O-ANTIGEN PHOSPHORYLATION IN Shigella flexneri: A CLUE TO THE ENIGMA OF THE MONOCLONAL ANTIBODY MASF IV-I SPECIFITY

摘要

The O-antigens of most S. flexneri serotypes share a linear O-unit containing one D-GlcNAc and three L-Rha residues, whereas differences between the serotypes are conferred by phage-encoded glucosylation or/and O-acetylation. Recently, S. flexneri strains exhibiting the multiantibiotic resistance have been isolated and found to belong to a novel serotype called Xv - X variant [1]. Xv strains react with group sera 7,8 and monoclonal antibody MASF IV-I against a serotype 4a strain. The 7,8 epitope is associated with a lateral glucose residue, whereas MASF IV-1 seems to be with the unidentified "variant" factor. There are unexplained peculiarities on the MASF IV-1 specificity: i) it recognizes only some serotype 4a strains and ii) it reacts with strains of some serotypes, including serotype X, which lack the type IV glucosylation [2, 3]. We found that the O-antigen of the novel serotype Xv differ from that of the typical serotype X in the presence of a 2-aminoethyl phosphate group (PEtN) at position 3 of the 2-substituted rhamnose residues. Earlier, a PEtN-containing O-antigen has been found in serotype 4a (here 4av) strains [4]. Major monophosphorylated and minor bisphosphorylated O-units are present in both serotypes.