Inhibition of Factor XI by Myeloma Protein M.

Abstract

Waldenstrom’s macroglobulinemia sometimes involves hemostatic disorders. It has been assumed that this may be due to interaction of the myeloma protein with soom blood coagulation factor(s). In the present investigation the sera of seven myeloma patients were studied for a possible interaction between the myeloma protein and clotting factors II, VIM, IX and XI.Normal human plasma was incubated for 30 mi η at 37°C with different dilutions of patients’ serum or of purified myeloma proteins. The ability of this mixture to restore the clotting times of various deficient plasmas was tested by the partial thromboplastin time test.Factor XI activity of normal plasma was substantially inhibited upon incubation with patient’s serum or with purified myeloma protein M. This effect seems to be specific for myeloma protein M since it was neither observed with myeloma proteins G or A, nor with normal IgM. Other coagulation factors investigated so far were not inhibited by myeloma protein M. It is concluded that this protein is specifically affine to factor XI resulting in hindering the latter’s activity.