The stress signal extracellular ATP modulates antiflagellin immune responses in intestinal epithelial cells

Although intestinal epithelial cells (IECs) are continually exposed to commensal microbes, under healthy conditions they contribute to intestinal homeostasis while keeping inflammatory responses in check. In response to invading pathogens, however, IECs respond vigorously by producing inflammatory mediators. To better understand the signals that regulate the inflammatory responses of IECs, we investigated whether the danger signal ATP (which is released from injured cells) could alter responses to bacterial products.

We measured chemokine production from Caco-2 cells stimulated with the Toll-like receptor 5 agonist flagellin with or without ATP. ATP increased flagellin-induced IL-8 secretion but reduced CCL20 secretion via distinct signaling pathways.

ATP-enhanced IL-8 production was only partly blocked by the P(2) receptor antagonist suramin and required activation of NF-κB while ATP-mediated reduction of CCL20 was completely blocked by suramin and required activation of ERK1/2. The effects of ATP on both chemokines required extracellular calcium but not phospholipase C, implicating P(2) X receptor involvement. To investigate how ATP alters IEC responses to bacterial products in vivo, mice receiving dextran sodium sulfate were given intrarectal flagellin with or without ATP. Addition of ATP to flagellin caused greater weight loss and increased antiflagellin antibody titers, as well as decreased colonic interferon gamma (IFN-γ) and higher antiflagellin IgG1/IgG2 ratios, which indicate decreased Th1 polarization.

Together, these data indicate that stress, in the form of extracellular ATP, reshapes both the inflammatory response of flagellin-stimulated IECs and downstream adaptive immunity, representing a possible strategy by which these cells differentiate between commensal and pathogenic bacteria.