Identification of novel glycolipid ligands activating a sulfatide-reactive, CD1d-restricted, type II natural killer T lymphocyte.

Sulfatide-reactive CD1d-restricted natural killer T (NKT) lymphocytes belong to the type II NKT cell subset with diverse TCRs, and have been found to regulate experimental auto-immune encephalomyelitis, tumor immunity, and experimental hepatitis in murine models. NKT cells can be activated by self-lipids presented by CD1d, manifested as autoreactivity. The identity of most of these self-lipids remains unknown. By isolating lipids from a CD1d-expressing, highly stimulatory antigen presenting cell, we identified isoforms of ß-glucosylceramide (GlcCer), with sphingosine and fatty acid chain lengths of C24:0 and C16:0, that activated a sulfatide-reactive type II NKT cell hybridoma. A screen of structurally related glycosphingolipids demonstrated ß-galactosylceramide (GalCer) as another ligand, and further, that the lysoforms were the most potent isoform of the glycosphingo-lipid ligands, followed by isoforms with a long fatty acid chain of C24. Thus, the same type II NKT cell was activated by several ligands, namely sulfatide, GlcCer, and GalCer. However, CD1d-dependent reactivity to antigen presenting cells lacking all GlcCer-based glycosphingolipids, or all glycosphingolipids, was maintained. This suggests that other endogenous, nonglycosphingolipid, lipid ligands contribute to steady-state autoreactivity by type II NKT cells.

In vivo administration of the C16:0 fatty acid isoform of sulfatide increases pancreatic sulfatide and enhances glucose-stimulated insulin secretion in Zucker fatty (fa/fa) rats.

BACKGROUND: Sulfatide is present in the secretory granules of beta cells and has been shown, in vitro, to be involved in insulin processing and secretion. Of particular interest is one of the major sulfatide isoforms in the beta cells, the C16:0 fatty acid isoform, which has been shown to be involved in insulin crystal preservation in vitro. The aim of this study was to investigate the ability of C16:0 fatty acid isoform of sulfatide to affect insulin secretion and/or action and glycaemic control in the adipogenic 'prediabetic' Zucker rat. METHODS: The C16:0 sulfatide was administered to Zucker rats for 10 weeks, and fasting levels of plasma insulin and glucose were measured as well as levels after an intravenous (i.v.) glucose load. In addition, the sulfatide expression, examined by thin-layer chromatography-enzyme-linked immunosorbent assay and mass spectrometry, in the pancreas of C16:0 sulfatide-treated Zucker rats was compared to controls. RESULTS: The in vivo treatment of Zucker rats with C16:0 sulfatide resulted in significantly elevated glucose-stimulated insulin secretion (60-80% increase, p < 0.05), without significant changes in glucose tolerance. The treatment was associated with an ameliorated first-phase insulin response (3-4-fold, p = 0.009, 0.016) and a 60% increase of pancreatic sulfatide content (p = 0.001), possible by an uptake of C16:0 sulfatide. The fasting hyperinsulinaemia and blood glucose levels were unchanged. CONCLUSIONS: The treatment with C16:0 sulfatide elevates glucose-stimulated insulin secretion and enhances sulfatide content in the pancreas of Zucker rats.

Developmental expression of the type I diabetes related antigen sulfatide and sulfated lactosylceramide in mammalian pancreas.

Previous studies have shown that sulfatide is present and functionally involved in beta cells, and that anti-sulfatide antibodies (ASA) exist during development of type I diabetes mellitus. To further explore the possible role of sulfatide in type I diabetes, developmental expression was examined in human pancreas and in pancreas of the type I diabetes models BB rat and NOD mouse compared to Lewis rat and BALB/c mouse, respectively. Sulfatide was not only expressed in adult pancreas, but also in human fetal and rodent neonatal pancreas, i.e., during the growing period of the immunological self. Sulfatide had a different expression pattern in human beings and rodents, concerning both the amounts of sulfatide and expression during development. There was no change in the sulfatide fatty acid isoform expression during development. The pancreatic expression of another sulfated glycosphingolipid, sulfated lactosylceramide, indicated that this molecule is a potential fetal/neonatal marker, which was further expressed in the type I diabetic models. In conclusion, these findings give further support to the possibility that sulfatide is a relevant autoantigen in type I diabetes and that sulfated lactosylceramide might function as a potential risk factor for disease development, at least in the animal models.