What is the primary advantage of Toll-like receptors (TLRs)?

Correct Answer: B

Rationale: The correct answer is B because Toll-like receptors (TLRs) recognize common molecular patterns shared by groups of microbes, allowing for rapid detection of a wide range of pathogens. This recognition triggers immune responses without the need for prior exposure to the specific pathogen. The other choices are incorrect because: A: TLRs are not highly specific to individual pathogens but rather recognize common patterns. C: TLRs do not directly activate B cell antibody production; they initiate immune responses by activating various immune cells. D: TLRs do not require antigen presentation to function; they directly recognize microbial patterns.

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.

Correct Answer: D

Rationale: The correct answer is D: Type IV hypersensitivity. This type is mediated by T cells, specifically CD4+ helper T cells and CD8+ cytotoxic T cells. The process involves antigen-presenting cells activating T cells, leading to a delayed response. Choices A, B, and C involve different mechanisms and are not mediated by T cells. Type I is mediated by IgE antibodies, Type II involves antibody-mediated cell destruction, and Type III involves immune complex deposition. Therefore, Type IV is the only hypersensitivity type directly mediated by T cells.