Studies on the specificity of smooth-muscle antibodies

Abstract

Purified contractile proteins from smooth and striated muscles have been used to test the specificity of human smooth muscle antibodies (SMA) from patients with chronic liver disease (IgG-SMA) and acute hepatitis (IgM-SMA). The reactions, as detected by indirect immunofluorescence, of IgG-SMA with renal vessel walls, renal glomeruli, peritubular fibrils and the luminal part of the tubular cells could be completely abolished by absorption with either smooth muscle or skeletal muscle F-actin, while absorption with myosin and tropomyosin had no effect. The specificity of IgG-SMA for actin was confirmed by their staining of the actin-rich I-bands of skeletal muscle myofibrils and by the blocking of this reaction by pretreatment of myofibrils and isolated smooth muscle cells with smooth muscle myosin subfragment 1 (S-1). IgM-SMA from patients with acute hepatitis-stained renal vessel walls and some sera also stained renal glomeruli. The IgM-SMA titres decreased after absorption both with myosin and F-actin but not with tropomyosin. The reactivity of some IgM-SMA could be blocked by S-1 while others could not. Thus the specificity of IgM-SMA seemed to be variable, and apparently differed from IgG-SMA in some cases.