Unmasking of intestinal epithelial lateral membrane beta 1 integrin consequent to transepithelial neutrophil migration in vitro facilitates inv-mediated invasion by Yersinia pseudotuberculosis

Idiopathic intestinal disease states characterized by active inflammation associated with transepithelial migration of neutrophils may, paradoxically, be associated with an increased risk of infection by enteric pathogens. Although the specific ligands with which various intestinal pathogens associate remain largely unknown, it is thought that many reside on the basolateral membrane. For example, beta 1 integrin, a basolateral membrane protein, mediates the specific interaction between epithelial cells and the inv gene product (invasin) on the surface of Yersinia pseudotuberculosis. Our observations indicate that neutrophil migration across model T84 cell intestinal epithelia produced transient separation of epithelial cells at sites of neutrophil migration, resulting in microdiscontinuities that remained unsealed for several hours. We hypothesized that such sites of microdiscontinuities would yield a potential route for luminal pathogens to gain access to basolateral ligands and, thus, provide a window of risk for enteric infection. The surface biotinylation and fluorescence localization studies reported here revealed that, as in natural intestinal epithelia, beta 1 integrin was strictly polarized to the basolateral membrane in confluent T84 monolayers. However, the transient microdiscontinuities resulting from neutrophil migration permitted access to beta 1 integrin from the apical reservoir. Coincident with such basolateral exposure of beta 1 integrin, monolayers became susceptible to invasion by Y. pseudotuberculosis. Fluorescence localization indicated that Y. pseudotuberculosis selectively associated with monolayers at sites where small discontinuities resulting from neutrophil transmigration were found. An increased risk for Y. pseudotuberculosis infection was specifically related to exposure of beta 1 integrin (normally concealed by tight junctions) to the apical compartment, as Y. pseudotuberculosis cells lacking the inv gene were unable to invade following neutrophil transepithelial migration. Following closure of the microdiscontinuities associated with neutrophil migration, a small pool of beta 1 integrin remained apically localized, presumably due to incomplete repolarization. However, this small apical pool of beta 1, integrin was insufficient to support a detectable increased risk of Yersinia infection. Together, these observations indicate that by transiently perturbing monolayer continuity, neutrophil transepithelial migration is associated with a window of risk in which luminal pathogens can access basolateral ligands web as beta 1 integrin.