Immunomodulatory effects of plasminogen activators on hepatic fibrogenesis

Tissue-type plasminogen activators (tPA) and urokinase-type plasminogen activators (uPA) are involved in liver repair. We examined the potential immunomodulatory actions of uPA, tPA and uPA-receptor (uPAR) in carbon-tetrachloride-induced hepatic fibrosis in wild-type (WT), tPA ^-/-, uPA^-/- and uPAR^-/- mice. Carbon-tetrachloride treatment increased fibrosis in four groups but significantly less in three knock-out models. Serum cytokines and intrahepatic T cells elevated significantly following fibrosis process in WT animals but not in the knock-out groups. In culture, uPA increased lymphocyte proliferation significantly in WT and uPA^-/- but not uPAR^-/- animals. Following uPA exposure in vivo, there was CD8 predominance. To isolate uPA's effect on lymphocytes, WT mice were irradiated sublethally and then reconstituted with WT or uPA^-/- lymphocytes. In these animals fibrosis was decreased and T cells were reduced in the uPA^-/- recipients. Based on these data we postulate that plasminogen activators affect fibrosis in part by liver-specific activation of CD8 subsets that govern the fibrogenic activity of hepatic stellate cells.