CYTOCHROME-P450 2E1 IS A CELL-SURFACE AUTOANTIGEN IN HALOTHANE HEPATITIS

Recent studies have shown that cytochrome P450 2E1 (CYP2E1) is a major catalyst of formation of trifluoroacetylated proteins, which have bee n implicated as target antigens in the mechanism of halothane hepatiti s. In the present investigation, trifluoroacetylated CYP2E1 was detect ed immunochemically in livers of rats treated with halothane. Furtherm ore, high levels of autoantibodies that recognized purified rat CYP2E1 but not purified rat CYP3A were detected by enzyme-linked immunosorbe nt assay in 14 of 20 (70%) sera from patients with halothane hepatitis . Only very low levels of such antibodies were detected in sera from h ealthy controls, from patients anesthetized with halothane without dev eloping hepatitis, or from patients with other liver diseases. The int racellular distribution of CF3CO-adducts was studied in highly differe ntiated FGC4 rat hepatoma cell cultures. High levels of adducts were f ound after 22-hr culture in the presence of halothane, and their gener ation was dependent on the expression of CYP2E1. Adducts were predomin antly located in the endoplasmic reticulum but also, to a minor extent , on the cell surface, as detected by immunofluorescence. A very simil ar distribution was found for CYP2E1 in FGC4 cells, and immunoprecipit ation experiments performed in cultures of FGC4-related Fao hepatoma c ells suggest that surface immunoreactivity originates from a small fra ction of intact CYP2E1 apoprotein. Human CYP2E1, expressed in V79 cell s after cDNA transfection, was also detected to a minor extent in the plasma membrane, whereas no immunofluorescence was evident in parental V79 cells. It is suggested that immune responses to cell surface CYP2 E1 could be involved in the pathogenesis of halothane hepatitis.