IgD/lambda plasmocytoma with immunoglobulin kappa light-chain genes in the germ-line configuration

Human immunoglobulin (Ig) genes are rearranged in an ordered sequence of events during B-cell differentiation: starting at the IgH locus, a productive VHDJH rearrangement leads to the expression of mu chains. Light-chain gene rearrangements have been found in pre-B cells which express mu chains. In these cells rearrangements of Ig kappa light-chain genes precede that of lambda genes. In an IgD/lambda-producing plasmocytoma, however, we found an apparent exception to this rule: the kappa genes were not rearranged. Together with the observation that roughly 90% of human IgD plasmocytomas produce lambda light-chain proteins, the finding reported here leads us to suggest that lambda light-chain genes are rearranged preferentially in IgD-producing plasma cells. Ig gene rearrangement, isotype switch, and the phenomenon of isotypic and allelic exclusion are discussed with special reference to our findings.