The expression in Escherichia coli of recombinant human platelet factor 4, a protein with immunoregulatory activity.

In order to establish more firmly the immunoregulatory effect of platelet factor 4 (PF4) and develop a means to provide material for possible clinical use, the nucleotide sequence for PF4 was synthesized utilizing a ligation strategy of six duplexes ranging from 27 to 43 base pairs in length. The individual oligodeoxynucleotides were synthesized on an automated system. The resultant gene segment (226 base pairs), which incorporated convenient HindIII and BamHI overhangs at the 5' and 3' ends, respectively, was cloned into the pIN-III-ompA-2-expression vector in Escherichia coli, affording a fusion protein of Mr = 8900 with 7 additional amino acids at the amino terminus and 4 at the carboxyl terminus and with aspartic acid rather than asparagine in position 47. The recombinant PF4 (rPF4) was purified by heparin-agarose affinity chromatography and reverse-phase high performance liquid chromatography. It reacted with a monoclonal mouse anti-human PF4 antibody on a Western blot and in an enzyme-linked immunosorbent assay. The rPF4 protein exhibited an immunoregulatory effect like that of human PF4 in its ability to reverse concanavalin A-induced immunosuppression in BALB/c mice.