How many Toll-like receptors (TLRs) are found in humans?

Correct Answer: C

Rationale: The correct answer is C: 10. Toll-like receptors (TLRs) are a family of proteins involved in the innate immune response. In humans, there are 10 known TLRs that recognize different pathogen-associated molecular patterns. Each TLR is specific to different types of pathogens, allowing for a diverse recognition and response system. Therefore, the correct answer is 10. Choices A, B, and D are incorrect because they do not match the known number of TLRs in humans, which is 10.

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.

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.