TNFα activates the sphingomyelin signaling pathway in CLENDO cells. (Panel A) CLENDO cells were treated for up to 30 min with TNFα (50 ng/ml) and ceramide levels were determined as described in the Materials and Methods. (Panel B) The numbers of non-apoptotic cells per field in each of 10 separate fields per dish were counted in which cultures of CLENDO cells were treated with exogenous ceramide (C2, 50 μM) for up to 72 h under serum- and growth factor-free conditions. Ctl, untreated controls cultured in parallel for 72 h in serum free, growth factor free medium. * = P < 0.05. These data represent mean ± SEM of at least three independent experiments.