Antibodies direct against the pancreatic islet cell plasma membrane. Detection and specificity.

Abstract

Rabbits were immunised with suspensions of viable, insulin-producing islet cells prepared from collagenase-isolated rat or ob/ob mouse pancreatic islets. Antibodies reactive with the surface of dispersed rat islet cells were present in both the rabbit anti-rat and the rabbit anti -ob/ob mouse islet sera as revealed by indirect immunofluorescence or by a radioligandassay using 125I-Protein A as a measure of cell bound IgG. In a competition assay the binding of 125I-Protein A was displaced in a concentration dependent manner by non-radioactive Protein A. Maximal displacement was found at concentrations of Protein A higher than 0.1 μg. added to 105 islet cells. Although not always detected by immunofluorescence there was a several-fold increase above normal rabbit serum of 125I-Protein A-binding to rat hepatocytes and spleen lymphocytes incubated with the islet cell antisera. Conversely, rabbit antisera against rat spleen lymphocytes or against a rat liver plasma membrane preparation reacted with rat islet cells. The rabbit anti-rat islet cell antiserum was absorbed to both spleen lymphocytes and hepatocytes until there was no binding of 125I-Protein A to either cell type. Islet specific antibodies were still present since this doubly absorbed antiserum induced cell surface immunofluorescence as well as 125I-Protein A-binding to rat islet cells. It is concluded that apart from common antigenic determinants immunisation with viable islet cells induces formation of antibodies directed against specific islet cell surface components.