Role of Hemopoietic Colony-Forming Cell Responses in the Pathogenesis of Ectromelia

Abstract

Intraperitoneal injection of complete Freund's adjuvant which caused an extensive cellular response in the reticuloendothelial system greatly increased the severity of infection which resulted from footpad inoculation of ectromelia virus in mice. The mortality was greatest during the proliferative phase of the cellular response, indicated by the colony-forming cell response. Exposure of colony-forming cells to virus in vitro showed that those from normal bone marrow were much less susceptible to virus than those from the bone marrow of adjuvant-treated mice and more particularly those from the spleen of adjuvant-treated mice. Severe bleeding to induce anemia and a consequent erythropoietic response did not increase the mortality from ectromelia. Previous results were interpreted on the basis of these findings and a more general application of them to the pathogenesis of poxvirus infection was discussed.It was reported in the previous paper (13) that during infection with ectromelia virus mice can develop an increase in the number of hemopoietic colony-forming cells (CFC) in bone marrow, blood, and spleen. However, it was also shown that the relationship between the level of infection and the CFC response in the different tissues was complex, and that this relationship in bone marrow was different from that in spleen and blood (13). No clear-cut pattern emerged regarding the possible role of a CFC response in the pathogenesis of the disease since the results could be interpreted in various ways. The experiments reported in this paper were carried out in an attempt to resolve these problems by (i) studying the infection in mice whose CFC system was stimulated before infection and (ii) by studying the susceptibility of CFC to virus infection in vitro. MATERIALS AND METHODSThe mice, the strain of virus, and the technique of virus and infectious cell assay were described or referred to in a previous paper (13).Hemopoietic stimuli. Intraperitoneal injection of complete Freund's adjuvant has been shown to give an intensive stimulus to the CFC system (12). The complete adjuvant (Difco) was used as supplied, without emulsification, but ensuring complete suspension of the mycobacterial component. Each mouse was given 0.2 ml by intraperitoneal inoculation.A strong erythropoietic stimulus was given by making mice anemic. This was achieved by bleeding 0.3 ml from the tail on 3 successive days, a procedure which resulted in the peripheral blood hematocrit falling from 45% to 20 to 25%7. Virus was given the day after the third bleeding. Infection of CFC in vitro. Bone marrow and spleen cells were collected from either normal mice or from mice which had been given adjuvant 7 days previously. Cell suspensions were made as described in the previous paper (13) and were diluted to a concentration of 4 X 106 per ml. A 1-ml amount of this suspension was mixed with an equal volume of Eagle's medium containing 4 X 107 plaque-forming-units (PFU) of ectromelia virus. The mixture was incubated at 37 C in a water bath for 2 hr with gentle s...

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

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