Nokea
All of the following are true with respect to IgE molecules, EXCEPT which one?
- A. They are the principal immunoglobulin class involved in allergic reactions.
- B. They are involved in mediating anti-parasitic immune responses.
- C. They will cross the placenta and fix complement.
- D. They can effect the release of histamine and other chemical mediators.
Correct Answer: C
Rationale: The correct answer is C. IgE molecules do not cross the placenta and fix complement, unlike IgG. IgE is the principal immunoglobulin in allergic reactions (A), mediates anti-parasitic immune responses (B), and triggers the release of histamine and other mediators (D). IgE plays a specific role in allergic responses and defense against parasites. IgG is the main immunoglobulin that crosses the placenta and fixes complement. Therefore, IgE does not share this function.
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Class switching of immunoglobulins occurs
- A. Usually with booster immunizations, going from IgM to IgG
- B. binds complement
- C. causes the histamine release
- D. mediates immunoglobulin class switching
Correct Answer: A
Rationale: The correct answer is A because class switching of immunoglobulins typically occurs during an immune response, leading to the production of antibodies of different classes like IgM to IgG. This process helps enhance the immune response and memory. Choice B, binding complement, refers to the function of antibodies in the classical pathway of the complement system, not class switching. Choice C, causing histamine release, is typically associated with IgE antibodies in allergic reactions, not class switching. Choice D, mediating immunoglobulin class switching, is too vague and does not provide a clear explanation compared to choice A.
What role do cytokines play in innate immunity?
- A. They directly kill pathogens
- B. They act as signaling molecules to coordinate immune responses
- C. They only function in adaptive immunity
- D. They inhibit phagocytosis
Correct Answer: B
Rationale: The correct answer is B because cytokines act as signaling molecules to coordinate immune responses in innate immunity. They help regulate inflammation, activate immune cells, and promote clearance of pathogens. Option A is incorrect because cytokines do not directly kill pathogens. Option C is incorrect as cytokines play a crucial role in both innate and adaptive immunity. Option D is incorrect because cytokines do not inhibit phagocytosis; instead, they enhance this process to help eliminate pathogens.
Which antibody isotype is primarily involved in mucosal immunity?
- A. IgG
- B. IgA
- C. IgM
- D. IgE
Correct Answer: B
Rationale: The correct answer is B: IgA. IgA is primarily involved in mucosal immunity as it is the most abundant antibody present in mucosal secretions like saliva, tears, and breast milk. IgA plays a crucial role in preventing pathogens from entering the body through mucosal surfaces. IgG is more involved in systemic immunity, IgM is the first antibody produced in response to an infection, and IgE is associated with allergic reactions. Therefore, IgA is the most appropriate choice for mucosal immunity.
A site of intense B cell proliferation in the lymph node is
- A. Germinal center
- B. Paracortex
- C. Medulla
- D. Infected tissue
Correct Answer: A
Rationale: The correct answer is A: Germinal center. Germinal centers are specialized regions within lymph nodes where B cells undergo intense proliferation, somatic hypermutation, and class switching to generate high-affinity antibodies. This process is crucial for the adaptive immune response. Paracortex (B) contains T cells, not B cells. Medulla (C) is mainly involved in filtering lymph. Infected tissue (D) is not a specific site for B cell proliferation.
If you were to observe the activity of methylated DNA, you would expect it to
- A. be unwinding in preparation for protein synthesis.
- B. be replicating nearly continuously.
- C. have turned off or slowed down the process of transcription.
- D. induce protein synthesis by not allowing repressors to bind to it.
Correct Answer: C
Rationale: The correct answer is C because methylation of DNA typically results in the inhibition or slowing down of transcription. Methylated DNA attracts proteins that bind to it, preventing transcription factors from accessing the DNA and initiating transcription. This interference with the transcription process leads to gene silencing or reduced gene expression.
A: DNA unwinding in preparation for protein synthesis is unrelated to DNA methylation.
B: Continuous replication is not a typical consequence of DNA methylation.
D: Methylation does not directly induce protein synthesis but rather affects transcription by influencing gene expression.