Which of the following statements is NOT true

Correct Answer: D

Rationale: The correct answer is D because CD3 is indeed necessary for TCR signaling in cytotoxic T cells. CD3 is a crucial component of the T cell receptor (TCR) complex, which is responsible for initiating intracellular signaling upon recognition of antigen-MHC complexes. Without CD3, TCR signaling cannot occur, leading to impaired T cell activation and cytotoxic function. Choices A, B, and C are incorrect because they accurately describe the functions and interactions of T cells expressing CD4 and CD8 with antigen presenting cells, as well as the role of CD4 T cells in helping B cells through antigen presentation.

Correct Answer: A

Rationale: Rationale: A. T regulatory cells can produce TGF-β, which is a key immunosuppressive cytokine regulating immune responses. B. T regulatory cells do not express AIRE, a transcription factor mainly involved in central tolerance. C. T regulatory cells can control both TH1 and TH2 responses, maintaining immune homeostasis. D. T regulatory cells do not act by killing other T cell subsets, but rather through suppressive cytokines and cell-cell interactions.

Correct Answer: A

Rationale: The correct answer is A. Integration is a stage of HIV life cycle that involves the insertion of viral DNA into the host cell's genome, facilitated by the enzyme integrase. To explain why A is incorrect, integrase is a viral enzyme, not a host enzyme. B is correct as some anti-HIV drugs target the integration stage to prevent viral replication. C is correct as integrated proviral DNA allows for duplication during cell division. D is correct as integration requires the formation of double-stranded viral DNA.

Correct Answer: C

Rationale: The correct answer is C: Natural killer cells. Natural killer cells are part of the innate immune system and play a crucial role in identifying and destroying infected or abnormal cells. They are able to recognize and target cells that lack specific markers, providing a rapid response to infections. Explanation for incorrect choices: A: B lymphocytes are part of the adaptive immune system, not innate immunity. B: T lymphocytes are also part of the adaptive immune system, not involved in innate immunity. D: Plasma cells are differentiated B cells that produce antibodies in the adaptive immune response, not part of innate immunity.

Correct Answer: C

Rationale: The correct answer is C: IFN-alpha. This is because IFN-alpha belongs to the interferon family, not the interleukin family. Interleukins are a subset of cytokines that are primarily involved in regulating immune responses, while interferons have antiviral properties. IL-1, IL-22, and IL-10 are all interleukins and are part of the interleukin family. Therefore, IFN-alpha is the only cytokine listed that is not included in the interleukin family.