Production and function of IL-12 in islets and beta cells.
OBJECTIVE
IL-12 is an important cytokine in early inflammatory responses and is implicated in the immune-mediated pathogenesis of pancreatic islets in diabetes. However, little is known about the direct effects of IL-12 on islets and beta cells.


METHODS
In this study, beta cell function, gene expression and protein production were assessed in primary human donor islets and murine beta cell lines in response to stimulation with IL-12 or a pro-inflammatory cytokine cocktail (TNF-α, IL-1β and IFN-γ).


RESULTS
The pro-inflammatory cytokine cocktail induced islet dysfunction and potently increased the expression and production of IL-12 ligand and IL-12 receptor in human islets. In human islets, the receptor for IL-12 co-localised to the cell surface of insulin-producing cells. Both IL-12 ligand and IL-12 receptor are expressed in the homogeneous beta cell line INS-1. IL-12 induced changes in gene expression, including a dose-dependent upregulation of IFNγ (also known as IFNG), in INS-1 cells. A neutralising antibody to IL-12 directly inhibited IFNγ gene expression in human donor islets induced by either IL-12 or pro-inflammatory cytokine stimulation. Functionally, IL-12 impaired glucose-stimulated insulin secretion (GSIS) in INS-1 cells and human donor islets. A neutralising antibody to IL-12 reversed the beta cell dysfunction (uncoupling of GSIS or induction of caspase-3 activity) induced by pro-inflammatory cytokines.


CONCLUSIONS
These data identify beta cells as a local source of IL-12 ligand and suggest a direct role of IL-12 in mediating beta cell pathology.
Strelitz Diabetes Center, Department of Internal Medicine, Eastern Virginia Medical School, 700 W. Olney Road, Norfolk, VA 23501, USA. Taylord@evms.edu
D A
DA
Taylor-Fishwick
J R
JR
Weaver
W
W
Grzesik
S
S
Chakrabarti
S
S
Green-Mitchell
Y
Y
Imai
N
N
Kuhn
J L
JL
Nadler
D000818:Animals; D057134:Antibodies, Neutralizing / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000276:immunology / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000276:immunology / Q000378:metabolism*; D007371:Interferon-gamma / Q000378:metabolism; D018664:Interleukin-12 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000378:metabolism; D007515:Islets of Langerhans / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D012333:RNA, Messenger / Q000378:metabolism; D053707:Receptors, Interleukin-12 / Q000378:metabolism*; D015398:Signal Transduction; D013499:Surface Properties; D046509:Tissue Culture Techniques; D014019:Tissue Donors
D057134:Antibodies, Neutralizing; D016207:Cytokines; C573415:IFNG protein, human; D007328:Insulin; D012333:RNA, Messenger; D053707:Receptors, Interleukin-12; D018664:Interleukin-12; D007371:Interferon-gamma