Flow cytometric analysis of CXCR4 internalization upon CXCL12 stimulation. Blood samples from WHIM patients and controls were placed at 37°C and incubated with or without addition of CXCL12 (1000 ng/mL). After 15 minutes, the samples were cooled in ice and CXCR4 expression evaluated by flow cytometry using anti-CXCR4 antibody. (A) Difference between CXCR4 mean intensity of fluorescence (on lymphogate) before stimulation (100%, bold line) and after CXCL12 stimulation (thin line). Filled black histograms indicate isotype control fluorescence. (B) Percentages of CXCR4 internalization in controls (C1, C2, C3; □) and WHIM patients (P2, P3; ▪). Error bars indicate SD. (C) Time course of CXCR4 internalization: control 1 (○) and patient P3 (•). Shown is 1 representative experiment of 2 performed.