What role do cytokines play in innate immunity?

Correct Answer: B

Rationale: The correct answer is B because cytokines act as signaling molecules to coordinate immune responses in innate immunity. They help regulate inflammation, activate immune cells, and promote clearance of pathogens. Option A is incorrect because cytokines do not directly kill pathogens. Option C is incorrect as cytokines play a crucial role in both innate and adaptive immunity. Option D is incorrect because cytokines do not inhibit phagocytosis; instead, they enhance this process to help eliminate pathogens.

Correct Answer: B

Rationale: The three main principles of adaptive immunity are Recognize, Respond, Remember. 1. Recognize: Immune system identifies specific pathogens through antigen recognition. 2. Respond: Immune response is triggered to eliminate the pathogen. 3. Remember: Immune system forms memory cells for faster and stronger response upon re-exposure. Other options are incorrect: A: Respond, Replace, Repair - Incorrect as it does not reflect the key processes of adaptive immunity. C: Resist, Retain, Recruit - Incorrect as these terms do not accurately describe the adaptive immune response. D: React, Replicate, Restore - Incorrect as it does not encompass the essential principles of adaptive immunity.

Correct Answer: B

Rationale: The correct answer is B: Fab region. The Fab region of an antibody contains the antigen-binding site, where specific interactions with antigens occur. This region is formed by the variable regions of both the heavy and light chains. The Fc fragment (choice A) is responsible for effector functions, not antigen specificity. The heavy chain constant region (choice C) and light chain constant region (choice D) are not involved in antigen binding, but rather provide structural support and determine the antibody class. Therefore, the Fab region is crucial for antigen specificity due to its variable regions that directly interact with antigens.

Correct Answer: B

Rationale: The correct answer is B: Thymus. T cells mature in the thymus, where they undergo selection and maturation processes essential for their function in the immune system. The thymus provides a specialized environment for T cell development, including positive and negative selection to ensure self-tolerance and functional T cell repertoire. A: Bone marrow is incorrect because it is the site of B cell maturation, not T cells. C: Spleen is incorrect as it acts as a secondary lymphoid organ for immune response but not the site of T cell maturation. D: Lymph nodes are incorrect as they are important for immune surveillance and activation but not the primary site for T cell maturation.

Correct Answer: B

Rationale: The correct answer is B: IgA. IgA is primarily involved in mucosal immunity as it is the most abundant antibody present in mucosal secretions like saliva, tears, and breast milk. IgA plays a crucial role in preventing pathogens from entering the body through mucosal surfaces. IgG is more involved in systemic immunity, IgM is the first antibody produced in response to an infection, and IgE is associated with allergic reactions. Therefore, IgA is the most appropriate choice for mucosal immunity.