There are now two agents which bind IL5 (mepolizumab [15,16], reslizumab [17]), an anti-IL5 receptor antagonist (benralizumab [18]), and more recently an anti-IL4 a receptor antagonist which blocks IL4 and IL13 signalling (dupilumab [19]) approved for the treatment of asthma. Here, IL4 is linked to asthma.