pre-B cell receptor complex An immunoglobulin-like complex that is present in at least the plasma membrane of pre-B cells, and that is composed of two identical immunoglobulin heavy chains and two surrogate light chains, each composed of the lambda-5 and VpreB proteins, and a signaling subunit, a heterodimer of the Ig-alpha and Ig-beta proteins. Despite its name, the pre-BCR is not a receptor complex, as it appears to provide a low level of signal not dependent on a ligand, but rather simply on correct assembly of the complex as a measure for correct Ig heavy chain recombination and folding. A significant proportion of pre-BCR complexes fail to reach the cell surface, and in some cases may provide their signaling function from the trans-Golgi network or lysosome. bf pre-BCR membrane protein complex