Interleukin-9 as a T helper type 17 cytokine

Abstract

The production of interleukin-9 (IL-9) by CD4 T cells has gathered renewed interest as the result of the observation that its expression is broader than originally thought. This includes the production of IL-9 by a recently characterized subset of CD4 helper T (Th) cells that are termed Th9 as well as production by additional T-cell subsets including Th17 cells. There is an incomplete understanding as to which IL-9-producing T-cell subsets develop under physiological conditions. We describe the conditions used to generate IL-9 in Th17 cells in vitro. We also summarize conditions where both IL-9 and IL-17 are found in vivo and propose that Th17 cells producing IL-9 may co-exist and interact with Th9 cells during conditions of autoimmunity, allergy and infection.

Figure 1

Proposed model of T helper type 17 (Th17), Th9, and mast cell interactions. Th17 derived interleukin-9 (IL-9) and IL-21 can act in a paracrine manner to further their own expansion or in an autocrine manner to further the expansion of Th9 cells. Interleukin-9 derived from both of these subsets can also act on mast cells. TGF-β, transforming growth factor-β.