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Background: T cell-mediated immunity plays a central part in the pathogenesis of tissue damage in inflammatory bowel disease (IBD). The mechanism by which T cells mediate tissue damage during IBD remains unclear, but evidence indicates that T cell-derived cytokines stimulate fibroblasts to synthesise matrix metalloproteinases (MMPs), which then mediate mucosal degradation. We have previously shown that, in IBD, there is high production of interleukin (IL) 21, a T cell-derived cytokine, which enhances Th1 activity. Aim: To investigate whether IL21 controls MMP production by intestinal fibroblasts. Methods: IL21 receptor (IL21R) was evaluated in intestinal fibroblasts by reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting. Fibroblasts were stimulated with IL21 and MMPs were evaluated by RT-PCR and western blotting. The effect of a neutralising IL21R fusion protein (IL21R/Fc) on the induction of MMPs in fibroblasts stimulated with IBD lamina propria mononuclear cell (LPMC) supernatants was also evaluated. Results: Intestinal fibroblasts constitutively express both IL21R and the common c chain receptor, which are necessary for IL21-driven signalling. IL21 enhances fibroblast production of MMP-1, MMP-2, MMP-3 and MMP-9, but not tissue inhibitors of MMP-1 and MMP-2. Moreover, IL21 synergises with tumour necrosis factor a to increase synthesis of MMP synthesis. IL21 enhances MMP secretion without affecting gene transcription and protein synthesis. IBD LPMC supernatants stimulate MMP secretion by intestinal fibroblasts, and this effect is partly inhibited by IL21R/Fc. Conclusions: These results suggest that fibroblasts are a potential target of IL21 in the gut and that IL21 controls MMP secretion by fibroblasts.

Immunologically mediated tissue damage in the gut is associated with increased production of proinflammatory cytokines, which activate the transcription factor NF-B in a variety of different cell types. The mechanisms/factors that negatively regulate NF-B in the human gut and the pathways leading to the sustained NF-B activation in gut inflammation remain to be identified. Pretreatment of normal human intestinal lamina propria mononuclear cells (LPMC) with transforming growth factor-␤1 (TGF-␤1) resulted in a marked suppression of TNF-␣؊induced NF-B p65 accumulation in the nucleus, NF-B binding DNA activity, and NF-B-dependent gene activation. TGF-␤1 also increased IB␣ transcripts and protein in normal LPMC. In marked contrast, treatment of LPMC from patients with inflammatory bowel disease with TGF-␤1 did not reduce TNFinduced NF-B activation due to the overexpression of Smad7. Indeed inhibiting Smad7 by specific antisense oligonucleotides increased IB␣ expression and reduced NF-B p65 accumulation in the nucleus. This effect was due to endogenous TGF-␤1. TGF-␤1 directly stimulated IB␣ promoter transcriptional activity in gut fibroblasts in vitro, and overexpression of Smad7 blocked this effect. These data show that TGF-␤1 is a negative regulator of NF-B activation in the gut and that Smad7 maintains high NF-B activity in gut inflammation by blocking TGF-␤1 signaling.

SUMMARYTransforming growth factor-b (TGF-b ) is an inhibitory cytokine recognized as a key regulator of immunological homeostasis and inflammatory responses. TGF-b is involved in experimental models of oral tolerance and in the pathogenesis of experimental colitis. Patients with inflammatory bowel disease (IBD) have inappropriate T cell responses to antigenic components of their own intestinal microflora, suggesting the presence of a disorder in the normal mucosal immune mechanism that ensures the downregulation of responses to harmless constituents in the microflora. To evaluate the contribution of TGFb to this imbalance, we measured TGF-b 1 production by lamina propria mononuclear cells (LPMC) and T cells isolated from tissue specimens of patients with Crohn's disease (CD), ulcerative colitis (UC) and controls. Cells were cultured in the presence or absence of anti-CD2 plus anti-CD28 MoAbs and TGFb 1 production in culture supernatants was measured by ELISA. LPMC isolated from CD patients produced significantly less TGF-b 1 than controls when stimulated via CD2 plus CD28 pathways ( P = 0·001)] conversely, in UC patients increased production of TGF-b 1 compared to controls was observed ( P = 0·0005). These differences were also observed with purified lamina propria (LP) T cells in both diseases and were associated with the presence of inflammation. Thus, TGF-b 1 production shows contrasting secretion in CD and in UC, probably as a consequence of the different Th polarization. The absolute or relative defect in TGF-b 1 production observed in CD and UC may contribute to the perpetuation of inflammation.