Immune cells constantly circulate in the body in search of pathogens or tissue damage. Because they move autonomously, immune cell trafficking must be tightly controlled and coordinated by extracellular cues. The main signals that guide immune cells are chemokines, small polypeptides that modulate the migratory behavior of cells. Remarkably, most chemokines are not only sensed but also secreted by immune cells, indicating that immune cells might either attract more of their own kind or trigger complex patterns of feedbacks between different cell populations. Such cascades might allow different immune cell types to orchestrate their sequential arrival at a site of infection (1). On page 1071 of this issue, Lim et al. (2) show that this is indeed the case with neutrophils and cytotoxic T cells, the former leaving a trail of cues for the latter to follow during the eradication of a viral infection.
