What is the main function of the Membrane Attack Complex (MAC)?

Correct Answer: C

Rationale: The main function of the Membrane Attack Complex (MAC) is to lyse pathogens by creating pores in their cell membranes. First, MAC assembles on the pathogen's surface. Then, it forms a pore, disrupting the pathogen's membrane integrity, leading to cell lysis. This mechanism is crucial for the immune system to effectively eliminate pathogens. Choice A (Recruitment of neutrophils) is incorrect because MAC is not involved in recruiting neutrophils. Neutrophil recruitment is typically mediated by other signaling molecules. Choice B (Phagocytosis activation) is incorrect as MAC does not directly activate phagocytosis. Phagocytosis is a separate process involving the engulfment of pathogens by immune cells. Choice D (Enhancing cytokine production) is incorrect because MAC does not directly enhance cytokine production. Cytokine production is mainly regulated by other immune cells and signaling pathways.

Correct Answer: C

Rationale: Answer C is correct because B cell antibody production is part of adaptive immunity, not innate immunity. Innate immunity is the body's first line of defense and includes mechanisms like cytokine secretion, NK cell activity, and phagocytosis by macrophages. B cells are part of the adaptive immune response, producing antibodies specific to pathogens upon exposure. This distinction is crucial in understanding the different roles innate and adaptive immunity play in protecting the body.

Correct Answer: B

Rationale: Perforin released by NK cells forms pores in target cell membranes, allowing for the entry of granzymes which induce target cell death. This process is crucial for the immune response against infected or abnormal cells. Activating B cells (A) is not the role of perforin, as B cells are primarily activated by antigens. Engulfing pathogens (C) is the role of phagocytes like macrophages, not perforin. Inducing inflammation (D) is not directly related to the function of perforin in forming pores in target cell membranes.

Correct Answer: D

Rationale: The correct answer is D: Present at birth. Adaptive immunity is not present at birth; it develops over time in response to exposure to pathogens. A: Adaptive immunity has a slower response compared to innate immunity as it requires activation and proliferation of specific immune cells. B: Adaptive immunity is highly specific in recognizing antigens through antigen receptors on T and B cells. C: Adaptive immunity has memory function, allowing the immune system to "remember" previous encounters with specific pathogens for a faster and stronger response upon re-exposure.

Correct Answer: B

Rationale: The correct answer is B because B cells express B cell receptors (BCR) on their surface for recognizing antigens. BCRs consist of immunoglobulin molecules that bind specifically to antigens. T cell receptors (A) are found on T cells, not B cells. Fc receptors (C) bind to the Fc region of antibodies, while complement receptors (D) recognize complement proteins, not antigens. Therefore, the BCR is the specific receptor on B cells for antigen recognition.