Repetitive antigen stimulation induces peripheral T cell tolerance in vivo. It is not known, however, whether multiple stimulations merely suppress T cell activation or, alternatively, change the transcriptional program to a distinct, tolerant state. In this study, we have discovered that STAT3 and STAT5 were activated in response to antigen stimulation in vivo, in marked contrast to the suppression of AP-1, NF-jB and NFAT. In addition, a number of transcription factors were induced in tolerant T cells following antigen challenge in vivo, including T-bet, Irf-1 and Egr-2. The altered transcription program in tolerant cells associates closely with the suppression of cell cycle progression and IL-2 production, as well as with the induction of IL-10. Studies of T-bet and Egr-2 show that the function of T-bet in peptide treatment-induced regulatory T cells is not associated with Th1 differentiation, but correlates with the suppression of IL-2, whereas expression of Egr-2 led to an up-regulation of the cell cycle inhibitors p21 cip1 and p27 kip . Our results demonstrate a balanced transcription program regulated by different transcription factors for T cell activation and/or tolerance during antigen-induced T cell responses. Persistent antigen stimulation can induce T cell tolerance by changing the balance of transcription factors.See accompanying commentary http://www.dx

Host-pathogen interactions that allow Helicobacter pylori to survive and persist in the stomach of susceptible individuals remain unclear. Human ␤-defensins (hBDs), epithelial-derived antimicrobial peptides are critical components of host-defense at mucosal surfaces. The role of H. pylori-mediated NF-B and epidermal growth factor receptor (EGFR) activation on ␤-defensin expression was investigated. Transient transfection studies utilizing ␤-defensin promoter constructs were conducted in gastric cells with contribution of individual signaling events evaluated by the addition of specific inhibitors, small interference nucleotide-binding oligomerization domain 1 (NOD1) RNA or plasmids encoding Vaccinia virus proteins that interrupt interleukin-1 and Toll-like receptor signaling. The role of individual MAPK pathways was further delineated in HEK-293 cells expressing conditional MAPK mutants. We found hBD2 expression exclusively dependent on the presence of the bacterial cag pathogenicity island, with NOD1 a critical host sensor. Impairment of murine ␤-defensin 4 (an orthologue of hBD2) expression in NOD1-deficient mice 7-days post-infection further confirmed the role of this cytoplasmic pattern-recognition receptor in eliciting host innate immunity. In contrast to hBD2, hBD3 expression was NOD1-independent but EGFR and ERK pathway-dependent. Importantly, Toll-like receptor signaling was not implicated in H. pylori-mediated hBD2 and hBD3 gene expression. The divergent signaling events governing hBD2 and hBD3 expression suggest temporal functional variation, such that hBD2 may contribute to antimicrobial barrier function during the inflammatory phase with hBD3 playing a greater role during the repair, wound healing phase of infection.

Modifications of mucosal phospholipids have been detected in samples from patients with Helicobacter pylori-positive gastritis. These alterations appear secondary to increased phospholipase A 2 activity (PLA 2 ). The cytosolic form of this enzyme (cPLA 2 ), normally involved in cellular signaling and growth, has been implicated in cancer pathogenesis. The aim of this study was to investigate cPLA 2 expression and PLA 2 activity in the gastric mucosae of patients with and without H. pylori infection. In gastric biopsies from 10 H. pylori-positive patients, cPLA 2 levels, levels of mRNA as determined by reverse transcriptase PCR, levels of protein as determined by immunohistochemistry, and total PLA 2 activity were higher than in 10 H. pylori-negative gastritis patients. To clarify whether H. pylori had a direct effect on the cellular expression of cPLA 2 , we studied cPLA 2 expression in vitro with different human epithelial cell lines, one from a patient with larynx carcinoma (i.e., HEp-2 cells) and two from patients with gastric adenocarcinoma (i.e., AGS and MKN 28 cells), incubated with different H. pylori strains. The levels of cPLA 2 , mRNA, and protein expression were unchanged in Hep-2 cells independently of cellular adhesion or invasion of the bacteria. Moreover, no change in cPLA 2 protein expression was observed in AGS or MKN 28 cells treated with wild-type H. pylori. In conclusion, our study shows increased cPLA 2 expression and PLA 2 activity in the gastric mucosae of patients with H. pylori infection and no change in epithelial cell lines exposed to H. pylori.Helicobacter pylori infection of the gastric mucosa is present worldwide and may be associated with several pathologic alterations, including gastric cancer (30). The relationship between this organism and the development of gastric cancer has been postulated mainly on the basis of epidemiological investigations and animal models of H. pylori infection (13,15,17,21,39,40,53). This relationship is further supported by the finding that some patients with H. pylori infection show the genetic abnormalities of dysplasia and metaplasia in mucosal areas before the development of carcinoma (35, 50). However, the molecular mechanisms underlying the multistep process of gastric carcinogenesis related to H. pylori infection remain undefined (57). It has been shown that H. pylori damages the gastric barrier function and induces a dramatic change in mucosal phospholipid composition (34). This is likely due to a local increase in phospholipase A 2 (PLA 2 ) activity (4, 27). The cytosolic form (cPLA 2 ), but not the secretory form, of this enzyme is involved in cellular signaling and growth (2,25,26,28,31,38,51) and has recently been implicated in the pathogenesis of malignant transformation (11,22,32,48,49,55,56). Furthermore, many human tumors have been reported to exhibit increased synthesis of prostaglandins, the formation of which is dependent on an increase in cPLA 2 activity (16,18,19,29).In this study, we analyzed cPLA 2 expression in gastric-mucosal b...

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