We hypothesised that increased cxcl12 expression provides more ligand, by heterodimerisation with Ccl2, also known as monocyte chemoattractant protein-1 (Mcp-1), for the recruitment of Ccr2-positive (Ccr2+) permissive or non-bactericidal macrophages to sites of infection (Cambier et al, 2014, 2017). Here, CXCL12 is linked to infection.