The incidence of precipitating activity in monoclonal proteins.

A survey of precipitating activity against dinitrophenyl (DNP) conjugated proteins, and a number of naturally occurring antigens was made in eighty-three sera from patients with multiple myeloma or Waldenströms macroglobulinaemia, thirty normal sera, and thirty-two sera from patients with a variety of non-neoplastic diseases. Three sera, an IgA myeloma serum, and two monoclonal IgM sera, had strong precipitating activity against DNP–protein conjugates. The precipitating activity was localized to the monoclonal proteins by immunoelectrophoresis and dextran gel chromatography. Weak anti-ascaris precipitin bands were noted in eight of the sera, but this activity probably was not a function of the monoclonal proteins. The IgA myeloma protein, which reacted with DNP conjugates, was also found to have a high rheumatoid factor activity.