PMNs facilitate translocation of platelets across human and mouse epithelium and together alter fluid homeostasis via epithelial cell–expressed ecto-NTPDases

Abstract

Mucosal diseases are often characterized by an inflammatory infiltrate that includes polymorphonuclear leukocytes (PMNs), monocytes, lymphocytes, and platelets. A number of studies have suggested that the interaction of platelets with leukocytes has an essential proinflammatory role. Here, we examined whether platelets migrate across mucosal epithelium, as PMNs are known to do, and whether platelets influence epithelial cell function. Initial studies revealed that human platelets did not efficiently transmigrate across human epithelial cell monolayers. However, in the presence of human PMNs, platelet movement across the epithelium was proportional to the extent of PMN transmigration, and strategies that blocked PMN transmigration diminished platelet movement. Furthermore, platelet-PMN comigration was observed in intestinal tissue derived from human patients with inflammatory bowel disease (IBD). The translocated platelets were found to release large quantities of ATP, which was metabolized to adenosine via a 2-step enzymatic reaction mediated by ectonucleotidases, including CD73 and ecto-nucleoside triphosphate diphosphohydrolases (ecto-NTPDases), expressed on the apical membrane of the intestinal epithelial cells. In vitro studies and a mouse model of intestinal inflammation were employed to define a mechanism involving adenosine-mediated induction of electrogenic chloride secretion, with concomitant water movement into the intestinal lumen. These studies demonstrate that ecto-NTPDases are expressed on the apical membrane of epithelial cells and are involved in what we believe to be a previously unappreciated function for platelets in the inflamed intestine, which might promote bacterial clearance under inflammatory conditions.

Ecto-Nucleoside Triphosphate Diphosphohydrolase 7 Controls Th17 Cell Responses through Regulation of Luminal ATP in the Small Intestine

“…These intestinal DCs might sense luminal ATP via purinergic receptors. Alternatively, as reported in several studies, ECs sense extracellular ATP (11,25,46). Therefore, intestinal ECs trigger inflammatory responses to activate T cell development via ATP sensing.…”

“…Indeed, severe inflammation was induced in mice lacking ENTPDase1/CD39 in several inflammatory models, including inflammatory bowel disease (21)(22)(23)(24). Combinational activity of ENTPDases such as CD39 with CD73 ecto-59-nucleotidase, which hydrolyzes AMP to adenosine, was also demonstrated in regulatory T cells and intestinal ECs (11,20,25). Thus, the immune-modulatory functions of ENTPDase1/CD39 have been well characterized.…”

Giardia duodenalis Cathepsin B Proteases Degrade Intestinal Epithelial Interleukin-8 and Attenuate Interleukin-8-Induced Neutrophil Chemotaxis

“…Several studies have demonstrated that G. duodenalis infections can occur concurrently with infections with proinflammatory gastrointestinal pathogens (15)(16)(17)(18). As previous studies have suggested that neutrophils can induce intestinal epithelial anion hypersecretion and, consequently, water loss and diarrhea via several mechanisms (84,85), our results may help to explain the lower inflammatory scores and reduced incidence of diarrhea in children infected with G. duodenalis (17,27,28). Indeed, diarrhea caused by experimental infection with enterohemorrhagic Escherichia coli was found to be directly induced by neutrophilic infiltration, independently of toxin production by the bacteria (86).…”

Giardia duodenalis: New Research Developments in Pathophysiology, Pathogenesis, and Virulence Factors

“…These findings demonstrate that assemblage A G. duodenalis trophozoites possess immunomodulatory factors that may inhibit pro-inflammatory intestinal responses in infected tissues. It is well known that neutrophils induce intestinal epithelial anion hypersecretion and, consequently, water loss, and diarrhea [97,98]. Hence, as neutrophil accumulation contributes to the development of diarrheal disease, the local release of direct immunomodulatory Giardia cathepsins may help explain the lower inflammation scores and reduced incidence of diarrhea in hosts co-infected with G. duodenalis and enteropathogens that cause diarrhea via intestinal inflammation.…”