A deep knowledge of EGPA pathogenesis allows the identifications of new targets for drug use: the emerging role of eosinophils and the Th2 interleukins (ILs) activation pathway led the way to the identification of new therapies targeting eosinophils biology, such as the anti-IL-5 mepolizumab; the role of B cell compartment in EGPA has not been completely cleared, but the anti-CD20 monoclonal antibody rituximab has been extensively studied in the others AAV and its use in EGPA is currently under investigation. The gene discussed is IL5; the disease is eosinophilic granulomatosis with polyangiitis.