Circulating factors may be responsible for murine strain-specific responses to mobilizing cytokines

Objective. To determine if circulating factors influence strain-specific re sponses to administration of hematopoietic stem-cell mobilizing cytokines, a murine model was employed, Methods. Plasma aliquots from intact DBA2, Balb/c, and C57Bl/6 mice were in jected into intact Balb/c mice prior to delivery of mobilizing cytokines, C ontrol Balb/c mice were injected with mobilizing cytokines alone. Plasma fr om hemi-body irradiated Balb/c mice, known to inhibit mobilization, was als o injected into Balb/c mice. Twenty-four hours later, spleen cells were har vested and assayed for granulocyte-macrophage colony-forming cells (GM-CFC) and high-proliferative-potential colony-forming cells (HPP-CFC). Simultane ously harvested blood aliquots were assayed for CD45(+)/CD34(+) cells using flow cytometric techniques. Results. Mice receiving plasma from any source demonstrated significant inh ibition of mobilization of HPP-CFC and GM-CFC to the spleen as compared to mobilized controls; for HPP-CFC, plasma from C57Bl/6 mice was more inhibito ry than plasma from Balb/c (p = 0.001) or from DBA2 mice (p = 0.01), while for GM-CFC, plasma from C57Bl/6 mice was more inhibitory than Balb/c plasma but not more inhibitory than DBA2 plasma. Mice injected with plasma from p reviously irradiated Balb/c mice exhibited the expected HPP-CFC and GM-CFC mobilization inhibition, which was not statistically different from the inh ibition seen in animals that received C57Bl/6 plasma. Mobilization of CD34( +)/CD45(+) cells to the blood also appeared to be inhibited by pretreatment with C57Bl/6 plasma, but not DBA2 plasma. Conclusion. These data suggest that strain-specific patterns of mobilizatio n may be influenced by a circulating mobilization inhibitor(s). (C) 2001 In ternational Society for Experimental Hematology, Published by Elsevier Scie nce Inc.