CCL2 and complex regional pain syndrome: However, an animal model of CRPS that used the transfer of purified serum immunoglobulin G (IgG) from human patients with longstanding CRPS into mice (in addition to plantar skin and muscle incision) showed that MCP-1 concentrations in the paw skin were increased from 1 to 3 days following injury, as in the current study, but were normalized at 6 and 13 days after model induction (Helyes et al., 2019).