We study the progressive emergence and functional traits of the innate immune system in vertebrate development, using the assets of a small tropical freshwater fish, the zebrafish, to address questions that are difficult to approach in mammals. The full transparency of zebrafish embryos and swimming larvae notably allows us to image cell behaviours in vivo at high resolution, in a totally non invasive manner. We study the successive developmental waves of hematopoiesis that ultimately give rise to the deployment of resident leukocytes in the tissues. Then among these leukocytes, we investigate the respective roles, behaviour, and mechanisms of chemoattraction of the professional phagocytes, macrophages and neutrophils, both in the uninfected organism and upon encounter of commensal or potentially pathogenic microbes. Finally we study the host response to viral infections in real time, to learn how a viral infection propagates in the organism, and which cellular and molecular defences the latter mobilizes to contain or eradicate the virus.
In the above video, a global view is followed by a close-up on the skin, then a progressively deeper focus shows the blood cells underneath – namely circulating proerythrocytes and macrophages.