Abstract

BACKGROUND: IL-9 is a growth factor for T- and mast-cells that is secreted by human Th2 cells. We recently reported that IL-4+TGF-beta directs mouse CD4(+)CD25(-)CD62L(+) T cells to commit to inflammatory IL-9 producing CD4(+) T cells. METHODOLOGY/PRINCIPAL FINDINGS: Here we show that human inducible regulatory T cells (iTregs) also express IL-9. IL-4+TGF-beta induced higher levels of IL-9 expression in plate bound-anti-CD3 mAb (pbCD3)/soluble-anti-CD28 mAb (sCD28) activated human resting memory CD4(+)CD25(-)CD45RO(+) T cells as compared to naïve CD4(+)CD25(-)CD45RA(+) T cells. In addition, as compared to pbCD3/sCD28 plus TGF-beta stimulation, IL-4+TGF-beta stimulated memory CD4(+)CD25(-)CD45RO(+) T cells expressed reduced FOXP3 protein. As analyzed by pre-amplification boosted single-cell real-time PCR, human CD4(+)IL-9(+) T cells expressed GATA3 and RORC, but not IL-10, IL-13, IFNgamma or IL-17A/F. Attempts to optimize IL-9 production by pbCD3/sCD28 and IL-4+TGF-beta stimulated resting memory CD4(+) T cells demonstrated that the addition of IL-1beta, IL-12, and IL-21 further enhance IL-9 production. CONCLUSIONS/SIGNIFICANCE: Taken together these data show both the differences and similarities between mouse and human CD4(+)IL9(+) T cells and reaffirm the powerful influence of inflammatory cytokines to shape the response of activated CD4(+) T cells to antigen.