OBJECTIVE To estimate the contribution of autoimmune thrombocytopenia to hepatitis C virus-related liver cirrhosis (type C cirrhosis), we evaluated the influence of splenectomy upon platelet-associated immunoglobulin G (PAIgG) levels and platelet numbers. METHODS PAIgG titers and immune markers were determined in 24 type C cirrhotic patients with an intact spleen, 17 type C cirrhotic patients submitted to splenectomy, and 21 non-C cirrhosis with an intact spleen. RESULTS Thrombocytopenia (PLT < 15 x 10(4)/microL) in type C cirrhosis was diagnosed in all patients with an intact spleen, 8 patients submitted to splenectomy, and in 19 non-C cirrhosis with intact spleen. Elevated titers of PAIgG at more than 25.0 ng/10(7) cells were detected in all cirrhotic patients except for one splenectomized patient. PAIgG titers (ng/10(7) cells) were significantly higher in the type C cirrhosis with an intact spleen (247.9+/-197.0) compared with the splenectomized patients (125.6+/-87.8) or non-C cirrhosis (152.4+/-127.4). PAIgG titers were negatively correlated with platelet counts in type C cirrhotic patients with an intact spleen. In comparison with the type C cirrhosis with an intact spleen, the splenectomized patients had a reduced CD4/CD8 ratio and serum neopterin levels. The spleen index (cm2) was negatively correlated with platelet counts in the non-C cirrhosis, but not in the type C cirrhosis. CONCLUSIONS Our data indicate that the autoimmune mechanism plays an important role in thrombocytosis complicated by HCV-positive cirrhosis. In addition, splenectomy may impair T cells function through, at least in part, a reduction of CD4/CD8 ratio, consequently suppressing PAIgG production.