What is the main purpose of complement component C5a?

Correct Answer: C

Rationale: The correct answer is C: Recruitment and activation of immune cells. C5a is a potent chemoattractant that attracts immune cells to the site of infection or inflammation. It also activates these immune cells, leading to enhanced immune responses. Option A (Opsonization) and B (Cell lysis) are not the main functions of C5a. Option D (Inhibition of inflammation) is incorrect because C5a actually promotes inflammation by recruiting and activating immune cells.

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 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.