Characterization of the microsomal antigen related to a subclass of active chronic hepatitis.

The liver—kidney microsomal (LKM) antigen related to a subgroup of patients with active chronic hepatitis was studied biochemically and by immuno-electronmicroscopy, using peroxidase-conjugated antibodies. The antigenic determinant appears to be on a lipoprotein membrane since it required both phospholipid and protein for antigenic integrity and could not be solubilized. Complement fixation and absorption of immunofluorescence with microsomal subfractions pointed to localization in both rough and smooth endoplasmic reticulum (ER). Immunoelectronmicroscopy on liver and kidney sections showed an association of the antigen with ribosomes and membranes in rough ER; granular staining was also seen between cisternae. Smooth membranes could not be preserved sufficiently to be recognized. The antigen is independent of ribosomal RNA.