Sera from 56 recipients of liver or heart transplants were investigated for monoclonal immunoglobulins (mIg) by immunofixation electrophoresis (IFE) at different times during 4 years after transplantation. Transient, changing, or stable mIgs were found in 18 patients. A significantly increased mIg incidence was observed in heart Tx patients, patients over 40 years of age, and those receiving azathioprine or antithymocyte globulin in addition to prednisolone and cyclosporine as immunosuppressive treatment. No correlations could be found between the presence of mIg and the number of rejection episodes or intercurrent infections. Such serum mIg represent monoclones of at least 1 x 10(9) cells of B lymphocyte lineage that apparently proliferate without adequate suppressive control. Since immunosuppressed allograft recipients are at risk of developing B cell lymphomas, such monoclones may be regarded as prelymphomas necessitating a careful follow-up in these patients.
