Polyneuropathy associated with monoclonal gammopathy of undetermined significance (PN-MGUS) is regarded as an immune-mediated disorder, where an expanded B cell clone secretes monoclonal IgM or IgG/A M-components (for review see [1,2]). About 50% of the patients with M-component of IgM isotype display a binding specificity for peripheral nerve myelin [3]. The target auto-antigen for these antibodies is mainly represented by carbohydrate epitopes shared by glycoproteins, like the myelin protein P 0 [4] and myelin-associated glycoprotein (MAG) [5], and glycolipids [6,7], like the sulphated glucuronic acid epitope present on, for example, sulphated glucuronyl paragloboside (SGPG). A direct pathogenic role of the antibodies against peripheral nerve myelin has been suggested based on findings that demyelination is associated with deposits of monoclonal antibodies and complement [8]
SUMMARYMonoclonal expansion of B cells and plasma cells, producing antibodies against 'self' molecules, can be found not only in different autoimmune diseases, such as peripheral neuropathy (PN), but also in malignancies, such as Waldenström's macroglobulinaemia and B-type of chronic lymphocytic leukaemia (B-CLL), as well as in precancerous conditions including monoclonal gammopathy of undetermined significance (MGUS). About 50% of patients with PN-MGUS have serum antibodies against peripheral nerve myelin, but the specific role of these antibodies remains uncertain. The aims of the study were to establish, and characterize, myelin-specific B cell clones from peripheral blood of patients with PN-MGUS, by selection of cells bearing specific membrane Ig-receptors for myelin protein P 0 , using beads coated with P 0 . P 0 -coated magnetic beads were used for selection of cells, which subsequently were transformed by Epstein-Barr virus. The specificity of secreted antibodies was tested by ELISA. Two of the clones producing anti-P 0 antibodies were selected and expanded. The magnetic selection procedure was repeated and new clones established. The cells were CD5 + positive, although the expression declined in vitro over time. The anti-P 0 antibodies were of IgM-l type. The antibodies belonged to the V H 3 gene family with presence of somatic mutations. The IgM reacted with P 0 and myelin-associated glycoprotein (MAG), and showed no evidence for polyreactivity, in contrast to other IgM CD5 + clones included in the study as controls. The expanded clones expressed CD80 and HLA-DR, which is compatible with properties of antigen-presenting cells. The immunomagnetic selection technique was successfully used for isolation of antimyelin protein P 0 -specific clones. The cell lines may provide useful tools in studies of monoclonal gammopathies, leukaemia, and autoimmune diseases, including aspects of antigen-presentation by these cells followed by T cell activation.
