INCREASED OPSONIZATION OF A PRTH-DEFECTIVE MUTANT OF PORPHYROMONAS-GINGIVALIS W83 IS CAUSED BY REDUCED DEGRADATION OF COMPLEMENT-DERIVED OPSONINS

Periodontitis is a disease of the supporting structures of the teeth t hat is caused by bacteria whose common ecologic niche is the gingival crevice or the periodontal pocket. Tissue destruction occurs in spite of both local and systemic immune responses against such bacteria. Por phyromonas gingivalis is considered to be an important pathogen in som e forms of human periodontitis and is particularly interesting because of its multiplicity of virulence factors. We have previously observed that phagocytosis-resistant invasive strains of P. gingivalis proteol ytically degrade C3 and IgG and accumulate less C3-derived opsonins du ring complement activation. We recently have cloned the prtH gene from P. gingivalis W83 that encodes a 97-kDa active protease, which has th e capacity to degrade purified C3 protein. By using this cloned gene w e created an allelic exchange mutant of P. gingivalis W83, designated V2296, in which the prtH gene was inactivated. This mutant was previou sly shown to be less virulent than its parent strain W83 in a mouse mo del of bacterial invasiveness. In the present study we have assessed t he relative capacity of V2296 and W83 to be opsonized by complement an d to be taken up by PMNs. The data demonstrate that V2296, in comparis on with its parent strain W83, is less able to degrade C3 and that it accumulates significantly greater numbers of molecules of C3-derived o psonins on the bacterial surface in the form of C3b and iC3b during co mplement activation. Furthermore, opsonized V2296 is taken up in much higher numbers by human PMNs than W83, suggesting that the prtH gene p roduct may be important in evasion of host defense mechanisms.