Differential Inactivation of Interferons by a Protease from Human Granulocytes

Abstract

Human leukocyte suspensions produced interferon-α (IFN-α) without induction during incubation at 37°C. The highest titers were obtained at about 30 million cells/ml. The best yields, ∼2 IU per 10⁶ cells, were achieved in medium with or without albumin; serum inhibited the production. The uninduced IFN-α peaked at 24 h. The titers dropped on further incubation due to release of a protease from polymorphonuclear cells. The protease inactivated all tested human class I IFNs, but recombinant IFN-α_, was clearly more resistant to the enzyme than rIFN-α₂. Human IFNs-γ from different sources exhibited striking differences in their sensitivity to the protease. Glycosylated natural IFN-γ from human leukocytes and glycosylated rIFN-γ from CHO cells were relatively resistant, whereas unglycosylated rIFN-γ from Escherichia coli was rapidly degraded by the protease. The protease was inhibited by PMSF and by ≥1% human or fetal bovine serum but not by EDTA or ≤1% human albumin. Its optimum pH was between 7 and 8. It was resistant to treatment for 30 min at 56°C.