Autofluorescence contributes to false-positive intracellular Foxp3 staining in macrophages: A lesson learned from flow cytometry

► Foxp3 has been reported to be expressed in macrophages. ► We determined the macrophage phenotype in bone marrow and spleen of apo E−/− mice. ► Flow cytometry analysis showed that the Foxp3-positive macrophages are an artifact. ► qPCR analysis confirmed flow cytometry data ► Foxp3 expression in macrophages is an artifact of autofluorescence.