Serum Fc gamma-receptor-like molecules in primary biliary cirrhosis: a possible immunoregulatory mechanism.

Functionally active Fc gamma-receptor-like molecules were isolated from normal human serum by affinity chromatography and shown to have an apparent molecular weight (MW) of approximately 60,000 as assessed by SDS-polyacrylamide gel electrophoresis. These low MW Fc gamma-receptor-like molecules were found to be significantly reduced in whole serum, and in all of six serum fractions, obtained from patients with primary biliary cirrhosis (PBC). A high MW IgG-binding factor, with partial Fc gamma-receptor-like activity, was also found in PBC serum. This factor was also observed to a lesser extent in normal serum. Detailed analysis of this factor suggests that it is a large macromolecule consisting of antigen (unknown). IgG class antibody and 60K Fc gamma-receptor-like molecules. Binding of serum Fc gamma R-like molecules to immune complexes may account for the apparent reduction in Fc gamma-receptor-like activity observed in whole PBC serum. These macromolecules may play an important role in immunoregulation.