IKZF3/Aiolos Is Associated with but Not Sufficient for the Expression of IL-10 by CD4(+) T Cells

The expression of anti-inflammatory IL-10 by CD4(+) T cells is indispensable for immune homeostasis, as it allows T cells to moderate their effector function. We previously showed that TNF-α blockade during T cell stimulation in CD4(+) T cell/monocyte cocultures resulted in maintenance of IL-10–producing T cells and identified IKZF3 as a putative regulator of IL-10. In this study, we tested the hypothesis that IKZF3 is a transcriptional regulator of IL-10 using a human CD4(+) T cell–only culture system. IL-10(+) CD4(+) T cells expressed the highest levels of IKZF3 both ex vivo and after activation compared with IL-10–CD4(+) T cells. Pharmacological targeting of IKZF3 with the drug lenalidomide showed that IKZF3 is required for anti-CD3/CD28 mAb–mediated induction of IL-10 but is dispensable for ex vivo IL-10 expression. However, overexpression of IKZF3 was unable to upregulate IL-10 at the mRNA or protein level in CD4(+) T cells and did not drive the transcription of the IL10 promoter or putative local enhancer constructs. Collectively, these data indicate that IKZF3 is associated with but not sufficient for IL-10 expression in CD4(+) T cells.