A human monoclonal IgM lambda specific for an epitope shared by the 200 kDa neurofilament protein, histones and ribosomal proteins.

Serum monoclonal IgM lambda from a patient with axonal neuropathy reacted with axonal, nuclear, cytoplasmic and cell surface components by immunofluorescence. Experiments performed with Fab fragments of the monoclonal IgM proved that this reactivity was clearly due to actual antibody activity. Further study by Western blotting and ELISA showed that the IgM lambda reacted with the 200 kDa neurofilament protein, H1 and H2b histones and L14, L24 and L7 ribosomal proteins. This reactivity was abolished after adsorption either on purified 200 kDa neurofilament protein or on ribosomal proteins, demonstrating that these reactive proteins share a common epitope which possibly reflects sequence similarities. Sequence homology pointed to the involvement of the peptide AKSPEKAK in the epitope, and this was confirmed by dot blot analysis and adsorption experiments with this peptide. In addition, monoclonal IgM showed low level polyreactivity.