Mutations in which of the following genes are considered a risk factor for Crohn's disease?

Correct Answer: B

Rationale: The correct answer is B: NOD2. Mutations in the NOD2 gene have been strongly associated with an increased risk of Crohn's disease. NOD2 is involved in the immune response to bacteria in the gut, and mutations in this gene can lead to dysregulation of the immune system, contributing to the development of Crohn's disease. A: TLR-4 is involved in the recognition of bacterial components but mutations in this gene are not strongly linked to Crohn's disease. C: NADPH oxidase is important for the production of reactive oxygen species in immune cells but mutations in this gene are not known to be a risk factor for Crohn's disease. D: IL-2 is a cytokine involved in immune regulation but mutations in this gene are not associated with an increased risk of Crohn's disease.

Correct Answer: B

Rationale: The correct answer is B: The type of pathogen it encounters. Dendritic cells produce different polarizing cytokines based on the type of pathogen they encounter. This is crucial for directing the differentiation of T helper (Th) subsets. Choice A is incorrect because the expression of MHC class I or II molecules by dendritic cells is important for antigen presentation to T cells, not for determining polarizing cytokines. Choice C is also incorrect because Fc receptors are involved in antibody-mediated immune responses, not in determining polarizing cytokines. Therefore, the correct answer is B as it directly influences the differentiation of Th subsets by providing appropriate polarizing cytokines based on the encountered pathogen.

Correct Answer: A

Rationale: The correct answer is A because T cells do not recognize three-dimensional structures of a pathogen. T cell receptors interact with processed antigen fragments presented by MHC molecules on antigen-presenting cells. Choice B is correct because T cell receptors possess specificity for antigens. Choice C is incorrect because T cell receptors have multiple antigen-binding sites. Choice D is incorrect as T cell receptors can be secreted as soluble forms.

Correct Answer: D

Rationale: The correct answer is D: Artificial passive. Plasma therapy involves administering preformed antibodies to provide immediate protection against a specific pathogen. This is considered artificial passive immunity because the antibodies are obtained from an external source rather than being produced by the individual's immune system. Explanation: 1. Natural active immunity (Choice A) is when the body produces its antibodies after exposure to a pathogen, which is not the case in plasma therapy. 2. Natural passive immunity (Choice B) is when antibodies are passed from mother to fetus or through breast milk, not obtained through plasma therapy. 3. Artificial active immunity (Choice C) involves vaccination to stimulate the body's immune response, which is different from plasma therapy. In summary, the correct answer is D (Artificial passive) because plasma therapy provides immediate immunity through externally sourced antibodies, distinguishing it from the other types of immunological protection.

Correct Answer: C

Rationale: The correct answer is C: 1-b, 2-d, 3-a, 4-c. 1. The first match should be b, as it aligns with the order given. 2. The second match should be d, as it aligns with the order given. 3. The third match should be a, as it aligns with the order given. 4. The fourth match should be c, as it aligns with the order given. Therefore, option C is the correct match based on the given order. Other choices are incorrect because they do not align with the given order of matches.