Protein kinase C theta is dispensable for suppression mediated by CD25+ CD4+ regulatory T cells

The activation of conventional T cells upon T cell receptor stimulation critically depends on protein kinase C theta (PKC theta). However, its role in regulatory T (Treg) cell function has yet to be fully elucidated. Using siRNA or the potent and PKC family-selective pharmacological inhibitor AEB071, we could show that murine Treg-mediated suppression in vitro is independent of PKC theta function. Likewise, Treg cells of PKC theta-deficient mice were fully functional, showing a similar suppressive activity as wild-type CD25(+) CD4(+) T cells in an in vitro suppression assay. Furthermore, in vitro-differentiated wild-type and PKC theta-deficient iTreg cells showed comparable Foxp3 expression as well as suppressive activity. However, we observed a reduced percentage of Foxp3(+) CD25(+) CD4(+) T cells in the lymphatic organs of PKC theta-deficient mice. Taken together, our results suggest that while PKC. is involved in Treg cell differentiation in vivo, it is dispensable for Treg-mediated suppression.