Clonality and specificity of cryoglobulins associated with HCV: pathophysiological implications

Background/Aims: Hepatitis C virus (HCV) infection plays a central role in the pathogenesis of mixed cryoglobulinemia through molecular mechanisms whi ch remain to be elucidated. The aim of this study was to investigate the ro le of antibody responses to HCV in the pathogenesis of cryoglobulinemia thr ough characterization of the anti-HCV specificity and immunochemical charac teristics of the immunoglobulins involved in cryoprecipitation. Methods: Sera from 50 consecutive patients with chronic HCV infection (RNA positive) were screened for the presence of cryoglobulins. The two major co mponents of cryoprecipitates, IgM rheumatoid factors and IgG, were separate d by high performance liquid chromatography and analyzed for immunochemical composition by immunoblotting and antibody specificity by ELISA and immuno blotting using recombinant HCV proteins and synthetic peptides as antigens. Results: Cryoprecipitates were observed in 27 patients and characterized by immunofixation: 13 (48%) were classified as type II and 14 (52%) as type I II, Monoclonal immunoglobulins were detected by immunoblotting in 20 cryopr ecipitates: IgM in 14 samples and IgG in 14, with a clear preponderance of IgG3 (12/14), Specificity studies on sera and purified IgM and IgG fraction s from cryoprecipitates revealed enrichment in cryoglobulins, predominantly polyclonal IgG1, reactive with the HCV structural proteins, whereas specif icities for nonstructural viral proteins were relatively less represented c ompared to whole serum. No restricted pattern of fine specificity was obser ved, IgG3 subclass was apparently not involved in HCV nucleoprotein binding . Conclusions: Our findings do not support a direct link between monoclonal c ryoglobulins and immune response to HCV. According to the proposed pathogen etic model, HCV infection can induce the formation of cryoprecipitable rheu matoid factors, sustain their production, and eventually lead to monoclonal B-cell expansion through several cooperative mechanisms.