NOD2

Correct Answer: D

Rationale: Step-by-step rationale: 1. NOD2 is a cytosolic receptor for bacteria, detecting bacterial molecules. 2. Mutations in NOD2 are found in 30% of patients with Crohn's disease. 3. NOD2 activation triggers NFκB signaling pathway. 4. Therefore, all the statements (A, B, C) are correct, making option D the correct answer. Other choices are incorrect as they do not encompass all the correct statements about NOD2.

Correct Answer: D

Rationale: The correct answer is D. Choice A is correct because flu viruses mutate frequently due to their error-prone RNA polymerase, leading to new strains. Choice B is correct because the segmented nature of the viral genome allows for reassortment of different strains, creating completely new variants. Therefore, new vaccines are needed to target these evolving strains. Choice C is incorrect as the need for new vaccines is primarily driven by the genetic variability of the virus, not solely by the short-lived nature of antibodies. Thus, choices A and B together provide a comprehensive explanation for the constant need for new flu vaccines.

Correct Answer: D

Rationale: The correct answer is D because all the statements in choices A, B, and C are valid reasons why we don't have a successful HIV vaccine. A: HIV has a high mutation rate, making it challenging to generate a protective memory response. B: Inducing mucosal immunity is difficult to block sexual transmission, a common route of HIV infection. C: HIV targets immune cells, which hinders the immune system's ability to mount an effective response. Therefore, all these factors combined pose significant challenges for creating an effective HIV vaccine.

Correct Answer: C

Rationale: The correct answer is C: Transplantation. MHC proteins play a crucial role in transplant rejection by presenting antigens to T cells, initiating an immune response against foreign tissues. This discovery was significant in understanding transplant immunology. Choices A, B, and D are incorrect because innate immunity involves nonspecific defense mechanisms, allergies are mediated by IgE antibodies, and autoimmunity involves the immune system attacking self-antigens, none of which directly relate to the discovery of MHC proteins in transplantation studies.

Correct Answer: B

Rationale: The correct answer is B because TH2 cells play a crucial role in protecting against parasitic worms by secreting cytokines that promote eosinophil activation and antibody production. This response helps to expel the parasites from the body. Incorrect choices: A: TH1 cells are responsible for protection against intracellular bacteria. C: TH3 cells, not TH2 cells, are known for secreting anti-inflammatory cytokines. D: Activation of macrophages is primarily mediated by TH1 cells through IFN-gamma secretion.