The class I protein HLA-B27 confers susceptibility to inflammatory arthritis in humans and when overexpressed in rodents for reasons that remain unclear. We demonstrated previously that HLA-B27 heavy chains (HC) undergo endoplasmic reticulum (ER)-associated degradation. We report here that HLA-B27 HC also forms two types of aberrant disulfide-linked complexes (dimers) during the folding and assembly process that can be distinguished by conformation-sensitive antibodies W6/32 and HC10. HC10-reactive dimers form immediately after HC synthesis in the ER and constitute at least 25% of the HC pool, whereas W6/32-reactive dimers appear several hours later and represent less than 10% of the folded HC. HC10-reactive dimers accumulate in the absence of tapasin or ␤ 2 -microglobulin, whereas W6/ 32-reactive dimers are not detected. Efficient formation of W6/32-reactive dimers appears to depend on the transporter associated with antigen processing, tapasin, and ␤ 2 -microglobulin. The unpaired Cys 67 and residues at the base of the B pocket that dramatically impair HLA-B27 HC folding are critical for the formation of HC10-reactive ER dimers. Although certain other alleles also form dimers late in the assembly pathway, ER dimerization of HLA-B27 may be unique. These results demonstrate that residues comprising the HLA-B27 B pocket result in aberrant HC folding and disulfide bond formation, and thus confer unusual properties on this molecule that are unrelated to peptide selection per se, yet may be important in disease pathogenesis.

onset in infancy (SAVI), and another by additive loss-of-function mutations in proteasome genes causing the proteasome-associated autoinflammatory syndromes (PRAAS) (also, chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperatures [CANDLE]), presented with chronically elevated interferon (IFN) signatures, suggesting a pathogenic role for type-I IFN in autoinflammatory diseases (2, 3). Type-I IFN was first discovered as a soluble antiviral factor over 50 years ago, and a role in sterile inflammation was proposed in patients with systemic lupus erythematosus (4). However, the discovery of genetic mutations that cause the autoinflammatory type-I interferonopathies CANDLE (2, 5), SAVI (3, 6-8), and Aicardi-Goutières syndrome (AGS) (9, 10) have shed light on pathomechanisms that drive chronic IFN signaling, and recent studies blocking IFN signaling validate a critical role for type-I IFNs (11). AGS-causing loss-of-function mutations in nucleases impair self-nucleic acid homeostasis, SAVI-causing

Methods. Eligible patients had been diagnosed by site rheumatologists (termed the "MD diagnosis") since 2004. This diagnosis was used as a reference standard for sensitivity and specificity testing of the 2 WG classification criteria. Descriptive analyses were confined to ACR-classified WG patients.Results. MD diagnoses of 117 patients (82 of whom were female) were WG (n ‫؍‬ 76), microscopic polyangiitis (n ‫؍‬ 17), ANCA-positive pauci-immune glomerulonephritis (n ‫؍‬ 5), Churg-Strauss syndrome (n ‫؍‬ 2), and unclassified vasculitis (n ‫؍‬ 17). The sensitivities of the ACR and EULAR/PRES classification criteria for WG among the spectrum of AAVs were

ObjectiveTo investigate the characteristics and risk factors of a novel parenchymal lung disease (LD), increasingly detected in systemic juvenile idiopathic arthritis (sJIA).MethodsIn a multicentre retrospective study, 61 cases were investigated using physician-reported clinical information and centralised analyses of radiological, pathological and genetic data.ResultsLD was associated with distinctive features, including acute erythematous clubbing and a high frequency of anaphylactic reactions to the interleukin (IL)-6 inhibitor, tocilizumab. Serum ferritin elevation and/or significant lymphopaenia preceded LD detection. The most prevalent chest CT pattern was septal thickening, involving the periphery of multiple lobes ± ground-glass opacities. The predominant pathology (23 of 36) was pulmonary alveolar proteinosis and/or endogenous lipoid pneumonia (PAP/ELP), with atypical features including regional involvement and concomitant vascular changes. Apparent severe delayed drug hypersensitivity occurred in some cases. The 5-year survival was 42%. Whole exome sequencing (20 of 61) did not identify a novel monogenic defect or likely causal PAP-related or macrophage activation syndrome (MAS)-related mutations. Trisomy 21 and young sJIA onset increased LD risk. Exposure to IL-1 and IL-6 inhibitors (46 of 61) was associated with multiple LD features. By several indicators, severity of sJIA was comparable in drug-exposed subjects and published sJIA cohorts. MAS at sJIA onset was increased in the drug-exposed, but was not associated with LD features.ConclusionsA rare, life-threatening lung disease in sJIA is defined by a constellation of unusual clinical characteristics. The pathology, a PAP/ELP variant, suggests macrophage dysfunction. Inhibitor exposure may promote LD, independent of sJIA severity, in a small subset of treated patients. Treatment/prevention strategies are needed.

The assembly of eukaryotic 20 S proteasomes involves the formation of half-proteasomes where precursor ␤-type subunits gather in position on an ␣-subunit ring, followed by the association of two half-proteasomes and ␤-subunit processing. In vertebrates three additional ␤-subunits (␤1i/LMP2, ␤2i/MECL1, and ␤5i/LMP7) can be synthesized and substituted for constitutive homologues (␤1/delta, ␤2/Z, and ␤5/X) to yield immunoproteasomes, which are important for generating certain antigenic peptides. We have shown previously that when all six ␤-subunits are present, cooperative assembly mechanisms limit the diversity of proteasome populations. Specifically, LMP7 is incorporated preferentially over X into preproteasomes containing LMP2 and MECL1. We show here that the LMP7 propeptide is responsible for this preferential incorporation, and it also enables LMP7 to incorporate into proteasomes containing delta and Z. In contrast, the X propeptide restricts incorporation to proteasomes with delta and Z. Furthermore, we demonstrate that the LMP7 propeptide can function in trans when expressed on LMP2, and that its NH 2 -terminal and mid-regions are particularly critical for function. In addition to identifying a novel propeptide function, our results raise the possibility that one consequence of LMP7 incorporation into both immunoproteasomes and delta/Z proteasomes may be to increase the diversity of antigenic peptides that can be generated.