SYNTHESIS AND REGULATION OF ACCESSORY PROINFLAMMATORY CYTOKINES BY INTESTINAL EPITHELIAL-CELLS

Intestinal epithelial cells (IEC) have been shown to act as antigen-pr esenting cells (APC) in vitro and may have this capacity in vivo. In o rder to determine whether IEC, like other APC, are able to produce acc essory cytokines which may play a role in T cell activation, we assess ed the accessory cytokine profile of IEC constitutively or after stimu lation. We measured expression, production and regulation of accessory cytokines (IL-1 beta, IL-6, tumour necrosis factor-alpha (TNF-alpha), transforming growth factor-beta (TGF-beta)) by the presence of mRNA a s well as secreted protein. Freshly isolated IEC from surgical specime ns were cultured in the presence or absence of lipopolysaccharide (LPS ), interferon-gamma (IFN-gamma), IL-1 beta or TNF-alpha. mRNA was asse ssed by a specific RNAse protection assay which controlled for contami nating cell populations while protein secretion was measured by ELISA (IL-1) or bioassay (TNF and IL-6). Neither IL-1 beta nor TNF-alpha wer e detectable in cultured IEC supernatants, supporting the lack of macr ophage contamination. All IEC spontaneously secreted IL-6 at levels co mparable to those of macrophages. IEC IL-6 mRNA also increased approxi mately 200-fold during the first 24 h of culture. LPS, IFN-gamma or TN F-alpha had no effect on spontaneous IL-6 production, and neither resu lted in the secretion of IL-1 beta or TNF-alpha. However, IL-1 beta up -regulated IL-6 synthesis by 6-7-fold. IEC express a profile of cytoki ne mRNAs distinct from conventional APC (low level constitutive IL-6 e xpression but no detectable IL-1 beta, TGF-beta or TNF-alpha), adding to their uniqueness as APC.