Absence of cytotoxicity of islet cell surface antibodies in vivo despite complement-mediated cytotoxic effects to islet cells in vitro.

Islet cell surface antibodies (ICSA) have been generated to investigate relations between recognition of specific antigens and cytotoxic reactions on pancreatic islet cells. Sera from rabbits which had been directly immunized with islet cells or intact rat islets exhibited positive immunofluorescence with both rat and rabbit pancreatic islet cells. Analysis by SDS polyacrylamide gel electrophoresis and autoradiography of islet cells proteins prelabeled with [35S]methionine revealed that these sera precipitated a specific protein of Mr 40000. Serum from immunized rabbits stimulated 51Cr-release in suspensions of dispersed islet cells prepared from neonatal rats. Absorption to lymphocytes and liver powder removed antibodies that were cytotoxic to lymphocytes but complement-mediated cytotoxicity against islet cells persisted. Circulating ICSA neither in rabbits nor in rats caused changes in blood glucose. Moreover, no major alterations of islet cells in the immunized rabbits were observed upon electron microscopic examination. It is concluded that ICSA are capable of recognizing specific islet cell antigens and thus mediate complement-dependent cytotoxic reactions in vitro, but the mere presence of ICSA is obviously not sufficient to induce diabetes in vivo under the conditions used.