EXPRESSION OF A NOVEL TYPE OF IMMUNOGLOBULIN-C-LAMBDA TRANSCRIPTS IN HUMAN MATURE LYMPHOCYTE-B PRODUCING CHI-LIGHT CHAINS

Ordered rearrangement of immunoglobulin genes (heavy chain then aleph and eventually lambda genes) is observed during B lymphocyte ontogeny. Unexpectedly, we found that human mature B cells producing aleph chains and having germ-line lambda genes contain lambda mRNA consisting of an invariant 5' region (herein termed X) and of one of the classical C-lambda exons. The X region of these transcripts originates from a unique exon located 5 kb upstream of the J-C-lambda-1 gene segment. X-C-lambda mRNA expression occurs without somatic DNA rearrangement. The use of the X DNA fragment as a probe allows definition of a family of human genes that comprises at least four members and includes the first exon of the lambda-14.1 gene. The latter is selectively transcribed in pre-B lymphocytes and directs the synthesis of a lambda-like chain. In contrast, the X-C-lambda transcripts do not appear to encode a C-lambda-related polypeptide in mature B cells. Thus, despite a 73% homology extending far beyond the exon sequences, the X and lambda-14.1 genes are expressed at different stages of B cell development and might serve different functions.