Eosinophils adhere to and stimulate replication of lung fibroblasts ‘<i>in vitro</i>’

SUMMARY Eosinophils have been implicated in several disorders associated with the development of fibrosis. This led us to investigate the interactions between eosinophils and fibroblasts in vitro. Adhesion between purified guinea pig peritoneal eosinophils and monolayers of human fetal lung fibroblasts was assessed using the rose bengal dye staining assay. Fibroblast replication was assessed using a colorimetric assay based upon the uptake and subsequent release of methylcnc blue. Addition of phorbol myristate acetate induced a rapid, time-dependent increase in cosinophil adhesion (127% and 328% over basal adhesion after 10 and 30 min, respectively). Phorbol myristate acetate-induced adhesion was inhibited by the peptides RGDS and GRGDS (48% and 42%, respectively using 1 mM peptide) and by nordihydroguaiaretic acid, an inhibitor of the lipoxygenase pathway of arachidonic acid metabolism (46% inhibition at 15 μm), In addition. 24 h culture of fibroblast monolayers with interleukin 1α (IL-lα) or tumour necrosis factor α (TNFα) resulted in enhanced adhesion (10 U/ml IL-lα stimulated adhesion by 55% of control, 500 U/ml TNFα by 75% of control). Conditioned media from cultured eosinophils stimulated fibroblast replication in a time-dependent fashion with maximal stimulation at 3 h. In contrast, media from guinea pig peritoneal macrophages in culture did not show such an effect. This study indicates that eosinophils are capable of both adhering to and releasing mitogens for fibroblasts in vitro. These observations suggest that eosinophils have the capacity to play a role in the development of fibrosis in disorders where they have been shown to be present.