Induction of autoimmune hepatitis and autoantibodies to liver antigens by neonatal thymectomy in mice

We examined development of autoimmune hepatitis in neonatally thymectomized C3H/HeN mice and tried to characterize the nature of liver antigens recognized by the autoantibodies at the molecular level. Autoantibodies to crude liver proteins detected by ELISA were found in 12 (67%) of 18 mice thymectomized 2 days after birth. However, autoantibodies were not detected in mice thymectomized 7 days after birth. The autoantibodies mainly consisted of IgG and reached the maximum level 8 weeks after birth. Hepatic inflammation, mononuclear cell infiltration in the portal area, was seen in 5 (28%) of 18 mice thymectomized 2 days after birth, but not in mice thymectomized 7 days after birth. Most infiltrating cells were Thy-1⁺ lymphocytes. The serum autoantibody level to crude liver proteins in mice with hepatitis was much higher than that in mice without hepatitis. We fractionated crude liver proteins by a Sepharose 6B column and examined the reactivity against the autoantibodies. The autoantibodies of three of five mice with hepatitis reacted with the ≈150 kD liver proteins other than liver-specific protein (LSP). By Western immunoblotting of SDS–PAGE using LSP and fractionated liver proteins, we found that the molecular weights of the target antigens were 52 kD in LSP and 150 kD (strong band), 138, 128, 120 and 110 kD (weak band) in fractionated liver proteins other than LSP. This 150-kD target molecule in crude liver proteins was found only in liver. These results indicate that hepatitis and autoantibodies to liver proteins are induced spontaneously by neonatal thymectomy in mice, and the candidates of autoantigen in this hepatitis model are 52-kD protein in LSP and 150-kD liver proteins different from LSP. Still more, we regard the 150-kD molecule as a new autoantigen related to hepatitis.