Cytokine gene expression profile in monocytic cells after a co-culture with epithelial cells

Epithelial cells represent an important source of cytokines that may modulate the influx and functions of mononuclear phagocytes. The aim of our study was to characterize changes in the gene expression of selected cytokines in human macrophages co-cultured with respiratory epithelial cells. The A549 alveolar type II-like cell line was co-cultured with THP-1 cells (monocyte/macrophage cell line) in filter-separated mode to avoid their cell-cell contact. At different time-points (0, 4, 8, 12 and 24 h), the cells were harvested separately to evaluate their gene and protein expression (IL-1 beta, IL-6, IL-8, IL-10 and GM-CSF). Quantitative RT-PCR analysis showed prominent changes in the THP-1 cytokine gene expression induced by a co-culture with A549 cells. Fourfold upregulation of mRNA expression has been found in 12 genes and 4-fold downregulation in 5 genes as compared to the unstimulated control sample with a p value smaller than 0.05. The induction of inhibin beta A and IL-1 beta mRNA after 12 h and the expression of IL-1 alpha and GM-CSF mRNA after 24 h were the most prominent. When looking at the cytokine levels in culture supernatants, IL-1 beta and IL-8 were induced early (at 8 h) as compared to the release of IL-6 and GM-CSF (at 24 h). We conclude that respiratory epithelial cells constitutively regulate the cytokine gene expression of macrophages located in their environment and might further modulate the release of cytokines by posttranslational pathways.