Lectin binding of rat bone marrow cells during colony-stimulating factor type 1--induced differentiation: soybean agglutinin as a marker of mature rat macrophages.

Rat bone marrow cells (BMC) cultured in the presence of murine colony-stimulating factor type 1 (CSF-1) differentiate within 7 days into a cell population containing 96-100% macrophages (M phi). In this study, binding of 10 different fluorescein isothiocyanate (FITC)-conjugated lectins to cultured BMC at various stages of differentiation into M phi was investigated. Only soybean agglutinin (SBA) showed a binding pattern that was significantly correlated to M phi differentiation. Nearly all adherent (A) cells bound SBA. Binding of SBA to nonadherent (NA) cells increased from 20% on day 0 to 80% on day 8. NA cells were separated by means of a fluorescence-activated cell sorter into SBA-, SBA +/-, and SBA+ fractions. On day 0 and day 2, M phi, blast-like cells, eosinophils, and some neutrophils were found in the SBA+ population. From day 4 onwards, the SBA+ fraction contained almost exclusively M phi. Neutrophils and some blasts were found in the SBA- population on days 0 and 2. In the SBA +/- fraction, mainly blasts and lymphocytes were identified. With increasing time of culture, M phi or M phi precursors prevailed also in the SBA-/ +/- cell population. Cells forming colonies in soft agar in the presence of CSF-1 were highly enriched in the SBA +/- fraction. A large number of cells in S-G2/M phases but few colony-forming cells were found in the SBA+ population. Our data suggest that SBA is a useful additional tool to define late stages of M phi differentiation.