A cytokine polarizing activated T cells towards a TH2 subset is

Correct Answer: C

Rationale: The correct answer is C: IL-10. IL-10 is known to polarize activated T cells towards a TH2 subset by suppressing TH1 cytokine production. IL-12 (A) promotes TH1 differentiation, IL-2 (B) supports T cell proliferation, and IL-5 (D) is involved in eosinophil activation and differentiation, not in polarizing T cells towards a TH2 subset.

Correct Answer: B

Rationale: The correct answer is B: gp41. Gp41 is responsible for the fusion of the viral envelope with the cell plasma membrane by undergoing conformational changes that allow the viral and cellular membranes to merge. Gp120 attaches to the host cell receptor (CD4), facilitating the binding of the virus to the host cell. Gp160 is the precursor protein that is cleaved into gp120 and gp41 during viral maturation. CXCR4 is a cellular co-receptor used by some strains of HIV to enter host cells but is not directly involved in the fusion process.

Correct Answer: B

Rationale: The correct answer is B: Thymus. The thymus is considered a primary lymphoid organ because it is where T lymphocytes (T cells) mature and differentiate. T cells play a crucial role in the adaptive immune response. The thymus is responsible for educating T cells to recognize self versus non-self antigens. Summary: A: Spleen is a secondary lymphoid organ involved in filtering blood and producing antibodies, not where T cells mature. C: Lymph node is also a secondary lymphoid organ where immune cells interact but not where T cells mature. D: Mucosal immune system refers to the immune system in mucosal tissues, not a specific primary lymphoid organ.

Correct Answer: B

Rationale: The correct answer is B because cytokines primarily function in an autocrine and paracrine manner. Autocrine signaling occurs when a cell produces a cytokine that acts on the same cell, while paracrine signaling involves cytokines acting on nearby cells. This allows cytokines to regulate immune responses locally. Option A is incorrect as endocrine signaling involves hormones acting on distant target cells via the bloodstream, which is not the primary function of cytokines. Option C is incorrect because cytokines do not require direct contact with pathogens to function. Option D is incorrect as cytokines do not degrade immune cells but rather regulate immune responses.

Correct Answer: B

Rationale: The correct answer is B because the immune system plays a crucial role in promoting wound healing and eliminating cell debris. When tissue is damaged, the immune response helps remove dead cells and debris, initiates the healing process, and supports tissue regeneration. This involves the recruitment of immune cells to the site of injury, releasing growth factors to stimulate cell proliferation, and resolving inflammation. Choice A (Preventing pathogen invasion) is incorrect because while the immune system does play a role in preventing pathogen invasion, this is not directly related to tissue regeneration. Choice C (Increasing cytokine production) is incorrect because although cytokines are involved in the immune response and can influence tissue repair, simply increasing cytokine production does not fully describe the immune system's role in tissue regeneration. Choice D (Suppressing adaptive immunity) is incorrect because suppressing adaptive immunity would hinder rather than promote tissue regeneration, as adaptive immunity plays a role in immune memory and long-term protection against pathogens.