Figure 6

Haptoglobin (Hp) induces chemokine (C-C motif) receptor 2 (CCR2) internalization. U937 cells and primary monocytes were incubated for 60 min at 37°C, 5% CO₂ with increasing concentrations of Hp or monocyte chemoattractant protein 1 (MCP1) as positive control. The relative surface expression of CCR2 was determined by flow cytometry after staining with monoclonal antibodies to the chemokine receptor. (a) Bar graph showing the relative mean fluorescence on U937 cells. The dark-striped white bar shows CCR2 expression on U937 cells without treatment. The white bar indicates the percentage of receptor present on the surface after incubation with MCP1 (10 μg/ml) and the black bars indicate the percentage of receptor present on the surface after incubation with Hp at the indicated concentrations. (b) Bar graph showing the relative mean fluorescence on primary monocytes. The dark-striped white bar shows CCR2 expression on U937 cells without treatment. The white bar indicates the percentage of receptor present on the surface after incubation with MCP1 (10 μg/ml) and the black bars indicate the percentage of receptor present on the surface after incubation with Hp at 8.7 μM. Data are expressed as means ± standard error of the mean (SEM) of three independent experiments. Student t test on the effect of treatment versus control: *P < 0.05; **P < 0.01; ***P < 0.001.