Effect of M-CSF on platelet survival. Eusplenic SW mice, or SW mice that had been splenectomized at least 4 weeks previously, were treated with M-CSF, 4 mg/kg/d for 3 days. On the fourth day, M-CSF was administered in the morning, and 3 hours later approximately 2.5 × 108 platelets that had been fluorescently labeled with CMFDA were injected into the tail veins of these mice. A control group of mice that had not received M-CSF also was injected with the same number of platelets. The percent of the maximum number of circulating labeled platelets was serially determined for 93 hours by flow cytometry, and the means ± 1 SE are shown by the closed symbols. The mean T1/2 for platelet survival in the control animals (▴) was 32.9 hours (n = 5). The T1/2 in the eusplenic M-CSF treated animals (•) (19.0 hours; n = 7) and in the asplenic M-CSF–treated animals (▪) (16.3 hours; n = 7) were both significantly shorter than that of the controls (P < .001). The T1/2 values for platelet survival in the 2 groups of M-CSF–treated animals were not significantly different from each other. Serial platelet counts for each group were obtained and are shown with the corresponding open symbols in the inset graph.
