Dendritic cells play a role in:

Correct Answer: D

Rationale: Dendritic cells play a crucial role in the immune system. Firstly, they provide costimulation to activate naïve T cells (A). Secondly, they process protein antigens into peptides for antigen presentation (B). Finally, dendritic cells present peptide-MHC complexes to T cell receptors for immune response activation (C). Therefore, the correct answer is D, as dendritic cells are involved in all these processes essential for initiating and regulating immune responses. Choices A, B, and C are incorrect as they are individual roles of dendritic cells and do not encompass the full range of functions that dendritic cells perform.

Correct Answer: C

Rationale: The correct answer is C: Paneth cells. Paneth cells are specialized intestinal epithelial cells located in the small intestine that produce antimicrobial peptides to help defend against pathogens. They play a crucial role in maintaining gut homeostasis. Goblet cells (A) secrete mucus, enterocytes (B) absorb nutrients, and epithelial stem cells (D) are responsible for cell regeneration, but they do not produce antimicrobial peptides like Paneth cells do.

Correct Answer: A

Rationale: The correct answer is A: IgG: Opsonization. IgG antibodies are known for their role in opsonization, where they tag pathogens for phagocytosis by immune cells. This process enhances the removal of pathogens. IgA is mainly involved in mucosal immunity and not complement activation, making choice B incorrect. IgE is associated with allergic reactions and not antibody-dependent cell-mediated cytotoxicity as stated in choice C. IgM is the first antibody produced in response to an infection and plays a role in neonatal immunity, making choice D incorrect.

Correct Answer: D

Rationale: The correct answer is D because some top-selling drugs for immune-mediated diseases target either an inflammatory cytokine or its receptor. Monoclonal antibodies specific for an inflammatory cytokine can block its activity, while those targeting the receptor can prevent the cytokine from binding and triggering immune responses. Choices A and B are correct examples of drugs targeting inflammatory pathways. Choice C, targeting T cell lymphocytes, is less common for immune-mediated diseases compared to targeting cytokines or receptors. Therefore, D is the correct answer as it encompasses both common targeting strategies.

Correct Answer: B

Rationale: The correct order of events in naïve T cell activation is: antigen recognition, clonal expansion, entry into the site of infection. First, T cells must recognize the specific antigen presented by antigen-presenting cells. This recognition triggers clonal expansion, where T cells proliferate and differentiate into effector cells. Finally, the activated T cells migrate to the site of infection to combat the pathogen. Option B is correct because it follows this sequential order. Options A, C, and D are incorrect because they do not adhere to the correct sequence of events in naïve T cell activation.