To investigate this issue, we performed infection of primary human monocyte-derived macrophages (MDMs) with individual HIV-1 or HIV-2 strains and compared the levels of M-CSF, a cytokine shown to promote HIV-1 infection and replication in our previous studies, and CXCL7, a chemokine identified as being expressed at levels correlated with HIV type by our preliminary gene-expression analysis. The gene discussed is CSF1; the disease is infection.