Binding of PF4 to the surface of monocytes with and without coincubation of RANTES. Monocytic MM6 cells were left untreated (A), incubated with PF4 (B), or were coincubated with RANTES and PF4 (C). Chemokines were applied for one hour at room temperature (5 μg/mL), formaldehyde fixed, and subsequently stained with an anti-PF4 antibody (solid line) or isotype control (filled) and analyzed by flow cytometry. MM6 cells were preincubated with chondroitinase ABC (0.5 U/mL) for one hour (empty bars in D). Mean fluorescence of isotype control binding was subtracted from PF4 antibody binding and expressed as mean specific fluorescence (D). Data represent mean ± SEM of 5 independent experiments (*P < .05 vs PF4).