Multi-photon microscopy has proved to be an invaluable tool for the evaluation of the dynamics of immune responses in vivo. The following is a list of observations derived from intra-vital microscopy. Identify the incorrect statement.

Correct Answer: D

Rationale: The correct answer is D because dendritic cells do not typically move rapidly through the germinal center during an immune response. Dendritic cells usually interact with T cells in the paracortex to present antigens, and they are not known to migrate rapidly through the germinal center. A: This statement is correct as T cells do make stable and prolonged contacts with APCs in the paracortex during immune responses. B: This statement is incorrect as B cells do not move at the same speed and randomly in follicles in the absence of antigens. They respond to signals and cues in the microenvironment. C: This statement is correct as specific B cells can quickly direct themselves towards the source of antigen during an infection. In summary, choice D is incorrect because dendritic cells do not move rapidly through the germinal center during an immune response, while the other choices accurately describe behaviors of immune cells during immune responses.

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.

Correct Answer: B

Rationale: Interferons are the correct answer as they are a cytokine group primarily associated with antiviral responses. They play a key role in the immune response against viral infections by inhibiting viral replication and spreading to other cells. Interleukins are more diverse and involved in various immune responses, not specifically antiviral. Tumor necrosis factors are more related to inflammation and cell death. Transforming growth factors are involved in cell growth and differentiation, not primarily antiviral responses. Therefore, B: Interferons is the most appropriate choice for cytokine group associated with antiviral responses.