Von Willebrand factor cleaving protease (ADAMTS-13) in 123 patients with connective tissue diseases (systemic lupus erythematosus and systemic sclerosis).

BACKGROUND AND OBJECTIVES: Autoantibodies inactivating the von Willebrand factor (VWF) cleaving protease, ADAMTS-13, are among the most frequent causes of thrombotic thrombocytopenic purpura (TTP). We evaluated whether or not ADAMTS-13 deficiency and autoantibodies inactivating the protease prevalent in patients with the prototypic autoimmune diseases systemic lupus erythematosus (SLE) and systemic sclerosis (SSc). DESIGN AND METHODS: We measured, in parallel, the protease and VWF antigen (VWF:Ag) in 123 patients, 36 of whom had SLE and 87 of whom had SSc. In 14 patients with either disease who had low plasma protease levels (below 40%) we also looked for anti-ADAMTS-13 inactivating antibodies. RESULTS: ADAMTS-13 levels were significantly lower in SLE (p=0.0013) and in SSc (p=0.0002) than in normal controls. No anti-ADAMTS activity was measurable in patients with low ADAMTS-13 levels. VWF:Ag was high in both SLE and SSc (p=0.001). INTERPRETATION AND CONCLUSIONS: Systemic connective tissue diseases are other conditions besides TTP that are associated in some instances with low but detectable levels of ADAMTS-13. Autoantibodies inactivating protease activity are not the cause of the low plasma levels of ADAMTS-13.

A sensitive ristocetin co-factor activity assay with recombinant glycoprotein Ibalpha for the diagnosis of patients with low von Willebrand factor levels.

BACKGROUND AND OBJECTIVES: The assay of ristocetin co-factor activity of von Willebrand factor (VWF:RCo) is used in the screening of patients with suspected von Willebrand's disease (VWD), the most frequent inherited bleeding disorder. A correct diagnosis of VWD relies on platelet agglutination tests that have a low accuracy within and between assays. A more accurate VWF:RCo assay would improve VWD diagnosis and classification. DESIGN AND METHODS: We describe here an ELISA method in which a recombinant fragment of the alpha-subunit of platelet glycoprotein Ib-IX-V complex (rGPIbalpha) is bound to an anti-GPIbalpha monoclonal antibody immobilized onto microtiter plate wells and which captures plasma VWF in the presence of ristocetin. The results obtained with this ELISA assay were compared blindly with values calculated from the agglutination test in normal subjects (n=60) and in type 1 (n=8), type 2A (n=16), type 2B (n=13), type 2M (n=17) or type 2M Vicenza (n=8) VWD patients which were characterized by low VWF levels. RESULTS: The two assays gave similar results in both normal subjects and VWD patients (r=0.93), but the ELISA test showed higher sensitivity (0.1 versus 6.25 U/dL). The repeatability and reproducibility gave coefficients of variation of 9% and 10%, respectively, for the ELISA, as compared to 14% and 15% for the agglutination test. INTERPRETATION AND CONCLUSIONS: This ELISA assay can be useful in the identification and classification of VWD patients in that it may provide a more accurate distinction between type 2 with abnormal VWF function and type 1 with a low plasma VWF concentration.