STUDIES ON HUMAN MONOCYTES WITH A MULTIPARAMETER

Suspensions of human lymphocytes and monocytes separated by the Ficoll-hypaque method from the peripheral blood show a Coulter volume distribution, measured with a multiparameter cell sorter, characterized by a minor peak at 500 IL3, containing 5-15% of the cells, and a major peak at 200 M3#{149} Using fluorescent latex particles we have found that the monocytes, the cells that ingest the latex particles, all lie in the 500 ,�peak; conversely, all of the cells in the 500 /L3 peak are monocytes. When the cell suspensions are incubated, the monocytes increase both in average volume and in absolute numbers. The number of monocytes approximately doubles during 3 days of incubation, when it reaches its maximum value. At that time we have found that all of the monocytes lack receptors for sheep red blood cells and all possess receptors for human -y-gbobulin. The increase in monocyte number appears, therefore, to arise from the enlargement of “monocyte precursors” that resemble lymphocytes in volume and resemble both the monocytes and the B lymphocytes with respect to surface sheep red blood cell and human -y-gbobulin receptors. In recent years, avid phagocytosis has been widely adopted as the principal functional critenon for distinguishing macmophages, monocytes and their precursor cells from other mononuclear cells (2, 3). We have been using the ingestion of latex particles to distinguish monocytes from lymphocytes in cell suspensions isolated by the Ficoll-hypaque method (1). Studies with a multipamameter cell sorter ( 11) of the growth of monocytes in culture have shown that the monocytes can be readily distinguished from the lymphocytes by cell volume. We have also shown that the monocytes increased not only in size but also in number during the first 3 days of cell culture. We present here data on the increase in monocyte number and volume with time in culture. We also show that the increase in monocyte numbers is due to the growth of monocyte precursors that resemble B bymphocytes in cell volume and in two cell surface characteristics, the presence of human ‘yglobulin receptors and the absence of sheep red blood cell receptors.