XCL2 and neoplasm: Studies using animal models have shown that CD163-positive macrophages have more pro-tumor functions than CD163-negative macrophages [33] and that CD163-mediated macrophage activation is linked to the secretion of pro-tumor cytokines, such as interleukin (IL)-6 and chemokine (C-X-C motif) ligand 2 (CXCL2) [34].