Development of specific receptors for N-formylated chemotactic peptides in a human monocyte cell line stimulated with lymphokines

Abstract

A human monocyte-like cell line, U937, when grown in continuous cultures, does not secrete lysosomal enzymes or migrate towards chemotactic factors. When the cells are stimulated by lymphokines, they develop the ability to migrate directionally and to secrete enzymes in response to several types of chemoattractants. The development by stimulated cells of chemotactic and secretory responses to 1 class of chemoattractants, the N-formylated peptides, is accompanied by the appearance on the cells of specific binding sites for these substances. Using tritiated N-formyl-methionyl-leucyl-phenylalanine (fMet-Leu-[3H]Phe) as a ligand, it was determined that unstimulated U937 cells possess no detectable binding sites. After stimulation with lymphocyte culture supernates for 24, 48 and 72 h, they developed 4505 .+-. 1138, 22,150 .+-. 4030 and 37,200 .+-. 8000 sites/cell, respectively. The dissociation constants for the interaction of fMet-Leu-[3H]Phe with the binding sites were approximately the same, regardless of stimulation time and ranged between 15-30 nM. The binding of fMet-Leu-[3H]Phe by stimulated U937 cells was rapid and readily reversed by the addition of a large excess of unlabeled peptide. The affinity of a series of N-formylated peptides for binding to U937 cells exactly reflected the potency of the peptides in inducing lysosomal enzyme secretion and chemotaxis. The availability of a continuous human monocytic cell line that can be induced to express receptors for N-formylated peptides will provide a useful tool for the characterization of such receptors and for the delineation of regulatory mechanisms involved in cellular differentiation and the chemotactic response.