Characteristics of human monocyte subpopulations with the use of flow cytometer

Human monocytes separated from peripheral blood by Ficoll-Hypaque and by adherence to serum-coated dishes showed a bimodal volume distribution measured with a fluorescence activated cell sorter. The rate of the fluorescein diacetate hydrolysis by small monocytes was lower than that of large ones. The majority of large monocytes reacted with sensitized SRBC while only a minority of small monocytes bound sensitized SRBC. Scatchard plots on the binding of FITC-labeled human monoclonal IgG1 to the two subpopulations indicated similar association constants, K = 1.2 +/- 0.3 x 10(5) M-1. The number of FcR was significantly different for the small (3.3 +/- 0.6 x 10(5)) and the large monocytes (10 +/- 1 x 10(5)).