The precise mechanism by which oral infection contributes to the pathogenesis of extra-oral diseases remains unclear. Here, we report that periodontal inflammation exacerbates gut inflammation in vivo. Periodontitis leads to expansion of oral pathobionts, including Klebsiella and Enterobacter species, in the oral cavity. Amassed oral pathobionts are ingested and translocate to the gut, where they activate the inflammasome in colonic mononuclear phagocytes, triggering inflammation. In parallel, periodontitis results in generation of oral pathobiont-reactive Th17 cells in the oral cavity. Oral pathobiont-reactive Th17 cells are imprinted with gut tropism and migrate to the inflamed gut. When in the gut, Th17 cells of oral origin can be activated by translocated oral pathobionts and cause development of colitis, but they are not activated by gut-resident microbes. Thus, oral inflammation, such as periodontitis, exacerbates gut inflammation by supplying the gut with both colitogenic pathobionts and pathogenic T cells.

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2 9 8 4 jci.org Volume 129 Number 8 August 2019 degrade ECM components. Humans express 24 MMPs that regulate diverse activities important for ECM remodeling and forward movement of the epithelium (reviewed in ref. 19). MMP endoproteinase activity facilitates removal of disorganized structural proteins from healing wounds to make room for newly synthesized collagen. Furthermore, MMP-mediated conversion of type III collagen to more stable type I collagen increases wound tensile strength. Fibroblast-and keratinocyte-derived MMP-1 promotes breakdown of excess collagen in murine and rabbit models of skin repair (20-22). Though not expressed in skin, epithelial cellderived matrilysin (MMP-7) is reportedly the key MMP involved in repairing injured intestinal mucosa in humans (23, 24). Signals that trigger epithelial migration and proliferation from injured sites are incompletely understood. Loss or modification in cell-cell contact and release of intracellular molecules initiates repair (25). These events set the stage for recruiting leukocytes and mesenchymal cells that orchestrate wound repair. Formylated peptides and ATP released by damaged cells, also referred to as damage-associated molecular patterns (DAMPs), orchestrate repair by promoting epithelial cell migration and proliferation. Epithelial wounds are also a source of intracellular Ca ++ waves that are rapidly transmitted into surrounding tissues to influence repair. Furthermore, ROS signaling and wound-associated physical cues influence epithelial repair. Small GTPases in the Rho family regulate remodeling of F-actin, intercellular junctions, and cell-matrix adhesions (26) and are crucial for epithelial cell migration and wound sealing. Similarly, the Rho GTPase Rac1 promotes intestinal epithelial proliferation by targeting β 1-integrin in cellular protrusions and modulating actin dynamics (26). Reparative signaling events are also regulated by extracellular mediators in the epithelial milieu, including annexin A1, annexin A2, and serum amyloid A1, which have been shown to influence integrin localization, focal adhesion kinase activation, and cell matrix remodeling in mouse and human intestinal mucosa (27-30). After injury, chemokines/cytokines and growth factors play crucial roles in epithelial c ell adhesion, migration, proliferation, and differentiation. TGF-β-dependent signaling pathways mediate the regulatory effects of many repair mediators, including PDGF, EGF, VEGF, IL-1, IL-2, IL-6, and IFN-γ (6). Canonical and noncanonical Wnt proteins also modulate epithelial wound repair. A recent in vivo study revealed a role of Wnt5a in orchestrating colonic crypt

The inflammatory bowel diseases (IBD; Crohn's disease and ulcerative colitis) are chronically relapsing, inflammatory disorders of the intestine and/or colon. The precise etiology of IBD remains unclear, but it is thought that a complex interplay between various factors including genetic predisposition, the host immune system, and the host response to luminal microbes play a role in disease pathogenesis. Further, numerous lines of evidence have implicated the accumulation of large numbers of PMN in the mucosa and epithelial crypts of the intestine as a hallmark of the active disease phase of IBD. Massive infiltration of PMNs is thought to be instrumental in the pathophysiology of IBD with the degree of PMN migration into intestinal crypts correlating with patient symptoms and mucosal injury. Specifically, migrated PMN have been implicated in the impairment of epithelial barrier function, tissue destruction via oxidative and proteolytic damage, and the perpetuation of inflammation through the release of inflammatory mediators. This review highlights the multifactorial role of PMN egress into the intestinal mucosa in the pathogenesis of IBD, as it represents an important area of research with therapeutic implications for the amelioration of the symptoms associated with IBD.

Summary The migration of polymorphonuclear leukocytes (PMN) across the intestinal epithelium is a histopathological hallmark of many mucosal inflammatory diseases including inflammatory bowel disease (IBD). The terminal transmigration step is the detachment of PMN from the apical surface of the epithelium and their subsequent release into the intestinal lumen. The current study sought to identify epithelial proteins involved in the regulation of PMN migration across intestinal epithelium at the stage where PMN reach the apical epithelial surface. A panel of antibodies reactive with IFNγ-stimulated T84 intestinal epithelial cells was generated. Screening efforts identified one mAb, GM35, which prevented PMN detachment from the apical epithelial surface. Microsequencing studies identified the GM35 antigen as human CD44. Transfection studies confirmed this result by demonstrating the loss of the functional activity of the GM35 mAb following attenuation of epithelial CD44 protein expression. Immunoblotting and immunofluoresence revealed the GM35 antigen to be an apically expressed v6 variant-exon containing form of CD44 (CD44v6). ELISA analysis demonstrated the release of soluble CD44v6 by T84 cells during PMN transepithelial migration (TEM). In addition, the observed release of CD44v6 was blocked by GM35 treatment supporting a connection between CD44v6 release and PMN detachment. Increased expression of CD44v6 and the GM35 antigen was detected in inflamed ulcerative colitis tissue. This study demonstrates for the first time that epithelial expressed CD44v6 plays a role in PMN clearance during inflammatory episodes through regulation of the terminal detachment of PMNs from the apical epithelial surface into the lumen of the intestine.

A characteristic feature of gastrointestinal tract inflammatory disorders, such as inflammatory bowel disease, is polymorphonuclear neutrophil (PMN) transepithelial migration (TEM) and accumulation in the gut lumen. PMN accumulation within the intestinal mucosa contributes to tissue injury. While epithelial infiltration by large numbers of PMNs results in mucosal injury, we found that PMN interactions with luminal epithelial membrane receptors may also play a role in wound healing. Intercellular adhesion molecule-1 (ICAM-1) is a PMN ligand that is upregulated on apical surfaces of intestinal epithelial cells under inflammatory conditions. In our study, increased expression of ICAM-1 resulted in enhanced PMN binding to the apical epithelium, which was associated with reduced PMN apoptosis. Following TEM, PMN adhesion to ICAM-1 resulted in activation of Akt and β-catenin signaling, increased epithelial-cell proliferation, and wound healing. Such responses were ICAM-1 dependent as engagement of epithelial ICAM-1 by antibody-mediated cross-linking yielded similar results. Furthermore, using an in-vivo biopsy-based, colonic-mucosal-injury model, we demonstrated epithelial ICAM-1 plays an important role in activation of epithelial Akt and β-catenin signaling and wound healing. These findings suggest that post-migrated PMNs within the intestinal lumen can regulate epithelial homeostasis, thereby identifying ICAM-1 as a potential therapeutic target for promoting mucosal wound healing.

Summary Polymorphonuclear neutrophils (PMNs) are innate immune system cells that play an essential role in eradicating invading pathogens. PMN migration to sites of infection/inflammation requires exiting the microcirculation and subsequent crossing of epithelial barriers in mucosa-lined organs such as the lungs and intestines. Although these processes usually occur without significant damage to surrounding host tissues, dysregulated/excessive PMN transmigration and resultant bystander-tissue damage are characteristic of numerous mucosal inflammatory disorders. Mechanisms controlling PMN extravasation have been well characterized, but the molecular details regarding regulation of PMN migration across mucosal epithelia are poorly understood. Given that PMN migration across mucosal epithelia is strongly correlated with disease symptoms in many inflammatory mucosal disorders, enhanced understanding of the mechanisms regulating PMN transepithelial migration should provide insights into clinically relevant tissue-targeted therapies aimed at ameliorating PMN-mediated bystander-tissue damage. This review will highlight current understanding of the molecular interactions between PMNs and mucosal epithelia and the associated functional consequences.

PMN migration across the intestinal epithelium closely parallels disease symptoms in patients with inflammatory bowel disease (IBD). PMN transepithelial migration (TEM) is a multistep process that terminates with PMN detachment from the apical epithelium into the lumen. Using a unique mAb (GM35), we have previously demonstrated that engagement of the V6 variant of CD44 (CD44v6) blocks both PMN detachment and cleavage of CD44v6. Here, we report that PMN binding to CD44v6 is mediated by protein-specific O-glycosylation with sialyl Lewis A (sLea). Analyses of glycosyltransferase expression identified fucosyltransferase 3 (Fut3) as the key enzyme driving sLea biosynthesis in human intestinal epithelial cells (IECs). Fut3 transfection of sLea-deficient IECs resulted in robust expression of sLea. However, this glycan was not expressed on CD44v6 in these transfected IECs, and therefore engagement of sLea had no effect on PMN TEM across these cells. Analyses of sLea in human colonic mucosa revealed minimal expression in noninflamed areas, with striking upregulation under colitic conditions that correlated with increased expression of CD44v6. Importantly, intraluminal administration of mAb GM35 blocked PMN TEM and attenuated associated increases in intestinal permeability in a murine intestinal model of inflammation. These findings identify a unique role for protein-specific O-glycosylation in regulating PMN-epithelial interactions at the luminal surface of the intestine.