Ex vivo analysis of resident hepatic pro-inflammatory CD1d-reactive T cells and hepatocyte surface CD1d expression in hepatitis C

Hepatic CD1d-restricted and natural killer T-cell populations are heterogeneous. Classical 'type 1' α-galactosylceramide-reactive CD1d-restricted T cells express 'invariant' TCRα ('iNKT'). iNKT dominating rodent liver are implicated in inflammation, including in hepatitis models. Low levels of iNKT are detected in human liver, decreased in subjects with chronic hepatitis C (CHC). However, high levels of human hepatic CD161(±) CD56(±) noninvariant pro-inflammatory CD1d-restricted 'type 2' T cells have been identified in vitro. Unlike rodents, healthy human hepatocytes only express trace and intracellular CD1d. Total hepatic CD1d appears to be increased in CHC and primary biliary cirrhosis. Direct ex vivo analysis of human intrahepatic lymphocytes (IHL), including matched ex vivo versus in vitro expanded IHL, demonstrated detectable noninvariant CD1d reactivity in substantial proportions of HCV-positive livers and significant fractions of HCV-negative livers. However, α-galactosylceramide-reactive iNKT were detected only relatively rarely. Liver CD1d-restricted IHL produced IFNγ, variable levels of IL-10 and modest levels of Th2 cytokines IL-4 and IL-13 ex vivo. In a novel FACS assay, a major fraction (10-20%) of hepatic T cells rapidly produced IFNγ and up-regulated activation marker CD69 in response to CD1d. As previously only shown with murine iNKT, noninvariant human CD1d-specific responses were also augmented by IL-12. Interestingly, CD1d was found selectively expressed on the surface of hepatocytes in CHC, but not those CHC subjects with history of alcohol usage or resolved CHC. In contrast to hepatic iNKT, noninvariant IFNγ-producing type 2 CD1d-reactive NKT cells are commonly detected in CHC, together with cognate ligand CD1d, implicating them in CHC liver damage.