C4 Ceramide is a bioactive sphingolipid and cell-permeable analog of naturally occurring ceramides. [1] [2] [3] It inhibits IL-4 production by 16% in EL4 T cells stimulated with phorbol 12-myristate 13-acetate when used at a concentration of 10 μM. [1] C4 Ceramide is cytotoxic to SK-BR-3 and MCF-7/Adr breast cancer cells (IC50s = 15.9 and 19.9 μM, respectively). [2] C4 Ceramide also increases maturation and stability of cystic fibrosis transmembrane conductance regulator (CFTR) proteins bearing the F508 deletion (F508del) mutation, enhances cAMP-activated chloride secretion, and suppresses secretion of IL-8 in primary epithelial cells isolated from patients with cystic fibrosis.[3]