Which of the following is NOT part of innate immunity?

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: 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.

Correct Answer: B

Rationale: The correct answer is B: Dendritic cells. Dendritic cells bridge innate and adaptive immunity by capturing antigens, processing them, and presenting them to T cells to initiate adaptive immune responses. NK cells (A) are part of innate immunity, while plasma cells (C) produce antibodies in adaptive immunity. Mast cells (D) are involved in allergic responses, not bridging innate and adaptive immunity.

Correct Answer: B

Rationale: The correct answer is B: Fc fragment. The Fc fragment of an antibody determines its physiological effects by interacting with immune cells and other effector molecules. It mediates processes like opsonization, complement activation, and antibody-dependent cell-mediated cytotoxicity. The Fab fragment (A) contains the antigen-binding site but does not directly influence physiological effects. The variable region (C) is part of both the Fab and Fc portions and contributes to antigen specificity but does not solely determine physiological effects. The antigen-binding site (D) is located within the Fab portion and is responsible for binding to specific antigens, not for exerting physiological effects.