What distinguishes NK cells from other lymphocytes?

Correct Answer: B

Rationale: The correct answer is B because NK cells do not require prior antigen sensitization to recognize and attack infected cells. This distinguishes them from other lymphocytes, such as T and B cells, which are part of adaptive immunity and require prior exposure to specific antigens. NK cells are part of innate immunity and can directly recognize and kill infected or abnormal cells without prior activation. Choices A, C, and D are incorrect as NK cells are not part of adaptive immunity, do not directly produce antibodies, and do not phagocytose pathogens.

Correct Answer: B

Rationale: The correct answer is B: IL-10. Regulatory T cells produce IL-10 to suppress immune responses by inhibiting the activation and function of other immune cells. IL-2 (A) is mainly produced by activated T cells to promote proliferation. IFN-gamma (C) is produced by T cells and NK cells to enhance immune response. TNF-alpha (D) is produced by macrophages and T cells to induce inflammation. IL-10 stands out as the suppressor cytokine in this context.

Correct Answer: B

Rationale: The correct answer is B because adaptive immunity involves memory, meaning the immune system can recognize and respond more effectively to specific antigens upon subsequent exposure. This high antigen specificity allows for tailored responses to different pathogens. In contrast, innate immunity lacks memory and specificity, providing only a rapid but non-specific response to a wide range of pathogens. Choices A, C, and D are incorrect because they do not adequately capture the key distinguishing features of adaptive immunity.

Correct Answer: A

Rationale: The correct answer is A: Two heavy chains and two light chains. Antibodies are composed of two identical heavy chains and two identical light chains. Heavy chains provide structural support and effector functions, while light chains contribute to antigen binding. Choice B is incorrect as antibodies do not have three heavy chains. Choice C is incorrect as antibodies do not have three light chains. Choice D is incorrect as antibodies do not have four heavy chains.

Correct Answer: B

Rationale: The correct answer is B: Cell-mediated immunity. T lymphocytes are a type of white blood cell that plays a critical role in cell-mediated immunity by directly attacking infected cells and coordinating the immune response. This type of immunity is essential for fighting intracellular pathogens such as viruses and certain bacteria. A: Humoral immunity is mediated by B cells and involves the production of antibodies to neutralize pathogens. T lymphocytes do not directly participate in humoral immunity. C: Passive immunity is acquired through the transfer of antibodies from one individual to another, providing immediate protection. T lymphocytes are not involved in passive immunity. D: Innate immunity is the body's first line of defense against pathogens and does not involve T lymphocytes, which are part of the adaptive immune response.