Abstract
We have infected ten‐day‐old primary cultures of human monocyte‐derived macrophages (MDM) with HIV‐1 by cocultivation with chronically infected monocytic cell lines. This work has involved the U‐937 monocytoid cell line, chronically infected with the HIV‐III~B~ strain of HIV‐1 (U‐937~HIV IIIB~) as well as a number of cell clones, termed UHC, which were derived from U‐937~HIV IIIB~ by limiting dilution. Cell‐free virus, derived from each of U‐937~HIV IIIB~ cells and the UHC1 clone were noninfectious for MDM, as determined by failure to express viral p24 antigen (Ag). In contrast, viral p24 Ag production was detected in MDM that had been cocultivated with U‐937~HIV IIB~, and with each of three UHC clones that produced infectious virus. Infection, in each case, was confirmed by polymerase chain reaction detection via the amplification of proviral DNA. In contrast, cocultivation with the UHC15.7 clone, which fails to cleave viral gp160 to its gp120 and gp41 products or the UHC8 clone, which lacks functional reverse transcriptase, did not lead to infection of MDM. Pretreatment of MDM for 2 hr with 1 μM AZT completely prevented infection by culture fluids containing HIV~ada'~ a macrophage‐tropic virus, but did not affect infection mediated by cocultivation. These results suggest that cell‐to‐cell transmission of HIV‐1, among monocyte‐derived macrophages, can be mediated by proviral DNA. Moreover, gp120 at the surface of infected cells may play an important role in this process, since cell‐to‐cell HIV transmission could not be demonstrated with the UHC clone that is defective in cleavage of the viral envelope glycoprotein gp160.