Which of the following is not a systemic cytokine?

Correct Answer: D

Rationale: The correct answer is D: IL-8. IL-8 is not a systemic cytokine because it mainly acts locally at the site of inflammation to recruit neutrophils. Systemic cytokines like TNF, IL-1, and IL-6 have widespread effects throughout the body, influencing various immune responses and inflammatory processes. IL-8's localized action distinguishes it from systemic cytokines, making it the correct choice. TNF, IL-1, and IL-6 are all systemic cytokines that play key roles in regulating the immune response and inflammation at a systemic level, unlike IL-8.

Correct Answer: A

Rationale: The correct answer is A: In many developing countries. Smallpox was indeed endemic in many developing countries in the 1960s, causing significant morbidity and mortality. This is supported by historical records and epidemiological data from that time period. Choices B, C, and D are incorrect because smallpox was not endemic in North America, England, or globally during the 1960s. Smallpox eradication efforts led to the global eradication of the disease in 1980, but in the 1960s, it was still prevalent in many developing countries.

Correct Answer: D

Rationale: The correct answer is D because M cells do not transport IgA from the lamina propria into the intestinal lumen. Instead, they transport antigens and pathogens from the gut lumen to underlying immune cells. Choice A is correct as M cells are found in Peyer's patches. Choice B is correct as M cells are specialized epithelial cells. Choice C is incorrect as M cells have microfolds on their luminal side, not microvilli.

Correct Answer: A

Rationale: The correct answer is A: CD4+ T cells. HIV primarily infects CD4+ T cells by binding to the CD4 receptor and a co-receptor, usually CCR5 or CXCR4. CD4+ T cells are crucial for coordinating the immune response. B cells (choice B) are not typically infected by HIV. CD8+ T cells (choice C) can be indirectly affected by HIV, but they are not the primary target of the virus. Therefore, the correct choice is A as it accurately reflects the primary target cells of HIV infection.

Correct Answer: B

Rationale: Correct Answer: B (VDJ gene rearrangement) Rationale: 1. VDJ gene rearrangement occurs during B cell development in the bone marrow, independent of T helper cells. 2. Somatic hypermutation and immunoglobulin class switching require T helper cell interactions. 3. Memory cell differentiation also involves T helper cells for activation and differentiation. 4. Therefore, VDJ gene rearrangement is the only process not directly dependent on antigen-specific T helper cells.