Transcriptional Activators of Helper T Cell Fate Are Required for Establishment but Not Maintenance of Signature Cytokine Expression

Abstract

The stability of helper T cell fates is not well understood. Using conditional introduction of dominant-negative factors, we now show that T-bet and GATA-3 are far more critical in establishment than maintenance of IFN-γ and IL-4 activity during Th1 and Th2 maturation, respectively. We also show that a genetic interaction between T-bet and its target Hlx seems to be required for Th1 maturation, but that Hlx may also be dispensable for maintenance of a transcriptionally permissive ifng gene. In parallel to progressive activator independence in the permissive lineage, the ifng gene becomes more recalcitrant to switching as the forbidden lineage matures. T-bet plus Hlx can disrupt ifng silencing when introduced into developing Th2 cells, but they fail to perturb ifng silencing in mature Th2 cells. In contrast, a hypermorphic allele of T-bet can reverse silencing of the ifng gene in mature Th2 cells. These results suggest that signature gene activity of helper T cells is initially plastic but later becomes epigenetically fixed and offer an initial strategy for inducing mature cells to switch their fate.

Temporal Dissection of T-bet Functions

“…Martins et al (34) recently suggested that while T-bet is essential for the establishment of the IFN-␥ gene activity, it might not be required for its maintenance in Th1 cells. These results are in apparent contradiction with our current data showing that T-bet activity is absolutely required at the time of the secondary activation to induce IFN-␥ production.…”

“…In these conditions, IFN-␥ expression by Th1 cells became resistant to the action of the dominant negative construct as Th1 maturation progressed in time. Differences between the two sets of experiments may be related to their time frame (1 vs 3 wk) as well as to the extensive restimulation under Th1 conditions that might favor a T-bet-independent maintenance of the cytokine gene activity (34). Our control of T-bet activity by the addition or removal of 4-HT from the cell cultures clearly established the need for constant T-bet activity to induce IFN-␥ by Th2 cells or by T-bet Ϫ/Ϫ Th1 cells.…”

The Central Memory CD4+ T Cell Population Generated duringLeishmania majorInfection Requires IL-12 to Produce IFN-γ

“…IL-12 is essential for generating a protective Th1 immune response following infection with L. major, acting directly to promote the survival of T cells that are expressing the Th1 transcription factor T-bet, and indirectly by inhibiting the Th2-inducing transcription factor, GATA3 (7,18,25). The requirement for IL-12 at the initiation of the infection is demonstrated by the fact that normally susceptible BALB/c mice are rendered resistant to L. major by IL-12 administration (26 -28).…”

“…It is well established that as CD4 ϩ T cells differentiate, they upregulate lineage-specific transcription factors such as T-bet, which leads to the up-regulation of IFN-␥, and the suppression of Th2-associated cytokines (7,(17)(18)(19). Recently, T-bet has also been shown to regulate memory T cell potential (7,20,21).…”

Role of IFN-α/β signaling in the prevention of genital herpes virus type 2 infection

“…The binding of T-bet alone is sufficient for IFN-γ expression, although the effect can be enhanced by interactions with other transcription factors. T-bet induces expression of the transcription factor H2.0-like homeobox (Hlx), and thereafter interacts with Hlx to induce higher levels of IFN-γ (Martins et al, 2005;Mullen et al, 2002). To enhance further IFN-γ production, T-bet interacts with the transcription factor E26 transformation-specific (Ets)-1 in fully differentiated Th1 cells, and this interaction further stabilizes the Th1 phenotype.…”