Nokea
Which characteristic corresponds with the acute stage of HIV infection?
- A. Burkitt’s lymphoma
- B. Temporary fall of CD4+ T cells
- C. Persistent fevers and night sweats
- D. Pneumocystis jiroveci pneumonia
Correct Answer: B
Rationale: During the acute stage of HIV infection, there is a temporary decline in CD4+ T cell counts followed by rebounding levels. Symptoms such as fever and night sweats may occur but are not definitive characteristics of this stage.
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Which of the following best describes the immune system's role in tissue regeneration?
- A. Preventing pathogen invasion
- B. Promoting wound healing and cell debris elimination
- C. Increasing cytokine production
- D. Suppressing adaptive immunity
Correct Answer: B
Rationale: The correct answer is B because the immune system plays a crucial role in promoting wound healing and eliminating cell debris. When tissue is damaged, the immune response helps remove dead cells and debris, initiates the healing process, and supports tissue regeneration. This involves the recruitment of immune cells to the site of injury, releasing growth factors to stimulate cell proliferation, and resolving inflammation.
Choice A (Preventing pathogen invasion) is incorrect because while the immune system does play a role in preventing pathogen invasion, this is not directly related to tissue regeneration.
Choice C (Increasing cytokine production) is incorrect because although cytokines are involved in the immune response and can influence tissue repair, simply increasing cytokine production does not fully describe the immune system's role in tissue regeneration.
Choice D (Suppressing adaptive immunity) is incorrect because suppressing adaptive immunity would hinder rather than promote tissue regeneration, as adaptive immunity plays a role in immune memory and long-term protection against pathogens.
Prophylactic measures that are routinely used as early as possible in HIV infection to prevent opportunistic and debilitating secondary problems include administration of
- A. isoniazid (INH) to prevent tuberculosis
- B. trimethoprim/sulfamethoxazole (TMP/SMX) for toxoplasmosis
- C. vaccines for pneumococcal pneumonia, influenza, and hepatitis A and B
- D. varicella-zoster immune globulin (VZIG) to prevent chickenpox or shingles
Correct Answer: C
Rationale: Vaccination protects against preventable infections that can become severe in immunocompromised individuals.
What is the significance of isotype switching in B cells?
- A. It enables the production of IgM only
- B. It enhances antibody affinity for antigens
- C. It changes the constant region to produce different antibody isotypes
- D. It eliminates antigen-specific B cells
Correct Answer: C
Rationale: Isotype switching in B cells involves changing the constant region to produce different antibody isotypes, such as IgG, IgA, or IgE. This is important for diversifying the functions of antibodies without altering antigen specificity. It allows for different effector functions, such as opsonization, neutralization, or complement activation. This process does not eliminate antigen-specific B cells, as it maintains the immunological memory. Isotype switching does not directly affect antibody affinity for antigens, which is primarily determined by somatic hypermutation and affinity maturation. It is not limited to producing IgM only, as B cells can switch to other isotypes based on the cytokine microenvironment.
The differentiation of activated Th cells into various effector subsets depends mostly on:
- A. Signal 1 of activation
- B. The influence of polarizing cytokines secreted by dendritic cells
- C. Whether the T cell expresses CD4 or CD8
- D. The duration of signaling induced by TCR binding to peptide-MHC
Correct Answer: B
Rationale: The correct answer is B because polarizing cytokines secreted by dendritic cells play a crucial role in determining the differentiation of activated Th cells into specific effector subsets. These cytokines guide the Th cells towards different functional phenotypes, such as Th1, Th2, Th17, or Treg cells. This process helps tailor the immune response to the specific type of pathogen encountered. Choices A, C, and D are incorrect because while signal 1 of activation, T cell receptor co-receptors, and duration of signaling are important factors in T cell activation and differentiation, they do not have as direct and significant an impact on effector subset differentiation as the influence of polarizing cytokines.
What is a characteristic feature of atopy?
- A. Tendency to produce IgE in response to allergens
- B. Excess production of IgA antibodies
- C. Suppressed immune response to allergens
- D. Delayed hypersensitivity reaction
Correct Answer: A
Rationale: Step-by-step rationale:
1. Atopy is a genetic predisposition to produce IgE antibodies in response to allergens.
2. IgE antibodies play a crucial role in allergic reactions.
3. Individuals with atopy have an exaggerated immune response to allergens.
4. Excess production of IgA antibodies (B) and suppressed immune response to allergens (C) are not characteristic features of atopy.
5. Delayed hypersensitivity reactions (D) involve a different immune mechanism compared to the immediate IgE-mediated response in atopy.