Liver Sinusoidal Endothelial Cells inhibit inflammatory cytokine responses of CD4 T cells through skewed accesory signals

Liver cells are able to down-regulate the inflammatory activity of infiltrating immune cells, however, the cellular and molecular activity behind this capability is unclear. Here, we investigated whether liver sinusoidal endothelial cells (LSEC) could abrogate inflammatory cytokine secretion by CD4 T cells. We induced inflammatory CD4 T cells by stimulating murine splenic CD4 T cells with dendritic cells (DC) and antibody to CD3. Upon restimulation, DC-primed CD4 T cells secreted high amounts of interferon-g (IFNg; (>1000 pg/ml) and IL17 (100 pg/ml). The DC-primed CD4 T cells were then restimulated twice either on LSEC or DC. Upon restimulation by LSEC, CD4 T cells failed to secrete IFNg (260 pg/ml after first, 0 pg/ml after second restimulation) and IL17 (25 pg/ml after first, 10pg/ml after second restimulation); in contrast, CD4 T cells restimulated by DC retained the ability to secrete IFNg (>1000 pg/ml) and IL17 (>75 pg/ml). Interestingly, CD4 T cells that were stimulated on LSEC/DC co-cultures also exhibited a markedly reduced ability to secrete IFNg (100 pg/ml vs. 3000 pg/ml by DC stimulation) and IL17 (10 pg/ml vs.100 pg/ml). However, when CD28 antibody was added to these co-cultures, LSEC failed to suppress DC-induced CD4 cytokine production (100pg/ml vs. 1500 pg/ml IFNg with CD28 antibody). Moreover, CD4 T cells from PD1-deficient mice were resistant to the impairment of IFNg secretion in LSEC/DC co-cultures (1100 pg/ml, compared to 1200 pg/ml induced by DC mono-culture). Furthermore, LSEC from IL10-deficient mice, which exhibit decreased PD-L1 expression and increased expression levels of MHCII and the costimulatory molecules CD40, CD80 and CD86, could not suppress DC-induced IFNg secretion by CD4 T cells (1000 pg/ml), unless LSEC were pre-incubated with IL10 (400 pg/ml). Our findings indicate that LSEC can potently suppress inflammatory CD4 T cell activity through skewed accessory signals, marked by dominant co-inhibitory over co-stimulatory signals.