FREQUENT N ADDITION AND CLONAL RELATEDNESS AMONG IMMUNOGLOBULIN-LAMBDA LIGHT-CHAINS EXPRESSED IN RHEUMATOID-ARTHRITIS SYNOVIA AND PBL, AND THE INFLUENCE OF V-LAMBDA GENE SEGMENT UTILIZATION ON CDR3 LENGTH

Background: Ln rheumatoid arthritis (RA), B-lineage cells in the synov ial membrane secrete large amounts of immunoglobulin that contribute t o tissue destruction. The CDR3 of an immunoglobulin light chain is for med by rearrangements of V-L and J(L) gene segments. Addition of non-g ermline-encoded (N) nucleotides at V(D)J joins by the enzyme terminal deoxynucleotidyl transferase (TdT) enhances antibody diversity. TdT wa s previously thought to be active in B cells only during heavy chain r earrangement, but we and others reported unexpectedly high levels of N addition in kappa light chains. We also found clonally related kappa chains bearing unusually long CDR3 intervals in RA synovium, suggestin g oligoclonal expansion of a set of atypical B lymphocytes. Ln this st udy, we analyzed lambda light chain expression to determine if N addit ion occurs throughout immunoglobulin gene rearrangement and to compare CDR3 lengths of lambda and kappa light chains in RA patients and norm al individuals. Materials and Methods: Reverse transcription-polymeras e chain reaction (RT-PCR) amplification of V lambda III transcripts wa s performed on RA synovia and peripheral blood lymphocytes (PBL) and n ormal PBL for which kappa repertoires were previously analyzed. Repres entative lambda(+) PCR products were cloned and sequenced. Results: An alysis of 161 cDNA clones revealed that N addition occurs in lambda li ght chains of RA patients and normal controls. The lambda light chain repertoires in RA were enriched for long CDR3 intervals. In both RA an d controls, CDR3 lengths were strongly influenced by which V lambda ge ne segment was present in the rearrangement. Five sets of clonally rel ated sequences were found in RA synovia and PBL; one set was found in normal PBL. Conclusions: In humans, unlike mice, N addition enhances a ntibody diversity at all stages of immunoglobulin assembly, and the st ructural diversity of lambda CDR3 intervals is greater than that of ka ppa light chains. Clonally related V lambda gene segments in RA suppor t an antigen-driven B-cell response.