CCL12 is a cloned mouse CC chemokine most closely related to human MCP-1 (66% amino acid (aa) sequence identity in the mature protein). Mouse CCL12 encodes a 104 aa residue precursor protein with a 22 aa residue predicted hydrophobic signal sequence that is cleaved to generate a 82 aa residue mature protein. CCL12 is expressed constitutively in the thymus and lymph nodes. Under inflammatory conditions, CCL12 expression is also induced in activated macrophages and mast cells. At high concentrations, CCL12 will also chemoattract eosinophils. CCL12 has been found to be a functional ligand for CCR2 but not CCR1, CCR3, or CCR5.