Formation of disulphide-linked mu 2 omega 2 tetramers in pre-B cells by the 18K omega-immunoglobulin light chain.

Pre-B cells are precursors of B lymphocytes that contain intracellular heavy-chain protein (mu) and are either yet to rearrange their light-chain genes or are in the process of doing so. These cells have traditionally been considered to contain intracellular mu-chain with no associated light chain. We demonstrate here that pre-B lymphoid lines synthesize a protein of relative molecular mass (Mr) 18,000 (18K), which we term omega, which forms disulphide-linked mu 2 omega 2 tetramers. This protein could be immunoprecipitated with mu-chain from pre-B lines, but not from T-cell and fibroblast lines that express transfected mu-genes, nor from a pre-B line that synthesizes a D mu-protein (which lacks a V domain). We view the omega-chain as being a pre-B specific surrogate light chain that may be essential for the important regulatory function that the mu-protein is believed to have at this stage of differentiation.