Which of the following statements is NOT true?

Correct Answer: C

Rationale: The correct answer is C because a B cell epitope is not a part of the antibody molecule that contacts an antigen. B cell epitopes are specific regions on an antigen that bind to B cell receptors. Choice A is incorrect because denaturation can expose B cell epitopes. Choice B is incorrect because pathogens typically have multiple B cell epitopes. Choice D is incorrect because B cell epitopes can be found on various parts of pathogens, not just on the surface.

Correct Answer: C

Rationale: The correct answer is C because in response to Leishmania parasites, the activation of Th cells into Th1 effectors that secrete IFNγ is crucial for activating macrophages to eliminate the intracellular parasites. IFNγ enhances the microbicidal activity of macrophages, helping to control the infection. Choice A is incorrect because IL-4 is not required to induce the appropriate antibody response against Leishmania parasites. Choice B is incorrect because Th2 effectors secreting IL-4 would not activate macrophages effectively against Leishmania, which is an intracellular pathogen. Choice D is incorrect because in the case of Leishmania, a Th1-mediated response is most effective due to the need for macrophage activation by IFNγ.

Correct Answer: B

Rationale: Step-by-step rationale: 1. Mucins are heavily glycosylated proteins that form a gel-like barrier on mucosal surfaces. 2. This barrier helps protect the underlying tissues from pathogens and physical damage. 3. Mucins are primarily produced by goblet cells in epithelial tissues. 4. Choice B correctly describes the function and structure of mucins. Summary: - Choice A is incorrect because not all epithelial cells produce mucins. - Choice C is incorrect as mucins are not natural antibiotics. - Choice D is incorrect as mucins are present in various mucosal surfaces, not exclusively in the respiratory tract.

Correct Answer: D

Rationale: The correct answer is D because both TLR4 and NOD1 are pattern recognition receptors (PRRs) that can activate the NF-κB pathway. TLR4 recognizes bacterial lipopolysaccharides, while NOD1 detects bacterial peptidoglycan fragments. NLRP3, choice C, is an inflammasome receptor that activates caspase-1, not NF-κB. Therefore, choices A, B, and C are incorrect as they do not directly activate NF-κB like TLR4 and NOD1.

Correct Answer: D

Rationale: The correct answer is D because all three choices are valid triggers for complement activation. A is correct as opsonins like MBL can bind to microbes and activate the complement system. B is correct as direct recognition of microbes can also trigger complement activation. C is correct as the formation of immune complexes can lead to complement activation through the classical pathway. Therefore, all of the above choices are triggers for complement activation.