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The structural basis for the cross-reactivity between theEscherichia coli K13, K20 and K23 capsular polysaccharides is the →)-β-ribofuranosyl-(1→7)-β-2-keto-3-deoxyoctonate polymer. Monoclonal antibodies againstE. coli K13 which require O-acetyl-2-keto-3-deoxyoctonate for binding were further investigated. Such antibodies, of both the IgG and the IgM isotype, opsonizedE. coli K13in vitro and protected against intraperitoneal infection in mice as well as ascending pyelonephritis in rats. A monoclonal IgG1 anti-idiotype, specific for the K13 polysaccharide combining site of a protective IgM idiotype, primed for protection against intraperitoneal infection with liveE. coli K13 following K13 injections at four as well as 12 weeks of age. the K13 polysaccharide alone did not immunize and protect. The monoclonal anti-K13 idiotype only primed for protection at four weeks of age. These findings suggest a strong effect of a single idiotype on the outcome of a bacterial infection.

The structural basis for the cross-reactivity between the Escherichia coli K13, K20 and K23 capsular polysaccharides is the ----)-beta-ribofuranosyl-(1----7)-beta-2-keto-3-deoxyoctonate polymer. Monoclonal antibodies against E. coli K13 which require O-acetyl-2-keto-3-deoxyoctonate for binding were further investigated. Such antibodies, of both the IgG and the IgM isotype, opsonized E. coli K13 in vitro and protected against intraperitoneal infection in mice as well as ascending pyelonephritis in rats. A monoclonal IgG1 anti-idiotype, specific for the K13 polysaccharide combining site of a protective IgM idiotype, primed for protection against intraperitoneal infection with live E. coli K13 following K13 injections at four as well as 12 weeks of age. the K13 polysaccharide alone did not immunize and protect. The monoclonal anti-K13 idiotype only primed for protection at four weeks of age. These findings suggest a strong effect of a single idiotype on the outcome of a bacterial infection.