Receptors for B-cell stimulatory factor-1 expressed on cells of haematopoietic lineage

Abstract

B-cell stimulatory factor-1 (BSF-1) is a T-cell product of relative molecular mass 20,000 (M_r 20K) initially described as a cofactor required for DNA synthesis by resting mouse B cells stimulated with low concentrations of anti-IgM antibodies¹. It acts on resting B cells to enhance the expression of class II major histocompatibility complex (MHC) molecules^2,3, to prepare these cells to respond more promptly to subsequent stimuli, such as anti-IgM antibodies^4,5, and causes the secretion of IgG₁ and IgE by B cells stimulated with lipopolysaccharide (LPS)^6–9. BSF-1 has been shown to stimulate T cell lines¹⁰, resting T cells¹¹ and some mast cell lines¹⁰. Recently, the designation interleukin-4 (IL-4) has been suggested for BSF-1. We report here the existence of high-affinity cell-surface receptors specific for BSF-1 on both B and T lymphocytes, and on cells of several other haematopoietic lineages, including mast cell, macrophage and undifferentiated haematopoietic cell lines. Resting B and T lymphocytes express receptors, which increase in number upon activation of B cells with LPS or anti-IgM, and of T cells with concanavalin A. Cross-linking of ¹²⁵I-labelled-BSF-l to its receptors creates a complex of M_r∼80,000.