What is the role of perforin released by NK cells?

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: 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.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Hypersensitivity in immunology refers to an exaggerated or inappropriate immune response. 2. This excessive response can lead to tissue damage and various immune-mediated conditions. 3. Choice A accurately describes this concept. Summary: - Choice A is correct as it accurately defines hypersensitivity. - Choice B is incorrect as hypersensitivity involves an exaggerated immune response, not an inability to mount one. - Choice C is incorrect as hypersensitivity is not a low-level immune reaction. - Choice D is incorrect as hypersensitivity is not a mechanism for faster immune response, but rather an overreaction.