DIRECT OBSERVATION AND QUANTIFICATION OF MACROPHAGE CHEMOATTRACTION TO THE GROWTH-FACTOR CSF-1

The cloned mouse macrophage cell line, BAC1.25F, resembles primary mac rophages in its dependence on colony stimulating factor-1 (CSF-1) for both viability and proliferation. Re-addition of CSF-1 to cytokine-dep rived cells, which are rounded with diffusely organised F-actin, stimu lates rapid cell spreading and cell polarisation. Using the Dunn chemo taxis chamber the movement of stimulated macrophages was monitored ove r a 2 hour period. Cells restimulated with 1.32 nM human recombinant C SF-1 migrated at a mean rate of 7.71 mu m per hour, but showed no dire ctional preferences. In a linear concentration gradient of CSF-1, cyto kine-deprived cells were again stimulated to migrate and the mean rate of cell motility, at 6.88 mu m per hour, was not significantly differ ent from that measured in an isotropic environment of CSF-1. However, there was a strong preference for the cells to orientate so that their long axes aligned with the CSF-1 gradient and they migrated preferent ially towards the source of CSF-1. Migrating cells contained abundant F-actin within the leading lamellae as judged by confocal imaging of f luorescent phalloidin, but the actin was not arranged into stress fibr e-like structures. These data support the proposition that CSF-1 is bo th a chemokinetic and chemotactic agent for macrophages. Tumour necros is factor (TNF-alpha) failed to stimulate cell migration and thus was neither chemokinetic nor a chemotactic agent. However, cells exposed t o a dual concentration gradient of both TNF-alpha and CSF-1 did migrat e successfully, although the chemotactic response to CSF-1 was abolish ed.