CX3CL1 and its receptor CX3CR1 were discovered more than twenty years ago [10,11,12], and a large amount of evidence has emerged linking the CX3CL1–CX3CR1 axis to various diseases, such as atherosclerosis [13], allergic diseases [14], neurodegeneration [15], and cancers [16,17]. The gene discussed is CX3CL1; the disease is allergic disease.