Isolation of a Biologically active fragment of human alpha interferon.

When treated with pepsin under limited digestion conditions, human leukocyte-derived alpha interferon (HulFN-alpha) is partially inactivated. While the initial HulFN-alpha preparation is about equally active on human and on bovine cells, the residual antiviral activity of HulFN-alpha after pepsin treatment is significantly more active on bovine cells than on human cells. Furthermore, pepsin-treated HulFN-alpha, when assayed on bovine cells, yields an active production which is smaller and antigenically distinguishable from the native forms of HulFN-alpha.