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Pathogenicity of Anti-ADAMTS13 Autoantibodies in Acquired Thrombotic Thrombocytopenic Purpura.

Thomas MR, de Groot R, Scully MA, Crawley JT - EBioMedicine (2015)

Bottom Line: We demonstrated markedly reduced ADAMTS13 antigen levels in all presentation samples, median 6% normal (range 0-47%), with 84/91 patients having < 25% ADAMTS13 antigen.ADAMTS13 antigen in the lowest quartile at first presentation was associated with increased mortality (odds ratio 5.7).Taken together, our results provide new insights into the pathophysiology of acquired TTP.

View Article: PubMed Central - PubMed

Affiliation: Haemostasis Research Unit, University College London, 51 Chenies Mews, London WC1E 6HX, United Kingdom ; Centre for Haematology, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, United Kingdom.

ABSTRACT

Background: Acquired thrombotic thrombocytopenic purpura (TTP) is an autoimmune disease in which anti-ADAMTS13 autoantibodies cause severe enzyme deficiency. ADAMTS13 deficiency causes the loss of regulation of von Willebrand factor multimeric size and platelet-tethering function, which results in the formation of disseminated microvascular platelet microthrombi. Precisely how anti-ADAMTS13 autoantibodies, or antibody subsets, cause ADAMTS13 deficiency (ADAMTS13 activity generally < 10%) has not been formally investigated.

Methods: We analysed 92 acquired TTP episodes at presentation, through treatment and remission/relapse using epitope mapping and functional analyses to understand the pathogenic mechanisms of anti-ADAMTS13 IgG.

Results: 89/92 of TTP episodes had IgG recognising the ADAMTS13 N-terminal domains. The central spacer domain was the only N-terminal antigenic target detected. 38/92 TTP episodes had autoantibodies recognising the N-terminal domains alone; 54/92 TTP episodes also had antibodies against the ADAMTS13 C-terminal domains (TSP2-8 and/or CUB domains). Changes in autoantibody specificity were detected in 9/16 patients at relapse, suggesting a continued development of the disease. Functional analyses on IgG from 43 patients revealed inhibitory IgG were limited to anti-spacer domain antibodies. However, 15/43 patients had autoantibodies with no detectable inhibitory action and as many as 32/43 patients had autoantibodies with inhibitory function that was insufficient to account for the severe deficiency state, suggesting that in many patients there is an alternative pathogenic mechanism. We therefore analysed plasma ADAMTS13 antigen levels in 91 acquired TTP presentation samples. We demonstrated markedly reduced ADAMTS13 antigen levels in all presentation samples, median 6% normal (range 0-47%), with 84/91 patients having < 25% ADAMTS13 antigen. ADAMTS13 antigen in the lowest quartile at first presentation was associated with increased mortality (odds ratio 5.7).

Conclusions: Anti-spacer domain autoantibodies are the major inhibitory antibodies in acquired TTP. However, depletion of ADAMTS13 antigen (rather than enzyme inhibition) is a dominant pathogenic mechanism. ADAMTS13 antigen levels at presentation have prognostic significance. Taken together, our results provide new insights into the pathophysiology of acquired TTP.

No MeSH data available.


Related in: MedlinePlus

Longitudinal analysis of acquired TTP patients.A–E) Longitudinal analysis of five acquired TTP patients following a first initial presentation. ADAMTS13 activity (blue), antigen (green), anti-ADAMTS13 IgG titre (red) are shown as % normal (left axis). Platelet counts are also shown (black, right axis). TTP episode number (e.g. # 32) refers to episodes denoted in Fig. 1. Points at which rituximab (Rtx) was given are highlighted by purple arrows. ADAMTS13 domain specificity results at different time points are marked in orange. A) represents a patient that did not relapse after their first episode. B) and C) are patients that relapsed and whose anti-ADAMTS13 domain specificity had changed at relapse. D) represents a patient that entered clinical remission, but had persistent low ADAMTS13 activity and inhibitory IgG and relapsed repeatedly. E) represents a patient that responded well to rituximab and entered remission. Despite persistent anti-ADAMTS13 antibodies, ADAMTS13 antigen and activity normalised.
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f0030: Longitudinal analysis of acquired TTP patients.A–E) Longitudinal analysis of five acquired TTP patients following a first initial presentation. ADAMTS13 activity (blue), antigen (green), anti-ADAMTS13 IgG titre (red) are shown as % normal (left axis). Platelet counts are also shown (black, right axis). TTP episode number (e.g. # 32) refers to episodes denoted in Fig. 1. Points at which rituximab (Rtx) was given are highlighted by purple arrows. ADAMTS13 domain specificity results at different time points are marked in orange. A) represents a patient that did not relapse after their first episode. B) and C) are patients that relapsed and whose anti-ADAMTS13 domain specificity had changed at relapse. D) represents a patient that entered clinical remission, but had persistent low ADAMTS13 activity and inhibitory IgG and relapsed repeatedly. E) represents a patient that responded well to rituximab and entered remission. Despite persistent anti-ADAMTS13 antibodies, ADAMTS13 antigen and activity normalised.

Mentions: All patients received standard PEX and steroid therapy in conjunction with rituximab. Median follow-up was 3.3 years (range 1–6.3 years) — Supplementary Table 1. Total anti-ADAMTS13 IgG titre fell following therapy with PEX, steroids and rituximab (Scully et al., 2007). There were two cases with solely anti-N-terminal antibodies at presentation that disappeared with time (one example is given in Fig. 6A). Four patients with both anti-N and C-terminal antibodies at presentation all cleared the anti-C-terminal antibodies prior to anti-N-terminal antibodies.


Pathogenicity of Anti-ADAMTS13 Autoantibodies in Acquired Thrombotic Thrombocytopenic Purpura.

Thomas MR, de Groot R, Scully MA, Crawley JT - EBioMedicine (2015)

Longitudinal analysis of acquired TTP patients.A–E) Longitudinal analysis of five acquired TTP patients following a first initial presentation. ADAMTS13 activity (blue), antigen (green), anti-ADAMTS13 IgG titre (red) are shown as % normal (left axis). Platelet counts are also shown (black, right axis). TTP episode number (e.g. # 32) refers to episodes denoted in Fig. 1. Points at which rituximab (Rtx) was given are highlighted by purple arrows. ADAMTS13 domain specificity results at different time points are marked in orange. A) represents a patient that did not relapse after their first episode. B) and C) are patients that relapsed and whose anti-ADAMTS13 domain specificity had changed at relapse. D) represents a patient that entered clinical remission, but had persistent low ADAMTS13 activity and inhibitory IgG and relapsed repeatedly. E) represents a patient that responded well to rituximab and entered remission. Despite persistent anti-ADAMTS13 antibodies, ADAMTS13 antigen and activity normalised.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4563118&req=5

f0030: Longitudinal analysis of acquired TTP patients.A–E) Longitudinal analysis of five acquired TTP patients following a first initial presentation. ADAMTS13 activity (blue), antigen (green), anti-ADAMTS13 IgG titre (red) are shown as % normal (left axis). Platelet counts are also shown (black, right axis). TTP episode number (e.g. # 32) refers to episodes denoted in Fig. 1. Points at which rituximab (Rtx) was given are highlighted by purple arrows. ADAMTS13 domain specificity results at different time points are marked in orange. A) represents a patient that did not relapse after their first episode. B) and C) are patients that relapsed and whose anti-ADAMTS13 domain specificity had changed at relapse. D) represents a patient that entered clinical remission, but had persistent low ADAMTS13 activity and inhibitory IgG and relapsed repeatedly. E) represents a patient that responded well to rituximab and entered remission. Despite persistent anti-ADAMTS13 antibodies, ADAMTS13 antigen and activity normalised.
Mentions: All patients received standard PEX and steroid therapy in conjunction with rituximab. Median follow-up was 3.3 years (range 1–6.3 years) — Supplementary Table 1. Total anti-ADAMTS13 IgG titre fell following therapy with PEX, steroids and rituximab (Scully et al., 2007). There were two cases with solely anti-N-terminal antibodies at presentation that disappeared with time (one example is given in Fig. 6A). Four patients with both anti-N and C-terminal antibodies at presentation all cleared the anti-C-terminal antibodies prior to anti-N-terminal antibodies.

Bottom Line: We demonstrated markedly reduced ADAMTS13 antigen levels in all presentation samples, median 6% normal (range 0-47%), with 84/91 patients having < 25% ADAMTS13 antigen.ADAMTS13 antigen in the lowest quartile at first presentation was associated with increased mortality (odds ratio 5.7).Taken together, our results provide new insights into the pathophysiology of acquired TTP.

View Article: PubMed Central - PubMed

Affiliation: Haemostasis Research Unit, University College London, 51 Chenies Mews, London WC1E 6HX, United Kingdom ; Centre for Haematology, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, United Kingdom.

ABSTRACT

Background: Acquired thrombotic thrombocytopenic purpura (TTP) is an autoimmune disease in which anti-ADAMTS13 autoantibodies cause severe enzyme deficiency. ADAMTS13 deficiency causes the loss of regulation of von Willebrand factor multimeric size and platelet-tethering function, which results in the formation of disseminated microvascular platelet microthrombi. Precisely how anti-ADAMTS13 autoantibodies, or antibody subsets, cause ADAMTS13 deficiency (ADAMTS13 activity generally < 10%) has not been formally investigated.

Methods: We analysed 92 acquired TTP episodes at presentation, through treatment and remission/relapse using epitope mapping and functional analyses to understand the pathogenic mechanisms of anti-ADAMTS13 IgG.

Results: 89/92 of TTP episodes had IgG recognising the ADAMTS13 N-terminal domains. The central spacer domain was the only N-terminal antigenic target detected. 38/92 TTP episodes had autoantibodies recognising the N-terminal domains alone; 54/92 TTP episodes also had antibodies against the ADAMTS13 C-terminal domains (TSP2-8 and/or CUB domains). Changes in autoantibody specificity were detected in 9/16 patients at relapse, suggesting a continued development of the disease. Functional analyses on IgG from 43 patients revealed inhibitory IgG were limited to anti-spacer domain antibodies. However, 15/43 patients had autoantibodies with no detectable inhibitory action and as many as 32/43 patients had autoantibodies with inhibitory function that was insufficient to account for the severe deficiency state, suggesting that in many patients there is an alternative pathogenic mechanism. We therefore analysed plasma ADAMTS13 antigen levels in 91 acquired TTP presentation samples. We demonstrated markedly reduced ADAMTS13 antigen levels in all presentation samples, median 6% normal (range 0-47%), with 84/91 patients having < 25% ADAMTS13 antigen. ADAMTS13 antigen in the lowest quartile at first presentation was associated with increased mortality (odds ratio 5.7).

Conclusions: Anti-spacer domain autoantibodies are the major inhibitory antibodies in acquired TTP. However, depletion of ADAMTS13 antigen (rather than enzyme inhibition) is a dominant pathogenic mechanism. ADAMTS13 antigen levels at presentation have prognostic significance. Taken together, our results provide new insights into the pathophysiology of acquired TTP.

No MeSH data available.


Related in: MedlinePlus