Uroepithelial cells are part of a mucosal cytokine network

This study compared the cytokine production of uroepithelial cell lines in response to gram-negative bacteria and inflammatory cytokines. Human kidney (A498) and bladder (J82) epithelial cell lines were stimulated with either Escherichia coli Hu734, interleukin 1α (IL-1α), or tumor necrosis factor alpha (TNF-α). Supernatant samples were removed, and the RNA was extracted from cells at 0, 2, 6, and 24 h. The secreted cytokine levels were determined by bioassay or immunoassay; mRNA was examined by reverse transcription-PCR. The two cell lines secreted IL-6 and IL-8 constitutively. IL-6 and IL-8 mRNA were constitutively produced in both cell lines; IL-1β mRNA was detected in J82 cells. IL-1α induced significantly higher levels of IL-6 secretion than did E. coli Hu734 or TNF-α. IL-1α and TNF-α induced significantly higher levels of IL-8 secretion than did E. coli Hu734. Secreted IL-1β was not detected; IL-1α and TNF-α were not detected above the levels used for stimulation. IL-1α, IL-1β, IL-6, and IL-8 mRNAs were detected in both cell lines after exposure to the stimulants. TNF-α mRNA was occasionally detected in the J82 cell line after TNF-α stimulation. Cytokine (IL-6 and IL-8) and control (glyceraldehyde 3-phosphate dehydrogenase [G3PDH] and β-actin) mRNA concentrations were quantitated with internal PCR standards. Cytokine mRNA levels relative to β-actin mRNA levels were the highest in E. coli- stimulated cells. In comparison, the cytokine mRNA levels relative to G3PDH mRNA levels were the highest in IL-1α-stimulated cells. β-Actin mRNA levels decreased after bacterial stimulation but not after cytokine stimulation, while G3PDH mRNA levels increased in response to all of the stimulants tested. These results suggested that E. coli Hu734 lowered the β-actin mRNA levels in uroepithelial cells, thus distorting the IL-6 and IL-8 mRNA levels relative to this control. In summary, E. coli IL-1α and TNF-α were found to activate the de novo synthesis and secretion of IL-6 and IL-8 in uroepithelial cells. These results emphasize the role of epithelial cells in cytokine-mediated responses during the early stages of infection.