C6 L-threo Ceramide is a bioactive sphingolipid and cell-permeable analog of naturally occurring ceramides., C6 L-threo Ceramide is cytotoxic to U937 cells in vitro (IC50 = 18 uM). It is metabolically inactive and, unlike C6 L-erythro ceramide , C6 L-threo ceramide cannot be converted to C6 glucosylceramide by ceramide glucosyltransferase. C6 L-threo Ceramide enhances IL-4 production induced by phorbol 12-myristate 13-acetate in EL4 T cells when used at a concentration of 10 uM.