Neutrophil aggregation and swelling induced by chemotactic agents.

An assay is described for measuring neutrophil aggregation and cell size with a Coulter Counter equipped with a mean cell volume computer and volume channalyzer. With this assay, it was found that several chemotactically active agents rapidly induce rabbit peritoneal polymorphonuclear neutrophils in suspension to aggregate reversibly. The aggregating activities of these chemotactic agents paralleled their in vitro chemotactic- and in vivo neutropenia-inducing potencies. Neutrophil aggregation may underlie the neutropenia which follows the infusion of these agents into rabbits. Chemotactic agents may also induce polymorphonuclear neutrophils to increase in volume; this effect appears to be independent of aggregation. The volume change develops more slowly and does not appear reversible under the conditions employed. The volume increase may be an expression of pseudopodia formation and membrane ruffling known to develop in neutrophils exposed to chemotactic agents.