Neutrophils (red) and monocytes (green) entering an area of tissue damage.

This representative video shows the immediate response of fast-migrating neutrophils (small red cells) towards a focal tissue damage site, while monocytes (green) migrate with slower speeds and follow the developing neutrophil cluster with delay.

–Neutrophil swarms require LTB4 and integrins at sites of cell death in vivo
Tim Lämmermann et al
Nature 498, 371–375 doi:10.1038/nature12175

(See also When Neutrophils Attack)