The w/X5 Surrogate Immunoglobulin Light Chain Is Expressed on the Surface of Transitional B Lymphocytes in Murine Bone Marrow

The membrane immunoglobulin heavy chain (Am) plays a feedback role during the pre-B stage of B lymphocyte differentiation . In pre-B cell lines, Am associates with two surrogate light chain proteins. The w chain is disulfide linked to p, and was predicted to be the product of the X5 gene. The t chain is noncovalently associated with Am. We demonstrate that the w protein is indeed the product of the X5 gene and that ft, co, and t are coassociated. in the same complex. Antibodies against the w/A5 protein demonstrate the existence ofa subpopulation of "transitional" bone marrow B cells that express Am and co on the cell surface . The majority of these cells also express surface « light chains, indicating that in B lymphoid ontogeny the A5 gene is inactivated after the onset of « light chain expression .