[Relation of the immunosuppressivity of virulent Shigella to the structure of O antigen].

The capacity of filtrates of virulent Shigella cultures (VSC) and their different fractions to render avirulent strains, injected intraperitoneally into mice simultaneously with these filtrates, capable of suppressing immune response (delayed hypersensitivity) has been studied. Among the fractions of VSC filtrates, the lipoid fraction soluble in the mixture of ethanol and ether has proved to be active. Active factors can be extracted from VSC filtrates by means of immunosorbents obtained from antibodies of pertinent specificity. VSC filtrates are completely inactivated by treatment with phenol and trichloroacetic acid. These data suggest that the immunosuppressive factors of shigellae, responsible for their capacity to suppress immunological memory, are incorporated into the O-antigen of these bacteria.