To gain more insight into the possible reasons for the differential permissivity to HIV-1 infection observed in our study, we examined M-CSF-derived MDM from three donors that were fractionated into Siglec-1LoCD4−MDM and Siglec-1hiCD4+MDM, in the absence or presence of HIV-1 for 3 h. The gene discussed is CSF1; the disease is HIV-1 infection.