Neutrophil-derived eosinophil chemotactic factor production induced by immune complexes

Immune complexes have previously been shown to be chemotactic for eosinophils in vivo. In this investigation, the in vitro chemotactic activity of human or guinea pig eosinophils was tested towards several types of immune complexes. Neither the immune complexes nor their individual components induced eosinophil migration. On incubation with purified human neutrophils, the immune complexes caused the release of a highly selective, low molecular weight (< 500 daltons) eosinophil chemotactic factor (ECF). Size and type of immune complexes influenced the amount of ECF released from the cells. The findings suggest that in vivo accumulation of eosinophils is not due to the immune complexes, but to the production of factors induced by them.