, D is the correct answer as it is not a consequence but rather an initiating event in anaphylactic shock.