Nokea
Rolling' of neutrophils on endothelial cells is mediated by:
- A. Selectins expressed on endothelial cells
- B. Integrins expressed on leukocytes
- C. Chemokines such as CXCL-8 (IL-8)
- D. TNF
Correct Answer: A
Rationale: The correct answer is A: Selectins expressed on endothelial cells. Rolling of neutrophils on endothelial cells is a crucial step in the process of inflammation and immune response. Selectins are cell adhesion molecules expressed on endothelial cells that facilitate the initial interaction between leukocytes (such as neutrophils) and endothelial cells. This interaction allows for the rolling of neutrophils along the endothelial surface, which is essential for the subsequent steps of adhesion and transmigration into the tissues. Integrins (Choice B) are involved in the firm adhesion of leukocytes to endothelial cells, not in the initial rolling process. Chemokines (Choice C) such as CXCL-8 are signaling molecules that help in the recruitment of leukocytes but do not directly mediate the rolling process. TNF (Choice D) is a pro-inflammatory cytokine but is not directly involved in the rolling of neutrophils on endothelial cells.
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In immune response mechanism clonal selection is a process in which:
- A. a special type of clone cell line is identified in a cell culture
- B. the proliferation and differentiation of lymphocytes occur in response to a specific antigen
- C. cloning of a specific gene is done by inserting the same into a bacteria by recombinant DNA technology
- D. selection of an appropriate cell type is done for the purpose of cloning
Correct Answer: B
Rationale: The correct answer is B because in immune response mechanism, clonal selection refers to the process where lymphocytes (T and B cells) proliferate and differentiate in response to a specific antigen. This process ensures that the immune system can effectively target and eliminate pathogens.
Option A is incorrect because clonal selection does not refer to identifying a specific type of clone cell line in cell culture.
Option C is incorrect because clonal selection does not involve cloning a specific gene by inserting it into bacteria using recombinant DNA technology.
Option D is incorrect because clonal selection is not about selecting an appropriate cell type for cloning purposes.
In summary, the correct answer, option B, best describes the process of clonal selection in the context of the immune response mechanism.
Which of the following is not usually observed in severe Covid-19 cases?
- A. Prompt and sustained production of type I Interferon
- B. Autoantibodies
- C. A delayed CD4 T cell response
- D. Elevated levels of inflammatory cytokines
Correct Answer: A
Rationale: Step-by-step rationale:
1. In severe Covid-19 cases, there is usually a dysregulated immune response.
2. Type I Interferon plays a crucial role in early antiviral defense.
3. However, in severe cases, there is often a blunted or delayed response of type I Interferon.
4. This delayed response contributes to viral persistence and hyperinflammation.
5. Therefore, the prompt and sustained production of type I Interferon is not usually observed in severe Covid-19 cases.
Summary:
- Choice A is correct as the prompt and sustained production of type I Interferon is not typically observed in severe Covid-19 cases.
- Choices B, C, and D are incorrect as autoantibodies, a delayed CD4 T cell response, and elevated levels of inflammatory cytokines are commonly observed in severe Covid-19 cases.
What is the immunologic term to indicate the process that eliminates developing T cells whose T-cell receptors bind too strongly to self-peptide/MHC complexes?
- A. Negative selection
- B. Positive selection
- C. Peripheral tolerance
- D. Lineage commitment
Correct Answer: A
Rationale: Negative selection is the correct answer because it refers to the process that eliminates developing T cells with high affinity for self-peptide/MHC complexes to prevent autoimmune reactions. During negative selection, T cells that bind too strongly to self-antigens are deleted or rendered functionally inactive. This ensures that only T cells with moderate affinity for self-antigens are allowed to mature and participate in immune responses.
Summary of other choices:
B: Positive selection involves the selection of T cells that can recognize self-peptide/MHC complexes, promoting their maturation and survival.
C: Peripheral tolerance refers to mechanisms that maintain self-tolerance in the mature immune system, not specifically related to eliminating self-reactive T cells during development.
D: Lineage commitment is the process by which precursor cells differentiate into specific immune cell types and is not directly related to eliminating self-reactive T cells.
Which of the following concerning nosocomial infections is incorrect?
- A. Caused by both Gram-negative and Gram-positive
- B. A common example is represented by Helicobacter pylori
- C. Caused by species that are often antibiotic-resistant
- D. Include infections by Clostridium difficile, a bacterial species that is often part of the commensal flora
Correct Answer: B
Rationale: The correct answer is B because Helicobacter pylori is not typically associated with nosocomial infections. Nosocomial infections are usually caused by bacteria commonly found in healthcare settings, such as Clostridium difficile, which is mentioned in choice D. Choices A, C, and D are correct as nosocomial infections can be caused by both Gram-negative and Gram-positive bacteria, often antibiotic-resistant species, and commensal flora bacteria like Clostridium difficile.
If the BCR of a developing cell has no binding affinity for self-antigens in the bone marrow the B cell will be:
- A. Clonally deleted
- B. Anergized
- C. A possible cause of autoimmunity in the periphery
- D. Allowed to mature and enter the periphery
Correct Answer: D
Rationale: The correct answer is D: Allowed to mature and enter the periphery. In this scenario, since the developing B cell has no binding affinity for self-antigens in the bone marrow, it will not undergo clonal deletion or anergy. Therefore, it will be allowed to mature and enter the periphery where it can encounter foreign antigens and participate in the immune response. Choices A and B are incorrect because clonal deletion and anergy are mechanisms used to eliminate or inactivate self-reactive B cells to prevent autoimmunity. Choice C is incorrect because a B cell without self-binding affinity is not a cause of autoimmunity in the periphery.