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Eosinophilic esophagitis (EoE) is a food allergy--associated inflammatory disease characterized by esophageal eosinophilia. Current management strategies for EoE are nonspecific, and thus there is a need to identify specific immunological [...]

Lim DM, Narasimhan S, Michaylira CZ, Wang ML. TLR3-mediated NF-[kappa]B signaling in human esophageal epithelial cells. Am J Physiol Gastrointest Liver Physiol 297: G1172--G1180, 2009. First published September 24, 2009; doi: 10.1152/ajpgi.00065.2009.--Despite its position at the front line against ingested pathogens, very little is presently known about the role of the esophageal epithelium in host innate immune defense. As a key player in the innate immune response, Toll-like receptor (TLR) signaling has not been well characterized in human esophageal epithelial cells. In the present study, we investigated the inflammatory response and signaling pathways activated by TLR stimulation of human esophageal cells in vitro. Using quantitative RT-PCR, we profiled the expression pattern of human TLRs 1-10 in primary esophageal keratinocytes (EPC2), immortalized nontransformed esophageal keratinocytes (EPC2-hTERT), and normal human esophageal mucosal biopsies and found that TLRs 1, 2, 3, and ; were expressed both in vivo and in vitro. Using the cytokine IL-8 as a physiological read out of the inflammatory response, we found that TLR3 is the most functional of the expressed TLRs in both primary and immortalized esophageal epithelial cell lines in response to its synthetic ligand polyinosinic polycytidylic acid [poly(I:C)]. Through reporter gene studies, we show that poly(I:C)-induced NF-[kappa]B activation is critical for the transactivation of the IL-8 promoter in vitro and that nuclear translocation of NF-[kappa]B occurs at an early time point following poly(I:C) stimulation of esophageal epithelial cells. Importantly, we also show that poly(I:C) stimulation induces the NF-[kappa]B-dependent esophageal epithelial expression of TLR2, leading to enhanced epithelial responsiveness of EPC2-hTERT cells to TLR2 ligand stimulation, suggesting an important regulatory role for TLR3-mediated NF-[kappa]B signaling in the innate immune response of esophageal epithelial cells. Our findings demonstrate for the first time that TLR3 is highly functional in the human esophageal epithelium and that TLR3-mediated NF-[kappa]B signaling may play an important regulatory role in esophageal epithelial homeostasis. esophagus; Toll-like receptor 3 doi: 10.1152/ajpgi.00065.2009

In the intestinal epithelium, activation of phosphatidylinositol 3-kinase (PI3-kinase)/AKT pathways, via growth factor-mediated signaling, has been shown to regulate cell proliferation and inhibit apoptosis. An immune-activated receptor critical for Th2 immune responses, IL-4R[alpha] can also activate PI3-kinase via insulin receptor substrate (IRS)-dependent signaling. Here, using the intestinal goblet cell-specific gene RELM[beta], we investigated the effect of PI3-kinase activation via Th2 immune responses on the goblet cell phenotype. IL-13 stimulation activated PI3-kinase and AKT signal transduction in LS 174T cells. Not only did pharmacological inhibition of PI3-kinase and AKT 1/2 inhibit RELM[beta] induction by IL-13, but AKT inhibition also significantly reduced constitutive basal expression of RELM[beta], a response reproduced by the simultaneous pharmacological inhibition of both epidermal growth factor receptor and IGF-I receptor signaling. In vivo, the disruption of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), an inhibitor of PI3-kinase activation, led to the activation of RELM[beta] expression in the small intestine. Furthermore, induction of an intestinal Th2 immune response by infection with a small intestinal nematode parasite, Heligmosomoides polygyrus, led to enhanced epithelial cell proliferation, activation of AKT as demonstrated by the loss of Foxol nuclear localization, and robust induction of RELM[3 expression in wild-type, but not IL-4R[alpha] knockout, mice. These results demonstrate that Th2 immune responses can regulate goblet cell responses by activation of PI3-kinase and AKT pathways via IL-4R[alpha]. phosphatidylinositol 3-kinase; epithelium; intestine

Host immune responses to commensal flora and enteric pathogens are known to influence gene expression in the intestinal epithelium. Although the Cdx family of caudal-related transcription factors represents critical regulators of gene expression in the intestinal epithelium, the effect of intestinal immune responses on Cdx expression and function has not been determined. We have shown that bacterial colonization and Th2 immune stimulation by intestinal nematode infection induce expression of the intestinal goblet cell-specific gene RELM[beta]. In this study, we investigated the transcriptional regulation of resistin-like molecule/found in inflammatory zone (RELM/FIZZ, RELM[beta]) and its isoforms RELM[alpha] and RELM[gamma] to ascertain the role of Cdx in modifying intestinal gene expression associated with innate and adaptive immune responses. Analysis of the RELM[beta] promoter showed that Cdx2 plays a critical role in basal gene activation in vitro. This was confirmed in vivo using transgenic mice, where ectopic gastric and hepatic expression of Cdx2 induces expression of RELM[beta], but not RELM[alpha] or RELM[gamma], exclusively in the stomach. Although there was no quantitative change in colonic Cdx2 mRNA expression, protein distribution, or phosphorylation of Cdx2, bacterial colonization induced expression of RELM[beta], but not RELM[alpha] or RELM[gamma]. In contrast, parasitic nematode infections activated colonic expression of all three RELM isoforms without alteration in Cdx2 expression. These results demonstrated that Cdx2 participates in directing intestine-specific expression of RELM[beta] in the presence of commensal bacteria and that adaptive Th2 immune responses to intestinal nematode infections can activate intestinal goblet cell-specific gene expression independent of Cdx2.