ROLE OF YOPS IN INHIBITION OF PHAGOCYTOSIS AND KILLING OF OPSONIZED YERSINIA-ENTEROCOLITICA BY HUMAN GRANULOCYTES

The virulence plasmid of Yersinia enterocolitica codes for the product ion of the outer membrane protein YadA and the secretion of several pr oteins, called Yops, which may play a role in the interaction between granulocytes and this bacterium. We investigated whether the expressio n of YadA or the secretion of Yops affected the phagocytosis and killi ng of opsonized Y. enterocolitica by human granulocytes. The rates of phagocytosis and killing of Y. enterocolitica by granulocytes in suspe nsion in the presence of rabbit Yersinia antibodies and complement wer e determined by microbiological assays. In addition, noningested cell- adherent bacteria were differentiated from ingested yersiniae by immun ofluorescence microscopy. Plasmid-bearing opsonized Y. enterocolitica was able to inhibit phagocytosis and killing by human granulocytes. Th e inhibition of phagocytosis was specific for the plasmid-bearing stra in of Y. enterocolitica, since granulocytes were still able to phagocy tose and kill Staphylococcus aureus in the presence of Y. enterocoliti ca. Plasmid-cured Y. enterocolitica was readily phagocytosed and kille d by these cells. To investigate the role of YadA or Yops in the inhib ition of phagocytosis by granulocytes, the phagocytosis of mutant stra ins unable to express YadA or to secrete Yops was studied. A Y. entero colitica mutant unable to secrete Yops lost its ability to inhibit pha gocytosis; a mutant expressing only YadA was readily ingested by granu locytes. These results indicate that after attachment of opsonized Y. enterocolitica to granulocytes, Yops play an important role in inhibit ing the ingestion of Y. enterocolitica by human granulocytes.