α-Lactosylceramide Protects Against iNKT-Mediated Murine Airway Hyperreactivity and Liver Injury Through Competitive Inhibition of Cd1d Binding.

Invariant natural killer T (iNKT) cells, which are activated by T cell receptor (TCR)-dependent recognition of lipid-based antigens presented by the CD1d molecule, have been shown to participate in the pathogenesis of many diseases, including asthma and liver injury. Previous studies have shown the inhibition of iNKT cell activation using lipid antagonists can attenuate iNKT cell-induced disease pathogenesis. Hence, the development of iNKT cell-targeted glycolipids can facilitate the discovery of new therapeutics. In this study, we synthesized and evaluated alpha-lactosylceramide (alpha-LacCer), an alpha-galactosylceramide (alpha-GalCer) analog with lactose substitution for the galactose head and a shortened acyl chain in the ceramide tail, toward iNKT cell activation. We demonstrated that alpha-LacCer was a weak inducer for both mouse and human iNKT cell activation and cytokine production, and the iNKT induction by alpha-LacCer was CD1d-dependent. However, when co-administered with alpha-GalCer, alpha-LacCer inhibited alpha-GalCer-induced IL-4 and IFN-gamma production from iNKT cells. Consequently, alpha-LacCer also ameliorated both alpha-GalCer and GSL-1-induced airway hyperreactivity and alpha-GalCer-induced neutrophilia when co-administered in vivo. Furthermore, we were able to inhibit the increases of ConA-induced AST, ALT and IFN-gamma serum levels through alpha-LacCer pre-treatment, suggesting alpha-LacCer could protect against ConA-induced liver injury. Mechanistically, we discerned that alpha-LacCer suppressed alpha-GalCer-stimulated cytokine production through competing for CD1d binding. Since iNKT cells play a critical role in the development of AHR and liver injury, the inhibition of iNKT cell activation by alpha-LacCer present a possible new approach in treating iNKT cell-mediated diseases.