Macrophages and neutrophils have important roles in the immune response to invading pathogens and contribute to pathogen clearance. However, the interplay and interactions between these leukocytes is not fully understood. On page 3385, Marcel Schaaf and colleagues use a combination of time-lapse confocal laser-scanning and 3D block-face electron microscopy in a zebrafish model for tuberculosis, a local Mycobacterium marinum infection in the tissue of the larval tail fin. This model is particularly valuable as it mimics infection within the tissue context and makes it possible to visualise the early infection steps from bacteria uptake by the phagocytes to the formation of granuloma. By tracking neutrophils and macrophages over time, the authors find that neutrophils phagocytose the mycobacteria and, as they are highly mobile, contribute to their dissemination. Subsequently, macrophages are highly involved in efferocytosis, the phagocytosis of dead, infected macrophages and neutrophils, which results in phagocytic cells with large bacterial aggregates. Bacteria can then be released through a detrimental necrosis-mediated bursting of macrophages or, as shown here for the first time, be extruded by the epithelium after macrophage death, which reduces bacterial burden. Taken together, the findings reported here not only highlight the differing roles of neutrophils and macrophages during initial Mycobacterium infection, but also provide new details of the ultrastructure of infected leukocytes.

• © 2016. Published by The Company of Biologists Ltd