The peripheral immune responses of adult Vietnamese patients infected with Shigella dysenteriae 1 and Shigella flexneri 1b and 2a and those of S. flexneri-infected Swedish patients were studied against various lipopolysaccharide and invasion plasmid-coded antigens (Ipa-s) and compared with the titers for the corresponding local healthy populations. Both Vietnamese and Swedish patients reacted with significant (P, < 0.05) titer increases in the immunoglobulin A and G classes against the homologous lipopolysaccharide antigen. However, significant titer responses against the Ipa-s were seen among only the Swedish patients. We surmise that the weak-to-moderate responses against the Ipa-s in Vietnamese patients are due to the fact that the high level of titers induced by previous infections in the local population could not be considerably increased further by a recent infection.
Adult Antibodies, Bacterial