The B-cells that express anti-MAG antibodies in neuropathy and non-malignant IgM monoclonal gammopathy belong to the CD5 subpopulation
B-cells that express monoclonal IgM anti-MAG antibodies (M-protein) in a patient with neuropathy and non-malignant IgM monoclonal gammopathy were studied by flow cytometry to determine if they bear the CD5 cell surface antigen. The CD5+ antigen is expressed on a subpopulation of B-cells which has been implicated in the secretion of autoantibodies and development of B-cell chronic lymphocytic leukemia (B-CLL). The monoclonal anti-MAG antibodies secreting B-cells were identified by a mouse monoclonal antibody to M-protein idiotype. Cytofluorometric analysis revealed that approximately 62% of the idiotype-positive B-lymphocytes expressed the CD5 antigen. The result of this study indicate that monoclonal anti-MAG antibodies may be secreted by CD5+ B-cells, and that B-cells in some cases of non-malignant IgM monoclonal gammopathy may be phenotypically similar to B-CLL cells.