Decreased STAT-1 phosphorylation by a thio analogue of beta-d-glucosylceramide is associated with altered NKT lymphocyte polarization

Abstract: Glycolipid presentation to natural killer T (NKT) lymphocytes by CD1 proteins is important for antigen recognition. It was recently suggested that beta-glycolipids exert an immune-modulatory effect on NKT lymphocytes, alleviating immune-mediated disorders. The current study aimed to determine the effect of ligand structure on intrahepatic NKT lymphocyte function in concanavalin A (ConA) hepatitis, an NKT-mediated disorder. C57BL/6 mice were injected with a non-degradable β-d-glucosylceramide containing a thioglycosidic bond (GCT), β-d-glucosylceramide (GC), or vehicle. The phosphorylation of STAT-1, intrahepatic NKT lymphocyte number, and serum IFN-γ levels were determined. Liver damage was assessed by serum transaminases and the degree of apoptosis. The administration of GCT led to a significant inhibitory effect on intrahepatic NKT lymphocytes. Both GCT and GC led to a decrease in STAT-1 phosphorylation and a decrease in IFN-γ serum levels. These effects were associated with the alleviation of ConA immune-mediated hepatitis, as determined by a similar substantial decrease in serum transaminases and a profound decrease in apoptosis as noted by TUNEL assay, and were NKT-type I dependent. Conclusion: Alteration of the chemical structure of the GC by replacing the O-glycosidic bond with an S-glycosidic bond results in a non-degradable molecule GCT and significantly suppresses intrahepatic NKT lymphocytes. These results suggest that cellular events that alter the enzymatic pathways of glycosylceramides serve as an initial stimulus for NKT cell polarization in vivo. [Copyright &y& Elsevier]