PF-4 is a CXC chemokine that is expressed in megakaryocytes and stored in the α-granules of platelets. PF-4 is chemotactic towards neutrophils and monocytes and has been shown to inhibit angiogenesis. Recombinant human PF-4 is a 7.8 kDa protein containing 70 amino acid residues, including the four highly conserved residues present in CXC chemokines.