Which of the following represents a typical match between pathogen type and Th subset response?

Correct Answer: A

Rationale: The correct answer is A. Virus typically triggers a Th1 response because Th1 cells are specialized in combating intracellular pathogens like viruses. Th2 response is more common for extracellular parasites, making choice B incorrect. TH17 response is usually associated with fungal infections and autoimmune diseases, making choice C incorrect. Parasitic worms usually induce a Th2 response due to their extracellular nature, making choice D incorrect.

Correct Answer: A

Rationale: Rationale for Choice A: Outbreaks of measles in developed countries are due to decreased vaccination rates, leading to lower herd immunity. This is supported by data showing increasing cases in countries with vaccine hesitancy. Other choices are incorrect because B is false - measles has not been eradicated globally, C is false - there is an effective vaccine for measles, and D is false - measles can lead to severe complications and long-term effects, especially in unvaccinated individuals.

Correct Answer: C

Rationale: The correct answer is C because the human microbiome does not secrete enzymes like lysozyme; instead, lysozyme is produced by the human body. A is correct as the microbiome can out-compete harmful bacteria. B is correct as the microbiome produces short chain fatty acids. D is correct as the microbiome helps in the development of the gut-associated immune system. Therefore, C is the only option that does not accurately describe a benefit from the human microbiome.

Correct Answer: B

Rationale: The correct answer is B because the major histocompatibility complex (MHC) plays a crucial role in the immune system by determining whether transplanted organs or cells will be accepted or rejected. MHC molecules present antigens to T cells, which then trigger an immune response leading to acceptance or rejection. Choice A is incorrect because T cell receptor gene rearrangement is not directly influenced by the MHC. Choice C is incorrect as MHC does not directly polarize T helper cells. Choice D is incorrect because MHC does not directly regulate the ratio of CD4+ and CD8+ T cells in an individual.

Correct Answer: C

Rationale: Passive immunization involves the transfer of pre-formed antibodies to confer immediate protection. Choice C is correct as it describes receiving serum containing antibodies from an immune individual. Choice A is incorrect because it describes active immunization. Choice B is incorrect as it refers to the primary immune response, which is part of active immunization. Choice D is incorrect as it describes the process of immunization itself, not passive immunization.