Interestingly, the heterogeneity was dramatically reduced or disappeared from the Caucasian subgroup after ethnicity subgroup analysis, and the subgroup pooled results showed an increased risk of asthma with MCP-1 -2518 G polymorphism in the Caucasian population, a protective effect for MCP-1 -2518 G polymorphism in the African population under the dominant model, and no significant association in the Asian population. Here, CCL2 is linked to asthma.