Variations in the interferon-inducing capacity of Sendai virus subpopulations

Several Sendai virus (SV) preparations, propagated through eggs from the same viral seed, exhibited significantly different capacities to induce interferon (IFN) in human leukocytes (nHu-IFN-alpha). The amount of induced IFN and the numbers of SV IFN-inducing particles (IFP) per cell were determined in dose (SV concentration)-response (IFN yield) curves, kinetics of IFN production, and coinfection experiments with SV preparations that differed in IFN-inducing capacities. The possible role of leukocyte sources and the quality of the SV preparations and of allantoic fluids in affecting the IFN-inducing capacity of SV populations also were tested. The data indicate that different SV preparations induced different amounts of IFN per leukocyte and contained approximately the same concentrations of IFN-inducing particles. There was no apparent correlation between the IFN induced and the apparent quality of the SV preparations examined (EID50, HAU, and EID50/HAU). The leukocyte source and the allantoic impurities of SV preparations did not have any influence on the magnitude of the IFN yield. Similar shapes of the dose-response curves, the absence of any lag in the kinetics of IFN production, and the ability of a viral preparation that induced low yields of IFN to suppress partially a high-yielding inducer suggest that a common mechanism of induction is always present. Hence, propagation of SV in eggs from low multiplicity produced virus stocks that differed significantly in their inducing capacity, suggesting that genetic bottlenecks may be operative.