MCP-2 and MCP-3 are two recently identified monocyte chemotactic proteins produced by human MG-63 osteosarcoma cells. Both MCP-2 and MCP-3 are members of the C-C family of chemokines and share 62% and 71% amino acid sequence identity, respectively, with MCP-1. MCP-3 also shares 58% amino acid identity with MCP-2. Similarly to other C-C chemokines, all three MCP proteins are monocyte chemoattractants. In addition, the three MCPs can chemoattract activated NK cells as well as CD4+ and CD8+ T lymphocytes. All three cytokines have also been shown to attract eosinophils and induce histamine secretion from basophils.