The Yersinia pseudotuberculosis adhesin YadA mediates intimate bacterial attachment to and entry into HEp-2 cells

We characterized a bacterium-host cell interaction that is mediated by the Yersinia adhesin YadA. Derivatives of the virulence plasmid pIB1 harboring mutations in yadA, yopE, or yopH or in a low-calcium-response regulatory locus were introduced into a Yersinia pseudotuberculosis YPIII strain defective for Inv. The mutant strains were tested for the capacity to attach to and enter HEp-2 cells and express the cytotoxic activities of YopE and YopH. As previously shown, expression of YadA was necessary for bacterial attachment and Yop activity in the absence of Inv (R. Rosqvist, A. Forsberg, M. Rimpilainen, T. Bergman, and H. Wolf-Watz, Mol. Microbiol. 4:657-667, 1990). In addition, bacterial entry into HEp-2 cells occurred efficiently when YadA was expressed in the absence of YopE and YopH. These results demonstrated that YadA mediates intimate attachment of Y. pseudotuberculosis to HEp-2 cells and that phagocytic uptake of bacteria by this pathway is inhibited by the synergistic activities of YopH and YopE. A role for beta 1 integrins as host cell receptors for this bacterial attachment and entry mechanism was supported by HEp-2 cell adhesion and monoclonal antibody neutralization studies.