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Published on: September 9, 2012
Measurement and prevalence of circulating ADAMTS13-specific immune complexes in autoimmune thrombotic
L A Lotta1, C Valsecchi, S Pontiggia
1Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Fondazione Luigi Villa and Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Milan, Italy.
Background:
The formation of ADAMTS13-specific circulating immune complexes (CICs) may be a pathophysiologic mechanism in autoimmune thrombotic thrombocytopenic purpura (TTP), but has not been systematically investigated.
Objectives:
(a) To develop an assay for ADAMTS13-specific CICs; (b) to evaluate their prevalence in autoimmune TTP; and (c) to assess their association with ADAMTS13-related measurements and clinical features in autoimmune TTP patients.
Patients/Methods:
We developed and validated an ELISA method for ADAMTS13-specific CICs. ADAMTS13-specific CICs were searched for in 55 patients with autoimmune TTP from the Milan TTP Registry (URL:http://www.ttpdatabase.org/) and 28 controls. The associations between ADAMTS13-specific CIC levels and ADAMTS13 activity, antigen, anti-ADAMTS13 IgGs and acute TTP clinical features were assessed by multivariate linear regression.
Results:
Intra- and inter-assay coefficients of variation of the new test were 5.3 and 9.6%. In 36 patients with severe ADAMTS13 deficiency and anti-ADAMTS13 autoantibodies, the prevalence of ADAMTS13-specific CICs was 47% (n = 17; 95% confidence interval [CI], 32-63%). ADAMTS13-specific CICs were detected also in seven of 19 (37%; 95% CI, 19-59%) patients with reduced ADAMTS13 activity, but apparently negative anti-ADAMTS13 autoantibodies. ADAMTS13-specific CICs were not associated with ADAMTS13 activity, antigen or anti-ADAMTS13 IgGs. In patients with acute TTP, increasing levels of ADAMTS13-specific CICs were associated with a higher number of plasma-exchange procedures required to attain remission (per 0.1 increase in normalized OD values, beta, 2.9; 95% CI, -0.7 to 6.5).
Conclusions:
Approximately one to two-thirds of patients with autoimmune TTP display ADAMTS13-specific CICs. A thorough investigation of the prognostic relevance of ADAMTS13-specific CIC levels in autoimmune TTP is warranted.
