Thymocytes undergoing positive selection express:

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.

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.

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.

Correct Answer: D

Rationale: The correct answer is D: Cell-mediated immunity. T lymphocytes are primarily involved in cell-mediated immunity, where they directly attack infected cells or pathogens. This type of immunity is crucial in fighting intracellular pathogens like viruses. Other choices are incorrect because: A: Passive immunity involves receiving pre-formed antibodies, not T lymphocytes. B: Humoral immunity involves B cells producing antibodies, not T lymphocytes. C: Acquired immunity is a general term encompassing both humoral and cell-mediated immunity, but T lymphocytes specifically play a key role in cell-mediated immunity.

Correct Answer: A

Rationale: The correct answer is A: Consult physician to confirm the dosage to be given. The nurse should consult the physician because missing three appointments may affect the patient's progress and tolerance to the allergen injections. The physician needs to reassess the situation and determine the appropriate action, which may involve adjusting the dosage or reevaluating the treatment plan. This ensures patient safety and effectiveness of the treatment. Summary: B: Administering the same dosage as the last visit may not be appropriate without physician consultation. C: Administering the dosage as originally prescribed may not account for any changes in the patient's condition. D: Restarting the entire immunotherapy schedule is an extreme measure and should only be considered after consultation with the physician.