Reaction of human smooth muscle autoantibody with gastric parietal cells: a pitfall in the diagnosis of parietal cell autoantibody

Eight of 13 smooth muscle antibody (SMA) sera obtained from patients with active chronic hepatitis and examined for immunofluorescence reactivity with gastric mucosal cells, 8 stained the cytoplasm of gastric parietal cells in a pattern indistinguishable from that obtained with parietal cell autoantibody (PCA). The staining reaction was localized to parietal cells by the demonstration that the same cells stained with both SMA and PCA in duble immunofluorescent tests. The SMA staining intensity for parietal cells was weaker than that for smooth muscle. Specificity of the staining reaction for actin was established by the observation that parietal cell staining by SMA was inhibited by serum absorption with skeletal muscle F-actin but not by a microsomal fraction derived from gastric mucosa.