Limits...
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

ADAMTS13 plasma antigen levels in acquired TTP patients.A) Plasma ADAMTS13 antigen levels (left axis, ng/ml; right axis % normal levels) were measured by ELISA in 67 normal healthy controls and 91 acquired TTP patient samples at presentation. To ensure that reduced ADAMTS13 levels were not attributable to epitope masking by the autoantibodies, ADAMTS13 levels were measured in pooled normal plasma (PNP) that was preincubated in the presence of IgG isolated from 14 different TTP patient episodes. Patient antibodies did not appreciably influence the ELISA. B) Plasma ADAMTS13 antigen levels at first presentation in acquired TTP patients separated into anti-N-terminal alone, anti-N- and C-terminal antibodies, and patients with apparently non-inhibitory antibodies (Group IV patients from Fig. 4). C) Plasma ADAMTS13 antigen levels in acquired TTP patients at first presentation that survived their first episode or died. In A–C, individual concentrations are shown, the median is represented by a horizontal line. Statistical comparisons made are marked.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4563118&req=5

f0025: ADAMTS13 plasma antigen levels in acquired TTP patients.A) Plasma ADAMTS13 antigen levels (left axis, ng/ml; right axis % normal levels) were measured by ELISA in 67 normal healthy controls and 91 acquired TTP patient samples at presentation. To ensure that reduced ADAMTS13 levels were not attributable to epitope masking by the autoantibodies, ADAMTS13 levels were measured in pooled normal plasma (PNP) that was preincubated in the presence of IgG isolated from 14 different TTP patient episodes. Patient antibodies did not appreciably influence the ELISA. B) Plasma ADAMTS13 antigen levels at first presentation in acquired TTP patients separated into anti-N-terminal alone, anti-N- and C-terminal antibodies, and patients with apparently non-inhibitory antibodies (Group IV patients from Fig. 4). C) Plasma ADAMTS13 antigen levels in acquired TTP patients at first presentation that survived their first episode or died. In A–C, individual concentrations are shown, the median is represented by a horizontal line. Statistical comparisons made are marked.

Mentions: In 91 TTP presentation samples (one sample was lost to analysis due to insufficient sample size), ADAMTS13 concentrations were significantly lower [median 58 ng/ml (6% normal); range 0–450 ng/ml (0%–47%)] than in 67 normal volunteers [median 951 ng/ml (range 515–1829 ng/ml) p < 0.0001] (Fig. 5A). Indeed, 84/91 (92%) patients had antigen levels < 25%.


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

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

ADAMTS13 plasma antigen levels in acquired TTP patients.A) Plasma ADAMTS13 antigen levels (left axis, ng/ml; right axis % normal levels) were measured by ELISA in 67 normal healthy controls and 91 acquired TTP patient samples at presentation. To ensure that reduced ADAMTS13 levels were not attributable to epitope masking by the autoantibodies, ADAMTS13 levels were measured in pooled normal plasma (PNP) that was preincubated in the presence of IgG isolated from 14 different TTP patient episodes. Patient antibodies did not appreciably influence the ELISA. B) Plasma ADAMTS13 antigen levels at first presentation in acquired TTP patients separated into anti-N-terminal alone, anti-N- and C-terminal antibodies, and patients with apparently non-inhibitory antibodies (Group IV patients from Fig. 4). C) Plasma ADAMTS13 antigen levels in acquired TTP patients at first presentation that survived their first episode or died. In A–C, individual concentrations are shown, the median is represented by a horizontal line. Statistical comparisons made are marked.
© Copyright Policy - CC BY-NC-ND
Related In: Results  -  Collection

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

f0025: ADAMTS13 plasma antigen levels in acquired TTP patients.A) Plasma ADAMTS13 antigen levels (left axis, ng/ml; right axis % normal levels) were measured by ELISA in 67 normal healthy controls and 91 acquired TTP patient samples at presentation. To ensure that reduced ADAMTS13 levels were not attributable to epitope masking by the autoantibodies, ADAMTS13 levels were measured in pooled normal plasma (PNP) that was preincubated in the presence of IgG isolated from 14 different TTP patient episodes. Patient antibodies did not appreciably influence the ELISA. B) Plasma ADAMTS13 antigen levels at first presentation in acquired TTP patients separated into anti-N-terminal alone, anti-N- and C-terminal antibodies, and patients with apparently non-inhibitory antibodies (Group IV patients from Fig. 4). C) Plasma ADAMTS13 antigen levels in acquired TTP patients at first presentation that survived their first episode or died. In A–C, individual concentrations are shown, the median is represented by a horizontal line. Statistical comparisons made are marked.
Mentions: In 91 TTP presentation samples (one sample was lost to analysis due to insufficient sample size), ADAMTS13 concentrations were significantly lower [median 58 ng/ml (6% normal); range 0–450 ng/ml (0%–47%)] than in 67 normal volunteers [median 951 ng/ml (range 515–1829 ng/ml) p < 0.0001] (Fig. 5A). Indeed, 84/91 (92%) patients had antigen levels < 25%.

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