Why did Barry Marshall drink a pure culture of Helicobacter pylori?

Correct Answer: B

Rationale: Barry Marshall drank a pure culture of H. pylori to demonstrate an association between H. pylori infection and gastric ulcers. This is because he wanted to prove the theory that the bacteria is a primary cause of stomach ulcers, contradicting the prevailing belief at the time. Choice A is incorrect because the direct link between H. pylori and gastric cancer was not the primary focus of his experiment. Choice C is incorrect as his goal was to show the bacterial link to ulcers, not to disprove stress as a factor. Choice D is incorrect because only choice B accurately reflects his intended purpose.

Correct Answer: C

Rationale: The correct answer is C because secondary lymphoid tissues, like lymph nodes and spleen, are where lymphocytes encounter antigens and become activated. This process leads to the proliferation and differentiation of lymphocytes, enabling them to mount an immune response against specific pathogens. Choices A, B, and D are incorrect because A pertains to primary lymphoid tissues, B describes a localized immune response, and D refers to the process of gene rearrangement that occurs in the primary lymphoid tissues during lymphocyte development.

Correct Answer: C

Rationale: After engagement of pattern recognition receptors, dendritic cells upregulate expression of the B7 molecule, which is essential for co-stimulation of naïve T cells. This step is crucial for activating T cells. MHC class I molecules present antigens to CD8+ T cells, not CD4+ T cells, so choice A is incorrect. Dendritic cells already have high antigen uptake ability, so choice B is not directly related to activation. PAMP-induced proliferation is not a typical response of dendritic cells after pattern recognition receptor engagement, making choice D incorrect.

Correct Answer: C

Rationale: The correct answer is C because celiac disease primarily involves an abnormal adaptive immune response to gluten, not an innate response. Here's the rationale: 1) Celiac disease is characterized by a T-cell mediated response to gluten peptides in genetically susceptible individuals. 2) The adaptive immune system, particularly T cells, plays a crucial role in the pathogenesis by recognizing gluten peptides presented by HLA-DQ2 or HLA-DQ8 molecules. 3) This adaptive immune response leads to inflammation and damage to the intestinal mucosa. 4) In contrast, the innate immune system may also be activated, but it is not the primary driver of the disease. Summary: A: Correct - There is a strong genetic association with HLA alleles. B: Incorrect - Celiac disease is primarily driven by an adaptive immune response, not just features of autoimmunity. D: Incorrect - While gluten exposure triggers the immune response, the disease is not solely driven by gluten intake.

Correct Answer: D

Rationale: The correct answer is D. Resident dendritic cells in the gut produce anti-inflammatory cytokines like TGF-beta, promoting tolerance. The production of antimicrobial peptides in response to microbiota antigens helps maintain a balance with the microbiota. Induction of regulatory T cells (Tregs) also plays a crucial role in preventing excessive immune responses. Therefore, all of the choices (A, B, and C) contribute to maintaining gut immune system homeostasis by promoting tolerance and preventing inflammation.