Zebrafish cells with the propensity to give rise to tumours behave similarly to wounded tissue, and call for assistance from the immune system. So say Paul Martin at the University of Bristol, UK, and his colleagues, who imaged the interactions between the cells in real time.

The authors expressed a cancer-associated mutant form of the Ras protein in zebrafish (Danio rerio). Because zebrafish larvae are translucent, the team was able to visualize fluorescently labelled immune cells as they responded to the transformed cells.

Cells expressing mutant Ras, and their healthy neighbours, released hydrogen peroxide, attracting immune cells called neutrophils and macrophages, which tethered themselves to the transformed cells. Blocking hydrogen peroxide synthesis — and so the recruitment of the immune cells — slowed the proliferation of transformed cells, suggesting that early immune responses may support tumour development.

PLoS Biol. 18, e1000562 (2010)