ACTIVATION OF SERUM COMPLEMENT BY POLYSACCHARIDE-CONTAINING ANTIGENS OF PORPHYROMONAS-GINGIVALIS

We previosly reported that hot aqueous phenol extraction of Porphyromo nas gingivalis yields a preparation containing both lipopolysaccharide (LPS) and an antigenically distinct capsular polysaccharide (PS). In the present study, we examined the capacity of phenol-water extracts f rom a number of strains of P. gingivalis to activate human serum compl ement. Anticomplementary activity of extracts from two invasive and tw o noninvasive strains of P gingivalis was assessed in a sheep erythroc yte hemolytic assay and in an alternative pathway-selective rabbit ery throcyte hemolytic assay. In the sheep erythrocyte assay, extracts fro m noninvasive strains were found to exhibit greater anticomplementary activity than extracts derived from invasive strains. A phenol-water e xtract from invasive strain ATCC 53977 was further resolved into its L PS and PS fractions. Whereas isolated LPS from this strain exhibited s trong anticomplementary activity, the PS fraction was only weakly acti ve. Phenol-water extracts from three of four strains were found to be potent activators of the alternative pathway, with extracts from the t wo noninvasive strains being most active. The extract from the remaini ng strain (ATCC 53977) was a poor activator of the alternative pathway . Further analysis of this extract revealed, however, that the LPS fra ction was a potent activator of the alternative pathway, although the PS fraction exhibited negligible activity. The results of this study i ndicate that phenol-water extracts of invasive and noninvasive strains of P gingivalis differ in their respective anticomplementary activiti es, with invasive strains being less active. Although extracts from bo th invasive and noninvasive strains activated the alternative pathway, this activity appears to be attributable to the LPS, rather than the PS, component.