Consequently, given that eosinophils play an important part in airway inflammation in asthma and that interleukin-5 (IL-5) is the primary cytokine involved in eosinophil differentiation, activation and survival [13–16], therapies that target IL-5 provide a precision-medicine approach for severe asthma with an eosinophilic phenotype [17, 18]. Here, IL5 is linked to asthma.