Alterations in the expression of colony-stimulating factor-1 and its receptor during an acute graft-vs-host reaction in mice

During the course of an acute graft-vs-host reaction in the mouse we observed a progressive increase in the concentration of CSF-1 in serum and liver, peaking at day 14. In contrast, there was a progressive decrease in the splenic CSF-1 concentration. In vivo studies of ¹²⁵I-CSF-1 uptake and degradation and in vitro studies of ¹²⁵I-CSF-1 binding by splenic cells demonstrated that within 24 h of the reaction the number of CSF-1 receptor⁺ cells had increased by 2-fold and their capacity to express the CSF-1 receptor by ∼3-fold, resulting in a ∼2.5-fold increase in the splenic clearance of CSF-1 from the circulation. Inasmuch as at 24 h, serum CSF-1 was not significantly altered, these results are suggestive of an increased rate of release of CSF-1 into the circulation early in the response. The splenic CSF-1-receptor bearing cells were in a Mac-1⁺ fraction that is consistent with a role for CSF-1 in the generation of host-derived splenic macrophages in acute graft-vs-host reaction.