Identify the mismatched receptor: ligand pair

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: The correct answer is B: IgG. IgG plays a major role in opsonization by binding to antigens and marking them for phagocytosis. IgM is the first antibody produced in response to an infection but is not as effective in opsonization. IgA primarily protects mucosal surfaces. IgD is involved in the activation of B cells, not opsonization. In summary, IgG is the correct choice due to its specific role in opsonization compared to the other isotypes.

Correct Answer: D

Rationale: The correct answer is D because T cell development starts in the thymus while the naïve T cell activation by antigen occurs outside of the thymus. T cell development involves positive and negative selection, establishing MHC restriction, and interaction with thymic dendritic cells for maturation. Naïve T cells are activated by antigens in the periphery, not during T cell development in the thymus. Therefore, D is the correct answer as it does not align with the process of T cell development.

Correct Answer: D

Rationale: Step 1: Jenner observed milkmaids were protected from smallpox due to prior exposure to cowpox. Step 2: Jenner decided to inoculate a young boy with cowpox first. Step 3: Jenner then inoculated the boy with smallpox to test immunity. Step 4: The boy did not contract smallpox, demonstrating immunity. Step 5: Conclusion: Jenner proved cowpox exposure can make individuals immune to smallpox. Other choices are incorrect: A: The boy never contracted smallpox, not just because of the mild form of smallpox in the milkmaid. B: Inoculating with virulent smallpox first would not demonstrate cowpox immunity. C: Jenner did not just substitute cowpox for smallpox; he specifically tested immunity by exposing the boy to both viruses.

Correct Answer: B

Rationale: The correct answer is B because Shigella is a non-motile species and does not possess a flagellum. Shigella relies on non-flagellar mechanisms for its movement within host cells. Choice A is true as Shigella causes bloody diarrhea. Choice C is also true as Shigella exploits M cells to infect the host. Choice D is true as Shigella can move from cell to cell using actin comets. In summary, choice B is incorrect because Shigella does not have a flagellum, while choices A, C, and D are all true characteristics of Shigella.