Diagnostic Dilemma in the Detection of Antibodies to Filamentous Actin

Antibodies to filamentous-actin (anti-F-actin) were identified as the serological hallmark of type 1 autoimmune hepatitis (AIH). However, the standardized assay for the autoantibody has not yet been established. The purposes of this study were to verify the sensitivity and specificity for anti-F-actin by different assays and to investigate the benefits of anti-F-actin.

Twenty-two patients with type 1 AIH, 8 patients with autoimmune hepatitis/primary biliary cirrhosis overlap syndrome (AIH/PBC), and 18 patients with HCV related chronic liver disease (CLD-C) were enrolled in this study. Smooth muscle antibodies (SMAs) were assessed by an indirect immunofluorescent (HF) assay. Anti-F-actin was determined by an IIF method and an enzyme-linked immunosorbent assay (ELISA) method. Seropositivity for anti-F-actin was defined as positive in both methods.

SMAs were present in the sera of 11 of 22 patients with AIH, 2 of 8 patients with AIH/PBC, and 3 of 18 patients with CLD-C. Ten AIH patients, 2 AIH/PBC patients, and no CLD-C patients were seropositive for anti-F-actin by the IIF method, while 13 AIH patients, 3 AIH/PBC patients, and no CLD-C patients were positive by the ELISA method. The prevalence of anti-F-actin in AIH, AIH/PBC, and CLD-C were estimated as 10 of 22 (48%), 1 of 8 (13%), and 0 of 26 (0%), respectively. Three AIH patients who showed a discrepancy in the anti-F-actin status were seropositive in ELISA, but seronegative in IIF. However, none of the AIH patients were seronegative in ELISA, but seropositive in IIF. The sera of 10 of 11 AIH patients with SMAs reacted with F-actin, while no sera of AIH patients without SMAs were directed against F-actin at all. AIH patients with anti-F-actin tended to have higher relapse rates during tapering of corticosteroid treatment. However, the declines in titers of anti-F-actin did not reflect the attenuation of the disease activity by the treatment with corticosteroids.

SMAs in the sera of AIH patients predominantly recognized filamentous actin, while SMAs in the sera of CLD-C patients did not. Anti-F-actin by IIF was superior in the specificity to those by ELISA. AIH patients seropositive for anti-F-actin may predict the relapse.