Macrophage growth rate treated with different M-CSF concentrations. BM, SPM and PM were cultured with M-CSF in concentrations of 2 ng/ml (A) or 10 ng/ml (B) for 0, 4, 7 and 14 days. The numbers of macrophages were quantified. Images are representative of 3 separate experiments. Data are mean ± SEM. *p < 0.05, **p < 0.01.