Objective To investigate the signaling mechanisms underlying up-regulation of nontypeable Haemophilus influenzae(NTHi)-induced MUC5AC mucin expression. Methods The expression of MUC 5AC at mRNA level was measured by reverse transcriptase-polymerase chain reaction (RT-PCR)and real-time fluorescent quantitative PCR.Immunoprecipitation and Western blot were performed tO examine the phosphorylation of p38 mitogen-activated protein kinase(p38MAPK)and epidermal growth factor receptor(EGFR)or the effect of dominant negative mutant of EGFR on the phosphorylation of p38MAPK in HM3 cells treated with NTHi.Luciferase assay was also performed to examine the effect of p38MAPK and EGFR inhibitors or dominant negative mutant of EGFR on NTHi-induced MUC5AC expression at transcription level.Results NTHi induced MUC5AC mucin expression at both mRNA and transcription levels.Phosphorylation of p38MAPK and EGFR were observed in HM3 cells treated with NTHi.Either SB203580,a specific inhibitor for p38MAPK or AGl478,a specific inhibitor for EGFR.inhibited NTHi-induced MUC5AC up-regulation at transcription level. Furthermore,Overexpressing dominant negative mutant of EGFR also inhibited NTHi-induced MUC5AC upregulation at transcription 1evel in a dos-dependent manner.EGFR inhibitor reduced NTHi-induced p38MAPK phosphorylation in HM3 cells.Conclusion Bacterium NTHi up-regulates MUC5AC mucin transcription via EGFR-p38MAPK signaling pathway.