During HIV-1/Treponema pallidum co-infection, compared with the healthy control group, the density of CX3CR1 was increased in all three monocyte subsets; the increase in CX3CR1 expression on monocytes indicates the presence of systemic inflammation during HIV-1/Treponema pallidum co-infection [80]. The gene discussed is CX3CR1; the disease is coinfection.