Objective To investigate whether the effect of E.coli on U937 cell lines apoptosis is mediated via p38 mitogen-activated protein kinase （MAPK） activation. Methods The U937 cell lines were treated with E.coli at different time or together with SB203580

an inhibitor for p38. Cell apoptosis was analyzed by flow cytometry. p38 activities were detected by Western blotting. Results E.coli induced apoptosis in cultured U937 cell lines in a time-dependent manner. The phosphorylation of p38 was induced after 10 minutes infection

reached the peak after 20 minutes

and started to decline after 30 minutes. In contrast

the level of total p38 protein was not changed in whole experimental period. Inhibition of p38 with SB203580 significantly inhibited E.coli induced apoptosis in U937 cells. Conclusion The activation of the p38 MAPK in U937 cell lines by E.coli is a major pathway to mediate the apoptosis.