Fc (IgG) receptor distributions in homogeneous and heterogeneous cell populations by flow microfluorometry

A flow microfluorometric method has been developed for quantitating the numbers of Fc receptors on individual cells. The cells were equilibrated at 0 degrees C with radiolabeled, affinity-crosslinked rabbit IgG dimers, washed, and treated with fluorescent antibodies against rabbit IgG. The stained cells were analyzed for fluorescence emission by using a fluorescence-activated cell sorter and for bound dimer molecules by using a gamma counter. Standard curves relating fluorescence emission to numbers of dimer molecules bound to cells were used to determine Fc receptor distributions on P388D1 cells, human peripheral blood lymphocytes, and normal mouse spleen cells. Essentially all of the P388D1 cells bore Fc receptors, distributed in a skewed Gaussian profile having a peak at 2 X 10(5) receptors per cell. Human peripheral blood lymphocytes and mouse spleen cells contained positive and negative subpopulations. The percentage of positive cells in human lymphocytes from different donors ranged from 50 to 25; the receptor distributions of these cells were symmetrical and similar in all donors in shape and average receptor density (4.2 X 10(4) receptors per cell). Mouse spleen cells contained 55% positive cells with nonsymmetrical heterogeneous distributions of receptor densities. These cells peaked at 1 to 2 X 10(4) receptors per cell, but significant numbers of cells had receptor densities 10- to 20-fold greater.