CCL22 and asthma: M2a macrophages expressing CD206 and MHCII are associated with asthma severity, and M2a macrophages expressing CCL17 and CCL22 induce the activation of T helper type 2 cells and initiate the infiltration of eosinophil in the lungs by secreting high levels of IL-5 and IL-13 [59, 60].