Opposing effects of soluble TNF receptor p55 on the biological action of TNF in a colonic epithelial cell line

Abstract

Background and Aim: In ulcerative colitis (UC), the levels of extracellular soluble TNF receptors (sTNFRs), known TNF antagonists, increase in the serum and in mucosal lesions. We examined the effect of sTNFRs on TNF-induced ICAM-I expression and IL-8 production in a colonic epithelial cell line to ascertain the role of sTNFRs in DC. Methods: Recombinant TNF (10ng/ml) and recombinant sTNFR (1-I,OOOng/ml) were simultaneously added to confluent HT-29 cells. After 24 hours of incubation, the cell surface expression of ICAM-I was analyzed by flow cytometry, and IL-8 production in the medium and concentrations ofTNF in the serum and colonic mucosa of DC patients were measured by enzyme linked immuno solvent assay (ELISA), and concentration of sTNFR in the serum and colonic mucosa was measured by enzyme linked immunological binding assay. Results: When the sTNFRp55/TNF concentration ratio was greater than or equal to 10, sTNFRs significantly suppressed TNF-induced ICAM-I expression and IL-8 production by HT-29 cells. On the other hand, when the sTNFRp55/TNF concentration ratio was between 1/10 and I, sTNFRs significantly increased TNF-induced ICAM·I expression and IL·8 production in HT-29 cells. The sTNFR concentration was significantly higher in the serum and colonic mucosa of patients with active DC than in controls or patients with inactive DC, but the sTNFRp55/TNF concentration ratio in mucosa did not exceed I in any patients with active DC. Conclusions: The results of the present study showed that relatively low concentrations of sTNFRs enhanced the physiological activity of TNF in a colonic epithelial cell line. The sTNFR concentration in DC patients did not exceed this relatively low concentration range, suggesting that the increase in sTNFRs in the mucosa of DC patients works synergistically with TNF to enhance inflammation. Thus, large quantities of sTNFRp55 are necessary to suppress TNF activity, caution should be exercised when administering sTNFRp55 in a clinical setting.