Julien Resseguier is a spatial immunologist interested in the spatial dynamics of immune responses with a particular emphasis on the branchial cavity lymphoid architecture of fish and nanomedicines. He completed his PhD in 2017 at the University of Lyon using the zebrafish model to study therapeutic nanoparticles. He then did a postdoc at the University of Oslo with Professor Gareth Griffiths studying the cell biology aspect of nanomedicines using fish models of human diseases. At the same time, Julien initiated his own research characterizing the spatial organization of the fish immune system using advanced microscopy techniques. After his postdoc, Julien worked as a researcher for 6 months with Professors Finn-Eirik Johansen and Shuo-Wang Qiao at the University of Oslo, studying the cod immune system. Both professors then hosted him as a guest-researcher for 1,5 years, allowing him to continue his own research project on fish immunology. Recently awarded a competitive Young Research talent grant from the Research Council of Norway, Julien is now a group leader within the comparative immunology group at the department of biosciences at the University of Oslo.

Using 3D high-resolution imaging, Julien and collaborators characterized the lymphoid organization of zebrafish gills, identifying the Amphibranchial lymphoid tissues (ALT) on the side of gill arches. More recently, they revealed the existence of the Nemausean Lymphoid organ (NELO), a lymphoid organ in the branchial cavity that is reminiscent of mammalian tonsils, in a study published in Science Advances.  In addition, Julien enthusiasm for the artistic aspect of microscopy to feature the use of fish models in research received several awards from the Nikon Small World competitions in 2022.