T cell receptor and B cell receptor genes both undergo:

Correct Answer: B

Rationale: The correct answer is B, germline gene rearrangement. T cell receptor and B cell receptor genes both undergo germline gene rearrangement during lymphocyte development, where gene segments are rearranged to generate diverse antigen receptor specificities. Somatic hypermutation and isotype switching are processes specific to B cells in the adaptive immune response, not T cells. Therefore, choices A and C are incorrect. Choice D is incorrect as well since somatic hypermutation is not a process involved in T cell receptor gene rearrangement.

Correct Answer: B

Rationale: The correct answer is B because Helicobacter pylori is not typically associated with nosocomial infections. Nosocomial infections are usually caused by bacteria commonly found in healthcare settings, such as Clostridium difficile, which is mentioned in choice D. Choices A, C, and D are correct as nosocomial infections can be caused by both Gram-negative and Gram-positive bacteria, often antibiotic-resistant species, and commensal flora bacteria like Clostridium difficile.

Correct Answer: C

Rationale: The correct answer is C: CARD. CARD stands for Caspase Activation and Recruitment Domain, which is crucial for the assembly of the inflammasome complex. It facilitates the recruitment and activation of caspase enzymes, leading to inflammatory responses. Leucine rich repeats (A) and TIR domain (B) are not directly involved in the assembly of the inflammasome. Therefore, the correct choice is C, as it specifically pertains to the structural domain essential for this process.

Correct Answer: B

Rationale: The correct answer is B because the statement is false. Memory B cells are formed during an immune response and persist long-term, allowing for a faster and more robust response upon reinfection with the same antigen. The number of memory B cells recognizing an antigen is typically greater than the number of naïve B cells, as they are specifically primed and preserved. In contrast, naïve B cells are naive to the antigen and need to undergo activation and differentiation upon encountering the antigen for the first time. Therefore, statement B is incorrect as it inaccurately suggests that memory B cells are always fewer than naïve B cells recognizing the same antigen.

Correct Answer: C

Rationale: The correct answer is C because both external barriers (Skin, Secretions, Mucous membranes) and internal defenses (Inflammatory response) are types of innate immunity. External barriers physically block pathogens from entering the body, while internal defenses involve cellular and molecular responses to eliminate pathogens. Choice A alone does not cover internal defenses, and choice B alone does not cover external barriers, making them individually incomplete. Choice D is incorrect as innate immunity does involve specific barriers and responses. Therefore, choice C is the best answer as it encompasses both types of innate immunity barriers.