Synthesis and regulation of accessory/proinflammatory cytokines by intestinal epithelial cells

SUMMARY Intestinal epithelial cells (IEC) have been shown to act as antigen‐presenting cells (APC) in vitro and may have this capacity in vivo. In order to determine whether IEC, like other APC, are able to produce accessory cytokines which may play a role in T cell activation, we assessed the accessory cytokine profile of IEC constitutively or after stimulation. We measured expression, production and regulation of accessory cytokines (IL‐1β, IL‐6, tumour necrosis factor‐alpha (TNF‐α), transforming growth factor‐beta (TGF‐β) by the presence of mRNA as well as secreted protein. Freshly isolated IEC from surgical specimens were cultured in the presence or absence of lipopolysaccharide (LPS), interferon‐gamma (IFN‐γ), IL‐1β or TNF‐α. mRNA was assessed by a specific RNAse protection assay which controlled for contaminating cell populations while protein secretion was measured by ELISA (IL‐1) or bioassay (TNF and IL‐6). Neither IL‐1β nor TNF‐α were detectable in cultured IEC supernatants, supporting the lack of macrophage contamination. All IEC spontaneously secreted IL‐6 at levels comparable to those of macro‐phages. IEC IL‐6 mRNA also increased approximately 200‐fold during the first 24 h of culture. LPS, IFN‐γ or TNF‐α had no effect on spontaneous IL‐6 production, and neither resulted in the secretion of IL‐1β or TNF‐α. However, IL‐1β up‐regulated IL‐6 synthesis by 6–7‐fold. IEC express a profile of cytokine mRNAs distinct from conventional APC (low level constitutive IL‐6 expression but no detectable IL‐1β, TGF‐β or TNF‐α), adding to their uniqueness as APC.