Which of the following does not describe defensins?

Correct Answer: B

Rationale: The correct answer is B: They function as opsonins. Rationale: 1. Defensins disrupt pathogen membranes by penetrating them (A), not by functioning as opsonins. 2. Defensins are amphipathic (C), having hydrophobic and hydrophilic regions, which aid in membrane disruption. 3. Defensins are contained in neutrophil granules (D), contributing to their role in the immune response. Summary: Choice B is incorrect because defensins do not function as opsonins, which are molecules that enhance phagocytosis of pathogens by immune cells. Choices A, C, and D correctly describe aspects of defensins' mechanism of action and localization.

Correct Answer: B

Rationale: The correct answer is B: Anchors the receptor in the T cell membrane. The constant region of a T cell receptor is responsible for anchoring the receptor in the T cell membrane, providing stability and structural support. This region does not mediate antigen binding (choice A), as that function is carried out by the variable region. It also does not directly interact with MHC molecules (choice C), which is primarily the role of the variable region. Lastly, the constant region is not structurally diverse amongst T cell receptors (choice D), as it remains relatively consistent within a specific T cell subtype.

Correct Answer: A

Rationale: The correct answer is A. Naïve lymphocytes require activation through recognition of specific antigen, costimulatory signaling, and cytokines. Migration into an inflammatory site is not a requirement for full activation. Naïve lymphocytes can be activated in secondary lymphoid organs where antigen presentation occurs. Migration to inflammatory sites occurs after activation to fight infections.

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: A

Rationale: Rationale: Option A is correct because genetic factors have been identified as playing a role in predisposition to develop MS. Studies have shown a higher risk among individuals with family history. Option B is incorrect because environmental factors, such as vitamin D levels and viral infections, are known to influence MS development. Option C is incorrect as MS is more prevalent in North America and Europe. Option D is incorrect because MS is primarily mediated by T-cell responses, not autoantibodies.