Smooth muscle antibodies and type 1 autoimmune hepatitis

Background/aim: Smooth muscle antibodies (SMA) characterize type 1 autoimmune hepatitis. Our aim was to evaluate sensitivity and specificity of different immunofluorescence substrates for the detection of SMA. Methods: Sera from 55 patients with type 1 AIH, 20 with primary biliary cirrhosis, 20 with HCV-related chronic hepatitis and 25 blood donors were studied for SMA and anti-microfilaments reactivity by immunofluorescence on rat tissue sections, cultured fibroblasts and commercially available HEp-2 cells (collectively revealing the so called anti-actin pattern), and for the XRI system by counterimmunoelectrophoresis. SMA was classified on the basis of its immunofluorescence pattern (V-vessels, G-glomerular, T-tubular). As further control group, we studied 26 patients with a diagnosis other than AIH, selected on the basis of a SMA-non-T/XR1 positivity. Results: In patients with AIH the SMA-T pattern on rodent tissue, and anti-MF on fibroblasts and on HEp-2 cells were present in 80, 82 and 80%, respectively. Five out of 11 SMA-non T positive AIH patients were anti-MF positive. None of the pathological and healthy controls was positive for SMA-T or anti-MF reactivity. XR1 system was present in 84% of AIH patients and in 5% of pathological controls (p = 0.01). Two out of 26 SMA-non-T/XR1 positive sera were positive for anti-MF by fibroblasts and HEp-2 cells. A significant correlation was found between SMA-T pattern and anti-MF reactivity; no correlation was found between XR1 system and SMA-T pattern or anti-MF reactivity. Conclusions: SMA-T pattern is highly sensitive and specific first diagnostic test for type 1 AIH; anti-MF can be used as additional tool for the diagnosis, particularly when, despite the absence of the SMA-T pattern, AIH is strongly suspected.