Identification of nonadherent mononuclear cells in human cord blood that differentiate into macrophages

We describe a population of nonadherent cells in neonatal cord blood that, upon in vitro cultivation, develop into monocyte-macrophages. These cells initially are negative for nonspecific esterase cytoplasmic activity, lack the monocyte marker MO.2, fall into smaller, nonmonocytic cell size areas, as determined by fluorescence-activated cell sorter (FACS)-assisted size analysis, and differentiate into macrophages under nonstimulatory culture conditions (in the absence of exogenous colony stimulating factors, less than 0.1 ng/ml endotoxin, and growth in suspension). In contrast to the adherent, committed macrophage precursors in cord blood, which differentiate into macrophages after 2-3 days of culture, the nonadherent precursor does not acquire monocyte-macrophage characteristics until day 14 of culture. Earlier induction is achieved by adding the monocyte-activating agents lipopolysaccharide or 1,25 dihydroxyvitamin D3 to cultures.