Which of the following is NOT an example of a pathogen-associated molecular pattern (PAMP)?

Correct Answer: D

Rationale: The correct answer is D, MHC molecules. PAMPs are conserved molecules found on pathogens that can trigger an immune response. MHC molecules are not PAMPs; they are part of the host's immune system used to present antigens to T cells. LPS, peptidoglycan, and viral RNA are examples of PAMPs as they are specific molecules found on pathogens that can be recognized by pattern recognition receptors on immune cells to initiate an immune response.

Correct Answer: B

Rationale: The correct answer is B because NK cells do not require prior antigen sensitization to recognize and attack infected cells. This distinguishes them from other lymphocytes, such as T and B cells, which are part of adaptive immunity and require prior exposure to specific antigens. NK cells are part of innate immunity and can directly recognize and kill infected or abnormal cells without prior activation. Choices A, C, and D are incorrect as NK cells are not part of adaptive immunity, do not directly produce antibodies, and do not phagocytose pathogens.

Correct Answer: B

Rationale: The correct answer is B: Dendritic cells. Dendritic cells are antigen-presenting cells that bridge the innate and adaptive immune responses by capturing and presenting antigens to T cells, thus initiating the adaptive immune response. They are crucial for activating T cells and initiating specific immune responses. A: B cells are responsible for antibody production in the adaptive immune response, not for linking innate and adaptive immunity. C: Eosinophils are primarily involved in parasitic infections and allergic reactions, not in linking innate and adaptive immunity. D: NK cells are part of the innate immune system and are involved in detecting and killing infected cells, but they do not directly link innate and adaptive immunity.

Correct Answer: B

Rationale: The correct answer is B: IL-10. Regulatory T cells produce IL-10 to suppress immune responses by inhibiting the activation and function of other immune cells. IL-2 (A) is mainly produced by activated T cells to promote proliferation. IFN-gamma (C) is produced by T cells and NK cells to enhance immune response. TNF-alpha (D) is produced by macrophages and T cells to induce inflammation. IL-10 stands out as the suppressor cytokine in this context.

Correct Answer: B

Rationale: The correct answer is B because adaptive immunity involves memory, meaning the immune system can recognize and respond more effectively to specific antigens upon subsequent exposure. This high antigen specificity allows for tailored responses to different pathogens. In contrast, innate immunity lacks memory and specificity, providing only a rapid but non-specific response to a wide range of pathogens. Choices A, C, and D are incorrect because they do not adequately capture the key distinguishing features of adaptive immunity.