CCL2 and arthritic joint disease: Using complementary reporter mouse models, CCL2mCherry to label CCL2-producing cells, and CCR2CRE/mKate2 marking CCR2 expressing monocytes, we demonstrated that RELMα-positive perivascular macrophages secrete CCL2 assisting in the recruitment of monocytes predominantly to the synovial interstitium at the onset of antigen-induced arthritis.