Analysis of autoantibody reactivity and common idiotype PR4 expression of myeloma proteins

Sera from 75 patients with monoclonal gammopathies and with no clinical evidence of autoimmune disease have been screened for a wide range of autoreactivity including binding to DNA, cardiolipin, extractable nuclear antigen (ENA), rheumatoid factor activity and the presence of the common anti-DNA antibody idiotype PR4. The sera of 17/75 (23%) patients possessed autoreactivity: six were positive for anti-DNA activity, two had anticardiolipin activity and the PR4 ID was found in two sera (both of which possessed anti-DNA activity). Antibodies to ENA were found in one serum (anti-Ro) and anti-organ-specific antibodies in five. Using iso-electric focusing and immunoblotting we have shown that the PR4 ID and DNA binding activity are carried on the paraprotein and not on some other serum constituent. The IgG subclass distribution of 55 IgG paraproteins has also been investigated. The majority of IgG paraproteins belong to IgG1 subclass (55%), with the others, being IgG2 (4%), IgG3 (9%) and IgG4 (27%). In this study we have shown that sera from myeloma patients frequently possess autoreactivity, and that in many cases this can be attributed to the paraprotein.