Virus susceptibility of mouse hemopoietic cells in vitro: inhibition of granulocyte-macrophage precursor cells by Newcastle disease virus.

Normal mouse bone marrow cells were exposed to encephalomyocarditis virus (EMC), reovirus type 3 (REO3), influenza virus (FLU), and Newcastle disease virus (NDV) then assayed for granulocyte-macrophage precursor cells by the technique of colony formation in agar. Exposure to EMC, REO3, and FLU caused a slight but variable loss of colony-forming potential, whereas exposure to NDV caused a very marked loss. NDV acted directly on the cells, not indirectly through release of colony-inhibiting factors or destruction of colony-stimulating factor. Experiments with NDV inactivated by heat, ether, or ultraviolet irradiation indicated that colony inhibition was associated with fully infective virus, even though some of the inactivated preparations had retained full hemagglutinin, neuraminidase, or hemolytic activity.