Complement-fixing Islet Cell Antibodies from Some Diabetic Patients Alter Insulin Release In Vitro

Abstract

To explore humoral immunity in insulin-dependent diabetic (IDDM) patients, we studied insulin release from isolated mouse islets stimulated by glucose + theophylline after incubation with the sera of these patients and complement. Eleven of 21 IDDM sera suppressed the stimulated insulin release while the arginine-stimulated glucagon release remained unchanged. Morphologic evidence and the trypan-blue exclusion test suggested that the suppression of insulin release was due to a cytotoxic effect of the sera. No beta-cell inhibition of morphologic damage was detectable in the presence of sera from 30 healthy subjects, 8 non-insulin-dependent diabetic patients, and 5 nondiabetic patients with autoimmune diseases. Beta-cell inhibition by IDDM sera was not observed when complement was omitted. After serum fractionation, the cytotoxic potency of IDDM sera was located in the immunoglobulin G fraction. Using human islets, insulin release was suppressed by 3 of 6 IDDM sera. Complement-dependent cytotoxicity was found in 1 of 5 recent-onset IDDM patients and 11 of 16 IDDM patients with autoimmune phenomena. It was associated in all cases with the presence of islet cell antibodies as detected by immunofluorescence, and with the presence of circulating lymphocytes which suppressed insulin release in vitro. Complement-fixing antibodies may contribute to the selective beta-cell damage in IDDM.

Anti-islet Cellular and Humoral Immunity, T-Cell Subsets, and Thymic Function in Type I Diabetes

“…23 By contrast, sera were toxic to islets only in 50-64% of patients according to the groups, a percentage very similar to that previously obtained by another technique. 26 Peak concentrations of circulating antibodies toxic to islet cells have been detected, in the diabetic BB rat, before or shortly after the occurrence of diabetes. 27 Wide fluctuations in circulating ICA concentrations can occur in humans.…”

“…Lymphocyte subsets have already been studied in diabetic subjects either by use of monoclonal antibodies directed toward T-cell markers, 26 or by using a functional test for con-A-activated suppressor lymphocytes. 78 OKT3 + and OKT4 + subsets were decreased in type I diabetic subjects, with disease lasting for more than a few weeks, in some 2 but not in all studies.…”

Time Course of Islet Cell Antibodies in Diabetic and Nondiabetic BB Rats

“…Rat immunoglobulins (obtained after serum fractionation by 40% ammonium sulfate) and islet-adsorbed sera were similarly tested. 19 The percent of 51 Cr release was compared with that of distilled water-lysed islet cells after subtraction of the 51 Cr release from labeled cells alone. All samples were measured in triplicate.…”

“…This assay was performed as previously published. 19 In brief, five Wistar rat islets in MEM containing glucose 4.4 mmol/L were incubated for 18 h in the presence of 100 fxl control or test serum diluted 1/2. Complement (80 |xl) was then added for a further 2-h incubation.…”

Anti-Beta-Cell Immunity in Insulinopenic Diabetic Dogs

“…The influence of sera + complement was studied as previously described. 11 Briefly, DBA/2 mouse islets were set into Falcon microtest plates (Becton-Dickinson and Co., Oxnard, California), 5 islets/well in 50 |xl basal medium, with 50 |xl control or IDD serum for 2 h. Complement (20 jxl) was then added 3 times at 1-h intervals. After an 18-h incubation period, the islets were washed 4 times with 200 |xl basal medium and successively incubated in the basal medium and in a stimulatory medium containing 16.6 mmol/L glucose + 5 mmol/L theophylline (Sigma Chemical Co., St. Louis, Missouri) for 30 min each time.…”