CCL2 and infection: Consequently, with the release of chemoattractant molecules by resident cells, such as C-C motif chemokine ligand (CCL2)/MCP-1, there is an expressive migration of macrophages, neutrophils, natural killer (NK) cells and lymphocytes to the primary sites of infection (e.g., joints and muscles), leading to hypertrophy of synovial cells and adjacent synovial vessels [215], and subsequent joint pain in patients [115,216].