['To study the effect of tumor necrosis factor-alpha (TNF-alpha) on the proliferation and apoptosis of type II lung alveolar epithelial cells and the regulation of retinoic acid (RA) to this effect.', 'Human type II lung alveolar epithelial cells of the line A569 were cultured and divided into 2 groups: control group (cultured in culture fluid only), TNF-group (cultured in the culture fluid with TNF-alpha 10 micromol/L for 24 or 46 h respectively), RA group (cultured in culture fluid without RA 1 microg/L), and TNF-alpha plus RA group (cultured in culture fluid with TNF-alpha 10 micromol/L + RA 1 microg/L). MTT method was used to test the proliferation of the A549 cells. The cell apoptosis was detected by flow cytometric assay.', 'The proliferation rates of A549 cells treated with TNF-alpha of the concentrations of 0, 0.1, 1, 5, and 10 microg/L were 95.0%, 90.0%, 79.6%, 72.4%, and 59.6% after 24 h (F = 18.04, P < 0.001), and were 93.2%, 82.7%, 61.5%, 50.3%, and 44.7% after 48 h (F = 40.61, P < 0.0001). The inhibition effect on the proliferation of A549 cells treated with 10 microg/L TNF-alpha for 24 h could be reversed, however, the inhibition effect on the proliferation of A549 cells treated with 10 microg/L TNF-a for 48h could not be reversed. RA alone did not significantly promote the proliferation of the A549 cells, but weakened the inhibitory effect of TNF-alpha on the proliferation of the A549 cells. The apoptotic rate of the A549 cells treated with TNF-alpha for 12 h, 24 h and 48 h respectively were 14.3% +/- 3.2%, 18.6% +/- 2.9%, and 43.4% +/- 3.5% respectively, all significantly higher than those of the control group (6.3% +/- 1.2%, 8.2% +/- 1.3%, and 26.1% +/- 2.5% respectively, all P < 0.01), and the apoptotic rate of the A549 cells treated with both TNF-alpha and RA for 12 h, 24 h, and 48h were 4.8% +/- 1.1%, 5.2% +/- 1.3%, and 16.4% +/- 2.3% respectively, all significantly lower than those of the TNF-alpha group (all P < 0.01), and the apoptotic rates of the A549 cells treated with both TNF-alpha and RA for 24 h and 48 h respectively were both significantly lower than those of the control group (both P < 0.05).'] Does [ Retinoic acid inhibit tumor necrosis factor-alpha induced injury in human lung epithelial cells ]?