Humoral immune responses to S-layer-like proteins of Bacteroides forsythus.

Bacteroides forsythus is one of the important periodontopathic bacteria, and this microorganism is known to have an S-layer outside the outer membrane. The S-layer-like antigens were recently isolated from B. forsythus, and they were found to be 270- and 230-kDa proteins in the envelope fraction. In this study, these proteins were confirmed to be specific to B. forsythus by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and they were clearly recognized by sera from patients with adult and early-onset periodontitis in Western immmunoblot analysis. We compared the immunoglobulin G (IgG) responses against the purified S-layer-like antigen by enzyme-linked immunosorbent assay. IgG responses against this antigen were low in healthy control subjects, but they were significantly higher in subjects with adult and early-onset periodontitis. Together with the fact that the IgG responses against the crude extract of B. forsythus did not rise significantly in patients with periodontitis, S-layer-like proteins are considered to be specific antigens of B. forsythus and may play an important role in the progression of periodontitis.