CCL2 and neoplasm: More specifically, CHI3L1 binds and signals through its cognate receptor IL13Rα2 on macrophages to induce tumor-promoting M2 polarization [35, 36, 39, 53], enhance PD-L1 expression on the macrophage surface [39] and stimulate production of pro-inflammatory factors MIP-2 and MCP-1 [20], respectively attracting neutrophils and additional macrophages to the TME for immunosuppression.