Confirmation of the PF-4 identity by immunocapture and immunodepletion. For immunocapture experiments, anti–PF-4 antibody was immobilized on a preactivated ProteinChip array, followed by incubation with platelet extracts derived from mice bearing the dormant clone of liposarcoma. Comparison of a profile generated by the recombinant PF-4 (first panel) with that generated by platelet lysates of dormant liposarcoma-bearing mice reveals an identical molecular weight and isoelectric point of the protein in question (second panel). Immunodepletion of the PF-4 protein is confirmed by the absence of its respective peak from the mobile phase (fourth panel).