Serum Requirement for Interferon Production by Suspended Human Leucocytes: Studies on Action of Serum

Suspensions of human leucocytes purified by NH4Cl produced interferon in the same time after induction by Sendai virus whether the medium contained serum or not. In the absence of serum the interferon titre levelled off after as little as 5 hr, and the yield was less than 10% of that obtained when serum was present. The production of interferon was completely inhibited by 2 μg./ml. of actinomycin D added simultaneously with the virus. Interferon synthesis gradually became insensitive to actinomycin during the first 4 to 5 hr after induction in both the presence and absence of serum. Large amounts of interferon rapidly appeared after addition of serum to cultures induced and incubated in serum-free medium. The cells responded to added serum by interferon production up to 16 to 20 hr after induction. The rate of interferon production after addition of serum was not affected by actinomycin. Removal of serum from the medium resulted in a reduced yield of interferon; which would not be prevented by addition of actinomycin. The low yields of interferon in a medium devoid of serum were not due to reduced synthesis of the DNA-dependent RNA needed for interferon production.