EXPRESSION OF ANTICARDIOLIPIN COFACTOR, HUMAN BETA-2-GLYCOPROTEIN-I, BY A RECOMBINANT BACULOVIRUS-INSECT CELL SYSTEM

A full-length cDNA coding a human beta2-glycoprotein I (beta2-GPI) was introduced into the baculovirus genome to construct a recombinant bac ulovirus. Spodoptera frugiperda (Sf 9) cells were infected with the re combinant baculovirus. A protein (mol. wt 43 000) reactive with anti-b eta2-GPI antisera was produced in the insect cells and secreted into t he culture medium. The recombinant beta2-GPI was purified from the cul ture supernatant by sequential cardiolipin (CL)-affinity column chroma tography and gel filtration. The N-terminal amino acid sequence of the protein was identical to that of the native beta2-GPI purified from h uman sera, and a putative signal peptide was cleaved from the secreted form of the recombinant protein. The purified recombinant protein had a cofactor activity which enhances CL binding of anticardiolipin anti bodies (aCL) in systemic lupus erythematosus (SLE) patients, as well a s the native beta2-GPI. Thus, the beta2-GPI expressed in insect cells is an immunologically active cofactor.