The IFN-alpha-inducing capacity of Sendai Virus in human leukocytes is independent from the hemagglutinating and hemolytic activities and from the viral proteins of the Sendai Virus preparations

About 30 Sendai Virus (SV) preparations, examined for their capacity to induce natural human interferon alpha from fresh human leukocytes (Le-IFN-alpha) of healthy donors, were characterized for hemagglutinating (HA) and hemolytic (HemA) activities and for SDS-PAGE proteic pattern. The SV preparations were produced by a single passage or by serial propagations through eggs in different conditions of multiplicity of infection (m.o.i.). The produced SV subpopulations showed variable IFN-inducing capacity, the values of which are distributed over a 6-fold range resembling a Gaussian distribution. No detectable difference was observed comparing the SV preparation obtained by serial propagations with those obtained by a single passage. The variability of the measured HA activity and HemA activity and as well as the SDS-PAGE proteic pattern of the SV preparations did not correlate with the induced amount of IFN per cell. In the same experimental conditions to produce Le-IFN-alpha, u.v.-treated SV preparations were unable to induce interferon depending on the u.v.-treatment. So it can be concluded that the distinct nHu-IFN-alpha-inducing capacity of SV subpopulation could be mainly associated with divergent compositions of the viral RNAs rather than with a different contents of viral proteins, among those detectable in SDS-PAGE and those responsible for HA activity and for HemA activity.

UV-A and PUV-A action on Sendai virus HN glycoprotein

The UV-A and PUV-A treatments were applied on the Sendai virus and the changes of the biological properties of HN surface glycoprotein were monitorized. Under the UV-A action the HA and NA activities are inhibited in a dose-correlated way. When the irradiation was done in the presence of a photoreagent (8-MOP) the HA activity remained unchanged, but the enzymic activity was affected. The possible mechanisms of these inhibition processes are discussed.

Loss of GSH, oxidative stress, and decrease of intracellular pH as sequential steps in viral infection

Madin-Darby canine kidney cells infected with Sendai virus rapidly lose GSH without increase in the oxidized products. The reduced tripeptide was quantitatively recovered in the culture medium of the cells. Since the GSH loss in infected cells was not blocked by methionine, a known inhibitor of hepatocyte GSH transport, a nonspecific leakage through the plasma membrane is proposed. UV-irradiated Sendai virus gave the same results, confirming that the major loss of GSH was due to membrane perturbation upon virus fusion. Consequent to the loss of the tripeptide, an intracellular pH decrease occurred, which was due to a reversible impairment of the Na+/H+ antiporter, the main system responsible for maintaining unaltered pHi in those cells. At the end of the infection period, a rise in both pHi value and GSH content was observed, with a complete recovery in the activity of the antiporter. However, a secondary set up of oxidative stress was observed after 24 h from infection, which is the time necessary for virus budding from cells. In this case, the GSH decrease was partly due to preferential incorporation of the cysteine residue in the viral proteins and partly engaged in mixed disulfides with intracellular proteins. In conclusion, under our conditions of viral infection, oxidative stress is imposed by GSH depletion, occurring in two steps and following direct virus challenge of the cell membrane without the intervention of reactive oxygen species. These results provide a rationale for the reported, and often contradictory, mutual effects of GSH and viral infection.