Analysis of human monocyte chemoattractant binding by flow cytometry.

The chemotactic peptide fMet-Leu-Phe-Lys is a potent chemoattractant for human blood monocytes. However, only one-third of the monocytes respond. To determine whether or not lack of response reflected absence of attractant receptors, we equilibrated peripheral blood mononuclear cells with fMet-Leu-Phe-Lys-FITC and analyzed binding by flow cytometry. The fluoresceinated peptide bound rapidly at 0 degree C, and the amount bound approached saturation with increasing concentration. The percentage of blood monocytes that bound the peptide was 60 +/- 8 (SEM for seven experiments). In contrast, only 36 +/- 3% (SEM for 16 experiments) of monocytes responded to the attractant by directed migration. It follows that, among the 64 nonmigrating monocytes per 100 total monocytes, approximately 40, or two-thirds of them, fail to bind attractant; the remaining one-third bind attractant but do not respond with directed movement.