Restricted Oligo-Clonal Usage of Monoclonal Immunoglobulin λ Light Chain Germline in POEMS Syndrome.

Background: POEMS syndrome (also known as Crow-Fukase or Takatsuki syndrome) is a rare plasma cell disorder characterized by peripheral neuropathy, a monoclonal plasma cell disorder, and other paraneoplastic features including organomegaly, endocrinopathy, skin changes, edema and effusions. High levels of vascular endothelial growth factor (VEGF) in the serum may contribute to pathology seen in this disease but exact pathogenetic mechanisms are still unclear. A unique feature of this syndrome is that the proliferating monoclonal plasma cells are virtually always λ-restricted. Here, we determined complete nucleotide sequences of monoclonal immunoglobulin λ light chain (IGL) variable regions in 10 patients with POEMS syndrome and found that Vλ germline usage is highly restricted to the Vλ1 family and oligoclonal germlines.

Materials and methods: Total RNA was extracted from bone marrow mononuclear cells of patients with POEMS syndrome and the V-J region of the IGL gene was amplified by RT-PCR using 5′ degenerative primers for the Vλ consensus leader lesion (5′-ATGGCCKGSWYYSYTCTCCTC-3′) and 3′ primers matching the consensus upstream part of the cl exon (5′-CTCCCGGGTAGAGAAGTCACT-3′). Monoclonal bands were detected by heteroduplex analysis or TA cloning and subjected to nucleotide sequencing. Sequence data were analyzed using the International ImMunoGeneTics information system (IMGT, http://imgt.cines.fr) and mutations were identified by comparison with the germline sequence databases.

Results: Of 13 POEMS syndrome patients with λ-type M protein, nucleotide sequencing of the IGL gene was successful in 10. The V-region of the IGL gene of all 10 patients was restricted to the Vλ1 family. Searching for homologies with IGL germlines revealed that only two were used, with an average homology of 90.1%. IGLV1-40*01 was used in 8 patients and IGLV1-44*01 in the remaining two. In the IGL-J region, the IGLJ3 gene was found in 9 of 10 patients and IGLJ2 in one (10%). All IGLV-J rearrangements were mutated with homologies to the germline sequence ranging from 77.66% to 96.10% (average homology: 90.1%). All CDR3 were composed of 11 amino acids, with identical acidic isoelectric point (pI) values (13.0) and similar molecular weights ranging from 1394.7 to 1552.8 (median, 1506.2).

Conclusions: IGL-M protein in POEMS syndrome belongs to the Vλ1 family and is markedly restricted to specific oligoclonal germlines. Our results suggest that the restricted use of IGL plays an important role in the pathogenesis of POEMS syndrome. These data provide an important insight for elucidating the pathogenesis of POEMS syndrome. To the best of our knowledge, this the first report of restricted oligo-clonal usage of monoclonal immunoglobulin germlines in plasma cell disorders.