CCL13 (aka MCP4) is a monocyte chemoattractant that has been proposed as a biomarker of asthma because its levels were higher in plasma of (1) asthma patients vs. non-asthma controls and (2) asthma patients with acute exacerbations vs. stable asthma [37], and its receptor, CCR3, has been shown to induce migration of ASM cells in vitro [38]. This evidence concerns the gene CCR3 and asthma.