Nokea
What triggers the release of mediators from mast cells during Type I hypersensitivity?
- A. Cross-linking of IgE molecules on the mast cell surface
- B. Activation of complement proteins
- C. Binding of IgG to antigen
- D. Phagocytosis of allergens
Correct Answer: A
Rationale: The correct answer is A. Cross-linking of IgE molecules on the mast cell surface triggers the release of mediators during Type I hypersensitivity. When allergens bind to IgE antibodies on mast cells, it leads to cross-linking of IgE molecules, causing the mast cell to release histamine and other inflammatory mediators. This process initiates the allergic response.
Explanation for incorrect choices:
B: Activation of complement proteins does not directly trigger mast cell degranulation in Type I hypersensitivity.
C: Binding of IgG to antigen is characteristic of Type II and Type III hypersensitivity reactions, not Type I.
D: Phagocytosis of allergens does not directly stimulate mast cells to release mediators in Type I hypersensitivity.
You may also like to solve these questions
Superoxide dismutase is an enzyme that catalyzes the conversion of oxygen radicals to peroxides. Which groups of organisms do not have this enzyme?
- A. aerobes
- B. facultative anaerobes
- C. oxyduric anaerobes
- D. oxylabile anaerobes
Correct Answer: D
Rationale: The correct answer is D: oxylabile anaerobes. These organisms cannot survive in the presence of oxygen and are sensitive to oxygen radicals. Superoxide dismutase is essential for organisms that are exposed to oxygen, as it helps convert harmful oxygen radicals into less harmful peroxides. Therefore, organisms that lack this enzyme, like oxylabile anaerobes, would not be able to detoxify oxygen radicals and would not survive in aerobic environments.
A: Aerobes have superoxide dismutase to protect against oxygen radicals.
B: Facultative anaerobes can switch between aerobic and anaerobic metabolism and would benefit from having superoxide dismutase.
C: Oxyduric anaerobes are resistant to oxygen and can still benefit from superoxide dismutase for detoxification.
The gut immune system at homeostasis is 'tolerogenic'. This is achieved by:
- A. The production of anti-inflammatory cytokines such as TGF-beta by resident dendritic cells
- B. Responding to innocuous microbiota antigens with production of antimicrobial peptides that limit microbiota overgrowth
- C. Induction of Tregs
- D. All of the above
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.
Thymocytes undergoing positive selection express:
- A. TCR
- B. CD4
- C. CD8
- D. All of the above
Correct Answer: D
Rationale: Thymocytes undergoing positive selection express both CD4 and CD8 co-receptors along with a functional T-cell receptor (TCR). CD4 and CD8 help in recognizing MHC molecules, while TCR is crucial for antigen recognition. Positive selection ensures that thymocytes with a functional TCR that can interact with self-MHC molecules survive. Therefore, the correct answer is D, as thymocytes undergoing positive selection express TCR, CD4, and CD8. Choice A, TCR alone, is incorrect as CD4 and CD8 are also expressed. Choices B and C are incorrect as positive selection involves the expression of both CD4 and CD8, not just one or the other.
Many clients with chronic fatigue syndrome (CFS) report severe,ongoing fatigue without any explanation that has lasted for at least — months.
- A. 12
- B. 6
- C. 3
- D. 2
Correct Answer: B
Rationale: Chronic fatigue syndrome is characterized by severe unexplained fatigue lasting for at least six months.
Why is smallpox considered a factor that greatly helped European explorers to defeat the Native populations of the Americas (e.g. Mexico)?
- A. When the Europeans arrived there was an ongoing smallpox epidemic in the Americas that weakened the ability of the Natives to fight back
- B. The Native populations used a form of vaccination against smallpox that was often lethal and therefore they lost more lives.
- C. Smallpox was introduced in Mexico by the European explorers therefore the Native population had no immunity to it and the disease spread rapidly
- D. Both A and B are correct
Correct Answer: C
Rationale: The correct answer is C because smallpox was indeed introduced to the Americas by European explorers, leading to devastating effects on the Native populations who had no immunity. This weakened the Natives' ability to fight back against the Europeans. Option A is incorrect as there was no ongoing smallpox epidemic in the Americas before the arrival of the Europeans. Option B is also incorrect as there is no evidence that the Native populations used a lethal form of vaccination against smallpox. Option D is incorrect as only option C accurately explains the impact of smallpox on the Native populations in relation to European conquest.