Studies on cell binding and internalization of human lymphoblastoid (Namalva) interferon

The binding of iodinated human lymphoblastoid Namalva interferon to Namalva cells, to a human fibroblast cell strain (FS11), and to a bovine kidney cell line (MDBK) was characterized. Scatchard analysis of the binding data indicated the presence of about 1000-2000 receptors per cell and dissociation constants of the order of 0.1 to 0.01 nM. Two subspecies of Namalva interferon (16 K and 20 K), which differ in their antiviral activity toward bovine and human cells, were found to bind with the same affinity toward bovine MDBK cells but to differ in their affinity to human cells. Experimental results indicated that at 37 degrees C the bound interferon is internalized within 15 min after binding to Namalva cells, and then degraded in the lysosomes. Exposure of Namalva cells to interferon resulted in a 40% reduction of the number of cell surface receptors (down-regulation).