Analysis of Human Monocyte Chemoattractant Binding by Flow Cytometry

Abstract
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°, 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.

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