Isolation and characterization of a Shigella flexneri invasin complex subunit vaccine

The invasiveness and virulence of Shigella spp. are largely due to the expr ession of plasmid-encoded virulence factors, among which are the invasion p lasmid antigens (Ipa proteins). After infection, the host immune response i s directed primarily against lipopolysaccharide (LPS) and the virulence pro teins (IpaB, IpaC, and IpaD). Recent observations have indicated that the I pa proteins (IpaB, IpaC, and possibly IpaD) form a multiprotein complex cap able of inducing the phagocytic event which internalizes the bacterium. We have isolated a complex of invasins and LPS from water-extractable antigens of virulent shigellae by ion-exchange chromatography. Western blot analysi s of the complex indicates that all of the major virulence antigens of Shig ella, including IpaB, IpaC, and IpaD, and LPS are components of this macrom olecular complex. Mice or guinea pigs immunized intranasally with purified invasin complex (invaplex), without any additional adjuvant, mounted a sign ificant immunoglobulin G (IgG) and IgA antibody response against the Shigel la virulence antigens and LPS. The virulence specific response was very sim ilar to that previously noted in primates infected with shigellae. Guinea p igs (keratoconjunctivitis model) or mice (lethal lung model) immunized intr anasally on days 0, 14, and 28 and challenged 3 weeks later with virulent s higellae were protected from disease (P < 0.01 for both animal models).