Activation of the alternate complement pathway by peptidoglycan of Actinomyces viscosus, a potentially pathogenic oral bacterium.

Peptidoglycans and cells walls from Actinomyces viscosus, Staphylococcus aureus, and group A streptococcus were compared for their relative abilities to activate the alternate complement pathway (ACP). On the dry-weight basis, the peptidoglycan from A. viscosus was 3.5 times more active than group A streptococcal peptidoglycan and 15.6 times more active than Staph. aureus peptidoglycan in activating the ACP. Consequently A. viscosus peptidoglycan is one of the most potent ACP-activators reported to date. For both A. viscosus and group A streptococcus, the peptidoglycan was a better ACP activator than cell walls from the same organism (125- and 52-fold, respectively) indicating that the peptidoglycan is probably the most important subcellular ACP-activator in these microorganisms. In contrast, cell walls from Staph, aureus were 9 times more active than peptidoglycan from Staph. aureus in activating the ACP, presumably because teichoic acids are the most important subcellular ACP activator in this microorganism.