A novel mechanism underlying allosteric regulation of ADAMTS-13 revealed by hydrogen-deuterium exchange plus mass spectrometry.

Background: ADAMTS-13, a plasma metalloprotease, cleaves von Willebrand factor. ADAMTS-13 activity appears to be regulated through allosteric inhibition by its distal C-terminus. Objectives: The objective of this study was to better understand how domain-domain interactions may affect ADAMTS-13 conformations and functions. Methods: We performed deuterium-hydrogen exchange plus mass spectrometry to assess the number and rate of deuterium incorporation into various peptides of full-length ADAMTS-13 and its truncated variants. Results: Under physiological conditions, a bimodal distribution of deuterium incorporation was detected in the peptides from metalloprotease (217-230 and 282-304), cysteine-rich (446-482), and CUB (for complement C1r/C1s, Uegf, Bmp1) domains (1185-1214, 1313-1330, 1341-1347, 1358-1378, and 1393-1407) of full-length recombinant ADAMTS-13, but not of truncated variants. These results suggest that the full-length ADAMTS-13 undergoes conformational changes. On removal of the middle and distal C-terminal domains, the number and rate of deuterium incorporation were increased in the peptides from cysteine-rich (445-467, 467-482, and 495-503) and spacer domains (621-642 and 655-654) but decreased in the peptides from metalloprotease (115-124, 217-230, and 274-281). Moreover, most peptides, except for 217-230 and 1357-1376, exhibited a pD-dependent deuterium incorporation in the full-length ADAMTS-13, but not in the truncated variant (eg, MDTCS or T5C). These results further suggest that the bimodal deuterium incorporation observed in the peptides from the full-length ADAMTS-13 is the result of potential impact from the middle to distal C-terminal domains. Surface plasmon resonance revealed the direct binding interactions between the distal and proximal domains of ADAMTS-13. Conclusion: Our results provide novel insight on how intramolecular interactions may affect conformations of ADAMTS-13, thus regulating its proteolytic functions.

Hepatitis A virus infection is complicated by both pancytopenia and autoimmune hemolytic anemia (AIHA).

Introduction: Hepatitis A infection affects liver tissue primarily and might have some extrahepatic manifestations. Hematologically, the extrahepatic manifestations include aplastic anemia, red cell aplasia, and thrombocytopenia. There were reports about pancytopenia among patients with Hepatitis A infections, however, its association with autoimmune hemolytic anemia is rare as in our case. Case presentation: A 30-year-old male visited the emergency room with tiredness, unmeasured fever, and jaundice. He also mentioned that recently he had anorexia and weight loss without night sweating. Initial laboratory findings showed pancytopenia and marked elevation of AST and ALT. Direct Coombs and IgM anti-Hepatitis A virus were positive. Consequently, he was diagnosed with HAV complicated by both pancytopenia and AIHA and treated with prednisone (1 mg/kg) leading to significant improvement in his anemia. Discussion: This report describes a case of acute viral hepatitis A complicated with severe autoimmune hemolytic anemia and pancytopenia, which was successfully treated by high dose (1 mg/kg/day) prednisolone therapy. Conclusion: This case represents a rare case in the literature review that can increase the awareness of the wide range of complications of HAV and its association with pancytopenia and AIHA.

Emerging Concepts in Immune Thrombotic Thrombocytopenic Purpura.

Immune thrombotic thrombocytopenic purpura (iTTP) is an autoimmune disorder of which the etiology is not fully understood. Autoantibodies targeting ADAMTS13 in iTTP patients have extensively been studied, the immunological mechanisms leading to the breach of tolerance remain to be uncovered. This review addresses the current knowledge on genetic factors associated with the development of iTTP and the interplay between the patient's immune system and environmental factors in the induction of autoimmunity against ADAMTS13. HLA-DRB1*11 has been identified as a risk factor for iTTP in the Caucasian population. Interestingly, HLA-DRB1*08:03 was recently identified as a risk factor in the Japanese population. Combined in vitro and in silico MHC class II peptide presentation approaches suggest that an ADAMTS13-derived peptide may bind to both HLA-DRB1*11 and HLA-DRB1*08:03 through different anchor-residues. It is apparent that iTTP is associated with the presence of infectious microorganisms, viruses being the most widely associated with development of iTTP. Infections may potentially lead to loss of tolerance resulting in the shift from immune homeostasis to autoimmunity. In the model we propose in this review, infections disrupt the epithelial barriers in the gut or lung, promoting exposure of antigen presenting cells in the mucosa-associated lymphoid tissue to the microorganisms. This may result in breach of tolerance through the presentation of microorganism-derived peptides that are homologous to ADAMTS13 on risk alleles for iTTP.

Case Report: Two Cases of Pediatric Thrombotic Thrombocytopenic Purpura Treated With Combined Therapy.

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by a severely reduced activity of the von Willebrand factor-cleaving protease ADAMTS13. Over 95% of TTPs are acquired, due to autoantibody inhibitors. In children, acquired TTP is a very rare, life-threatening disease. To date, no consensus exists on the treatment strategy of pediatric TTP. We report the cases of two pediatric patients with a diagnosis of TTP, successfully treated with a combination of various therapeutic approaches. Although the patients complained of different sets of symptoms, laboratory data showed Coombs negative hemolytic anemia, renal impairment, and low platelet count in both cases. The diagnosis of acquired TTP was supported by the PLASMIC score and confirmed by the reduction of the ADAMTS13 activity and the presence of anti-ADAMTS13 antibodies. Intravenous immunoglobulin, corticosteroids, and plasma exchange (PEX) were performed without delay. As soon as available, caplacizumab was added to the therapy, with a prompt normalization of platelet count. Nevertheless, ADAMTS13 activity was persistently low, and anti-ADAMTS13 antibodies level was high; thus, a course of rituximab was administered, with persistent normalization of laboratory findings. No adverse events were observed during the treatment. In our experience, the combined use of PEX, caplacizumab, and immunosuppressive therapy during the acute phase of the disease is safe and may have a significant impact on the prognosis with successful clinical outcome and decrease in life-threatening events.

Complement Regulatory Genetic Mutations in the Setting of Autoimmune Thrombotic Thrombocytopenic Purpura: A Case Series.

OBJECTIVE: To explore the benefits of adding eculizumab for the treatment of refractory autoimmune thrombotic thrombocytopenic purpura (iTTP) with complement dysregulation. PATIENTS AND METHODS: From January 1, 2014, through July 1, 2017, we identified patients with iTTP defined by ADAMTS13 (disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) levels less than 5% and the presence of ADAMTS13 inhibitor. Patients who progressed after receiving standard of care management for iTTP were subjected to a comprehensive evaluation to look for evidence of complement activation. Herein, we share our single-institute experience regarding the clinical course and treatment algorithm for 3 patients with refractory iTTP. RESULTS: All the patients had clinical deterioration despite treatment with plasma exchange, corticosteroids, rituximab, and vincristine, which prompted us to look for evidence of complement activation and associated genetic mutations. Complement-related genetic aberrations were present in all 3 patients, who had had different degrees of complement activation. The first 2 patients did not benefit from eculizumab when treatment was started before complete clearance of inhibitors to ADAMTS13. However, they had durable remissions when eculizumab was introduced after clearance of ADAMTS13 inhibitors. The third patient started eculizumab therapy after inhibitor levels were undetectable. CONCLUSION: We found eculizumab therapy to be effective in all 3 patients. However, its efficacy was prominent only after clearance of antibodies against ADAMTS13 via therapeutic plasma exchange.

Vasculitic syndromes in hepatitis C virus: A review.

Vasculitis is a remarkable presentation of the extrahepatic manifestations of HCV. According to the presence or absence of cryoglobulins it is subdivided into two main types: cryoglobulinemic vasculitis and non cryoglobulinemic vasculitis based on the attribution of vasculitis to serum cryoglobulins as a pathogenic factor. The attribution of cryoglobulinemia to HCV represents a success story in the history of immunology, microbiology, and clinical medicine. HCV can bind to and invade lymphocytes, consequently triggering an immune response through different mechanisms. The epidemiology of the disease is well described and the clinical picture describes cutaneous, pulmonary, musculoskeletal, neurological, renal, endocrine, gastrointestinal, hepatic and cardiovascular manifestations. It may also be associated with sicca symptoms, an increased risk of lymphoma and serious catastrophic events. The pathology is well characterized. A classification criteria of the syndrome that was validated in 2014 is discussed. Management of CV is decided according to the presence and severity of its clinical presentation. It is divided into asymptomatic, mild, moderate, severe and life threatening disease. Recently introduced direct antiviral agents are proving safe and effective in the management of cryoglobulinemic vasculitis, and it is advocated that the two types of vasculitis be given prioritization in the Egyptian mass campaign to eradicate HCV.