Further studies on the chemotactic factor of complement and its formation in vivo.

The chemotactic factor, generated in whole rabbit serum following treatment with immune precipitates, was found to be principally associated with fractions containing the fifth and sixth components of complement (C′ and C′) after electrophoretic separation of serum. The chemotactic factor could also be generated in the intact animal, adding credence to its importance in tissue reactions induced by immunological agents. The isolated and activated C′ and C′ complex was found to be at least 10–20 times more active in the chemotaxis of rabbit polymorphonuclear leucocytes (PMNs) than bradykinin, kallidin, histamine, serotonin and extracts of PMN granules. The amino acid derivatives N-CBZ-glycyl-L-phenylalanine and N-CBZ-α glutamyl-L-tyrosine inhibited formation of the chemotactic factor in serum. The latter derivative also caused loss of activity of the preformed chemotactic factor in rabbit serum and in density gradient ultracentrifugation it was found that the C′ and C′ complex dissociated in the presence of this inhibitor. Chemotactically active C′ to C′ fractions, when added to the suspension of PMNs, prevented the ability of these cells to migrate toward a chemotactic source. It was also found that the ratio of combination of C′ and C′ was critical for the full expression of chemotactic activity. Utilizing purified components of human C′, very recently obtained data indicate the requirement of the seventh component of C′ (C′) for generation of chemotactic activity. No later reacting components of C′ are required. Whether C′ is incorporated into the chemotactically active complex which sediments rapidly in the ultracentrifuge is not yet established. Similar data with guinea-pig C′ complexes were also obtained.