“…The homologous IF preparations were as follows; 1) IFs induced with poly I.poly C, NDV or ET which possessed different sensitivities to heat and pH [5], 2) early-and late-appearing IFs which were prepared at different times after induction with poly I-poly C, 3) IFs induced with high and low concentrations of poly I.poly C and then diluted to equal concentrations, 4) partially purified IFs induced with NDV [4]. Pretreatment of L cells with all these mouse IFs showed similar enhancing effects upon IF production.…”