Figure 3. Sub-lethal irradiation reduces the number of total BM cells, an effect partially dependent on TNF-α.

A. WT and TNF-α KO mice were sub-lethally irradiated and the total number of BM cells was counted as explained in Methods. As shown, TNF-α KO mice were more resistant to the apoptotic effects of irradiation. On day 3 following irradiation, the number of total BM cells is significantly higher in TNF-α KO mice than in WT mice. The results shown were obtained from two independent experiments, using 12 animals per experimental group and 3 animals per time point. *: p<0.05. B. WT mice were injected with PBS (control) or with antibody anti-TNFα prior to sub-lethal irradiation and total BM cells were counted. Like for TNF-α KO mice, anti-TNFα neutralized mice were more resistent to irradiation; here, the number of total BM cells is significantly higher (*: p<0.02) by 24 hours after irradiation than in controls. C. The percentage of apoptotic cells 24 hours after irradiation was obtained in control and neutralized mice by flow cytometry. Both precursor (Sca1+) and myeloid (CD11b+) cells were protected from irradiation-induced apoptosis in the anti-TNF-α treated mice, where the number of cells positive for annexin V is lower than in the controls. *: p<0.01 for CD11b+; for Sca1+ a p value could not be calculated due to the absence of Sca1+Annexin+ cells in neutralized mice. The results shown in B and C were obtained from one experiment, using 12 animals per experimental group and 3 animals per time-point.