Animals
CCR2 knockout (KO) mice on C57BL/6 (B6) background were purchased from Jackson laboratory (Bar Harbor, ME, USA). Wildtype (WT) C57BL/6J (CD45.2+ and CD45.1+) mice were purchased from Charles River (Beijing, China). CCR2 KO mice displayed a stable phenotype based on sufficient backcrossing with B6 mice. Mice were bred and placed in a specific-pathogen–free animal department. Male and female mice between 2-6 months old were used for the experiments. All studies were conducted in a non-blinded fashion. Animal experimentation was reviewed and approved by the Institutional Animal Care and Ethics Committee of Animal Experimentation of Tongji Medical College.