Expression of human thyroid peroxidase in insect cells using recombinant baculovirus

The baculovirus expression system was used to overexpress recombinant human thyroid peroxidase. Sf-9 cells infected with the recombinant virus AcMNPV-hTPO synthesized hTPO protein (hTPO-bac) immunogenic on Western blots when probed with either rabbit anti-TPO peptide sera or pooled human anti-TPO sera (MS12/89). hTPO-bac was a major constituent of the membrane fraction from the infected cells, constituting 14.9% and 10.1% of the 1% deoxycholate-soluble and insoluble fractions, respectively, as judged by densitometry. Recombinant hTPO-bac was extracted from cellular membranes with 1% deoxycholate and partially purified by Sepharose 6B column chromatography. Specific immunoreactivity of MS12/89 to hTPO-bac on microtiter plates was seen using ELISA. Detergent extract from wild-type virus-infected Sf-9 cells was used as background control antigen; no specific reactivity to either hTPO-bac or control antigen was seen with control sera. To determine antigenic potency, MS12/89 was incubated with increasing concentrations of various preparations of hTPO antigen and with ovalbumin as control. The capacity of the partially purified hTPO-bac to immunoneutralize human anti-hTPO standard at 50% inhibition of binding was 0.01 U/μg hTPO-bac (NIBSC Units), compared with 0.5 U/μg and 0.06 U/μg for natural hTPO and CHO-hTPO, respectively. When ELISA was performed using clinical samples of human sera to detect hTPO autoantibodies, results using hTPO-bac correlated well with those using hTPO from Graves' thyroid tissue (r = 0.85, p = 0.02) and those using recombinant hTPO from Chinese hamster ovary cells (hTPO-CHO) (r = 0.85, p = 0.02). These data demonstrate that recombinant hTPO-bac is reactive with human autoantibodies and can be produced in large quantities in a baculovirus expression system.