naïve T cells can be found in

Correct Answer: A

Rationale: The correct answer is A: Blood. Naïve T cells are circulating in the blood, ready to encounter antigens. They can move to secondary lymphoid organs like lymph nodes. Germinal centers (B) are sites of B cell maturation, not where naïve T cells are primarily found. While some naïve T cells enter lymph nodes (C), they are not mostly located in the medullary region. Naïve T cells can also migrate to non-lymphoid tissues (D), but their primary residence is in the blood.

Correct Answer: C

Rationale: The correct answer is C because it indicates a specific reason for the intense debate within the scientific community regarding ferrets in Flu research. Mutations in H5N1 creating a strain transmissible among ferrets is significant as it highlights a potential threat of cross-species transmission and the need for further study. A is incorrect as it does not provide a specific reason related to ferrets and their role in Flu research. B is incorrect because it focuses on a specific strain (H1N1) rather than mutations in H5N1. D is incorrect as it mentions publications being put on hold but does not address the core issue of mutations and transmissibility among ferrets.

Correct Answer: B

Rationale: Step-by-step rationale for Choice B (IL-1β) being correct: 1. The TIR domain is present in Toll-like receptors (TLRs) and IL-1 receptor. 2. TLRs recognize various microbial products, while IL-1 receptor binds IL-1 cytokines. 3. Both TLRs and IL-1 receptor signal through the TIR domain. 4. IL-1β is a cytokine that binds to IL-1 receptor, which contains a TIR domain. Summary of why the other choices are incorrect: A: Type I Interferons - Type I interferons signal through JAK-STAT pathway, not TIR domain. C: TNF-α - TNF receptor family signals through TNF receptor-associated death domain, not TIR domain. D: IL-8 - IL-8 binds to CXCR1 and CXCR2 receptors, which do not contain a TIR domain. In summary, Choice B

Correct Answer: A

Rationale: Step 1: Evolutionary arms race involves a continuous cycle of adaptations by both hosts and pathogens to gain an advantage. Step 2: Both parties strive to outcompete each other to survive and reproduce. Step 3: This leads to a dynamic process where hosts evolve defense mechanisms while pathogens evolve ways to overcome them. Step 4: Therefore, the key concept is that both hosts and pathogens evolve to outcompete each other in the evolutionary arms race. Summary: - Option B is incorrect as hosts can also evolve rapidly through mechanisms like recombination. - Option C is incorrect as hosts do evolve through genetic changes, not just relying on chemical barriers. - Option D is incorrect as pathogens continuously evolve strategies, not just when hosts fail to adapt.

Correct Answer: B

Rationale: The correct answer is B: Phagocytosis. Elie Metchnikoff is credited with discovering phagocytosis, the process in which certain cells engulf and digest foreign particles or microorganisms. He observed this phenomenon in starfish larvae, leading to a groundbreaking understanding of how immune cells defend the body against pathogens. Choice A (Antitoxins) is incorrect because although Metchnikoff made contributions to immunology, his notable discovery was phagocytosis, not antitoxins. Choice C (Germ theory of disease) is incorrect as this theory was developed by Louis Pasteur and Robert Koch. Choice D (Smallpox eradication) is incorrect as this achievement is primarily attributed to the efforts of Edward Jenner and the World Health Organization.