Complex kinetics of binding of human alpha-2 interferon to human, but not bovine cells

Human alpha-2 interferon (HuIFN-alpha 2) is an effective antiviral agent for bovine cells, but does not inhibit the proliferation of these heterologous cells. A comparison of the kinetics of binding of 125I-HuIFN-alpha 2 at 4 degrees C to several bovine and human cells, shows that the kinetics of the initial receptor interactions are very different in the two species. Binding of HuIFN-alpha 2 to bovine cells follows the simple kinetics predicted for one species of ligand interacting with one type of high-affinity receptor. The kinetics of binding to human cells showing a range of sensitivities to the antigrowth effect are complex and indicate that receptor occupancy increases the rate of association of ligand. It is suggested that dimers of HuIFN-alpha 2 may be formed on the human, but not the bovine receptor, and where these occur between receptors, their formation may relate to the inhibition of cell growth.