Role of hemopoietic colony-forming cell responses in the pathogenesis of ectromelia

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.

Granulocyte-macrophage precursor cell responses in mice of different strain, sex and age

Mice inoculated with Freund's complete adjuvant show an increase in the number of granulocyte-macrophage precursor cells (colony-forming cells) in haemopoietic tissues. This effect is most marked in spleen and reaches a maximum 7 days after inoculation.

The magnitude of the cellular response was measured in five mouse strains (C57B1, CBA, VSBS, TO and HR) and some significant differences were found, although no differences in the level of serum regulating factors were apparent. Colony-forming cell responses were weaker in young adult males than in females and were also weaker in mice at extremes of age.

It was suggested that differences in the magnitude of cellular responses could reflect differences in the responsiveness of target cells to the same stimulus and that broad parallels may exist between myelopoietic and immunological responsiveness.

Suppression of immune and hemopoietic cellular responses by methisazone

The antiviral drug methisazone (N-methylisatin beta-thiosemicarbazone) was tested for its effect on immune responses to sheep erythrocytes and on hemopoietic colony-forming cell (granulocyte-macrophage progenitor cell) responses to complete Freund's adjuvant in mice. Suppressive activity was demonstrated in both systems, the immune system being more readily and more consistently susceptible. Evidence is presented which suggests that the insoluble particulate form of the drug has both stimulatory and suppressive effects on the colony-forming cell system, whereas the soluble form is only suppressive. Methisazone increased the mortality from ectromelia in adjuvant-treated animals.