Humoral Immunity to Commensal Bacteria: Quantification, Specificity and Avidity of Serum IgG and IgM Antibodies Reactive with the Oral BacteriaPrevotella intermediaandPrevotella nigrescens

Abstract

The concentrations and avidities of naturally-occurring IgM and IgG antibodies reactive with Prevotella intermedia (Pi) and Prevotella nigrescens (Pn), two closely related oral, saccharolytic, anaerobic, gram-negative rods were determined by enzyme-linked immunosorbent assay in the 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 corporis (Pc), Bacteroides fragilis (Bf) and Porphyroinonas gingivalis (Pg). The prevalence of Pi/Pn group bacteria in the oral cavity was determined by DNA-DNA hybridisation. All children exhibited low avidity IgM and IgG antibodies reactive with Pi and Pn regardless of whether or not these bacteria were detected in the oral cavity. A considerable fraction of these antibodies was directed against common determinants shared by the related oral and non-oral anerobic gram-negative rods. The induction by the host of low avidity, potentially polyreactive antibodies, that are ineffective in immune elimination may be a mechanism by which commensal bacteria persist in the mouth and at other mucosal surfaces. Keywords: Prevotella nigrescens ; Prevotella intermedia ; antibody; specificity; avidity