Since Arg1 is a prototypic marker for M2 activation and IL-4 may induce macrophage differentiation to M2 phenotypes in asthma [37, 48], the consistency regarding these findings between lung tissues and cells supported the consideration that M2 polarization could be of particular importance in the Th2 pathology asthma since IL-4 is a key cytokine in the development of allergic inflammation [44, 49]. The gene discussed is ARG1; the disease is asthma.