Comparison of rates of clearance of human fibroblast and leukocyte interferon from the circulatory system of rabbits.

In view of the lower physical stability of human fibroblast interferon than of human leukocyte interferon, the rates of clearance of the two types of interferon were compared in vivo. Both types were injected intravenously and intramuscularly into rabbits, and serum titers were determined at various times after injection. The rates of clearance of the two types of interferon were very similar after both intravenous and intramuscular injection, a finding which indicated that, at least in the circulatory system of rabbits, human fibroblast interferon is not less stable than human leukocyte interferon. After intravenous injection of either type, very little interferon was found in soluble extracts of the rabbit liver. This result implies that heterologous interferon is broken down rapidly in the liver, that it is bound to some particulate fraction, or that it does not accumulate in the liver.