Islet-cell antibodies (ICA) in diabetes mellitus (evidence of an autoantigen common to all cells in the islet of Langerhans).

Pancreatic islet-cell antibodies (ICA) are important markers for two subtypes of insulin-dependent diabetes mellitus and stain the entire islet in the standard immunofluorescence test. This could indicate either a mixture of antibodies each directed against one cell type, or a population of antibodies reacting with a single antigen common to the endocrine pancreas. In the present experiments such a common antigen was demonstrated visually by application of animal antisera raised to each of the 4 pancreatic hormones, together with ICA-positive sera in a four-layer double immunofluorescent technique employing green and red anti-Ig conjugates. Double exposure photographs demonstrated that the patients' sera reacted equally with the different endocrine cells. The ICA antigen did not cross-react with gastric glucagon- or somatostatin-cells. By contrast, human antibodies against glucagon-cells (GCA) or somatostatin-cells (SCA) reacted with discrete antigens specific to each cell type and in 50% of cases the antibodies also stained the respective endocrine cells in the gastrointestinal tract. These refined discriminatory properties of human autoantibodies may lead to a better understanding of the intracellular membrane systems in these important endocrine organs.