HUMORAL IMMUNITY TO COMMENSAL BACTERIA - QUANTIFICATION, SPECIFICITY AND AVIDITY OF SERUM IGG AND IGM ANTIBODIES REACTIVE WITH THE ORAL BACTERIA PREVOTELLA-INTERMEDIA AND PREVOTELLA-NIGRESCENS

The concentrations and avidities of naturally-occurring IgM and IgG an tibodies reactive with Prevotella intermedia (Pi) and Prevotella nigre scens (Pn), two closely related oral, saccharolytic, anaerobic, gram-n egative rods were determined by enzyme-linked immunosorbent assay in t he serum of 50 children aged between 6 and 14 yr. Antibody specificity was examined by absorption with the homologous bacterium and with the related oral and non-oral, anaerobic gram-negative rods Prevotella co rporis (Pc), Bacteroides fragilis (Bf) and Porphyromonas gingivalis (P g). The prevalence of Pi/Pn group bacteria in the oral cavity was dete rmined by DNA-DNA hybridisation. All children exhibited low avidity Ig M and IgG antibodies reactive with Pi and Pn regardless of whether or not these bacteria were detected in the oral cavity. A considerable fr action of these antibodies was directed against common determinants sh ared by the related oral and non-oral anerobic gram-negative rods. The induction by the host of low avidity, potentially polyreactive antibo dies, that are ineffective in immune elimination may be a mechanism by which commensal bacteria persist in the mouth and at other mucosal su rfaces.