Identification of a specific granular marker of zebrafish eosinophils enables development of new tools for their study

Eosinophils control many aspects of the vertebrate innate immune response. They contribute to homeostasis, inflammatory conditions and defense against pathogens, yet, their function in disease often remains enigmatic. The zebrafish has emerged as a useful model organism for human diseases but tools to study eosinophils in this model are severely limited. Here, we characterize a new and highly specific marker for eosinophils in zebrafish and report a new transgenic reporter line to visualize eosinophils in vivo. In addition, we created a polyclonal antibody that allows the identification of eosinophils ex vivo. These new tools expand the toolkit to study eosinophils in the zebrafish model. Using our tools, we have been able to identify the likely ortholog of eosinophil major basic protein, a critical mediator of eosinophil function, in zebrafish. These advances will allow for the investigation of eosinophil biology in the zebrafish model organism, allowing researchers to identify the contribution of eosinophils to the many diseases that are modeled within zebrafish and also shed light on the evolution of eosinophils within vertebrates.