Enhancement of eosinophil leukocyte chemotaxis by a factor in normal human serum (SEF).

An activity in normal human serum is described which enhances the migration of eosinophils towards neutrophil-derived eosinophil chemotactic factor (ECF). The serum-enhancing factor (SEF), in contrast to the inhibitors in serum, is expressed primarily during weak chemotaxis, acts in a cell-directed fashion, increases the chemokinesis of eosinophils and, in the presence of ECF, enhances chemotaxis in a synergistic fashion. SEF is found in sera of several mammalian species, affects human and guinea pig eosinophils, and it is heat-labile (56 degrees C). On Sephadex column chromatography, SEF has a molecular weight of approximately 800,000 daltons. In some sera, a second activity with a molecular weight of approximately 200,000 daltons is eluted. SEF does not enhance eosinophil migration once the cells have been deactivated in vitro by their chemotactic factor. Because of its wide distribution, SEF may play an important modulating role both in in vitro assay systems and in vivo.