CCL17 and asthma: Cytokines including interleukin 4 (IL-4), interleukin 5 (IL-5), IL-6, IL-8, interleukin 10 (IL-10), monocyte chemoattractant protein (MCP)-1/CCL2, and thymus and activation-regulated chemokine (TARC)/CCL17 trigger secondary inflammatory events, aggravating asthma pathogenesis.