Nokea
Benefits from the human microbiome include all the following except:
- A. Out-competition of pathogenic species
- B. Production of important metabolites called short chain fatty acids
- C. Secretion of enzymes such as lysozyme that degrade the cell wall of pathogenic species
- D. Provision of signals leading to the development of the gut-associated immune system
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.
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What is NOT true about Shigella?
- A. Causes a form of bloody diarrhea
- B. It is a motile species possessing a flagellum
- C. It exploits specialized intestinal cells, called M cells, to infect the host
- D. It can travel from cell to cell, propelled by actin comets
Correct Answer: B
Rationale: The correct answer is B because Shigella is a non-motile species and does not possess a flagellum. Shigella relies on non-flagellar mechanisms for its movement within host cells. Choice A is true as Shigella causes bloody diarrhea. Choice C is also true as Shigella exploits M cells to infect the host. Choice D is true as Shigella can move from cell to cell using actin comets. In summary, choice B is incorrect because Shigella does not have a flagellum, while choices A, C, and D are all true characteristics of Shigella.
Which of the following is NOT true about live attenuated vaccines
- A. Usually effective at a single dose
- B. Expensive handling and storage
- C. Potential hazard due to reversion to a virulent form
- D. Able to induce only a humoral response
Correct Answer: D
Rationale: The correct answer is D: Able to induce only a humoral response. Live attenuated vaccines can induce both humoral and cellular immune responses, not just humoral. This is because they mimic natural infection, leading to a broader immune response.
A: Usually effective at a single dose - This is true for live attenuated vaccines, as they often provide long-lasting immunity with just one dose.
B: Expensive handling and storage - Live attenuated vaccines can be more cost-effective due to fewer doses needed, not expensive.
C: Potential hazard due to reversion to a virulent form - This is a concern with live attenuated vaccines, as there is a risk of the weakened virus reverting to a virulent form.
Which of the following is NOT true with respect to T cell development?
- A. It establishes MHC restriction of the T cell repertoire
- B. It takes place in the thymus
- C. Thymic dendritic cells are involved
- D. It only occurs after the naïve T cell has been activated by antigen
Correct Answer: D
Rationale: The correct answer is D because T cell development starts in the thymus while the naïve T cell activation by antigen occurs outside of the thymus. T cell development involves positive and negative selection, establishing MHC restriction, and interaction with thymic dendritic cells for maturation. Naïve T cells are activated by antigens in the periphery, not during T cell development in the thymus. Therefore, D is the correct answer as it does not align with the process of T cell development.
Which of the following statements is incorrect?
- A. The gut microbiome composition in obese individuals is altered and shows overrepresentation of less beneficial species
- B. Fecal transplants have been used to treat Clostridium difficile infections
- C. Crohn's disease is considered a disease caused by loss of tolerance to the gut microbiota
- D. The bacterial type III secretion system is used by species of the gut microbiota to inject effector proteins into intestinal epithelial cells and invade them, as observed in Crohn's disease
Correct Answer: D
Rationale: The correct answer is D because the statement incorrectly implies that the bacterial type III secretion system is used by gut microbiota to invade intestinal epithelial cells in Crohn's disease. In reality, Crohn's disease is not directly caused by invasion of gut microbiota into intestinal cells; it is a complex autoimmune condition. The gut microbiota dysbiosis is associated with Crohn's disease, but invasion of epithelial cells is not the primary mechanism. Choices A, B, and C are correct: A highlights the altered microbiome in obesity, B discusses the use of fecal transplants for C. difficile infections, and C mentions Crohn's disease related to issues with gut microbiota tolerance.
What is included in the humoral immune response?
- A. Surveillance for malignant cell changes
- B. Production of antigen-specific immunoglobulins
- C. Direct attack of antigens by activated B lymphocytes
- D. Releasing cytokines responsible for destruction of antigens
Correct Answer: B
Rationale: The humoral immune response involves the production of antigen-specific antibodies (immunoglobulins) by B cells, which neutralize pathogens.