CCL2 and infection: Mammary epithelial cells (MECs) recognize bacterial components through pattern recognition receptors, including toll-like receptors (TLRs), and produce pro-inflammatory cytokines, such as interleukin 6 (IL-6), tumor necrosis factor α (TNFα), and IL-1β, as well as the chemokines C-X-C motif chemokine ligand 1 (CXCL1) and C-C motif chemokine ligand 2 (CCL2)9, which recruit other immune cells to the infection sites to ultimately eliminate bacteria10,11.