Identification by flow cytometry of human monocytes with fucose-binding lectin (FBL) from Lotus tetragonolobus seeds

Fucose binding lectin (FBL) from Lotus tetragonolobus seeds has previously been shown by fluorescence microscopy to bind to human neutrophils. This study shows using highly sensitive flow cytometry that this lectin binds both to human peripheral blood neutrophils and monocytes but not to lymphocytes. This binding is blocked by the presence of free L-fucose and is reversible when neutrophils or monocytes stained with fluorescent FBL are subsequently incubated in 0.05 M L-fucose. Quantitative comparison of neutrophils and monocytes from the same individual show that neutrophils bind approximately 2.6 times more FBL than monocytes and that FBL binding is more efficiently reversed with neutrophils, as compared with monocytes, by L-fucose. Additional double-labeling studies of cells with FBL and the OKM1 monoclonal antibody, which identifies monocytes and granulocytes, show that all cells binding FBL also stain with the OKM1 monoclonal antibody. This study shows that qualitatively, FBL may be utilized as a human myeloid cell marker to differentiate peripheral blood monocytes and neutrophils from lymphocytes.