The dominant
antigen of Actinobacillus actinomycetemcomitans recognized by high-titer sera from patients with localized
juvenile periodontitis is the serotype
antigen located in the O-side chains of
lipopolysaccharide. Whether such sera contain
antibodies reactive with other
epitopes in
lipopolysaccharide, as is the case for patients with rapidly progressive
periodontitis, remains unknown. We prepared and characterized by gas liquid chromatography
lipopolysaccharide,
lipid A, core
carbohydrate with no or few O-side chains (core) and high-molecular-mass
carbohydrate-rich in O-side chains (
oligosaccharide) from A. actinomyce-temcomitans ATCC 43718 (serotype b, Y4). Using
enzyme-linked
immunosorbent assay (ELISA), sera from 36 patients with localized
juvenile periodontitis were surveyed using whole-cell sonicate as plate
antigen. The seven highest titer sera were selected for further study. Specific
IgG antibody binding was observed to intact
lipopolysaccharide and to all the
lipopolysaccharide fractions. The mean titers were highest for intact
lipopolysaccharide (138.8 ELISA units), and
lipid A (122 ELISA units), followed by the core fraction (81 ELISA units) and the
oligosaccharide fraction (69.5 ELISA units). ELISA inhibition revealed that the core fraction at a concentration of 10 micrograms/test well inhibited antibody binding to A. actinomycetemcomitans
lipopolysaccharide by a mean value of 56.7%. To further characterize antibody binding to the core fraction, ELISA inhibition was performed using as inhibitor the core
carbohydrate fraction of the Re mutant of Salmonella minnesota, which is known to contain only alpha-keto-3-deoxyoctonate residues and
phosphate. This fraction
at 10 micrograms/test well inhibited binding of
antibodies from 6 of 7 test sera with a mean value of 49.2%. Thus, sera from patients with localized
juvenile periodontitis contain
antibodies that bind to the O-side chains of
lipopolysaccharide, as has been previously reported, but they also contain
antibodies that bind to
lipid A and to
lipopolysaccharide core
polysaccharide epitopes, specifically to alpha-keto-3-deoxyoctonate moieties. The humoral immune response to A. actinomycetemcomitans in patients with localized
juvenile periodontitis is more complex than previously reported and is very similar to that of patients with rapidly progressive
periodontitis.