Thus the addition of CXCL-1, IFN-γ, IL-5, IL-17A, EGF, eotaxin, IL-lβ, IL-4, IL-12p40, IL-13, and MDC serum concentrations to blood eosinophils and neutrophils adds significant value to the definition of the Difficult-to-Control asthma endotype. This evidence concerns the gene IL4 and asthma.