F-actin reactive smooth muscle antibody in subjects with normal liver function

Aims: Smooth muscle antibody SMA with F-actin reactivity has been reported as a diagnostic marker of autoimmune hepatitis. We re-visited this relationship by randomly selecting SMA-positive sera to test for reactivity with F-actin by ELISA. We correlated such reactivity with liver function tests. Methods: Sera positive for SMA by indirect immunofluorescence were tested for reactivity by F-actin ELISA and the results correlated with liver function tests. Results: 89 SMA-positive sera reacted with F-actin by ELISA. Of these, 35 39 had normal liver enzymes, while 54 60 had elevated liver enzymes. There was no difference between the groups with respect to age at presentation, female preponderance or presence of anti-nuclear antibody. In both groups, high titre SMA antibody predominantly with immunofluorescence staining of renal glomeruli and peritubular fibrils of renal tubules 'GT' subset correlated with makedly elevated F-actin values by ELISA. 'Actin cables' by immunofluorescence staining of Hep-2 cells were infrequently found in both groups. Conclusions: This is the first report of SMA with F-actin reactivity in subjects with normal liver function.