Interferon production in mouse spleen cells and mouse fibroblasts (L cells) stimulated by various strains of Newcastle disease virus.

Interferon production in mouse spleen cells and mouse fibroblasts (L cells) stimulated by three strains of Newcastle disease virus (NDV), Italian, La Sota and Ulster, was investigated. Strain Italian was fully infectious and highly virulent; strain Ulster exhibited very low infectivity and very low virulence; strain La Sota was between these extremes. All of these strains of MDBK cell-grown NDV could induce interferon in mouse spleen cells, and it was concluded that proteolytic cleavage of F0 protein of NDV and, consequently, virus penetration are not necessary for interferon induction in these cells. On the other hand, NDV with uncleaved F0, which was characterized by an apparent lack of haemolytic and cell fusion activity and infectivity for tissue culture cells, had no interferon-inducing ability in L cells. The cleavage of F0 protein was paralleled by an appearance of interferon-inducing activity in L cells.