Light Chain Loss and Reexpression Leads to Idiotype Switch. Surrogate Light Chains are Probably Responsible for this Process

Summary

The murine B-lymphocyte cell line 38C-13 is characterized by several cell surface markers typical for an early stage of B-cell differentiation. Cells of this cell line posses cell surface membrane IgM molecules composed of µ and κ polypeptide chains. They also produce “surrogate” or “pseudo” light chains (ΨL) coded by the λ5 and VpreB genes. Variants of the 38C-13 cell line which do not synthesize κ chains can be isolated from the 38C-13 population by the use of anti-idiotype antibodies in vivo and in vitro. In some κ chain-deficient variant cell lines, cells which have regained surface IgM expression but have lost the original idiotype specificity, can be isolated. This idiotype switch is probably due to a secondary rearrangment of the κ gene. In the κ chain-deficient variant cells, the ii chains assemble with the surrogate light chains but the assembled IgM-like molecules are not expressed on the cell surface. It is suggested that surrogate light chains play an important role in the induction of κ gene rearrangement but that surface expression of µ-ΨL complexes is not required for this process.