High plasma fibronectin levels in multiple myeloma patients: possible mechanisms and clinical implications.

Fibronectin (FN) has been implicated in the formation of cryoprecipitates in rheumatic diseases and is present in tissues where, under pathological conditions, immune complexes are frequently deposited. We found elevated levels of FN in the plasma of 92% of multiple myeloma patients tested compared with a group of normal subjects, although the level of FN did not correlate with the level of the paraprotein. We then characterized the interacting fragments on both molecules and found that under physiological conditions of pH and ionic strength both heavy and light chain of all multiple myeloma and normal IgG showed affinity to FN; the active fragment on FN was found to be the aminoterminal heparin-binding domain. These findings raise the possibility that FN might be implicated in some of the clinical symptoms of multiple myeloma.