rTat and VEGF-A₁₆₅ activate human monocytes through the same receptor. (A) Homologous and heterologous desensitization of monocyte migration by rTat (□), VEGF-A₁₆₅ (▪), and FMLP (▨). Monocytes were preincubated with optimal chemotactic concentrations of the agonists (10 ng/mL rTat, 10 ng/mL VEGF-A₁₆₅ , and 10 nmol/L FMLP) at 37°C for 30 minutes. The cells were then washed and assayed for their migration toward homologous of heterologous stimuli used at the same concentrations. Results are expressed as percent of activity with respect to relative control group (cell incubated with medium and tested against the 4 single agonists). The mean numbers (±SE) of three separate experiments performed in triplicate are reported. (B) Monocyte migration by optimal chemotactic concentrations of the agonists (10 ng/mL rTat and 10 ng/mL VEGF-A₁₆₅ ) was evaluated in the absence or in the presence of 210 ng/mL sFlt-1. Results (mean ± SD) of one experiment (performed in triplicate and representative of at least 3 independent experiments) are shown. In the same experiment, migration to an optimal concentration (10 nmol/L) of FMLP was 114 ± 7 monocytes. *P = .05 or lower versus rTat or VEGF-A₁₆₅ .