In vivo T lymphocyte origin of macrophage-tropic strains of HIV: Role of monocytes during in vitro isolation and in vivo infection

Previously published isolation techniques with T cell blasts and monocyte-derived macrophages (MDM) were used to recover HIV from the PBMC of a group of 23 asymptomatic seropositive individuals. Viral isolation was more readily accomplished by MDM coculture resulting in 9 isolates being obtained exclusively by this method (macrophage tropic strains). To determine the in vivo cellular source of these isolates we separated PBMC from 5 of these 9 patients into T lymphocyte and monocyte fractions by flow microfluorometry. These fractions were then analyzed by polymerase chain reaction (PCR) for the presence of HIV-1 proviral DNA. In 4 out of these 5 patients HIV-1 proviral DNA could be detected exclusively in T lymphocytes but not in monocytes, although the virus could be isolated only by MDM coculture. In the remaining patient HIV could be amplified in both T lymphocytes and monocytes. Further phenotypic analysis revealed that, among T lymphocytes, only the CD4⁺ subset was infected with HIV. We conclude that among PBMC the most common in vivo source of HIV strains which preferentially infect macrophages in vitro is the CD4⁺ T lymphocyte. These data also suggest that the macrophage tropism characteristic of some HIV strains reflects predominantly an in vitro phenomenon.