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BACKGROUND: Acquired von Willebrand syndrome (aVWS) is common in patients with mechanical circulatory support (MCS) devices. In these patients, the high shear stress in the device leads to increased shear-induced proteolysis of von Willebrand factor (VWF) by ADAMTS13 (A Disintegrin And Metalloprotease with Thrombospondin type 1 repeats, number 13). As a result, the high molecular weight (HMW) VWF multimers are lost, leading to a decreased VWF function and impaired haemostasis which could explain the bleeding complications that are frequently observed in these patients. To counteract this abnormal VWF degradation by ADAMTS13, we developed a novel targeted therapy, using an anti-ADAMTS13 monoclonal antibody (mAb) that inhibits the shear-induced proteolysis of VWF by ADAMTS13. METHODS: Human or bovine blood was circulated through in vitro MCS device systems with either inhibitory anti-ADAMTS13 mAb 3H9 or 17C7 (20 μg/mL) or control anti-ADAMTS13 mAb 5C11 or PBS. VWF multimers and function (collagen binding activity) were determined at different time points. Next, Impella® pumps were implanted in calves and the calves were injected with PBS and subsequently treated with mAb 17C7. VWF, ADAMTS13 and blood parameters were determined. RESULTS: We demonstrated that blocking ADAMTS13 could prevent the loss of HMW VWF multimers in in vitro MCS device systems. Importantly, our antibody could reverse aVWS in a preclinical Impella®-induced aVWS calf model. CONCLUSION: Hence, inhibition of ADAMTS13 could become a novel therapeutic strategy to manage aVWS in MCS device patients.

Introduction Bleeding is the most frequent adverse event in patients with continuous flow mechanical circulatory support (CF-MCS) and has been linked to the occurrence of acquired von Willebrand syndrome (aVWS). MCS devices cause an increased shear-induced proteolysis of von Willebrand factor (VWF) by ADAMTS13, leading to aVWS. Hence, specifically blocking ADAMTS13 might be an efficient way to rescue the loss of HMW VWF multimers in CF-MCS patients. Purpose To investigate if blocking ADAMTS13, using an in-house developed inhibitory anti-ADAMTS13 monoclonal antibody (mAb), prevents the loss of high molecular weight (HMW) VWF multimers in in vitro CF-MCS systems and to determine the efficacy of this therapy in a CF-MCS calf model. Methods Human blood was perfused through in vitro CF-MCS systems (Heartmate II and Impella CP, axial flow heart pumps) in the presence of the inhibitory or control mAb (20 μg/mL). Bovine blood was perfused through an in vitro Impella 5.5 system with the inhibitory mAb (20 μg/mL) or PBS. Next, Impella 5.5 pumps were implanted in calves. One dose of the inhibitory mAb (600 μg/kg) or PBS was injected eight days after Impella implantation. Plasma samples were analysed for VWF multimers, VWF antigen (VWF:Ag) and VWF collagen binding activity (VWF:CB). Results A time-dependent decrease in HMW VWF multimers was observed in both in vitro CF-MCS systems in the presence of the control mAb, leading to a 70% reduction of HMW VWF multimers, 180 minutes (min) after blood perfusion (p=0.01 for HM II and p=0.0003 for Impella). This was also reflected by a severely decreased VWF:CB/VWF:Ag ratio (0.59±0.11 and 0.52±0.10 at 180 min versus 1.00±0.06 and 1.07±0.09 before perfusion, for the HM II (p=0.03) and Impella (p=0.001) respectively). Interestingly, blocking ADAMTS13 using the inhibitory mAb prevented the loss of HMW VWF multimers in both systems (p=0.50 for the HM II and p=0.06 for the Impella, 180 min after the start of perfusion). The preservation of HMW VWF multimers was also reflected by normal VWF:CB/VWF:Ag ratios (0.92±0.16 and 0.97±0.11 at 180 min versus 0.93±0.09 and 1.19±0.12 before perfusion for the HM II (p=0.75) and Impella (p=0.06) respectively). Blocking bovine ADAMTS13 using the inhibitory mAb could prevent the loss of HMW VWF multimers in the in vitro Impella 5.5 system, showing that the calf is a good preclinical animal model to study the in vivo effect of this novel therapy. Impella implantation in the calves led to a decrease in HMW VWF multimers (Figure 1A and B). Hence, this animal model represents the VWF laboratory features of MCS-induced aVWS. Moreover, the loss of HMW VWF multimers after pump implantation could be rescued after injection of the inhibitory mAb (Figure 1A and B). Conclusion Blocking ADAMTS13 rescues MCS-induced VWF proteolysis in calves. Hence, inhibiting ADAMTS13 function could become a promising therapeutic strategy to rescue aVWS-induced bleeding in MCS patients. Figure 1. Impella calf model Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): Fund for Scientific Research Flanders

BACKGROUND: In immune-mediated thrombotic thrombocytopenic purpura (iTTP), patients develop an immune response against the multidomain enzyme ADAMTS13. ADAMTS13 consists of a metalloprotease (M) and disintegrin-like (D) domain, 8 thrombospondin type 1 repeats (T1-T8), a cysteine-rich (C), a spacer (S), and 2 CUB domains (CUB1-2). Previous epitope mapping studies have used relatively large overlapping ADAMTS13 fragments. OBJECTIVES: We aimed at developing small nonoverlapping ADAMTS13 fragments to fine map anti-ADAMTS13 autoantibodies in iTTP patients. METHODS: A library of 16 ADAMTS13 fragments, comprising several small (M, DT, C, S, T2-T5, T6-T8, CUB1, CUB2), and some larger fragments with overlapping domains (MDT, MDTC, DTC, CS, T2-T8, CUB1-2, MDTCS, T2-C2), were generated. All fragments, and ADAMTS13, were expressed as a fusion protein with albumin domain 1, and purified. The folding of the fragments was tested using 17 anti-ADAMTS13 monoclonal antibodies with known epitopes. An epitope mapping assay using small ADAMTS13 fragments was set up, and validated by analyzing 18 iTTP patient samples. RESULTS: Validation with the monoclonal antibodies demonstrated that single S and CUB1 were not correctly folded, and therefore CS and CUB1-2 fragments were selected instead of single C, S, CUB1, and CUB2 fragments. Epitope mapping of antibodies of patients with iTTP confirmed that 6 nonoverlapping ADAMTS13 fragments M, DT, CS, T2-T5, T6-T8, and CUB1-2 were sufficient to accurately determine the antibody-binding sites. CONCLUSION: We have developed a tool to profile patients with iTTP according to their anti-ADAMTS13 antibodies for a better insight in their immune response. ispartof: RESEARCH AND PRACTICE IN THROMBOSIS AND HAEMOSTASIS vol:4 issue:5 pages:918-930 ispartof: location:United States status: published

Recently, we showed that ADAMTS13 circulates in an open conformation during the acute phase of immune-mediated thrombotic thrombocytopenic purpura (iTTP). Although the cause of this conformational change remains elusive, ADAMTS13 is primarily closed in iTTP patients in remission with ADAMTS13 activity >50% and undetectable anti-ADAMTS13 autoantibodies, as well as after rituximab treatment, suggesting a role for anti-ADAMTS13 autoantibodies. Therefore, immunoglobulin G from 18 acute iTTP patients was purified and added to closed ADAMTS13 in healthy donor plasma. This resulted in open ADAMTS13 in 14 of 18 (78%) samples, proving that anti-ADAMTS13 autoantibodies can induce an open ADAMTS13 conformation. To further elucidate the conformation of ADAMTS13 in iTTP patients, we studied a novel iTTP patient cohort (n = 197) that also included plasma samples from iTTP patients in remission in whom ADAMTS13 activity was 50%, although free anti-ADAMTS13 autoantibodies were not always detected. Thus, open ADAMTS13 is a hallmark of acute iTTP, as well as a novel biomarker that can be used to detect subclinical iTTP in patients in remission. Finally, a long-term follow-up study in 1 iTTP patient showed that the open conformation precedes a substantial drop in ADAMTS13 activity. In conclusion, we have shown that anti-ADAMTS13 autoantibodies from iTTP patients induce an open ADAMTS13 conformation. Most importantly, an open ADAMTS13 conformation is a biomarker for subclinical iTTP and could become an important tool in TTP management. ispartof: BLOOD vol:136 issue:3 pages:353-361 ispartof: location:United States status: published

In autoantibody-mediated autoimmune diseases, autoantibody profiling allows patients to be stratified and links autoantibodies with disease severity and outcome. However, in immune-mediated thrombotic thrombocytopenic purpura (iTTP) patients, stratification according to antibody profiles and their clinical relevance has not been fully explored. We aimed to develop a new type of autoantibody profiling assay for iTTP based on the use of anti-idiotypic antibodies. Anti-idiotypic antibodies against 3 anti-spacer autoantibodies were generated in mice and were used to capture the respective anti-spacer idiotopes from 151 acute iTTP plasma samples. We next deciphered these anti-spacer idiotope profiles in iTTP patients and investigated whether these limited idiotope profiles could be linked with disease severity. We developed 3 anti-idiotypic antibodies that recognized particular idiotopes in the anti-spacer autoantibodies II-1, TTP73 or I-9, that are involved in ADAMTS13 binding; 35%, 24% and 42% of patients were positive for antibodies with the II-1, TTP73 and I-9 idiotopes, respectively. Stratifying patients according to the corresponding 8 anti-spacer idiotope profiles provided a new insight into the anti-spacer II-1, TTP73 and I-9 idiotope profiles in these patients. Finally, these limited idiotope profiles showed no association with disease severity. We successfully developed 3 anti-idiotypic antibodies that allowed us to determine the profiles of the anti-spacer II-1, TTP73 and I-9 idiotopes in iTTP patients. Increasing the number of patients and/or future development of additional anti-idiotypic antibodies against other anti-ADAMTS13 autoantibodies might allow idiotope profiles of clinical, prognostic value to be identified. ispartof: HAEMATOLOGICA vol:104 issue:6 pages:1268-1276 ispartof: location:Italy status: published

Plasma ADAMTS13 circulates in a folded conformation that is stabilized by an interaction between the central Spacer domain and the C-terminal CUB (complement components C1r and C1s, sea urchin protein Uegf, and bone morphogenetic protein-1) domains. Binding of ADAMTS13 to the VWF D4(-CK) domains or to certain activating murine monoclonal antibodies (mAbs) induces a structural change that extends ADAMTS13 into an open conformation that enhances its function. The objective was to characterize the mechanism by which conformational activation enhances ADAMTS13-mediated proteolysis of VWF. The activating effects of a novel anti-Spacer (3E4) and the anti-CUB1 (17G2) mAbs on the kinetics of proteolysis of VWF A2 domain fragments by ADAMTS13 were analyzed. mAb-induced conformational changes in ADAMTS13 were investigated by enzyme-linked immunosorbent assay. Both mAbs enhanced ADAMTS13 catalytic efficiency (kcat/Km) by ∼twofold (3E4: 2.0-fold; 17G2: 1.8-fold). Contrary to previous hypotheses, ADAMTS13 activation was not mediated through exposure of the Spacer or cysteine-rich domain exosites. Kinetic analyses revealed that mAb-induced conformational extension of ADAMTS13 enhances the proteolytic function of the metalloprotease domain (kcat), rather than augmenting substrate binding (Km). A conformational effect on the metalloprotease domain was further corroborated by the finding that incubation of ADAMTS13 with either mAb exposed a cryptic epitope in the metalloprotease domain that is normally concealed when ADAMTS13 is in a closed conformation. We show for the first time that the primary mechanism of mAb-induced conformational activation of ADAMTS13 is not a consequence of functional exosite exposure. Rather, our data are consistent with an allosteric activation mechanism on the metalloprotease domain that augments active site function. ispartof: BLOOD ADVANCES vol:4 issue:6 pages:1072-1080 ispartof: location:United States status: published

Several studies have already identified atopy as a risk factor for the development of exercise-induced bronchoconstriction (EIB) in adult elite athletes (1-3). Skin prick test or serum specific IgE to common aero-allergens is used to determine the patient's atopy status (4). In 2009, Bonini M et al. introduced a screening tool to predict atopy in elite adult athletes, namely the Allergy Questionnaire for Athletes or short the AQUA© questionnaire (5). This article is protected by copyright. All rights reserved. ispartof: PEDIATRIC ALLERGY AND IMMUNOLOGY vol:29 issue:6 pages:648-650 ispartof: location:England status: published

INTRODUCTION: Patients suffering from congenital thrombotic thrombocytopenic purpura (cTTP) have a deficiency in ADAMTS13 due to mutations in their ADAMTS13 gene. OBJECTIVE: The aim of this study was to determine ADAMTS13 parameters (activity, antigen, and mutations), to investigate if the propositus suffered from child-onset cTTP, and to study the in vitro effect of the ADAMTS13 mutations. METHODS: ADAMTS13 activity and antigen were determined using the FRETS VWF73 assay and ELISA and ADAMTS13 mutations via sequencing of the exons. Mutant proteins were expressed in Chinese hamster ovary cells, and their expression was studied using fluorescence microscopy and ELISA. Molecular modeling was used to evaluate the effect of the mutations on ADAMTS13 structure and stability. RESULTS: The propositus was diagnosed with cTTP at the age of 20. ADAMTS13 activity was below 10%, and 2 compound heterozygous mutations, the p.R498C point and the p.G259PfsX133 frameshift mutation, were identified. Expression of ADAMTS13 mutants revealed that the p.R498C and the p.G259PfsX133 mutation cause secretion and translation defects in vitro, respectively. Molecular modeling showed that the R498 intra-domain interactions are lacking in the p.R498C mutant, resulting in protein instability. CONCLUSION: The ADAMTS13 mutations result in a severe ADAMTS13 deficiency explaining the patient's phenotype. ispartof: EUROPEAN JOURNAL OF HAEMATOLOGY vol:0 issue:2 pages:1-9 ispartof: location:England status: published

Preemptive rituximab infusions prevent relapses in immune thrombotic thrombocytopenic purpura (iTTP) by maintaining normal ADAMTS13 activity. However, the long-term outcome of these patients and the potential adverse events of this strategy need to be determined. We report the long-term outcome of 92 patients with iTTP in clinical remission who received preemptive rituximab after identification of severe ADAMTS13 deficiency (activity 1 iTTP episode, and the median cumulative relapse incidence before preemptive rituximab was 0.33 episode per year (interquartile range [IQR], 0.23-0.66). After preemptive rituximab, the median cumulative relapse incidence in the whole population decreased to 0 episodes per year (IQR, 0-1.32; P < .001). After preemptive rituximab, ADAMTS13 activity recovery was sustained in 34 patients (37%) during a follow-up of 31.5 months (IQR, 18-65), and severe ADAMTS13 deficiency recurred in 45 patients (49%) after the initial improvement. ADAMTS13 activity usually improved with additional courses of preemptive rituximab. In 13 patients (14%), ADAMTS13 activity remained undetectable after the first rituximab course, but retreatment was efficient in 6 of 10 cases. In total, 14 patients (15%) clinically relapsed, and 19 patients (20.7%) experienced benign adverse effects. Preemptive rituximab treatment was associated with a change in ADAMTS13 conformation in respondent patients. Finally, in the group of 23 historical patients with iTTP and persistently undetectable ADAMTS13 activity, 74% clinically relapsed after a 7-year follow-up (IQR, 5-11). In conclusion, persistently undetectable ADAMTS13 activity in iTTP during remission is associated with a higher relapse rate. Preemptive rituximab reduces clinical relapses by maintaining a detectable ADAMTS13 activity with an advantageous risk-benefit balance. ispartof: Blood vol:132 issue:20 pages:2143-2153 ispartof: location:United States status: published

Background. Deficient ADAMTS13 activity (TS13:act 50%. However, also iTTP patients in remission with a persistent ( Aim. Determine ADAMTS13 conformation in plasma of iTTP patients during acute TTP and remission when TS13:act is 50% and investigate if anti-ADAMTS13 autoAbs induce conformational changes in ADAMTS13. Methods. TS13:act was determined in 120 iTTP plasma samples from 4 different centers (Marseille, Milan, Budapest, Utrecht). Samples were categorized according to the presence of clinical symptoms (acute versusremission) and their TS13:act in remission (>50%, 10-50%, Results. Of the 120 iTTP plasma samples, 46 were obtained during the acute (clinical signs present) and 74 during the remission phase (clinical signs absent). Further subdividing remission samples showed that TS13:act was >50% in 41, 10-50% in 14 and 50%, confirming our previous results. Interestingly, ADAMTS13 was open in 93% and 89% of remission samples with TS13:act 10-50% and Conclusion. We show that ADAMTS13 is not only in the open conformation in iTTP patient plasma during the acute phase but also in remission when TS13:act is Disclosures Peyvandi: Octapharma US: Honoraria; Kedrion: Consultancy; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Grifols: Speakers Bureau; Sobi: Speakers Bureau; Shire: Speakers Bureau; Novo Nordisk: Speakers Bureau; Octapharma US: Honoraria; Octapharma US: Honoraria; Novo Nordisk: Speakers Bureau; Kedrion: Consultancy; Roche: Speakers Bureau; Novo Nordisk: Speakers Bureau; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Shire: Speakers Bureau; Sobi: Speakers Bureau; Roche: Speakers Bureau; Roche: Speakers Bureau; Shire: Speakers Bureau; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Octapharma US: Honoraria; Roche: Speakers Bureau; Roche: Speakers Bureau; Grifols: Speakers Bureau; Sobi: Speakers Bureau; Ablynx: Other: Member of Advisory Board, Speakers Bureau; Sobi: Speakers Bureau; Shire: Speakers Bureau; Sobi: Speakers Bureau; Novo Nordisk: Speakers Bureau; Shire: Speakers Bureau; Kedrion: Consultancy; Novo Nordisk: Speakers Bureau; Grifols: Speakers Bureau; Grifols: Speakers Bureau; Kedrion: Consultancy; Kedrion: Consultancy; Grifols: Speakers Bureau; Octapharma US: Honoraria. Coppo:Ablynx: Consultancy. Veyradier:LFB: Other: Investigator. Vanhoorelbeke:Shire: Consultancy; Ablynx: Consultancy.

In this study, we investigated a case of pregnancy-onset thrombotic thrombocytopenic purpura (TTP). The patient had severely decreased ADAMTS13 ( a d isintegrin a nd m etalloprotease with t hrombo s pondin type 1 motif, member 13) activity levels during acute phase and the presence of inhibitory anti-ADAMTS13 autoantibodies was demonstrated, which led to the diagnosis of immune-mediated TTP. However, ADAMTS13 activity was only mildly restored during remission, although inhibitory anti-ADAMTS13 antibodies were no longer detected. We hypothesized that genetic abnormalities could account for this discrepancy between ADAMTS13 activity and antigen. Genetic analysis revealed the presence of two heterozygous substitutions on the same allele: a single nucleotide polymorphism (SNP) c.2699C > T (p.A900V), located in the beginning of the T5 domain, and a mutation c.3530G > A (p.R1177Q) located in the third linker region of ADAMTS13. In vitro testing of those substitutions by expression of recombinant proteins revealed a normal secretion but a reduced ADAMTS13 activity by the novel p.R1177Q mutation, which could partially explain the subnormal activity levels found during remission. Although changes in the linker region might induce conformational changes in ADAMTS13, the p.R1177Q mutation in the third linker region of ADAMTS13 did not expose a cryptic epitope in the metalloprotease domain. In conclusion, we report on an immune-mediated pregnancy-onset TTP patient who had inhibitory anti-ADAMTS13 autoantibodies during acute phase, but not during remission. Genetic analysis confirmed the diagnosis of immune-mediated TTP and revealed the novel p.R1177Q mutation which mildly impaired ADAMTS13 activity. ispartof: TH Open vol:0 issue:1 pages:1-8 ispartof: location:Germany status: published

Background ADAMTS13 circulates in a folded conformation, which is mediated by interactions between the C-terminal CUB domains and its central Spacer domain. Binding of ADAMTS13 to the VWF D4-CK domains disrupts the CUB-Spacer interaction, inducing a structural change that extends ADAMTS13 into an open conformation that enhances catalytic efficiency ~2-fold. This mechanism supports a model in which ADAMTS13 unfolding induces exposure of an exosite in the Spacer domain that interacts with the VWF A2 domain, increasing the affinity between the two molecules, and, therefore, the rate of proteolysis. The D4-CK-mediated conformational activation of ADAMTS13 can be mimicked in vitro with the use of antibodies that disrupt the CUB-Spacer interaction, such as the previously published anti-CUB antibody, Ab17G2. We recently generated a novel, activating antibody against the Spacer domain (Ab3E4). Aim To characterize the mechanism by which the Ab17G2 and Ab3E4 enhance the catalytic efficiency of ADAMTS13. Methods The effects of the Ab17G2 and Ab3E4 on the activity of ADAMTS13 were studied using FRETS-VWF73. The effects of the Ab17G2 and Ab3E4 on the kinetics of VWF96 (VWF G1573-R1668) proteolysis were characterized using an in-house assay. ELISA was used to investigate conformational changes in ADAMTS13 induced by the Ab17G2 and Ab3E4. Results Both Ab17G2 and Ab3E4 enhanced FRETS-VWF73 proteolysis by ~1.7-fold. This result was reproduced using the VWF96 substrate; the Ab17G2 and Ab3E4 enhanced the catalytic efficiency (kcat/Km) of ADAMTS13 by ~1.8- and ~2.0-fold, respectively. The activation was dependent on the conformational extension of ADAMTS13, since the antibodies could not enhance the activity of an ADAMTS13 variant that lacks the TSP2-CUB2 domains (MDTCS). Surprisingly, ADAMTS13 activation was not mediated through exposure of the Spacer or Cys-rich domain exosites as previously proposed, as the Ab17G2 and Ab3E4 efficiently enhanced proteolysis of VWF96 variants in which the Spacer/Cys-rich exosite binding sites were disrupted. Kinetic analysis of VWF96 proteolysis showed that the Ab17G2- and Ab3E4-induced activation of ADAMTS13 is primarily manifest through a ~1.5- to ~2-fold increase in enzyme turnover (kcat). Thus, contrary to the current model, this suggests that the conformational extension of ADAMTS13 influences the functionality of the active site, and not substrate binding affinity (Km). Incubating ADAMTS13 with either Ab17G2 or Ab3E4 exposed a cryptic epitope in the metalloprotease domain that was specifically detected by ELISA, further corroborating that the antibodies induce a conformational change in ADAMTS13 affecting the M domain. Conclusion Antibodies can be used as tools for understanding the structure/function of enzymes. Using activating antibodies against the Spacer and CUB1 domains of ADAMTS13, we show for the first time that the activation of ADAMTS13 following its unfolding is not a result of exposure of a functional exosite in Spacer/Cys-rich domain that increases affinity to VWF. Rather, our data are consistent with an allosteric activation mechanism upon the metalloprotease domain. We propose that ADAMTS13 unfolding causes a conformational change in the active site that further activates the enzyme. We are currently investigating whether the D4-CK-induced enhancement of ADAMTS13 proteolytic activity is also mediated by conformational changes in the active site. Disclosures Vanhoorelbeke: Ablynx: Consultancy; Shire: Consultancy.

A deficiency in ADAMTS13 (A Disintegrin And Metalloprotease with ThromboSpondin type-1 repeats, member 13) is associated with thrombotic thrombocytopenic purpura (TTP). Congenital TTP is caused by a defect in the ADAMTS13 gene resulting in decreased or absent enzyme activity; acquired TTP results from autoantibodies that either inhibit the activity or increase the clearance of ADAMTS13. Despite major progress in recent years in our understanding of the disease, many aspects around the pathophysiology of TTP are still unclear. Newer studies expanded the TTP field from ADAMTS13 and inhibitory antibodies to immune complexes, cloned autoantibodies, and a possible involvement of other proteases. Additionally, several new treatment strategies supplementing plasma-exchange and infusion are under investigation for a better and more specific treatment of TTP patients. In this review, we discuss the recent insights in TTP pathophysiology and describe upcoming therapeutic opportunities.

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 FEV 1 ≥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 FEV 1 , which is equivalent to 85% of MVV in adults. A threshold of 70% of MVV (21 times FEV 1 ) 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.

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