Macrophages have been generated from bone marrow progenitor cells （BMPCs） with macrophage colony-stimulating factor （M-CSF）. Rapamycin （rapa） is an immunosuppressive drug, which could prevent renal graft rejection and inhibit tumor growth to yield antiproliferative activity in a variety of malignancies. However, the direct effect of rapa on the development of macrophages is unknown. In this study, we explored the direct effect of rapa on the differentiation and function of macrophages differentiated from mouse BMPCs in vitro in the presence of M-CSF. The experimental data showed that rapa prevented the differentiation of macrophagcs by down-regulating CD80 and CD86 expression but upregulating F4/80 expression, as well as by reducing the capacity of differentiated macrophages to stimulate lymphocyte proliferation in the allogeneic mixed lymphocyte reaction. Furthermore, the phagocytic capacity of differentiated macrophages was significantly reduced by rapa. Therefore, rapa may directly inhibit macrophage differentiation and function, which may have been one of the major targets for rapa to mediate its immunosuppressive properties.
