Non-criteria antiphospholipid antibodies and calprotectin as potential biomarkers in pediatric antiphospholipid syndrome.

Our study aimed to evaluate the presence, clinical associations, and potential mechanistic roles of non-criteria antiphospholipid antibodies (aPL) and circulating calprotectin, a highly stable marker of neutrophil extracellular trap release (NETosis), in pediatric APS patients. We found that 79% of pediatric APS patients had at least one non-criteria aPL at moderate-to-high titer. Univariate logistic regression demonstrated that positive anti-beta-2 glycoprotein I domain 1 (anti-D1) IgG (p = 0.008), anti-phosphatidylserine/prothrombin (aPS/PT) IgG (p < 0.001), and aPS/PT IgM (p < 0.001) were significantly associated with venous thrombosis. Positive anti-D1 IgG (p < 0.001), aPS/PT IgG (p < 0.001), and aPS/PT IgM (p = 0.001) were also associated with non-thrombotic manifestations of APS, such as thrombocytopenia. Increased levels of calprotectin were detected in children with APS. Calprotectin correlated positively with absolute neutrophil count (r = 0.63, p = 0.008) and negatively with platelet count (r = -0.59, p = 0.015). Mechanistically, plasma from pediatric APS patients with high calprotectin levels impaired platelet viability in a dose-dependent manner.

Anti-Neutrophil Extracellular Trap Antibodies in Antiphospholipid Antibody-Positive Patients: Results From the Antiphospholipid Syndrome Alliance for Clinical Trials and InternatiOnal Networking Clinical Database and Repository.

OBJECTIVE: This study aimed to elucidate the presence, antigen specificities, and potential clinical associations of anti-neutrophil extracellular trap (anti-NET) antibodies in a multinational cohort of antiphospholipid (aPL) antibody-positive patients who did not have lupus. METHODS: Anti-NET IgG/IgM levels were measured in serum samples from 389 aPL-positive patients; 308 patients met the classification criteria for antiphospholipid syndrome. Multivariate logistic regression with best variable model selection was used to determine clinical associations. For a subset of the patients (n = 214), we profiled autoantibodies using an autoantigen microarray platform. RESULTS: We found elevated levels of anti-NET IgG and/or IgM in 45% of the aPL-positive patients. High anti-NET antibody levels are associated with more circulating myeloperoxidase (MPO)-DNA complexes, which are a biomarker of NETs. When considering clinical manifestations, positive anti-NET IgG was associated with lesions affecting the white matter of the brain, even after adjusting for demographic variables and aPL profiles. Anti-NET IgM tracked with complement consumption after controlling for aPL profiles; furthermore, patient serum samples containing high levels of anti-NET IgM efficiently deposited complement C3d on NETs. As determined by autoantigen microarray, positive testing for anti-NET IgG was significantly associated with several autoantibodies, including those recognizing citrullinated histones, heparan sulfate proteoglycan, laminin, MPO-DNA complexes, and nucleosomes. Anti-NET IgM positivity was associated with autoantibodies targeting single-stranded DNA, double-stranded DNA, and proliferating cell nuclear antigen. CONCLUSION: These data reveal high levels of anti-NET antibodies in 45% of aPL-positive patients, where they potentially activate the complement cascade. While anti-NET IgM may especially recognize DNA in NETs, anti-NET IgG species appear to be more likely to target NET-associated protein antigens.