An IgM monoclonal protein with multiple serological specificities

An IgM lambda M-component with a false Wasserman reaction and 'false' rheumatoid factor activity from a patient suffering from a well-differentiated lymphocytic lymphoma is presented. The monoclonal protein showed antibody activity against cardiolipin and cross-reacted with acryl particles, not with human IgG. Both these activities were found in the Fab fragment. The reduction of the 19S IgM to 7S IgM subunits was responsible for a strong decrease in activity. The importance of the IgM quaternary structure in determining antibody affinity is emphasized.