Abnormalities in thrombin-antithrombin pathway in AL amyloidosis.

Various pathogenic factors have been proposed to explain the abnormal hemostasis observed in AL amyloidosis. Since imbalance between clotting factors and inhibitors could play a pathogenic role in both hemorrhagic and thrombotic manifestations, we investigated the thrombin-antithrombin pathway in 35 patients with AL amyloidosis. Ten patients suffered from bleeding while 3 patients experienced deep venous thrombosis. Thrombin time was prolonged in 29 subjects, the mean values of antithrombin III activity (ATIII Act) were significantly lower than those of antithrombin III antigen (ATIII Ag) with loss of relationship between these two different techniques of ATIII detection, normally observed in healthy controls. In 19 patients increased levels of thrombin-antithrombin (TAT) complexes were present. Crossed immunoelectrophoresis of ATIII, performed in presence of heparin, evidenced ATIII forms with reduced binding capacity to heparin and TAT complexes of various electrophoretic mobilities. In conclusion, the impairment of the thrombin-antithrombin pathway, in association with the low ATIII biological activity, might play a pathogenic role in the hypercoagulable state reported in AL amyloidosis, despite the higher frequency of bleeding manifestations.

Expression of dipeptidylaminopeptidase IV/CD26 in peripheral blood lymphocytes of hemophilic subjects.

CD26 antigen, a 110 kDa membrane glycoprotein with exopeptidase activity (DAP IV), is an activation marker of T lymphocytes preferentially expressed on CD4+ memory cells and involved in T cell proliferation and IL-2 production after antigenic stimulation. We employed cytochemical and immunocytochemical techniques to study DAP IV/CD26 expression in circulating lymphocytes from 40 hemophilic patients, chronically treated with coagulation factors, in order to verify the possible involvement of this molecule in the immunological alterations of hemophilia. In all the hemophiliacs DAP IV activity was significantly lower than in the controls, independently of the quantity of blood transfused and previous exposure to viruses. This reduction may be responsible for the impaired proliferative response of lymphocytes to antigens and mitogens, notoriously observed in hemophilia. Whereas in the group of HIV- patients CD26 expression was similar to that of normal controls, in the 8 HIV+ hemophilic patients both percentages of positive lymphocytes and intensity of staining were significantly lower. In only 4 of the 8 cases was this deficit associated with CD4+ cell depletion. The significant selective loss of CD26 expression observed in HIV+ patients is probably an early event after HIV infection and seems to occur even before CD4 cell depletion. In conclusion, evaluation of DAP IV/CD26 might be a useful option for monitoring the immunological alterations of all hemophilic patients, HIV positive or not, chronically treated with coagulation factors.