Incidence and titres of smooth-muscle antibodies in human sera.

By means of the indirect immunofluorescence method smooth-muscle antibodies (SMA) were determined in 182 patients with various diseases and the findings were compared with those of 7 patients with chronic active hepatitis (CAH) and 580 normal controls. IgG-SMA were found in 85.7% of the patients with CAH, titres above 80 occurred only in Hepatitis B-associated antigen (HBAg)-negative CAH, but IgG-SMA in low titres were also found with increased incidence in syphilis (16.7%) and in infections of the central nervous system (19%). In other diseases (Sjøgren's syndrome, ulcerative colitis, regional enteritis, myasthenia gravis, progressive muscular dystrophy, atopic dermatitis and mycoplasma pneumoniae infection) the prevalence did not differ from that of controls (3.6%). IgM-SMA were found more often in CAH (28.6%), in infections of the central nervous system (14.3%) and in the mycoplasma pneumoniae infections (13%) than in controls (2.6%), but titres above 20 occurred only in controls. IgA-SMA were detected only in a patient with syphilis. Demonstration of IgG-SMA titres above 80 seems to support the diagnosis of HBAg-negative CAH, while the demonstration of IgA- and IgM-SMA seems to be without diagnostic value in chronic hepatitis.