['To study the relationship between the downregulated expression of secretory leukocyte proteinase inhibitor (SLPI) in human bronchial epithelial cells and transforming growth factor (TGF)-beta1/Smads pathway.', 'Normal human bronchial epithelial cells of the line HBE were cultured and divided into 4 groups: TGF-beta1 stimulation group stimulated by TGF-beta1, interference group preincubated with Smad4 siRNA and then stimulated by TGF-beta1, interference control group preincubated with negative siRNA and then stimulated by TGF-beta1, and normal control group. Forty-eight hours later immunocytochemistry was used to observe the SLPI positive staining in the cells, and the protein and mRNA expression levels of Smad4 and SLPI were detected by Western blotting and RT-PCR respectively.', 'Immunocytochemistry showed that the Smad4 staining was strongly positive in the TGF-beta1 stimulation group and interference control group, and the SLPI staining was strongly positive in the normal control group, positive in the interference group, and only weakly positive in the TGF-beta1 stimulation and interference control groups. The protein and mRNA expression levels of Smad4 in the HBE cells of the TGF-beta1 stimulation group were 1.18 +/- 0.17 and 1.33 +/- 0.16 respectively, both significantly higher than those of the normal control group (0.29 +/- 0.06 and 0.31 +/- 0.07 respectively, both P < 0.01) and interference group (0.27 +/- 0.08 and 0.34 +/- 0.09 respectively, both P < 0.01). The protein and mRNA expression levels of SLPI in the HBE cells of the TGF-beta1 stimulation group were 0.17 +/- 0.10 and 0.11 +/- 0.05 respectively, both significantly lower than those of the normal control group (1.29 +/- 0.21 and 0.83 +/- 0.13 respectively, both P < 0.01), and those of the interference group (1.22 +/- 0.18 and 0.81 +/- 0.11 respectively, both P < 0.01). There were no significant differences in the expression levels of Smad4 and SLPI between the TGF-beta1 stimulation group and interference control group.'] Is [ Expression of secretory leukocyte proteinase inhibitor in human bronchial epithelial cell downregulated by transforming growth factor-beta1/Smads pathway ]?