Nokea
Which of the following is a feature of antigen recognition by B cells?
- A. Their antigen receptors are never secreted
- B. Their antigen receptors recognize a fragment of protein in combination with an MHC molecule
- C. Their receptors each have two identical antigen binding sites
- D. They recognize pattern associated molecular structures (PAMPs) that are unique to a particular pathogen
Correct Answer: C
Rationale: The correct answer is C because B cell receptors, known as antibodies, are Y-shaped proteins with two identical antigen-binding sites. This feature allows B cells to bind to specific antigens with high specificity. Each B cell receptor can bind to a unique antigen, leading to the initiation of an immune response.
Choice A is incorrect because B cell receptors can be secreted as antibodies to target antigens outside the cell.
Choice B is incorrect because B cell receptors recognize antigens directly, not in combination with MHC molecules.
Choice D is incorrect because B cells primarily recognize specific antigens rather than general PAMPs associated with pathogens.
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Memory T cells
- A. Recirculate through blood and secondary lymphoid tissues
- B. Have never encountered antigen
- C. Have a lower threshold of activation than naïve T cells
- D. Have a higher frequency than their naïve counterparts
Correct Answer: C
Rationale: The correct answer is C because memory T cells have a lower threshold of activation than naïve T cells. This is because memory T cells have already been primed by previous exposure to antigens, making them more responsive upon re-exposure. This heightened sensitivity allows memory T cells to mount a faster and stronger immune response upon encountering the same antigen again.
Choice A is incorrect because memory T cells primarily reside in peripheral tissues and not in secondary lymphoid tissues. Choice B is incorrect because memory T cells have encountered antigens before. Choice D is incorrect because memory T cells exist in a lower frequency compared to naïve T cells due to clonal expansion during the primary immune response.
The inflammatory response produced
- A. by microbial-infected cells
- B. Internal tissue injury
- C. migration of erythrocyts from the spleen
- D. All above
Correct Answer: D
Rationale: The correct answer is D. The inflammatory response can be triggered by microbial-infected cells releasing cytokines, internal tissue injury leading to the release of inflammatory mediators, and the migration of erythrocytes from the spleen in response to inflammation. Therefore, all of the choices - A, B, and C - are correct in contributing to the inflammatory response. Each option plays a role in the complex cascade of events that lead to inflammation.
With regard to NADPH oxidase, which of the following statements in not correct?
- A. It is the enzyme involved in the respiratory burst that follows the engagement of phagocytic receptors
- B. Individuals with mutations of NADPH oxidase subunits suffer repeated infections because of defective killing of phagocytosed pathogens
- C. It is constitutively expressed as a complex of 5 subunits in unstimulated cells
- D. It controls the formation of reactive oxygen species
Correct Answer: C
Rationale: The correct answer is C because NADPH oxidase is not constitutively expressed as a complex of 5 subunits in unstimulated cells. Instead, it is assembled and activated upon stimulation, such as during the respiratory burst following phagocytosis. Choice A is correct as NADPH oxidase is indeed involved in the respiratory burst. Choice B is correct as mutations in NADPH oxidase subunits lead to impaired pathogen killing and recurrent infections. Choice D is correct as NADPH oxidase controls the production of reactive oxygen species.
The nurse is caring for a patient who has had a total hip replacement and is using an abductor wedge. For which finding should the nurse assess?
- A. Muscle spasms
- B. Alteration in peripheral circulation
- C. Compression fracture
- D. Appropriateness of the size of the wedge
Correct Answer: B
Rationale: The correct answer is B: Alteration in peripheral circulation. The abductor wedge can affect blood flow to the legs, leading to potential complications like deep vein thrombosis. The nurse should assess for signs of impaired circulation such as color changes, temperature differences, and peripheral pulses. Muscle spasms (A) may occur due to the surgery but are not directly related to the wedge. Compression fracture (C) is not typically a concern with an abductor wedge. Assessing the appropriateness of the wedge size (D) is important but not as critical as monitoring for alterations in peripheral circulation.
The process of somatic hypermutation:
- A. Can lead to the formation of antibodies with higher affinity for the antigen
- B. Occurs mainly in the CDR regions of immunoglobulin heavy and light chain genes
- C. Occurs in germinal centres
- D. All of the above are correct
Correct Answer: D
Rationale: The correct answer is D because somatic hypermutation can lead to the formation of antibodies with higher affinity for the antigen by introducing point mutations in the variable regions of immunoglobulin genes. This process mainly occurs in the complementarity-determining regions (CDRs) of immunoglobulin heavy and light chain genes, which are critical for antigen binding. Somatic hypermutation takes place in the germinal centers of secondary lymphoid organs, where B cells undergo rapid proliferation and selection based on antigen binding affinity. Therefore, all the statements in choices A, B, and C are correct, making option D the right answer.