Differential inactivation of interferons by a protease from human granulocytes

Human leukocyte suspensions produced interferon-alpha (IFN-alpha) without induction during incubation at 37 degrees C. The highest titers were obtained at about 30 million cells/ml. The best yields, approximately 2 IU per 10(6) cells, were achieved in medium with or without albumin; serum inhibited the production. The uninduced IFN-alpha 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-alpha 1 was clearly more resistant to the enzyme than rIFN-alpha 2. Human IFNs-gamma from different sources exhibited striking differences in their sensitivity to the protease. Glycosylated natural IFN-gamma from human leukocytes and glycosylated rIFN-gamma from CHO cells were relatively resistant, whereas unglycosylated rIFN-gamma from Escherichia coli was rapidly degraded by the protease. The protease was inhibited by PMSF and by greater than or equal to 1% human or fetal bovine serum but not by EDTA or less than or equal to 1% human albumin. Its optimum pH was between 7 and 8. It was resistant to treatment for 30 min at 56 degrees C.