ITK tunes the Th17/Treg switch response by controlling calcium dependent signaling.

Abstract

Abstract Naïve CD4+ T cells can differentiate into pro inflammatory T helper type 17 (Th17) and anti inflammatory T regulatory (Treg) lineages following T cell receptor (TCR) activation. The strength of the TCR signal is tuned by Interleukin-2 inducible T cell Kinase (ITK) and ITK can tune the development of Th17 and Treg cells. ITK signals can also tune a Th17/Treg switch under Th17 conditions. How ITK mediated tuning of TCR signal control naïve CD4+ T cell commitment into Th17/Treg lineages is unclear. Here we used ITK inhibitors, conventional ITK and allele specific ITK (ITKas) IL17 GFP/Foxp3 RFP reporter mice, to track naïve CD4+ T cell commitment into Th17/Treg lineages. Under Th17 conditions, reduced TCR signal strength in absence of ITK activity/expression, tuned naïve CD4+ T cell fate by reducing Th17 differentiation and inducing switch to cells resembling Tregs expressing Foxp3. The ITKas model showed this switch is due to specific ITK inhibition. The switched Treg like cells resemble Tregs by expression of Treg markers (CD25, CTLA4, PD1) and suppression of effector T cell proliferation. Transcriptomic analysis of switched Treg like cells by RNA Seq indicate they resemble Tregs, with reduced Th17 (Rorc, Il17) and increased Treg (Foxp3, Nrp1, Ikzf2) gene expression. Analysis of chromatin accessibility by ATAC Seq indicated closed loci for Th17 (Rorc, Il17) genes. Activating intracellular calcium dependent pathways led to a loss of the Th17/Treg switch response in naïve CD4+ T cell commitment, effectively bypassing ITK mediated tuning of the TCR signal critical for the switch response. In conclusion, we show here ITK tunes a Th17/Treg switch response in naïve CD4+ T cell commitment under Th17 conditions by controlling calcium dependent signaling. Supported by grants from NIH (NIH AI129422).