Haptoglobin (Hp)-mediated chemotaxis is inhibited by blocking extracellular signal-regulated kinase (ERK)1/2 intracellular pathway. (a) Bar graph showing the effect of pretreatment with U0126 (10 min, 1 μM at 37°C, black bars), or bovine serum albumin (BSA) (1 mg/ml, white bars) on the capacity of U937 cells to migrate towards monocyte chemoattractant protein 1 (MCP1) (100 ng/ml) and Hp (0.1 and 0.5 mg/ml). Data are expressed as means ± standard error of the mean (SEM) of migrated cells for at least three experiments. Two-way analysis of variance (ANOVA) P < 0.001. Bonferroni post-test versus pretreatment with BSA ***P < 0.001. (b) As (a) using human primary monocytes. Two-way ANOVA P < 0.001. Bonferroni post-test versus pretreatment with BSA ***P < 0.001.