Hirofumi Tachibana

Inducing the Loss of Immunoglobulin Light Chain Production and the Rearrangement of a Previously Excluded Allele in Human Plasma B Cell Lines with Concanavalin A

We investigated the expression of differential λ light chains in human B cell lines secreting immunoglobulin (Ig). When these cell lines were cultured with concanavalin A for a long period of time, a subpopulation of some but not all of these cell lines was induced to express new λ light chains replacing the original λ chain (light chain shifting). Production of the new λ chain, which replaces the original λ chain, results from a VJ rearrangement at a previously excluded allele and a dramatic reduction of the original λ chain transcript, although no difference was found in the level of heavy chain transcript. Recombination activating genes RAG-1 and RAG-2, which are normally expressed during specific early stages of lymphocyte development, were expressed in not only the light chain shifting-inducible lines but also in the non-inducible cells. Treatment of these Ig secreting cell lines with dibutyryl cAMP, which is known to enhance expression of the RAG genes, could not induce the creation of new λ light chain-producing cells from the inducible lines, suggesting that the expression of the two RAG genes is not sufficient for inducing new λ light chain production. Concanavalin A induced a gradual but significant production lost of the original λ chain in a subpopulation of the light chain shifting-inducible cells but not in the non-inducible cells. Association of new λ light chain production with loss of original λ chain raises the possibility that, when the RAG genes are expressed, concanavalin A may act on a novel intracellular mechanism controlling λ light chain allelic exclusion in these plasma cell lines.

A Retrovirus-Associated Antigen Expressed in Human Lung Carcinoma

A cDNA fragment, detectable in a human lung adenocarcinoma cell line A549, was amplified using PCR technique with oligonucleotide primers specific to cytochrome c from Candida krusei which was recognized by the lung cancer-specific human monoclonal antibody HB4C5. We screened the A549 cDNA library with the PCR product as a probe, and isolated a cDNA clone, named PRI-23. Sequencing analysis of the PRI-23 clonal cDNA revealed a 570 bp open reading frame (ORF) which encodes a 190 amino acid residue near the 3′-terminal region of the cDNA. A partial nucleotide sequence in the ORF exhibited about 90% homology to the long terminal repeat (LTR) sequence of the human endogenous retrovirus HERV-K10. Northern blot analysis indicated that the antigen mRNA was also detected in stomach and mammary carcinoma lines, but was not in normal fibroblast. These results suggest that this antigen may be tumor-associated and is expressed during or after carcinogenesis.