Under homeostasis, liver sinusoidal endothelial cells (LSECs) shift intrahepatic T-cell responses towards tolerance. However, the role of LSECs in the regulation of T-cell-induced liver inflammation is less clear. Here, we studied the capacity of LSECs to modulate pro-inflammatory Th1-cell differentiation in mice. Using in vitro co-culture systems and subsequent cytokine analysis, we showed that LSECs induced high amounts of the anti-inflammatory cytokine IL-10 in developing Th1 cells. These LSEC-stimulated Th1 cells had no pro-inflammatory capacity in vivo but instead actively suppressed an inflammatory Th1-cell-induced delayed-type hypersensitivity reaction. Blockage of IL-10 signaling in vivo inhibited immunosuppressive activity of LSEC-stimulated Th1 cells. We identified the Notch pathway as a mechanism how LSECs trigger IL-10 expression in Th1 cells. LSECs expressed high levels of the Delta-like and Jagged family of Notch ligands and induced expression of the Notch target genes hes-1 and deltex-1 in Th1 cells. Blockade of Notch signaling selectively inhibited IL-10 induction in Th1 cells by LSECs. Our findings suggest that LSEC-induced IL-10 expression in Th1 cells via the Notch pathway may contribute to the control of hepatic inflammatory immune responses by induction of a self-regulatory mechanism in pro-inflammatory Th1 cells.
