Controls the development of red pulp macrophages required for red blood cells recycling and iron homeostasis. Transcription factor that binds to the PU-box, a purine-rich DNA sequence (5'-GAGGA[AT]-3') that can act as a lymphoid-specific enhancer. Regulates VCAM1 gene expression. Binds DNA as a monomer. Expressed in lymphoid tissues, including spleen, bone marrow and thymus. According to PubMed:19037245, highly expressed in red pulp macrophages and, at lower, levels in B-cells, but not in other cells, including, monocytes, dendritic cells and other tissue macrophages. According to PubMed:10464163 expressed in pre- and mature B-cells but not in immature B-cells; according to PubMed:10187812 not expressed in pre- but predominantly in mature B-cells and at lower levels in macrophages. Cell-autonomous defect in the development of red pulp macrophages, but normal monocyte and other macrophage subsets. Mice show normal trapping of red blood cells in the spleen, but fail to phagocytose these cells efficiently and develop an iron overload localized selectively to splenic red pulp. Belongs to the ETS family.