Cells showing monocytic enzyme characteristics are found in both the normal and PU.1−/− double staining populations. The MP12⁺Moma-2⁺ population from normal and PU.1−/− livers was isolated using magnetically labeled antibodies (see Materials and Methods). Flow cytometry data show the enrichment of the double positive cells from (A) normal and (B) PU.1−/− livers. Cytochemical stains of normal or PU.1−/− MP12⁺Moma-2⁺ cells for NSE (black stain) and peroxidase (PO; red stain) activity are also presented.