Human anti-CD38 autoantibodies raise intracellular calcium and stimulate insulin release in human pancreatic islets

CD38 is involved in transmembrane signaling in many cell types; anti-CD38 autoantibodies have been described in diabetic patients. We tested whether human anti-CD38 antibodies possess signaling properties by measuring their ability to raise intracellular calcium ([Ca2+](i)) using the fluo-3-acetoxymethyl ester method in a human-derived T-cell line (Jurkat T-cells, expressing high levels of surface CD38) and in dispersed human islet cells from normal donors. In Jurkat T-cells, 11 of 19 anti-CD38-positive sera raised [Ca2+](i) (by greater than or equal to 20% of baseline), whereas no [Ca2+](i)-mobilizing activity was found in 27 anti-CD38-negative sera (chi (2) = 20.5, P < 0.0001). In dispersed human islet cells, 5 of 11 anti-CD38-positive sera (and none of three anti-CD38-negative sera) raised [Ca2+](i) significantly. When preincubated with Staphylococcus aureus protein A to remove IgG, anti-CD38-positive sera showed a 70 +/- 5% reduction in [Ca2+](i)-mobilizing activity. Preincubation with CD38-transfected NIH-3T3 fibroblasts, but not with mock-transfected NIH-3T3 cells, abolished [Ca2+](i) mobilization. In blocking experiments, preincubation with nonagonistic anti-CD38 monoclonal antibodies also prevented [Ca2+](i) mobilization. In cultured human islets, anti-CD38-positive sera exhibiting [Ca2+](i)-mobilizing activity in Jurkat T-cells (n = 6) significantly stimulated insulin release at 3.3 mmol/l glucose (median [interquartile range] 738 muU/ml [234],P = 0.0001 vs. 320 [52] muU/ml of control), whereas 6 anti-CD38-positive sera without [Ca2+](i)-mobilizing activity and 10 anti-CD38-negative did not. In further incubations, the five anti-CD38-positive sera displaying [Ca2+](i)-mobilizing activity in dispersed islet cells significantly stimulated insulin release at both 3.3 mmol/l glucose (2.2 +/- 0.3% of insulin islet content, P < 0.002 vs. 1.2 + 0.1% of control) and 16.7 mmol/l glucose (3.7 +/- 0.3 vs. 2.3 +/- 0.3%, P < 0.002). We conclude that human anti-CD38 autoantibodies with agonistic properties on the CD38 effector system occur in nature; in human islets, their [Ca2+](i)-mobilizing activity is coupled with the ability to stimulate insulin release.