Final answer:
Expression of IFN-γ in a CD4 TH1 cell is directed by the transcription factor T-bet, which is essential for the TH1 cell phenotype and its role in cell-mediated immunity. The correct option is a.
Step-by-step explanation:
Expression of IFN-γ is induced in a CD4 TH1 cell under the direction of the transcription factor T-bet.
When a CD4+ helper T cell binds MCH II-antigen complex on an antigen-presenting cell, both the antigen-presenting cell and the T cell release cytokines.
These cytokines, along with the influence of specific transcription factors, guide the differentiation of T cells.T-bet is the transcription factor responsible for the induction of IFN-γ in CD4 TH1 cells.
This transcription factor is crucial for the development of the TH1 cell phenotype, promoting the cell's role in cell-mediated immune responses against intracellular pathogens.
On the other hand, other transcription factors such as FoxP3 and GATA-3 are respectively associated with regulatory T cells and TH2 cell differentiation.
The interaction of CD4+ helper T cells with MHC II-antigen complexes and release of cytokines are central events in the immune response, leading to cell activation and subsequent secretion of various cytokines, including IFN-γ, which serve to orchestrate an effective immune response. The correct option is a.