The major population of PHA-stimulated PBMC infected by R5 or X4 HIV variants after a single cycle of infection is predominantly composed of CD45RO + CD4 + T lymphocytes

Summary. PHA-stimulated peripheral blood mononuclear cells (PBMCs) are widely used for investigating replication and neutralization of HIV primary isolates in vitro . The objective of this study was to identify the T lymphocyte subset(s) that are found infected after one replication cycle by either R5- or X4-HIV-1 variants in PHA-stimulated PBMCs from healthy donors. Infected T lymphocytes were detected by intracellular p24 staining and characterized by cell surface immunophenotyping using flow cytometry. The predominant lymphocyte subset expressing p24 after 24 h of infection with either R5 or X4 HIV-1 strains was found to exhibit mainly the memory CD45RO phenotype, a greater percentage of CD62L + CD45RO + central memory T lymphocytes was infected with X4 HIV strains. Although some CD45RA + lymphocytes were also infected, these cells co-expressed CD45RO + . The proportion of lymphocytes expressing CD4 and CD4/CD45RO decreased by 20% after 24 h of infection. A 2-fold decrease of CD4 + CD8 + T lymphocytes could also be recorded, even though this subset accounted for less than 5% of total lymphocytes in control cultures. Moreover, CD4 + CD8 + T cells further decreased by 90% after 4 days of infection, a time at which they scored p24 + . Therefore, our results indicate that the in vitro infection system of PHA-stimulated PBMC utilized in neutralization assays provides an appropriate model for the study of infected CD45RO + lymphocytes but not CD45RA + lymphocytes.