[Physiopathology of monoclonal IgM associated with peripheral neuropathy]

Monoclonal IgM associated with a peripheral neuropathy often feature an antibody activity directed against the myelin-associated-glycoprotein. The main characteristics of the structure of these IgM are reviewed: the variable gene repertoire used by these antibodies is rather large. The VH genes belong to the different variability subgroups; this also holds true for the VL repertoire although the single V kappa 4 gene may be used quite often. These variable segments often exhibit somatic mutations clustered in the CDR regions suggesting an antigen driven process. The monoclonal IgM is produced by a B cell clone which may be undetectable in the majority of patients. Nevertheless, it is possible to detect clonal B cells in the blood which have the remarkable capacity to differentiate spontaneously in vitro to plasma cells. This process is dependent upon an IL6-autocrine differentiation pathway which may be modulated by some drugs such as interferons or all trans retinoic acid.