Gastric parietal cell antigens of 60-90, 92, and 100-120 kDa associated with autoimmune gastritis and pernicious anemia. Role of N-glycans in the structure and antigenicity of the 60-90-kDa component

Thirty-four human sera containing parietal cell autoantibodies (PCA) specifically immunoprecipitated two antigens, with apparent molecular masses of 60-90 kDa and 100-120 kDa under nonreducing conditions and 60-90 kDa and 120-150 kDa under reducing conditions, from porcine gastric membrane extracts. A third antigen of 92 kDa was only observed in immunoprecipitates analyzed under reducing conditions. By immunoblotting, 24 of the 34 PCA-positive sera reacted with only the 60-90-kDa antigen, three reacted with a broad 60-120-kDa smear, one reacted only with a 92-kDa antigen and six did not react. Reactivity with the 60-90-kDa antigen was observed with gastric membranes from dog, pig, rat, and rabbit. Twenty PCA-negative sera did not react with these components by immunoprecipitation or immunoblotting. PCA reactivity with the 60-90-kDa antigen was abolished when the gastric membranes were (a) digested with Pronase, (b) reduced with 100 mM dithiothreitol, (c) treated with sodium periodate, or (d) digested with N-glycanase. The 60-90-kDa and 100-120-kDa components were insensitive to neuraminidase treatment. N-glycanase digestion of 125I-labeled antigens purified by immunoprecipitation and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis collapsed the 60-90-kDa antigen to a sharp 34-kDa band; the 100-120-kDa component was unaffected. These observations suggest that (i) parietal cell antigens comprise three components of 60-90, 92, and 100-120 kDa; (ii) the epitopes differ in conformational sensitivity; (iii) the 60-90-kDa antigen is a conserved molecule comprising a 34-kDa core protein extensively glycosylated with N-linked oligosaccharides; (iv) sialic acid residues are not present in the 60-90- and 100-120-kDa molecules, and (v) the carbohydrate and protein moieties of the 60-90-kDa molecule are required for antibody binding.