Expression of anticardiolipin cofactor, human β2-glycoprotein I, by a recombinant baculovirus/insect cell system

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Abstract
A full‐length cDNA coding a human β2‐glycoprotein I (β2‐GPI) was introduced into the baculovirus genome to construct a recombinant baculovirus. Spodoptera frugiperda (Sf9) cells were infected with the recombinant baculovirus. A protein (mol. wt 43000) reactive with anti‐β2‐GPI antisera was produced in the insect cells and secreted into the culture medium. The recombinant β2‐GPI was purified from the culture supernatant by sequential cardiolipin (CL)‐affinity column chromatography and gel filtration. The N‐terminal amino acid sequence of the protein was identical to that of the native β2:‐GPI purified from human 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 antibodies (aCL) in systemic lupus erythematosus (SLE) patients, as well as the native β2‐GPI. Thus, the β2‐GPI expressed in insect cells is an immunologically active cofactor.