A COMPLEX OF GLYCOPROTEINS IS ASSOCIATED WITH V(PREB)/LAMBDA(5) SURROGATE LIGHT-CHAIN ON THE SURFACE OF MU HEAVY CHAIN-NEGATIVE EARLY PRECURSOR B-CELL LINES

Monoclonal antibodies (mAbs) have been made specific for the pre-B cell-specific proteins V(preB) and lambda5 which together form the surrogate light (L) chain. mAbs specific for V(preB) protein identified the 16-kD molecule associated on precursor B cell lines with lambda5 protein as the product of the V(preB) gene. Surrogate L chain was detectable even in the absence of mu heavy (H) chain on the surface of early precursor cell lines such as pro-B cell lines where all immunoglobulin (Ig) loci are in the germline configuration, as well as early pre-B cell lines where Ig H chain loci are D(H)J(H) rearranged in reading frame I or III, which does not allow the expression of a D(H)J(H)Cmu protein. A complex of glycoproteins (200, 130, 105, and 65-35 kD) was identified as coprecipitated with the V(preb)/lambda5 surrogate L chain in mu H chain-negative precursor B cell lines. The 130-kD protein was most strongly labeled with iodine and most consistently detected in noncovalent association with surrogate L chain. This protein turned out to be a N-linked glycoprotein with a 100-kD protein core and isoelectric point 5.8, indicating that it is distinct from CD43 and the BP-1/6C3 antigen. The surface deposition of the surrogate L chain in association with the newly identified glycoproteins suggests that the surrogate L chain may function as a receptor even before the association with mu H chain in early precursor B cells.