ANTIBODY-RESPONSE OF MONKEYS TO INVASION PLASMID ANTIGEN-D AFTER INFECTION WITH SHIGELLA SPP

The antigen preparation most often used for determining the levels of antibodies to virulence-associated proteins of Shigella spp. consists of a mixture of proteins (including IpaB, IpaC, IpaD, and VirG) extra cted from virulent shigellae with water (water extract). To overcome t he lack of specificity for individual antigens in the water-extract en zyme-linked immunosorbent assay (ELISA), the ipaD gene from S. flexner i has been cloned, expressed to a high level, acid purified for use in a nem ELISA for the determination of the levels of antibody against I paD in monkeys and humans challenged with shigellae. The IpaD ELISA fo r serum immunoglobulins G and A correlated well with the water-extract ELISA in that monkeys infected with S. flexneri or S. sonnei responde d with high serum antibody titers in both assays. The IpaD assay requi red less antigen per well, had much lower background levels, and did n ot require correction with antigens from an avirulent organism. In con junction with the water-extract ELISA, it was possible to identify inf ected animals that did not respond to IpaD but did produce antibodies that reacted in the water-extract ELISA. This indicates that even thou gh IpaB, IpaC, and IpaD are essential for the invasiveness phenotype, the infected host does not always produce antibodies against all compo nents of the invasiveness apparatus.