CHARACTERIZATION OF B-CELL EPITOPES ON IPAB, AN INVASION-ASSOCIATED ANTIGEN OF SHIGELLA-FLEXNERI - IDENTIFICATION OF AN IMMUNODOMINANT DOMAIN RECOGNIZED DURING NATURAL INFECTION

The invasion plasmid antigen B (IpaB), a 62-kDa plasmid-encoded protei n associated with the ability of shigellae to invade epithelial cells, is the bacterial antigen most strongly and consistently recognized by the host during infection. The strong systemic and mucosal immune res ponses observed against this invasin prompted us to map its B-cell epi topes. For this purpose, IpaB was first overexpressed in Shigella flex neri and used to raise rabbit polyclonal antiserum and murine monoclon al antibodies, which were subsequently used to screen a lambdagt11 ipa B library. Inserts of recombinant DNA clones that were specifically re cognized by the antisera and antibodies were sequenced, and three dist inct determinants were identified. Further characterization of these d eterminants showed that they were recognized by sera from patients con valescent from shigellosis, suggesting that they are relevant to the h umoral response during natural infection. Moreover, the IpaB region co mprising the three determinants was systematically recognized by all s era from infected patients that we tested, whereas other regions of th e protein were not. These data suggest that this region, located betwe en amino acid residues 147 and 258, is the major immunogenic domain of the invasin in the course of natural infection.