Thermal and vortical stability of purified human fibroblast interferon

The loss of biological activity upon heating or agitation of human interferons is markedly altered by changing their aqueous environment. Low pH significantly stabilizes liquid fibroblast interferon at 68 degrees C and 37 degrees C whereas chaotropic salts stabilize at 68 degrees C but not at 37 degrees C; this anomalous result may be due to reactivation of biological activity at the higher temperature. The concentration of extraneous proteins influences the apparent thermal stability at any temperature and pH; thus, interferon was not stable even at low pH at protein concentrations less than 5 microgram/ml. Solutions of partially purified fibroblast interferon can be inactivated by mechanical stress; the addition of proteins or nonionic detergents prevents such inactivation. Freeze-dried preparations show the greatest thermal stability. The use of high-temperature, accelerated storage tests makes it possible to predict the shelf-life of freeze-dried interferon.