Representative images from confocal microscopy using rhodamine-phalloidin to delineate F-actin.

Neutrophils isolated from circulating blood (A) were spherical, and the small amount of F-actin was located within the central regions of these cells. Occasional neutrophils showed pseudopod formation and contained F-actin within these pseudopods. On stimulation with fMLP (B), their shape became markedly distorted, with numerous pseudopods and irregularities to the plasma membrane. F-actin was no longer observed within the central regions of the neutrophils. Increased amounts of F-actin were present in the submembrane region, forming a shell beneath the membrane. Quiescent neutrophils isolated from the BM (C) were spherical. The amount of F-actin was greater than in the quiescent neutrophils isolated from the circulating blood. Although these cells contained a small amount of F-actin in the central regions, similar to the circulating neutrophils, the increase in F-actin was located primarily in the submembrane region. Stimulation of BM neutrophils with fMLP (D) induced only small changes in shape that were minimal compared with those observed in the circulating blood. As in the circulating neutrophils, the BM neutrophils showed a marked increase in F-actin within the submembrane region and no identifiable F-actin within the central region. n = 3 rats in each group.