A case of microscopic polyangiitis with interstitial pneumonia after coronavirus disease-2019 infection, evidenced by positivity for multiple autoantibodies.

Anti-neutrophil cytoplasmic antibody-associated vasculitis is triggered by infection, dust exposure, and drugs. A 73-year-old male presented with dyspnea. Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection was confirmed upon admission. Exacerbation of interstitial pneumonia and renal dysfunction were observed. Analysis revealed positivity for myeloperoxidase-anti-neutrophil cytoplasmic antibody, other anti-aminoacyl transfer RNA synthetase antibodies, and anti-melanoma differentiation-associated gene 5. Renal biopsy confirmed crescentic glomerulonephritis, leading to the diagnosis of microscopic polyangiitis. Combination therapy with prednisolone and cyclophosphamide was initiated, resulting in improved respiratory and renal failure. There is a potential association between SARS-CoV-2 infection and the onset of autoimmune diseases.

Characterization of conformational deformation-coupled interaction between immunoglobulin G1 Fc glycoprotein and a low-affinity Fcγ receptor by deuteration-assisted small-angle neutron scattering.

A recently developed integrative approach combining varied types of experimental data has been successfully applied to three-dimensional modelling of larger biomacromolecular complexes. Deuteration-assisted small-angle neutron scattering (SANS) plays a unique role in this approach by making it possible to observe selected components in the complex. It enables integrative modelling of biomolecular complexes based on building-block structures typically provided by X-ray crystallography. In this integrative approach, it is important to be aware of the flexible properties of the individual building blocks. Here we examine the ability of SANS to detect a subtle conformational change of a multidomain protein using the Fc portion of human immunoglobulin G (IgG) interacting with a soluble form of the low-affinity Fcγ receptor IIIb (sFcγRIIIb) as a model system. The IgG-Fc glycoprotein was subjected to SANS in the absence and presence of 75%-deuterated sFcγRIIIb, which was matched out in D2O solution. This inverse contrast-matching technique enabled selective observation of SANS from IgG-Fc, thereby detecting its subtle structural deformation induced by the receptor binding. The SANS data were successfully interpreted by considering previously reported crystallographic data and an equilibrium between free and sFcγRIIIb-bound forms. Our SANS data thus demonstrate the applicability of SANS in the integrative approach dealing with biomacromolecular complexes composed of weakly associated building blocks with conformational plasticity.