Characterization of the high-affinity cell-surface receptor for murine B-cell-stimulating factor 1.

Radiolabeled recombinant murine B-cell-stimulatory factor 1 (BSF-1) was used to characterize receptors specific for this lymphokine on the surface of primary B and T cells and in vitro cell lines representing the B-cell, T-cell, mast cell, macrophage, and myelomonocytic lineages. BSF-1 binding was rapid and saturable at 4 degrees C and 37 degrees C with a slow dissociation rate. On all cell types examined, BSF-1 bound to a single class of high-affinity receptor (less than 2000 receptors per cell) with a Ka of 10(10)-10(11) M-1. Receptor expression on resting primary B and T cells was low (less than 100 receptors per cell), whereas activation with lipopolysaccharide or Con A produced a 5- to 10-fold increase in receptor numbers. Among a panel of lymphokines and growth hormones, only unlabeled BSF-1 was able to compete for the binding of 125I-labeled BSF-1. Affinity crosslinking experiments resulted in the identification on all cells tested of a receptor protein with an average Mr of 75,000.