Lack of specificity of islet cell surface antibodies (ICSA) in IDDM.

Human islets were isolated by collagenase digestion and tissue culture from pancreata obtained from organ donor subjects and dispersed islet cells were prepared from hand-picked islets. Islet cell surface antibodies (ICSA), detected by indirect immunofluorescence on isolated islet cells, were present in sera from nine of 22 (41%) subjects with recent-onset insulin-dependent diabetes mellitus (IDDM) and three of 11 (27%) control subjects. Sera had been heat inactivated, adsorbed against a human B lymphoblastoid cell line (IM-9) and tested in the presence of 4% bovine serum albumin. However, with a double labelling technique, we were unable to show that ICSA were specific for beta cells. Of the nine ICSA-positive IDDM sera, three stained both beta and non-beta cells, three beta cells only and three non-beta cells only; the three ICSA-positive control sera stained both beta and non-beta cells. There was no apparent relationship between ICSA and standardised measurements of islet cell antibodies (ICA) and insulin autoantibodies (IAA). These results lead us to question whether, despite previous reports, ICSA are specific for beta cells or indeed for IDDM.