Chemotactic activity for eosinophils and neutrophils has been studied using guinea-pig serum activated by preformed antigen–antibody complexes.
Rabbit complexes or complexes prepared either with guinea-pig IgG2 or IgG1 were equally capable of generating a heat stable activity from guinea-pig serum that was chemotactic for guinea-pig eosinophils and for neutrophils of both the guinea-pig and the rabbit. This was distinguished from a relatively heat-labile chemotactic activity present in untreated guinea-pig serum.
The heat-stable complex-mediated chemotactic activity was thought to be complement dependent since chemotaxis for eosinophils or neutrophils could not be generated from heated serum, ammonia treated serum or from serum treated with complexes in the presence of 0·01 M EDTA.
Guinea-pig sera, activated either with rabbit, guinea-pig IgG1 or IgG2 complexes, was fractionated by sucrose-density gradient ultracentrifugation and by Sephadex chromatography. In all experiments two peaks of cell specific chemotactic activity could be separated. The peak of activity for guinea-pig neutrophils was approximately 4·5S and in the fractionation range of proteins having a molecular weight of between 65,000 and 85,000. The peak of guinea-pig eosinophil chemotactic activity was 1·5S–2S and in the molecular weight range of between 15,000 and 20,000. Those fractions which were chemotactic for guinea-pig neutrophils did not attract rabbit neutrophils. Rabbit neutrophils migrated towards those fractions of guinea-pig serum chemotactic for guinea-pig eosinophils; therefore, the properties associated with guinea-pig eosinophil chemotactic activity were similar to previously published data for a fragment cleaved from the 5th component of complement.