[A protective factor of ribosomal shigellosis vaccine]

Shigella ribosomal vaccine was shown previously to possess protective properties in the keratoconjunctival test on guinea pigs and to be capable of preventing experimental infection in 90% of challenged monkeys. The presence of the O-specific component (OSC) constituting about 0.5% of the ribosomal preparation by serological activity suggested its importance for the protective effect. This was studied in experiments with two O-specific immunosorbents prepared by coupling anti-O rabbit antibodies with Staphylococcus aureus cells or with CNBr-Sepharose. Ribosomes treated with immunosorbents proved to be lacking the serologically active OSC and lost their ability to induce O-antibody response in rabbits and mice. After the removal of this component ribosomal preparations were incapable of ensuring protection from Shigella kerato-conjunctival infection. The isolated OSC was also inactive in this test. The data obtained in this investigation confirm the hypothesis stating that the protective activity of Shigella ribosomal vaccine is based on the combined action of ribosomes and O-specific factor whose nature and properties require further study.