64,000 M(r) autoantigen in type I diabetes. Evidence against its surface location on human islets

Abstract

The sera of type I (insulin-dependent) diabetic subjects are reported to contain autoantibodies against a 64,000 M(r) protein identified in [35S]methionine biosynthetically labeled pancreatic islet cells. We have attempted to localize this autoantigen to the surface of the β-cell and to define its properties. Sera from 10 newly diagnosed type I diabetic subjects, including five of the index sera originally used to identify the autoantigen, were shown to specifically precipitate a reduced protein of 67,000 M(r) from Triton-solubilized, surface 125I-labeled cultured adult human islet and rat insulinoma (RINm5F) cells but not from fresh rat spleen cells. Further characterization revealed that t..