Which of the following complement components is an opsonin?

Correct Answer: B

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

Correct Answer: C

Rationale: Step 1: Innate immunity is the body's first line of defense against pathogens. Step 2: Physical defenses include barriers like skin and mucous membranes. Step 3: Cellular defenses include immune cells like macrophages and natural killer cells. Step 4: These defenses are present from birth and do not require prior exposure to pathogens. Step 5: Choice C is true as innate immunity encompasses both physical and cellular defenses, making it the correct answer. Other choices are incorrect: A: Innate immunity does play a role in stimulating adaptive immunity through antigen presentation. B: It does not require prior exposure to function, as it is a rapid and non-specific response. D: Innate immunity is not antigen-specific; adaptive immunity is responsible for antigen-specific responses.

Correct Answer: B

Rationale: Granzyme entering a target cell activates apoptosis pathways by inducing cell death. Firstly, granzyme activates caspases leading to cell death. Secondly, it triggers DNA fragmentation and cell shrinkage. Lastly, it enhances membrane blebbing and apoptotic body formation. The other choices are incorrect because granzyme does not neutralize toxins, inhibit cytokine secretion, or promote antigen presentation within a target cell.

Correct Answer: A

Rationale: The correct answer is A because memory function in adaptive immunity allows for rapid and stronger responses to previously encountered antigens. This is achieved through the presence of memory cells, such as memory B and T cells, which can quickly recognize and respond to specific pathogens upon re-exposure. This leads to a faster and more efficient immune response, providing better protection against future infections. Choice B is incorrect because direct killing of pathogens without prior activation is a function of innate immunity, not adaptive immunity. Choice C is incorrect as enhanced cytokine secretion is not the primary advantage of memory function. Choice D is incorrect because while memory function provides protection against previously encountered antigens, it does not confer resistance to all infections without exposure.

Correct Answer: B

Rationale: After clonal selection and expansion, B cells differentiate into plasma cells to produce antibodies. This is crucial for the immune response as plasma cells are specialized in antibody production. B cells do not produce cytokines (choice A), initiate phagocytosis (choice C), or present antigens to T cells (choice D) post-clonal selection. Plasma cell differentiation is the key outcome of the B cell activation process, enabling the body to mount an effective immune response against pathogens.