Dispersive locomotion of human neutrophils in response to a steroid-induced factor from monocytes

A monocyte-derived factor that stimulates the locomotion of human neutrophils on an albumin-coated glass surface has been prepared from the culture supernatant of dexamethasone-treated human monocytes and called STMS (steroid-treated monocyte supernatant). A modified cell tracking program has been developed and the parameters of locomotion determined by the analysis of Gail and Boone for cells moving in a persistent random walk. Cells moving in uniform concentrations of STMS, interleukin-8 (IL-8) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) chosen to give a sub-maximal speed of locomotion show persistent, random and constrained random diffusion, respectively, with augmented diffusion coefficients of 0.8±0.1, 0.14±0.02 and 0.12±0.03 μm2 per second for STMS, IL-8 and fMLP, respectively. The augmented diffusion coefficient and the underlying persistence are therefore sensitive quantitative assay parameters for STMS activity and the qualitative characteristics of locomotion allow STMS activity to be distinguished from that of all other factors tested. The contribution of lowered adhesion to locomotion was examined in a novel tilt-assay, which demonstrated that cells in the presence of STMS, but not other factors, moved down slope with significantly increased speed while maintaining contact with the substratum. The results were interpreted in terms of the bipolar form of STMS-treated cells, contrasting with multipolar forms in response to other agents. This together with low adhesiveness plus an inherent tendency of a single locomotor focus to continue motion in its original direction has been used to explain the difference between response to STMS and other factors. STMS has been proposed either to prevent directed locomotion of neutrophils to an inflammatory site or to promote dispersive locomotion away from such a site and perhaps to inhibit neutrophil transmigration between endothelial cells.