A new antigen recognized by anti-liver-kidney-microsome antibody (LKMA)

Sera from 23 children with autoimmune chronic active hepatitis and positive for anti-liver-kidney-microsome antibody (LKMA), as defined by immunofluorescence, were analysed by Western blot (WB) and two-dimensional gel electrophoresis using rat liver microsomes as antigen, and by WB and dot-blot analysis with rat liver microsomal subfractions. Western blot analysis showed three patterns of reactivity: 13 sera recognized a 50 kD polypeptide, six sera a 66 kD polypeptide and four sera both of them. Two-dimensional gel electrophoresis, WB, and dot-blot analysis showed the 66 kD antigen to have a pI of 5.4 and to be located in the smooth domain of the endoplasmic reticulum. Western blot analysis using monospecific antisera against human IgG subclasses showed the LKMA directed against the 66 kD antigen to be mainly of the IgG1 subclass. These results indicate that LKMA associated with a subgroup of autoimmune hepatitis of children react with at least two different microsomal antigens in rat liver: (1) the 50 kD polypeptide, recently shown to be a cytochrome P-450 of the IID subfamily, and (2) a new antigen of 66 kD, the location of which suggests it may also be part of the mono-oxygenase complex.