IL-9 and Th9 cells: progress and challenges

Abstract

T(h)9 cells are a new subset of helper T cells, and the signature cytokine for T(h)9 cells is IL-9. Both T(h)9 cells and T(h)9 products are implicated in multiple disease settings. Thus, a clear understanding of how T(h)9 cells are induced and controlled is an important and clinically relevant issue. There are different molecular pathways identified thus far in the induction of T(h)9 cells, and activation of such diverse pathways requires integration of signals from TGF-β and IL-4 cytokine receptors as well as costimulatory molecules. These signals converge on the induction of multiple transcription factors that collectively drive the development of T(h)9 cells.

Keywords: IL-9; Th9; allergy; inflammation.

Fig. 1.

Pathways of T_h9 induction. Naive CD4⁺ T cells can be converted to IL-9-producing T_h9 cells via different molecular pathways. Depending on the presence or absence of OX40 costimulation, T_h9 cells can develop from a subset of T_h2 cells (shown in purple) or directly from CD4⁺ T-cell precursors under TGF-β/IL-4-polarizing conditions.