Complement factor D-like activity of Porphyromonas gingivalis W83

Porphyromonas gingivalis is a proteolytic gram-negative anaerobic bacterium that is frequently isolated from lesions of human periodontal disease. Previous studies have shown that P. gingivalis strain W83 inactivates C3 in pooled normal human serum (NHS) by a mechanism that is inhibitable by EDTA, yet it degrades purified complement proteins by a mechanism that is not EDTA-inhibitable. Furthermore, during complement activation, only a small number of C3 molecules accumulate on the surface of this organism unless the bacteria are treated with the protease inhibitor TLCK prior to complement activation. The hypothesis was tested that P. gingivalis W83 contains protease activity mimicking that of complement factor D, thus enabling it to activate C3 in serum without significant C3 accumulation on the cell surface. It was first noted that incubation of P. gingivalis W83 in absorbed human serum that was depleted of factor D resulted in C3 consumption that was reversed in the presence of the protease inhibitor TLCK. To directly demonstrate that factor B-dependent C3 consumption occurs in the absence of factor D, P. gingivalis W83 was incubated with purified C3 or a mixture of C3 and B. Although some proteolysis of C3 was noted, increased C3 consumption was noted in mixtures containing both C3 and B. This increment in C3 consumption was inhibited by both EDTA and TLCK. Furthermore, the addition of purified factor H to this mixture inhibited the increment in C3 consumption, indicating that a C3 convertase was probably formed.(ABSTRACT TRUNCATED AT 250 WORDS)