A factor released by monocytes in the presence of dexamethasone stimulates neutrophil locomotion.

1. Steroid-treated monocyte supernatants cause a dramatic increase in the speed of locomotion of human neutrophils and a significant decrease in their adhesion to protein-coated glass. In contrast, control monocyte supernatants have a smaller effect on the speed of locomotion, but cause a large increase in their adhesiveness. 2. This supernatant activity was produced equally well in the presence or absence of serum after 24 h culture at 37 degrees C with 10(-6) M dexamethasone. 3. The effect of the steroid-treated monocyte supernatants on the speed of locomotion of human peripheral blood neutrophils was not altered by rabbit polyclonal antisera against lipocortins 1-6. 4. Rabbit anti-interleukin-8 antibody which blocked the effect of IL-8 on the speed of locomotion of neutrophils did not antagonize the locomotion stimulating action of steroid-treated monocyte supernatants. 5. The exocellular release of this factor(s) by human mononuclear leucocytes suggests that it may be an in vivo mediator of the anti-inflammatory effect of glucocorticoids.