Changes in ceramide but not sphingomyelin and Gb3/CD77 levels in BL cells treated by 38.13 MoAb. (A) CD77⁺ Ramos and Daudi cells and CD77⁻ Namalwa cells were cultured with 38.13 anti-CD77 MoAb; Ramos cells were also cultured with DA4.4 anti-human IgM MoAb. Ceramide was quantitated by the DAG kinase assay. Results are representative of six independent experiments. (B) Ramos cells, prelabeled with ³H-palmitate, were cultured with (+) or without (−) 38.13 anti-CD77 MoAb. Lipids were extracted and chromatographed on HPTLC plates using chloroform: methanol: acetic acid: water (100:60:20:5) as solvent system. Radioactive spots were visualized by autoradiography. Sphingomyelin (Spm) and Gb3/CD77 were identified by comigration with standards.