Comparative analysis of circulating CX3CL1 and CCL2 levels. Serum samples from Cx3cr1^−/−, Ccr2^−/−, and Cx3cr1^−/−Ccr2^−/− double-knockout mice were assayed by ELISA for the presence of CX3CL1 and CCL2, and results are shown in the left y-axis (open symbols) and right y-axis (filled symbols), respectively. Bars show mean value with 95% confidence interval (CI) of chemokine in pg/mg of protein. Each point represents an individual mouse.