KINETICS OF HIV-INFECTION OF HUMAN PLACENTAL SYNCYTIOTROPHOBLAST CULTURES - AN ULTRASTRUCTURAL AND IMMUNOCYTOCHEMICAL STUDY

We previously demonstrated that syncytiotrophoblast (ST) cells from term human placentas could be infected when cocultured with HIV-infected lymphocytic cells, Here, we have used fluorescence microscopy and transmission electron microscopy to examine the kinetics of this infection process, Molt-4 clone 8 cells infected with HIV-1(Lai) or filtered supernatant from these cultures were incubated with ST cells for different times, In cell-associated infection, immunofluorescence microscopy revealed that some ST colonies were positive for HIV core proteins (p24,p55) after 1 hr, The number of positive colonies and the intensity of the ST-associated fluorescence increased with time, Transmission electron microscopy showed viral particles with HIV morphology associated with the ST cell surface at 1 hr, Immature virions with budding morphology were observed at 2 hr, In cell-free infection, positive p24,p55 staining was first detected in a few ST colonies at 4 hr, The number of positive colonies increased with time, At 24 hr, the fluorescence pattern and intensity resembled that seen with cell-mediated infection at 4 hr, Transmission electron microscopy revealed an increasing number of viral particles associated with the ST cell plasma membrane with respect to time, and budding virions first appeared at 8 hr, These results demonstrate that HIV infection of placental ST cells proceeds very rapidly in culture and that, furthermore, cell-associated infection of ST is much more efficient than the infection with cell-free virus.