For example, novel anti‐ferret CD4‐, CD8‐ and CD5‐specific antibodies were derived by immunising mice with the CD4 ectodomain,107 whole CD4 protein108 or ferret thymocytes.83 Efforts to develop novel antibody‐based reagents to define various ferret immune cell subpopulations are accelerating, particularly through the Centers of Excellence for Influenza Research and Surveillance (CEIRS) network,109 and are reviewed in detail further below. This evidence concerns the gene CD4 and influenza.