[Immunosuppressive properties of virulent Shigella strains].

The review presents data which show the existence of significant difference between the virulent and avirulent Shigella species. This difference is displayed in the virulent Shigella's ability to inhibit immune memory and secondary immune response. The existance of immunosuppressive activity in virulent Shigella has been demonstrated in the case of experimental Shigella infection in animals as well as natural infection in humans. The immunosuppressive property of Shigella sonnei is determined by the invasiveness genes of the virulence plasmid. Lipopolysaccharide (LPS) from virulent Shigella sonnei differs from the avirulent Shigella sonnei LPS. It possesses the property to induce in avirulent bacteria the ability to inhibit secondary immune response. This inductive immunosuppressive property of LPS is also encoded by invasiveness genes. Thus, literature data suggest that the ability to inhibit immune memory, secondary immune response and the existence of inductive immunosuppressive property in LPS are Shigella's signs of virulence as well as its ability to invade epithelial cells.