HIV-1 replication in HCs and MDMs. Since HCs appear to be primary targets for HIV-1 infection, we compared HIV-1 replication in HCs to MDMs. HCs (closed square) and MDMs (open square) infected by HIV-1BaLin vitro showed differences in HIV-replication over time. HIV-1 replication was measured in the cell supernatants by HIV-1 p24 viral antigen ELISA (A). HIV-1 release over time from HCs and MDMs was quantified as the percentage of p24 antigen in supernatants as a fraction of p24 antigen in supernatant plus cell lysate (B). Six days post infection, mRNA levels were measured by real-time PCR to determine fold-changes in env and gag transcription (C). Cell cytotoxicity was assessed by MTT assay (D). The ratio of optical density from infected cells to optical density from control cells reflected the percentage of surviving cells. Data shown are expressed as the mean ± SE of triplicate samples and are representative of 3 independent experiments from 10 different donors (**p < 0.01).