DEGRADATION OF IMMUNOGLOBULIN-G BY PERIODONTAL BACTERIA

Several subgingival microorganisms were tested for their ability to ut ilize human immunoglobulin G (IgG) as a substrate for growth. This was done using a protein-free chemically defined medium, supplemented wit h IgG. Stimulation of growth was observed for Capnocytophaga ochracea, Porphyromonas asaccharolytica, Porphyromonas endodontalis, Porphyromo nas gingivalis, Prevotella intermedia, Prevotella oralis, Lactobacillu s catenaforme and Streptococcus intermedius. Immunoelectrophoresis, so dium dodecyl sulfate-polyacrylamide gel electrophoresis and a protein assay demonstrated that P, intermedia and P. endodontalis completely d egraded the protein chains of IgG. Partial breakdown of IgG was observ ed for P. asaccharolytica and C. ochracea, whereas P. oralis cleaved t he IgG heavy chain, yielding Fc and Fab fragments. All these bacteria utilized IgG as a substrate for growth. Binding studies using an enzym e-linked immunosorbent assay, revealed complete loss of in vitro antig en-antibody binding capacity after incubation of specific IgG with P. endodontalis and partial loss of binding with P. intermedia, P, gingiv alis, C. ochracea or Fusobacterium nucleatum. Degradation or inactivat ion of IgG by oral bacteria is thought to be important in the causatio n of polymicrobial infections.