HUMORAL IMMUNITY TO COMMENSAL ORAL BACTERIA - QUANTITATION, SPECIFICITY AND AVIDITY OF SERUM IGG AND IGM ANTIBODIES REACTIVE WITH ACTINOBACILLUS-ACTINOMYCETEMCOMITANS IN CHILDREN

The levels, specificity and avidities of serum IgM and IgG antibodies reactive with Actinobacillus actinomycetemcomitans (Aa) serotypes a, b and c were determined in periodontally healthy (PH) children and comp ared with subjects with localized juvenile periodontitis (LJP). All PH children exhibited IgM and IgG Aa-reactive antibodies whether or not Aa was detected subgingivally but the antibodies were not specific for Aa. In contrast, LJP sera contained high concentrations of IgM and Ig G antibodies reactive with Aa that were largely specific for this bact erium, IgM and IgG antibodies in both PH and WP subjects were Of low a vidity, With one exception, the avidities of IgG anti-iia antibodies w ere significantly greater than those of IgM antibodies in both PH and LJP subjects. However, although the LJP subjects had as much as 115-fo ld more Aa-reactive IgG antibody than did the PH subjects the aviditie s of their IgG antibodies were no greater than those of the PH group, The induction by the host of low-avidity antibodies, that are ineffect ive in immune elimination, may be a reason why commensal bacteria pers ist at mucosal surfaces and why persons with LJP fail to eliminate Aa from their periodontal pockets.