Helicobacter pylori (Hp)-associated gastritis is characterized by an increased number of acute and chronic inflammatory cells secreting cytokines that contribute to maintain and expand the local inflammation. Locally induced IL-8 is believed to play a major role in the Hp-associated acute inflammatory response. Factors/mechanisms that regulate IL-8 induction are, however, not fully understood. In the present study we investigated whether Hp infection is associated with an increased production of IL-17, a T cell-derived cytokine capable of modulating IL-8 gene expression. We showed that both IL-17 RNA transcripts and protein were expressed at a higher level in the whole gastric mucosal and lamina propria mononuclear cell samples from Hp-infected patients than in those from uninfected subjects. Hp eradication was associated with a marked down-regulation of IL-17 expression. The addition of a neutralizing anti-IL-17 Ab to the gastric lamina propria mononuclear cell cultures resulted in a significant inhibition of IL-8 secretion, indicating that IL-17 contributes to enhance IL-8 in the Hp-colonized gastric mucosa. Consistently, stimulation of MKN 28 cells, a gastric epithelial cell line, with IL-17 increased IL-8 secretion. Finally, conditioned medium from the IL-17-stimulated MKN 28 cell cultures promoted the in vitro polymorphonuclear leukocyte migration. This effect was inhibitable by a neutralizing IL-8 but not IL-17 Ab. Together, these data indicate that biologically active IL-17 production is increased during Hp infection, suggesting the possibility that this cytokine may play an important role in the inflammatory response to the Hp colonization.

Crohn’ s disease (CD) is a chronic intestinal inflammatory disorder characterized by aberrant mucosal Th1 cell activation and production of IL-12, the major Th1-driving factor. The T cell response to IL-12 is dependent on the expression of a specific receptor composed of two subunits, termed IL-12Rβ1 and IL-12Rβ2. The content of IL-12Rβ2, as measured at the mRNA level, is crucial in regulating Th1 differentiation. In this study we therefore investigated IL-12Rβ2 RNA transcripts in CD. IL-12Rβ2 expression was increased in active CD as well as Helicobacter pylori (HP)-associated gastritis and Salmonella colitis compared with that in inactive CD, ulcerative colitis, noninflammatory controls, and celiac disease. In contrast, IL-12Rβ1 transcripts were expressed at comparable levels in all samples. In CD, IL-12Rβ2 expression strictly correlated with tyrosine phosphorylation of STAT4, a key component of the IL-12-dependent Th1 polarization. This was associated with a pronounced expression of IFN-γ. Transcripts for IL-12/p40 were detected in CD, HP-positive, and Salmonella colitis patients, but not in celiac disease, indicating that IL-12Rβ2 up-regulation occurs only in IL-12-associated Th1 gastrointestinal diseases. Finally, we showed that stimulation of lamina propria mononuclear cells with IL-12 enhanced IL-12Rβ2, suggesting that IL-12 regulates IL-12Rβ2 expression in human gastrointestinal mucosa. The data show that the signaling pathway used by IL-12 to induce Th1 differentiation is increased at the site of disease in CD, further supporting the view that IL-12/IL-12R signals contribute to the inflammatory response in this condition.

No abstract

Conclusions-IL-12induces human T-LPLs to produce and release IFN-, and IL-15 and IL-7 cooperate with IL-12 in expanding the IFN-mucosal response. (Gut 1998;43:620-628)

SUMMARYIL-12 modulates Th1 immune response during chronic colitis. Mechanisms regulating IL-12 synthesis in human intestine are poorly understood. The aim of this study was to investigate the effect of IFN-g and PGE 2 on lipopolysaccharide (LPS)-stimulated LPMC IL-12 production. Normal LPMC cultures were run in the presence or absence of IFN-g and/or PGE 2 before LPS stimulation. To examine the role of endogenous PGE 2 on LPS-stimulated IL-12 release, LPMC cultures were added of indomethacin before LPS stimulation. IL-12, IL-10 and IL-8 were measured by ELISA. No IL-12 was detected in either unstimulated or LPS-stimulated LPMC cultures. In contrast, LPMC released IL-8 (650 6 125 pg/ml) and IL-10 (75 6 25 pg/ml) in response to LPS. Treatment of LPMC with IFN-g facilitated LPS-stimulated IL-12, whereas it completely abrogated IL-10 production. IL-12 release by LPMC stimulated with IFN-g and LPS was signi®cantly inhibited by exogenous IL-10. The addition of PGE 2 to IFN-g-treated LPMC cultures inhibited in a dose-dependent manner LPS-induced IL-12 secretion. Furthermore, IL-12 was detectable (85 6 25 pg/ml) in the supernatants of LPMC cultures treated with indomethacin and LPS. In contrast to the effect on IL-12, PGE 2 signi®cantly augmented LPS-stimulated LPMC IL-10 production. However, the inhibition of IL-12 by PGE 2 was only partially reversed by anti-IL-10. In a simpli®ed model of LPS tolerance, we ®nally showed that monocyte-derived macrophages exhibited reduced IL-12 production after repeat LPS stimulation. In these cell cultures, indomethacin abrogated the induction of LPS desensitization. IFN-g and PGE 2 modulate differently the LPMC responsiveness to LPS in terms of IL-12 synthesis.