Induction of leukochemotaxis by protein A of Staphylococcus aureus

The mechanism of the leukochemotactic activity of staphylococcal protein A (pA) has been studied by in vitro and in vivo experiments. Protein A alone or mixed with heat-inactivated serum induced no migration of polymorphonuclear leukocytes, demonstrating that pA is not a cytotaxin, but a cytotaxigen. Protein A, activating both pathways of the C system, induced chemotaxis in a C4 deficient serum, but not in a C5 deficient serum. This shows that the chemotactic mediator elaborated is a split product of C5, i.e. C5a. The chemotactic activity of pA observed in the presence of normal sera (in vitro) and in wound chambers (in vivo) was exclusively caused by C activation via reaction with Fc.