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 ('G/T' 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.