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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.

Human renal epithelial cells might play an important role during the allograft rejection by producing chemokines in response to proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta produced by endothelial and epithelial cells early after transplantation. The production of chemokines allows inflammatory cells to be drawn into the kidney graft and therefore plays a critical role in the pathophysiologic processes that lead to the rejection of renal transplant. In this process, two chemokine superfamilies, the CC and the CXC chemokines, are the most important. The CC chemokines target mainly monocytes and T lymphocytes, while most of the CXC chemokines attract neutrophils. We showed in our study that in vitro, in unstimulated cells, basal mRNA expression of CXC chemokines (Groalpha, Grobeta, Grogamma, ENA-78 and GCP-2, IL-8) that attract neutrophils was detectable and expression of these genes and chemokine release were increased in TNF-alpha- and IL-1beta-induced renal epithelial cells. Most of the CC chemokines [monocyte chemotactic protein-1 (MCP-1), macrophage Inflammatory protein 1 beta (MIP-1beta), regulated upon activation, normal T cell expressed and secreted (RANTES) and macrophage inflammatory protein (MIP-3alpha)] showed detectable mRNA expression only after stimulation with proinflammatory cytokines and not in control cells. TNF-alpha seems to induce preferably the expression of RANTES, MCP-1, interferon-inducible protein (IP-10) and Interferon-Inducible T-cell Alpha Chemoattractant (I-TAC), while IL-1beta induces mainly IL-8 and epithelial neutrophil-activating peptide 78 (ENA-78).

Interleukin 18 (IL-18) is a potent proinflammatory cytokine involved in the host defence by upregulating both innate and acquired immune responses and may be of particular importance also in mechanisms of kidney allograft rejection. Immunohistochemical staining of protocol biopsies showed constitutive IL-18 expression in the epithelium of distal tubules with the induction of immunoreactivity in acute rejection patients where also proximal tubules, infiltrating leukocytes, and endothelium were strongly positive. Furthermore, serum levels of IL-18 were significantly elevated in patients with acute rejection of kidney allograft (1247+/-389 pg/l) as compared to patients with uncomplicated outcome of kidney transplantation (444+/-164 pg/l) and subjects with acute tubulointerstitial nephropathy (385+/-155 pg/l, p<0.0001 for both comparisons). Tissue culture model of renal epithelial cells expressed IL-18 mRNA constitutively and released mature IL-18 in response to TNF-alpha and IFN-gamma. We assume that upregulation of epithelial IL-18 plays an important role in immune and immunopathological reactions in renal parenchyma and contributes to rejection mechanisms of kidney allograft.