Liver/kidney microsomal antibody type 1 targets CYP2D6 on hepatocyte plasma membrane

Background-Liver/kidney microsomal antibody type 1 (LKM1) is the marker of type 2 autoimmune hepatitis (AIM) and is detected in up to 6% of patients w ith hepatitis C virus (MCV) infection. It recognises linear and conformatio nal epitopes of cytochrome P450IID6 (CYP2D6) and may have liver damaging ac tivity, provided that CYP2D6 is accessible to effector mechanisms of autoim mune attack. Methods-The presence of LKM1 in the plasma membrane was investigated by ind irect immunofluorescence and confocal laser microscopy of isolated rat hepa tocytes probed with 10 LKM1 positive sera (five from patients with AIM and five from patients with chronic MCV infection) and a rabbit polyclonal anti -CYP2D6 serum. Results-Serum from both types of patient stained the plasma membrane of non -permeabilised cells, where the fluorescent signal could be visualised as d iscrete clumps. Conversely, permeabilised hepatocytes showed diffuse submem branous/cytoplasmic staining. Adsorption with recombinant CYP2D6 substantia lly reduced plasma membrane staining and LKM1 immunoblot reactivity. Plasma membrane staining of LKM1 colocalised with that of anti-CYP2D6. Immunoprec ipitation experiments showed that a single 50 kDa protein recognised by ant i-CYP2D6 can be isolated from the plasma membrane of intact hepatocytes. Conclusions-AIH and MCV related LKM1 recognise CYP2D6 exposed on the plasma membrane of isolated hepatocytes. This observation supports the notion tha t anti-CYP2D6 autoreactivity may be involved in the pathogenesis of liver d amage.