Development of a baculovirus expression system for soluble porcine tumor necrosis factor receptor type I and soluble porcine tumor necrosis factor receptor type I-IgG fusion protein

Tumor necrosis factor-α (TNF-α) is a key mediator of inflammatory responses and gram-negative bacterial sepsis, but the role that it plays during Salmonella enterica species bacterial infections in swine has not yet been elucidated. To facilitate studies on the role of TNF-α on the pathology associated with Salmonella infections in pigs, recombinant soluble porcine TNF receptor type I (rspTNF-RI) and soluble TNF receptor type I fused to the Fc region of porcine IgG1 (rspTNF-RI-IgG) were expressed in insect cells using a baculovirus expression system. The proteins were secreted into the cell culture media and purified by anti-soluble porcine TNF-RI antibody and protein G affinity chromatography, respectively. The yield of protein using this method was approximately 1.5 mg rspTNF-RI and 4 mg rspTNF-RI-IgG/L of cell culture medium. In in vitro assays, rspTNF-RI-IgG was approximately 10-fold (0.97 vs. 10.00 pmol/ml) more effective than rspTNF-RI at completely inhibiting the cytotoxic activity of 500 U of recombinant porcine TNF-α on 3×104 WEHI 164 murine fibrosarcoma, clone 13, cells. Compared to previously described methods, this method yields significantly more biologically active rspTNF-RI.