Which cells play a key role in linking innate and adaptive immunity?

Correct Answer: B

Rationale: The correct answer is B: Dendritic cells. Dendritic cells are antigen-presenting cells that bridge the innate and adaptive immune responses by capturing and presenting antigens to T cells, thus initiating the adaptive immune response. They are crucial for activating T cells and initiating specific immune responses. A: B cells are responsible for antibody production in the adaptive immune response, not for linking innate and adaptive immunity. C: Eosinophils are primarily involved in parasitic infections and allergic reactions, not in linking innate and adaptive immunity. D: NK cells are part of the innate immune system and are involved in detecting and killing infected cells, but they do not directly link innate and adaptive immunity.

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.

Correct Answer: B

Rationale: The correct answer is B because Type V hypersensitivity involves antibodies stimulating receptors instead of destroying them. In Type II hypersensitivity, antibodies target antigens on cell surfaces, leading to cell destruction. In Type V, antibodies bind to cell receptors, causing abnormal receptor activation. Choices A, C, and D are incorrect because Type V hypersensitivity is not mediated by T cells (A), does not involve immune complex formation (C), and does involve the immune system (D). Therefore, the unique characteristic of Type V hypersensitivity is the stimulation of receptors by antibodies, making choice B the correct answer.