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 > or =20% of baseline), whereas no [Ca2+]i-mobilizing activity was found in 27 anti-CD38-negative sera (chi2 = 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 microU/ml [234], P = 0.0001 vs. 320 [52] microU/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.
Antonelli
A
A
Consiglio Nazionale delle Richerche Institute of Clinical Physiology and Department of Internal Medicine, University of Pisa, Italy.
Baj
G
G
Marchetti
P
P
Fallahi
P
P
Surico
N
N
Pupilli
C
C
Malavasi
F
F
Ferrannini
E
E
D016475:3T3 Cells; D036541:ADP-ribosyl Cyclase; D051997:ADP-ribosyl Cyclase 1; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D015703:Antigens, CD / Q000276:immunology*; D000943:Antigens, Differentiation / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D004768:Enterotoxins / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D019169:Jurkat Cells; D008562:Membrane Glycoproteins; D051379:Mice; D009244:NAD+ Nucleosidase / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology; D018089:Superantigens / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology; D014162:Transfection
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D001323:Autoantibodies; D004768:Enterotoxins; D007328:Insulin; D008562:Membrane Glycoproteins; D011994:Recombinant Proteins; D018089:Superantigens; C026066:enterotoxin A, Staphylococcal; D036541:ADP-ribosyl Cyclase; C498154:CD38 protein, human; C498155:Cd38 protein, mouse; D009244:NAD+ Nucleosidase; D051997:ADP-ribosyl Cyclase 1; D002118:Calcium