Identify the incorrect statement

Correct Answer: D

Rationale: The correct answer is D because a lower number of gut bacteria is not associated with obesity. In fact, research shows that an imbalance in gut bacteria, not a lower number, can contribute to obesity. Choice A is correct as there are indeed more bacteria in the gut than human cells in the body. Choice B is also correct as babies develop their commensal flora after birth. Choice C is correct, as studies on germ-free mice have shown the importance of microbiota in immune system development.

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 a given MHC molecule can bind only one peptide at a time. This is essential for the proper presentation of antigens to immune cells. MHC class I and class II molecules do not consist of two transmembrane protein chains (A), MHC class I molecules have one peptide-binding site while MHC class II molecules have one peptide-binding site (B), and MHC molecules on the cell surface typically have peptides bound to their peptide-binding sites, even in the absence of infection (D).

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.