Comparison of the effects of various reagents that can modulate the sphingomyelinase pathway on the maintenance of CFC and LTC-IC activity in 24-hour serum-free cultures of CD34⁺CD38⁻ human marrow cells.

Values shown are the mean ± SEM of data from 3 independent experiments (different marrow samples). All cultures contained 100 ng/mL FL and SF, 20 ng/mL IL-3, IL-6, and G-CSF, and 30 μmol/L concentrations of various ceramide analogs: dihydro-C2-ceramide (D-C2), C2-ceramide (C2), C6-ceramide (C6), or 5 μmol/L D-erythro-MAPP (D-MAPP), with or without 20 ng/mL TNF or diluent (0), as indicated. Input CFCs and 6-week LTC-IC–derived CFC values (per 1000 initial CD34⁺CD38⁻ cells) were 45 ± 10 and 12 400 ± 1200, respectively.