Independent control of immunoglobulin heavy and light chain expression in a murine pre-B-cell line

Abstract

B lymphocytes differentiate from multipotential stem cells by an unknown number of intermediate stages. Although the earliest stages of this sequence remain obscure, cells, which appear to be intermediate in this process, have been described^1–7. Large, proliferating, rapidly sedimenting cells which synthesize immunoglobulin chains that can be easily detected in the cytoplasm (cIg) but are either absent or less stable on the cell surface (sIg) have been found in both fetal liver and adult bone marrow. Smaller cIg⁺ sIg⁻ cells have also been described^2,5,7. These cells are designated pre-B cells and may comprise a functionally heterogeneous group of progenitors⁸. Several cell lines, which share many properties with these postulated precursors, have been useful in establishing an asynchronous onset of immunoglobulin expression characterized by the appearance of μ heavy chains in the absence of light chain expression^10–12. We confirm here that the mitogen-responsive pre-B-like cell line, 70Z/3, in normal growth conditions, only expresses heavy chain, although it has a fully rearranged light chain gene¹³. 70Z/3 cells can also display the μ chain on the cell surface in the absence of light chain induction, most notably after exposure to dextran sulphate.