Which of the following is a characteristic of the constant region of a T cell receptor?

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: 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.

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.