Which of the following is not required for full activation of a naïve lymphocyte?

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: 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.

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.