A schematic model of complex formation between PF4 and nucleic acids is shown. (A) The basic amino acid residues (+) in the PF4 tetramer interact with the negatively charged phosphate groups (−) in double-stranded nucleic acids, thereby forming large multimolecular complexes. (B) PF4 binds to the negatively charged sulfate groups (−) on both sides of the heparin molecule, resulting in the formation of large multimolecular complexes. (C) Due to their high flexibility, single-stranded nucleic acids potentially wrap around PF4 tetramers, thereby inhibiting the formation of large, multimolecular complexes with PF4.