An open conformation of ADAMTS-13 is a hallmark of acute acquired thrombotic thrombocytopenic purpura.

Essentials Conformational changes in ADAMTS-13 are part of its mode-of-action. The murine anti-ADAMTS-13 antibody 1C4 discriminates between folded and open ADAMTS-13. ADAMTS-13 conformation is open in acute acquired thrombotic thrombocytopenic purpura (TTP). Our study forms an important basis to fully elucidate the pathophysiology of TTP. SUMMARY: Background Acquired thrombotic thrombocytopenic purpura (aTTP) is an autoimmune disorder characterized by absent ADAMTS-13 activity and the presence of anti-ADAMTS-13 autoantibodies. Recently, it was shown that ADAMTS-13 adopts a folded or an open conformation. Objectives As conformational changes in self-antigens play a role in the pathophysiology of different autoimmune diseases, we hypothesized that the conformation of ADAMTS-13 changes during acute aTTP. Methods Antibodies recognizing cryptic epitopes in the spacer domain were generated. Next, the conformation of ADAMTS-13 in 40 healthy donors (HDs), 99 aTTP patients (63 in the acute phase versus 36 in remission), 12 hemolytic-uremic syndrome (HUS) patients and 63 sepsis patients was determined with ELISA. Results The antibody 1C4 recognizes a cryptic epitope in ADAMTS-13. Therefore, we were able to discriminate between a folded and an open ADAMTS-13 conformation. We showed that ADAMTS-13 in HDs does not bind to 1C4, indicating that ADAMTS-13 circulates in a folded conformation. Similar results were obtained for HUS and sepsis patients. In contrast, ADAMTS-13 of acute aTTP patients bound to 1C4 in 92% of the cases, whereas, in most cases, this binding was abolished during remission, showing that the conformation of ADAMTS-13 is open during an acute aTTP episode. Conclusions Our study shows that, besides absent ADAMTS-13 activity and the presence of anti-ADAMTS-13 autoantibodies, an open ADAMTS-13 conformation is also a hallmark of acute aTTP. Demonstrating this altered ADAMTS-13 conformation in acute aTTP will help to further unravel the pathophysiology of aTTP and lead to improved therapy and diagnosis.

Feasibility to apply eucapnic voluntary hyperventilation in young elite athletes.

INTRODUCTION: Exercise-induced bronchoconstriction (EIB) is more common in athletes compared to the general population. The eucapnic voluntary hyperventilation test is used to detect EIB in adult athletes. It is however unclear whether this technique is also applicable to young athletes. METHODS: Young athletes (basketball (n = 13), football (n = 19), swimming (n = 12)) were recruited at the start of their elite sports career (12-14 years). Eight age-matched controls were also recruited. Eucapnic voluntary hyperventilation test was performed according to ATS guidelines in all subjects. A second (after 1 year, n = 32) and third (after 2 years, n = 39) measurement was performed in a subgroup of athletes and controls. RESULTS: At time of first evaluation, 3/13 basketball players, 4/19 football players, 5/11 swimmers and 1/8 controls met criteria for EIB (fall in FEV1≥10% after EVH). A ventilation rate of >85% of the maximal voluntary ventilation (MVV) is recommended by current guidelines (for adults) but was only achieved by a low number of individuals (first occasion: 27%, third occasion: 45%) However, MVV in young athletes corresponds to 30 times FEV1, which is equivalent to 85% of MVV in adults. A threshold of 70% of MVV (21 times FEV1) is feasible in the majority of young athletes. CONCLUSION: EIB is present in a substantial number of individuals at the age of 12-14 years, especially in swimmers. This underscores the importance of screening for EIB at this age. EVH is feasible in young elite athletes, however target ventilation needs to be adjusted accordingly.