Complement Activation by Clumping Factor and Protein a From Staphylococcus Aureus Strain E 2371

Purified surface components from Staphylococcus aureus strain E 2371, which bind to human plasma proteins, were tested for their ability in vitro to activate complement present in normal human serum. Staphylococcal clumping factor as well as protein A both isolated from strain E 2371 were capable of activate complement, while the fibronectin-binding protein showed no activity. At identical molar concentrations clumping factor was more potent than protein A to induce complement consumption. Both clumping factor and protein A were able to activate the alternative complement pathway as demonstrated in serum chelated with ethylene-glycerol-tetra-acetic acid (10 mM) in the presence of MgCl2 (10 mM).