HIV binding to PBMC is variable between donors. (A) Freshly isolated PBMC (3 × 106) were incubated with HIVTH (2000 pg of p24) in serum-free RPMI-1640 medium for 45 minutes on ice. After incubation with HIV, cells were washed to remove unbound virus. Cells were pelleted, lysed and HIV p24 was measured by ELISA. Shown are values from 19 different healthy PBMC donors. (B) HIVTH was bound to freshly isolated or PHA-stimulated donor PBMC. For virus binding to freshly isolated PBMC, HIV p24 was measured by ELISA as described above. HIV replication of donor PBMC was assessed by p24 ELISA after 5 days of culture. (C) HIVTH was bound to freshly isolated PBMC either in the presence of anti-CD4, isotype control antibody, or in the absence of antibody. Cell-bound virus was measured as described above. Results are the means ± SD of triplicate determinations.