Colony-forming units adhere to immobilized PF4. Attached to the bottom of separate triplicate plastic tissue culture wells and then washed were 10 μg/mL PF4, 10 μg/mL poly-L-lysine, and 5% albumin. CD34⁺-enriched cells (10 000) were suspended in IMDM and incubated in wells with bound ligands for 2 hours at 37°C. Nonadherent cells and adherent cells were separated and plated in short-term methylcellulose cultures. E indicates burst forming units–erythrocytes; GM, colony-forming units–granulocytes macrophages; and GEMM, mixed colonies. Error bars represent SEMs.