Interleukin-1β-induced IRAK1 ubiquitination is required for TH-GM-CSF cell differentiation in T cell-mediated inflammation.

Accumulating evidence suggests granulocyte macrophage-colony stimulating factor (GM-CSF) can function as an inflammatory mediator, but whether GM-CSF-producing CD4+ T cells (TH-GM-CSF) are a distinct T helper cell subset is lacking. Herein we demonstrate that interleukin (IL)-1β exclusively drives differentiation of naïve CD4+ T cells into TH-GM-CSF cells via inducing ubiquitination of IL-1 receptor-associated kinase 1 (IRAK1) and subsequent activation of the transcription factor NF-kappaB (NF-κB), independent of RAR-related orphan receptor gamma (RORγt) required for TH17 differentiation. In vivo, TH-GM-CSF cells are present in murine Citrobacter Rodentium infections and mediate colitis following adoptive transfer of CD4+ T cells into Rag1-/- mice via GM-CSF-induced macrophage activation. The TH-GM-CSF cell phenotype is stable and distinct from the TH17 genetic program, but IL-1β can convert pre-formed TH17 cells into TH-GM-CSF cells, thereby accounting for previously reported associations between IL-17 and GM-CSF. Together, our results newly identify IL-1β/NF-κB-dependent TH-GM-CSF cells as a unique T helper cell subset and highlight the importance of CD4+ T cell-derived GM-CSF induced macrophage activation as a previously undescribed T cell effector mechanism.