A study on the role of humoral antibody against Bacteroides gingivalis.

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Bacteroide gingivalis has been implicated in many cases of adult periodontitis. Elevation of humoral immune responses to B. gingivalis in subjects with adult periodontitis has been reported in our laboratory. In the present study, we investigated the relationship between bactericidal activity for B. gingivalis in human serum and IgG antibody levels to the organisms.Susceptibility of B. gingivalis strains to the complement mediated bactericidal activity of human serum was examined under anaerobic conditions. Serum containing high concentrations of IgG antibody to the microorganisms enhanced the bactericidal activity. No enhancement was found in serum which did not contain the specific antibody or in serum absorbed with intact cells. The sensitivity to the killing by pooled serum differed among B. gingivalis strains. Cells of B. gingivalis activated the pooled human serum complement not only through the classical pathway but also through an alternative pathway. It was found that the susceptibility of B. gingivalis to the bactericidal activity was classical pathway-dependent.We reported that gingival crevicular fluid contained both appreciable amounts of immunoglobulins containing IgG antibody to B. gingivalis and a complement system. These findings may support the argument that the specific antibody and complement in the gingival crevice are important determinants of host resistance to the micro-organism in vivo.