PF4 directly stimulates VSMC cytokine production. (A) Dose response. VSMCs were treated with PF4, and IL-6 levels were measured by ELISA (n = 4 ± SD; *P < .01 vs 0). (B-C) LRP1 inhibition attenuates PF4-mediated cytokine production. HCASMCs were treated with (B) control GST or GST-RAP (15 µg/mL), or (C) control IgG or LRP1-blocking antibody (25 µg/mL), before overnight incubation with PF4 (1 µg/mL). IL-6 and IL-8 in the supernatant were measured by ELISA (n = 3 ± SD; *P < .01).