Specific immunoglobulin A-secreting cells in peripheral blood of humans following oral immunization with a bivalent Salmonella typhi-Shigella sonnei vaccine or infection by pathogenic S. sonnei.

The ability of bivalent Salmonella typhi-Shigella sonnei vaccine strain 5076-1C to stimulate an intestinal immunoglobulin A response in humans was evaluated by detecting gut-derived, trafficking antibody-secreting cells (ASC) in peripheral blood. Following vaccination, an immunoglobulin A-ASC response to O antigens of S. typhi and S. sonnei was observed in 10 of 13 and 13 of 13 vaccine recipients, respectively. Experimental challenge with pathogenic S. sonnei stimulated an ASC response to the S. sonnei O antigen in all subjects who developed clinical illness. The magnitude of the ASC response to challenge was significantly greater than that resulting from vaccination. Furthermore, compared with the response of the unimmunized controls, individuals previously immunized with 5076-1C demonstrated a significantly greater ASC response following challenge with S. sonnei.