Which of the following is NOT a function of innate immunity?

Correct Answer: D

Rationale: The correct answer is D. Innate immunity does not involve producing antigen-specific antibodies. This is because innate immunity is the first line of defense against pathogens and does not have the ability to produce antibodies that target specific antigens. Instead, innate immunity works through mechanisms like phagocytosis and killing infected cells to eliminate pathogens. Choices A, B, and C are functions of innate immunity. A - Killing virally infected cells is a common function of innate immunity. B - Phagocytosis is the process by which immune cells engulf and destroy pathogens, a key function of innate immunity. C - Activating adaptive immunity is also a role of innate immunity, as it helps initiate the adaptive immune response for a more targeted defense.

Correct Answer: B

Rationale: The correct answer is B: C3b acts as an opsonin to enhance phagocytosis. C3b binds to pathogens and enhances their recognition by phagocytic cells, facilitating their engulfment and destruction. This process is crucial for efficient immune responses. A, MAC formation, is initiated by the membrane attack complex, not C3b. C, inflammation, is triggered by various mediators such as histamine and cytokines, not C3b. D, neutralizing cytokines, is not a function of C3b; cytokines are regulatory proteins involved in immune responses.

Correct Answer: B

Rationale: The main limitation of innate immunity compared to adaptive immunity is that innate immunity lacks memory and specificity. This means that innate immune responses do not improve upon repeated exposure to the same pathogen and cannot target specific antigens efficiently. Adaptive immunity, on the other hand, can remember previous encounters with pathogens and mount targeted responses. Choices A, C, and D are incorrect because innate immunity can produce cytokines, includes physical barriers like skin and mucous membranes, and can activate complement as part of its defense mechanisms.

Correct Answer: C

Rationale: Helper T cells primarily secrete cytokines to activate other immune cells. This is crucial for coordinating and amplifying the immune response. They do not kill infected host cells (A), as that is the role of cytotoxic T cells. Producing antibodies (B) is the function of B cells. Suppressing immune responses (D) is the role of regulatory T cells, not Helper T cells.

Correct Answer: B

Rationale: The primary characteristic of a secondary immune response is that it is faster, stronger, and more specific. This is because memory cells generated during the primary response allow for a quicker and more efficient recognition and response to the same antigen upon re-exposure. This results in a faster production of antibodies, a stronger immune response, and increased specificity. Choice A is incorrect as secondary responses are actually faster and more specific. Choice C is incorrect as secondary responses can produce IgG antibodies in addition to IgM. Choice D is incorrect because memory cells are essential for secondary immune responses.