In particular, since the MCP-1/CCR2 axis has also been recently found to be involved in cell-mediated clearance of treponemal infection [37, 38], we speculate that CMV-mediated altered recruitment and function of monocytes/macrophages via the MCP-1/CCR2 axis may in turn affect the early immune response to Treponema pallidum and therefore increase the probability of acquisition of this pathogen. Here, CCR2 is linked to Treponema infectious disease.