279 R5 but Not X4 Primary Viral Isolates of HIV-1 Can Localize Their cDNA to the Nucleus in Monocyte Derived Macrophages J. W. Choi*, I. A. Teo, S. Shaunak Imperial Coll, London, UK
Background: Monotropic HIV-1.R5 isolates can productively infect monocyte derived macrophages. However, this seems to occur sporadically when monotropic HIV-1.X4 isolates are used. Therefore, we have used several monotropic X4 isolates to determine whether they can productively infect monocyte derived macrophages as measured by quantitative HIV-1 cDNA synthesis and by p24 antigen production.
Methods: Five (5)-day old monocyte derived macrophages (CD4+, CD14+, CD68+, CD11c+, HLA-DR+) were infected with low passage R5, X4, or R5X4 CD11c+ primary viral isolates of HIV-1. DNA was harvested at an early and a late time point. Quantitative LIghtCycler based PCR assays were performed and were used to measure the early RU5 cDNA transcript, the late gag cDNA transcript and integrated HIV-1 cDNA. Nuclear localization of the pre-integration complex was determined by measurement of HIV-1 2-LTR circles. P24 antigen production was measured with a Coulter EIA.
Results: At 24 h post-inoculation, the RU5 and the gag transcripts were detectable for all of the viral isolates studied. HIV-1 2-LTR circles were found after infection with R5 and R5X4 viruses. However, HIV-1 2-LTR circles were not detected at any time after inoculation with monotropic X4 viruses. P24 antigen production was detectable for the R5 and R5X4 viruses by day 14 but not for the X4 viruses.
Conclusions: Viruses that can only use the X4 co-receptor can gain entry into monocyte derived macrophages. Reverse transcription was initiated and linear cDNA synthesized, but nuclear localization of the HIV-1 cDNA pre-integration complex did not occur as indicated by the absence of the HIV-1 2-LTR circles. This block was overcome by those X4 viruses that had acquired the capacity to also use the R5 co-receptor (e.g., R5X4 phenotype).
