HETEROGENEITY OF ANTIBODIES REACTIVE WITH THE DOMINANT ANTIGEN OF ACTINOBACILLUS-ACTINOMYCETEMCOMITANS

The serotype b-specific carbohydrate antigen (SbAg) of Actinobacillus actinomycetemcomitans Yl is reported to be the O antigen of lipopolysa ccharide, and the highest titers of serum antibody reactive with A. ac tinomycetemcomitans in early-onset periodontitis (EOP) patients bind S bAg. These high titers of serum antibody reactive with SbAg are associ ated with a lesser extent and severity of periodontal disease. The aim of this study was to determine if a limited number of genes code for anti-SbAg antibodies as has been shown for immunoglobulin G (IgG) reac tive with the type b polysaccharide from Haemophilus influenzae. Serum IgG reactive with the SbAg was prepared from 20 high-titer EOP patien ts by affinity chromatography. The Ige subclass concentrations were de termined, and heterogeneity was analyzed by isoelectric focusing (IEF) , IgG2 was the dominant subclass (83% of total IgG) in the anti-SbAg I ge fraction and represented an average of 1.33% of total serum IgG2. T he IgG2 reactive with SbAg was isolated from the affinity-purified Ige fraction by affinity chromatography with protein A and subclass-speci fic monoclonal antibodies, On IEF gels, only 4 to 20 bands were observ ed in the anti SbAg IgG fractions, indicating limited heterogeneity, N -terminal amino acid sequence analysis of eight representative anti-Sb Ag IgG2 preparations indicated that variable heavy and light chains co nsisted largely of VHIII and VKII, respectively, However, a significan t fraction of anti-SbAg may use V-H and (lambda) genes with blocked N termini. In short, these findings indicate that Ige reactive with SbAg is very much like the antibody reactive with H. influenzae type b pol ysaccharide, Similarities include IgG2 dominance, limited bands on IEF gels, supporting an oligoclonal response, and use of genes from VHIII and VKII regions.