Background/aim: Anti-neutrophil cytoplasmic antibodies (ANCA) are a group of autoantibodies first associated with Wegener's granulomatosis and microscopic polyangiitis. The significance of ANCA in autoimmune hepatitis remains uncertain; the nature of the antigen or antigens has not been defined yet. The purpose of this study was to identify the target antigen of ANCA in patients with autoimmune hepatitis.
Methods/results: Sera from 32 type-1 autoimmune hepatitis patients were used in the present study. ANCA were detected in 24 of 32 sera (75%). A diffuse cytoplasmic staining pattern (C-ANCA) was detected in 14 patients; the P-ANCA pattern was observed in 10 patients. An extract of human neutrophils was prepared and subjected to SDS-PAGE and Western Blot analysis. A 43-kD dominant immunoreactive protein was found in 20 (63%) autoimmune hepatitis patients. Aminoacid sequence analysis of the 43 kD protein identified actin. Cytoplasmic or perinuclear staining pattern could be reduced after absorption of sera with actin and after removing anti-actin antibodies by affinity chromatography. This was observed for all C-ANCA and for 8 out of 10 P-ANCA. Moreover in double-staining indirect immunofluorescence, the same type of diffuse cytoplasmic staining was observed with autoimmune hepatitis-sera and anti-actin antibodies. In Western Blot analysis with actin, 17 (53%) patients gave a positive result, while 15 (47%) patients had a positive actin-ELISA.
Conclusion: This is the first report to identify the cytoskeletal protein actin as an ANCA antigen.