Smooth-muscle antibodies in rheumatoid arthritis

Smooth-muscle antibodies (SMA) detected by the indirect immunofluorescence method were found more often in rheumatoid arthritis (RA) patients (15.3%) than in normal controls (7.6%) (0.02 > p > 0.01). The increased frequency was due to IgG-antibodies which occurred in 12.2% of RA patients, in 4.1% of normal controls and in 7.3% of patients with other arthritic diseases. Eight of 9 IgG-SMA-positive RA sera reacted with F-actin, and one serum contained non-actin antibodies. In RA, ANA were found in 35.7%, glomerular antibodies in 1.0%, parietal cell antibodies in 4.1% and mitochondrial antibodies in 2.0%. SMA were associated with the occurrence of rheumatoid factors and mitochondrial antibodies (0.02% > p and 2p = 0.04, respectively). In the SMA-positive group the erythrocyte sedimentation rate was higher and elevated serum alkaline phosphatase values were found more often than in the SMA-negative group.