What is the role of complement component C3b in immune responses?

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: 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.

Correct Answer: C

Rationale: The correct answer is C, displaying antigen fragments for T cell recognition. MHC molecules bind to antigen fragments and present them on the cell surface for T cells to recognize. This process is crucial for activating the immune response. Choice A is incorrect as MHC molecules do not secrete cytokines. Choice B is incorrect as MHC molecules do not directly destroy pathogens. Choice D is incorrect as MHC molecules do not produce antibodies; that is the function of B cells.

Correct Answer: B

Rationale: The correct answer is B: Plasma cells. Plasma cells are a type of white blood cell that produces antibodies in response to antigens. They are essential in the immune response to help fight off infections and other diseases. Helper T cells (A) assist other immune cells but do not directly produce antibodies. Cytotoxic T cells (C) are responsible for killing infected cells, not producing antibodies. Regulatory T cells (D) help regulate the immune response but do not produce antibodies. In summary, only plasma cells are specifically designed to produce antibodies in the immune system.