Serum Biomarkers of Vascular Involvement in Childhood Uveitis.

Purpose: Nonanterior uveitis frequently involves the retinal vasculature; however, no molecular markers associated with the retinal vascular disease are currently known. In this study, we aimed to identify serum biomarker signatures associated with retinal vascular involvement in noninfectious pediatric uveitis. Methods: We performed a 384-plex targeted proteomic analysis of serum samples of 154 noninfectious pediatric uveitis patients diagnosed with nonanterior uveitis (n = 74), idiopathic chronic anterior uveitis (iCAU, n = 36), or juvenile idiopathic arthritis-associated uveitis (JIA-U, n = 44), as well as 22 noninflammatory pediatric controls. Data on retinal vascular involvement (i.e., papillitis, cystoid macular edema, retinal vasculitis, or retinal capillary leakage on optical coherence tomography and/or fluorescein angiography) were used to stratify cases in the nonanterior uveitis group. Results: In the analysis of nonanterior uveitis, we identified nine proteins significantly associated with retinal vascular involvement, including F13B, MYOM3, and PTPN9. These proteins were enriched through pathway enrichment analysis for the coagulation cascade. Comparing cases and controls, we identified 63 differentially expressed proteins, notably proteins involved in platelet biology and complement cascades, which could be primarily attributed to differences in serum proteomes between anterior uveitis and nonanterior uveitis groups. Conclusions: Serum proteins related to the coagulation and complement cascade are associated with retinal vascular involvement in pediatric uveitis patients. Our results indicate involvement of mediators that could interact with the microcirculation in pediatric uveitis and might serve as potential biomarkers in personalized medicine in the future. Translational Relevance: Our targeted proteomics analysis in serum of pediatric uveitis patients indicates involvement of mediators that could interact with the microcirculation in pediatric uveitis and might serve as potential biomarkers in personalized medicine in the future.

A cis-regulatory element regulates ERAP2 expression through autoimmune disease risk SNPs.

Single-nucleotide polymorphisms (SNPs) near the ERAP2 gene are associated with various autoimmune conditions, as well as protection against lethal infections. Due to high linkage disequilibrium, numerous trait-associated SNPs are correlated with ERAP2 expression; however, their functional mechanisms remain unidentified. We show by reciprocal allelic replacement that ERAP2 expression is directly controlled by the splice region variant rs2248374. However, disease-associated variants in the downstream LNPEP gene promoter are independently associated with ERAP2 expression. Allele-specific conformation capture assays revealed long-range chromatin contacts between the gene promoters of LNPEP and ERAP2 and showed that interactions were stronger in patients carrying the alleles that increase susceptibility to autoimmune diseases. Replacing the SNPs in the LNPEP promoter by reference sequences lowered ERAP2 expression. These findings show that multiple SNPs act in concert to regulate ERAP2 expression and that disease-associated variants can convert a gene promoter region into a potent enhancer of a distal gene.

Uveitis Associated with Juvenile Idiopathic Arthritis.

Juvenile idiopathic arthritis (JIA) is the most common cause of uveitis in children. While symptoms are usually mild, persistent eye inflammation could lead to severe complications and impaired vision. It is essential that JIA patients at risk are diagnosed with uveitis early, receive adequate treatment, and avoid developing complications, such as cataract, glaucoma, and amblyopia. The purpose of this mini-review is to summarize the screening strategies and clinical management for JIA-associated uveitis (JIA-U) as well as the current state of molecular markers linked to this condition. Because glaucoma is one of the most common causes of visual loss in JIA-U, special focus will be put on this serious complication. We conclude by describing the current evidence regarding the long-standing question of whether chronic anterior uveitis without arthritis may be the same disease entity as JIA-U.

Evolutionary immuno-genetics of endoplasmic reticulum aminopeptidase II (ERAP2).

Endoplasmic reticulum aminopeptidase 2 (ERAP2) is a proteolytic enzyme involved in adaptive immunity. The ERAP2 gene is highly polymorphic and encodes haplotypes that confer resistance against lethal infectious diseases, but also increase the risk for autoimmune disorders. Identifying how ERAP2 influences susceptibility to these traits requires an understanding of the selective pressures that shaped and maintained allelic variation throughout human evolution. Our review discusses the genetic regulation of haplotypes and diversity in naturally occurring ERAP2 allotypes in the global population. We outline how these ERAP2 haplotypes evolved during human history and highlight the presence of Neanderthal DNA sequences in ERAP2 of modern humans. Recent evidence suggests that human adaptation during the last ~10,000 years and historic pandemics left a significant mark on the ERAP2 gene that determines susceptibility to infectious and inflammatory diseases today.

CRB1-Associated Retinal Dystrophy Patients Have Expanded Lewis Glycoantigen-Positive T Cells.

Purpose: Eye inflammation may occur in patients with inherited retinal dystrophies (IRDs) and is seen frequently in IRDs associated with mutations in the CRB1 gene. The purpose of this study was to determine the types of inflammatory cells involved in IRDs, by deep profiling the composition of peripheral blood mononuclear cells of patients with a CRB1-associated IRD. Methods: This study included 33 patients with an IRD with confirmed CRB1 mutations and 32 healthy controls. A 43-parameter flow cytometry analysis was performed on peripheral blood mononuclear cells isolated from venous blood. FlowSOM and manual Boolean combination gating were used to identify and quantify immune cell subsets. Results: Comparing patients with controls revealed a significant increase in patients in the abundance of circulating CD4+ T cells and CD8+ T cells that express sialyl Lewis X antigen. Furthermore, we detected a decrease in plasmacytoid dendritic cells and an IgA+CD24+CD38+ transitional B-cell subset in patients with an IRD. Conclusions: Patients with a CRB1-associated IRD show marked changes in blood leukocyte composition, affecting lymphocyte and dendritic cell populations. These results implicate inflammatory pathways in the disease manifestations of IRDs.

Association of Risk Variants in the CFH Gene With Elevated Levels of Coagulation and Complement Factors in Idiopathic Multifocal Choroiditis.

Importance: Idiopathic multifocal choroiditis (MFC) is poorly understood, thereby hindering optimal treatment and monitoring of patients. Objective: To identify the genes and pathways associated with idiopathic MFC. Design, Setting, and Participants: This was a case-control genome-wide association study (GWAS) and protein study of blood plasma samples conducted from March 2006 to February 2022. This was a multicenter study involving 6 Dutch universities. Participants were grouped into 2 cohorts: cohort 1 consisted of Dutch patients with idiopathic MFC and controls, and cohort 2 consisted of patients with MFC and controls. Plasma samples from patients with idiopathic MFC who had not received treatment were subjected to targeted proteomics. Idiopathic MFC was diagnosed according to the Standardization of Uveitis Nomenclature (SUN) Working Group guidelines for punctate inner choroidopathy and multifocal choroiditis with panuveitis. Data were analyzed from July 2021 to October 2022. Main outcomes and measures: Genetic variants associated with idiopathic MFC and risk variants associated with plasma protein concentrations in patients. Results: This study included a total of 4437 participants in cohort 1 (170 [3.8%] Dutch patients with idiopathic MFC and 4267 [96.2%] controls; mean [SD] age, 55 [18] years; 2443 female [55%]) and 1344 participants in cohort 2 (52 [3.9%] patients with MFC and 1292 [96.1%] controls; 737 male [55%]). The primary GWAS association mapped to the CFH gene with genome-wide significance (lead variant the A allele of rs7535263; odds ratio [OR], 0.52; 95% CI, 0.41-0.64; P = 9.3 × 10-9). There was no genome-wide significant association with classical human leukocyte antigen (HLA) alleles (lead classical allele, HLA-A*31:01; P = .002). The association with rs7535263 showed consistent direction of effect in an independent cohort of 52 cases and 1292 control samples (combined meta-analysis OR, 0.58; 95% CI, 0.38-0.77; P = 3.0 × 10-8). In proteomic analysis of 87 patients, the risk allele G of rs7535263 in the CFH gene was strongly associated with increased plasma concentrations of factor H-related (FHR) proteins (eg, FHR-2, likelihood ratio test, adjusted P = 1.1 × 10-3) and proteins involved in platelet activation and the complement cascade. Conclusions and relevance: Results suggest that CFH gene variants increase systemic concentrations of key factors of the complement and coagulation cascades, thereby conferring susceptibility to idiopathic MFC. These findings suggest that the complement and coagulation pathways may be key targets for the treatment of idiopathic MFC.

Distinct modulation of cellular immunopeptidome by the allosteric regulatory site of ER aminopeptidase 1.

ER aminopeptidase 1 (ERAP1) is an ER-resident aminopeptidase that excises N-terminal residues of peptides that then bind onto Major Histocompatibility Complex I molecules (MHC-I) and indirectly modulates adaptive immune responses. ERAP1 contains an allosteric regulatory site that accommodates the C-terminus of at least some peptide substrates, raising questions about its exact influence on antigen presentation and the potential of allosteric inhibition for cancer immunotherapy. We used an inhibitor that targets this regulatory site to study its effect on the immunopeptidome of a human cancer cell line. The immunopeptidomes of allosterically inhibited and ERAP1 KO cells contain high-affinity peptides with sequence motifs consistent with the cellular HLA class I haplotypes but are strikingly different in peptide composition. Compared to KO cells, allosteric inhibition did not affect the length distribution of peptides and skewed the peptide repertoire both in terms of sequence motifs and HLA allele utilization, indicating significant mechanistic differences between the two ways of disrupting ERAP1 function. These findings suggest that the regulatory site of ERAP1 plays distinct roles in antigenic peptide selection, which should be taken into consideration when designing therapeutic interventions targeting the cancer immunopeptidome.

Transcriptome network analysis implicates CX3CR1-positive type 3 dendritic cells in non-infectious uveitis.

Background: Type I interferons (IFNs) promote the expansion of subsets of CD1c+ conventional dendritic cells (CD1c+ DCs), but the molecular basis of CD1c+ DCs involvement in conditions not associated without elevated type I IFNs remains unclear. Methods: We analyzed CD1c+ DCs from two cohorts of non-infectious uveitis patients and healthy donors using RNA-sequencing followed by high-dimensional flow cytometry to characterize the CD1c+ DC populations. Results: We report that the CD1c+ DCs pool from patients with non-infectious uveitis is skewed toward a gene module with the chemokine receptor CX3CR1 as the key hub gene. We confirmed these results in an independent case-control cohort and show that the disease-associated gene module is not mediated by type I IFNs. An analysis of peripheral blood using flow cytometry revealed that CX3CR1+ DC3s were diminished, whereas CX3CR1- DC3s were not. Stimulated CX3CR1+ DC3s secrete high levels of inflammatory cytokines, including TNF-alpha, and CX3CR1+ DC3 like cells can be detected in inflamed eyes of patients. Conclusions: These results show that CX3CR1+ DC3s are implicated in non-infectious uveitis and can secrete proinflammatory mediators implicated in its pathophysiology. Funding: The presented work is supported by UitZicht (project number #2014-4, #2019-10, and #2021-4). The funders had no role in the design, execution, interpretation, or writing of the study.

EULAR study group on 'MHC-I-opathy': identifying disease-overarching mechanisms across disciplines and borders.

The 'MHC-I (major histocompatibility complex class I)-opathy' concept describes a family of inflammatory conditions with overlapping clinical manifestations and a strong genetic link to the MHC-I antigen presentation pathway. Classical MHC-I-opathies such as spondyloarthritis, Behçet's disease, psoriasis and birdshot uveitis are widely recognised for their strong association with certain MHC-I alleles and gene variants of the antigen processing aminopeptidases ERAP1 and ERAP2 that implicates altered MHC-I peptide presentation to CD8+T cells in the pathogenesis. Progress in understanding the cause and treatment of these disorders is hampered by patient phenotypic heterogeneity and lack of systematic investigation of the MHC-I pathway.Here, we discuss new insights into the biology of MHC-I-opathies that strongly advocate for disease-overarching and integrated molecular and clinical investigation to decipher underlying disease mechanisms. Because this requires transformative multidisciplinary collaboration, we introduce the EULAR study group on MHC-I-opathies to unite clinical expertise in rheumatology, dermatology and ophthalmology, with fundamental and translational researchers from multiple disciplines such as immunology, genomics and proteomics, alongside patient partners. We prioritise standardisation of disease phenotypes and scientific nomenclature and propose interdisciplinary genetic and translational studies to exploit emerging therapeutic strategies to understand MHC-I-mediated disease mechanisms. These collaborative efforts are required to address outstanding questions in the etiopathogenesis of MHC-I-opathies towards improving patient treatment and prognostication.

Non-Infectious Uveitis Secondary to Dupilumab Treatment in Atopic Dermatitis Patients Shows a Pro-Inflammatory Molecular Profile.

Severe uveitis is a rare complication of interleukin-4 receptor alpha blocking by dupilumab in topic dermatitis (AD) patients. The aim of this study was to describe five moderate-to-severe AD patients who developed uveitis during dupilumab treatment and to compare the proteomic profile of aqueous humor (AqH) of dupilumab-associated uveitis (n=3/5 available samples) with non-infectious uveitis (n=27) and cataract controls (n=11). Included patients were treated at the University Medical Center Utrecht (the Netherlands). Active dupilumab-associated uveitis complicated by serous detachment, cystoid macular edema, or secondary glaucoma developed within a median of 6.0 months (interquartile range 2.3-16.5 months) after starting dupilumab. Uveitis resolved after discontinuation of dupilumab and/or treatment with local or systemic corticosteroids. Proteomic profiling of AqH revealed that the molecular profile of dupilumab-associated uveitis resembled that of non-infectious uveitis. In conclusion, dupilumab-associated uveitis is a severe adverse event of dupilumab therapy, requiring urgent referral to an ophthalmologist.

Uncovering the genomic toll of the Black Death.

The Black Death, a notorious devastating pandemic caused by Yersinia pestis infection during the 14th century, posed a formidable challenge to human immune defenses. A new article by Klunk et al. reports that a variant in an antigen-processing gene may have favored survival during the plague and may have undergone genomic selection in Europeans at unprecedented speed.

Nuclear Receptor Subfamily 4A Signaling as a Key Disease Pathway of CD1c+ Dendritic Cell Dysregulation in Systemic Sclerosis.

OBJECTIVE: This study was undertaken to identify key disease pathways driving conventional dendritic cell (cDC) alterations in systemic sclerosis (SSc). METHODS: Transcriptomic profiling was performed on peripheral blood CD1c+ cDCs (cDC2s) isolated from 12 healthy donors and 48 patients with SSc, including all major disease subtypes. We performed differential expression analysis for the different SSc subtypes and healthy donors to uncover genes dysregulated in SSc. To identify biologically relevant pathways, we built a gene coexpression network using weighted gene correlation network analysis. We validated the role of key transcriptional regulators using chromatin immunoprecipitation (ChIP) sequencing and in vitro functional assays. RESULTS: We identified 17 modules of coexpressed genes in cDCs that correlated with SSc subtypes and key clinical traits, including autoantibodies, skin score, and occurrence of interstitial lung disease. A module of immunoregulatory genes was markedly down-regulated in patients with the diffuse SSc subtype characterized by severe fibrosis. Transcriptional regulatory network analysis performed on this module predicted nuclear receptor 4A (NR4A) subfamily genes (NR4A1, NR4A2, NR4A3) as the key transcriptional regulators of inflammation. Indeed, ChIP-sequencing analysis indicated that these NR4A members target numerous differentially expressed genes in SSc cDC2s. Inclusion of NR4A receptor agonists in culture-based experiments provided functional proof that dysregulation of NR4As affects cytokine production by cDC2s and modulates downstream T cell activation. CONCLUSION: NR4A1, NR4A2, and NR4A3 are important regulators of immunosuppressive and fibrosis-associated pathways in SSc cDCs. Thus, the NR4A family represents novel potential targets to restore cDC homeostasis in SSc.

A Network of Serum Proteins Predict the Need for Systemic Immunomodulatory Therapy at Diagnosis in Noninfectious Uveitis.

Purpose: Early identification of patients with noninfectious uveitis requiring steroid-sparing immunomodulatory therapy (IMT) is currently lacking in objective molecular biomarkers. We evaluated the proteomic signature of patients at the onset of disease and associated proteomic clusters with the need for IMT during the course of the disease. Design: Multicenter cohort study. Participants: Two hundred thirty treatment-free patients with active noninfectious uveitis. Methods: We used aptamer-based proteomics (n = 1305 proteins) and a bioinformatic pipeline as a molecular stratification tool to define the serum protein network of a Dutch discovery cohort (n = 78) of patients and healthy control participants and independently validated our results in another Dutch cohort (n = 111) and a United States cohort (n = 67). Multivariate Cox analysis was used to assess the relationship between the protein network and IMT use. Main Outcome Measures: Serum protein levels and use of IMT. Results: Network-based analyses revealed a tightly coexpressed serum cluster (n = 85 proteins) whose concentration was consistently low in healthy control participants (n = 26), but varied among patients with noninfectious uveitis (n = 52). Patients with high levels of the serum cluster at disease onset showed a significantly increased need for IMT during follow-up, independent of anatomic location of uveitis (hazard ratio, 3.42; 95% confidence interval, 1.22-9.5; P = 0.019). The enrichment of neutrophil-associated proteins in the protein cluster led to our finding that the neutrophil count could serve as a clinical proxy for this proteomic signature (correlation: r = 0.57, P = 0.006). In an independent Dutch cohort (n = 111), we confirmed that patients with relatively high neutrophil count at diagnosis (> 5.2 × 109/L) had a significantly increased chance of requiring IMT during follow-up (hazard ratio, 3.2; 95% confidence interval, 1.5-6.8; P = 0.002). We validated these findings in a third cohort of 67 United States patients. Conclusions: A serum protein signature correlating with neutrophil levels was highly predictive for IMT use in noninfectious uveitis. We developed a routinely available tool that may serve as a novel objective biomarker to aid in clinical decision-making for noninfectious uveitis.

Systems genomics in age-related macular degeneration.

Genomic studies in age-related macular degeneration (AMD) have identified genetic variants that account for the majority of AMD risk. An important next step is to understand the functional consequences and downstream effects of the identified AMD-associated genetic variants. Instrumental for this next step are 'omics' technologies, which enable high-throughput characterization and quantification of biological molecules, and subsequent integration of genomics with these omics datasets, a field referred to as systems genomics. Single cell sequencing studies of the retina and choroid demonstrated that the majority of candidate AMD genes identified through genomic studies are expressed in non-neuronal cells, such as the retinal pigment epithelium (RPE), glia, myeloid and choroidal cells, highlighting that many different retinal and choroidal cell types contribute to the pathogenesis of AMD. Expression quantitative trait locus (eQTL) studies in retinal tissue have identified putative causal genes by demonstrating a genetic overlap between gene regulation and AMD risk. Linking genetic data to complement measurements in the systemic circulation has aided in understanding the effect of AMD-associated genetic variants in the complement system, and supports that protein QTL (pQTL) studies in plasma or serum samples may aid in understanding the effect of genetic variants and pinpointing causal genes in AMD. A recent epigenomic study fine-mapped AMD causal variants by determing regulatory regions in RPE cells differentiated from induced pluripotent stem cells (iPSC-RPE). Another approach that is being employed to pinpoint causal AMD genes is to produce synthetic DNA assemblons representing risk and protective haplotypes, which are then delivered to cellular or animal model systems. Pinpointing causal genes and understanding disease mechanisms is crucial for the next step towards clinical translation. Clinical trials targeting proteins encoded by the AMD-associated genomic loci C3, CFB, CFI, CFH, and ARMS2/HTRA1 are currently ongoing, and a phase III clinical trial for C3 inhibition recently showed a modest reduction of lesion growth in geographic atrophy. The EYERISK consortium recently developed a genetic test for AMD that allows genotyping of common and rare variants in AMD-associated genes. Polygenic risk scores (PRS) were applied to quantify AMD genetic risk, and may aid in predicting AMD progression. In conclusion, genomic studies represent a turning point in our exploration of AMD. The results of those studies now serve as a driving force for several clinical trials. Expanding to omics and systems genomics will further decipher function and causality from the associations that have been reported, and will enable the development of therapies that will lessen the burden of AMD.

A Blood Protein Signature Stratifies Clinical Response to csDMARD Therapy in Pediatric Uveitis.

PURPOSE: To identify a serum biomarker signature that can help predict response to conventional synthetic disease-modifying antirheumatic drug (csDMARD) therapy in pediatric noninfectious uveitis. METHODS: In this case-control cohort study, we performed a 368-plex proteomic analysis of serum samples of 72 treatment-free patients with active uveitis (new onset or relapse) and 15 healthy controls. Among these, 37 patients were sampled at diagnosis before commencing csDMARD therapy. After 6 months, csDMARD response was evaluated and cases were categorized as "responder" or "nonresponder." Patients were considered "nonresponders" if remission was not achieved under csDMARD therapy. Serum protein profiles were used to train random forest models to predict csDMARD failure and compared to a model based on eight clinical parameters at diagnosis (e.g., maximum cell grade). RESULTS: In total, 19 of 37 (51%) cases were categorized as csDMARD nonresponders. We identified a 10-protein signature that could predict csDMARD failure with an overall accuracy of 84%, which was higher compared to a model based on eight clinical parameters (73% accuracy). Adjusting for age, sex, anatomic location of uveitis, and cell grade, cases stratified by the 10-protein signature at diagnosis showed a large difference in risk for csDMARD failure (hazard ratio, 12.8; 95% confidence interval, 2.5-64.6; P = 0.002). CONCLUSIONS: Machine learning models based on the serum proteome can stratify pediatric patients with uveitis at high risk for csDMARD failure. TRANSLATIONAL RELEVANCE: The identified protein signature has implications for the development of clinical decision tools that integrate clinical parameters with biological data to better predict the best treatment option.

Next-Generation HLA Sequence Analysis Uncovers Shared Risk Alleles Between Clinically Distinct Forms of Childhood Uveitis.

Purpose: Classical alleles of the human leukocyte antigen (HLA) complex have been linked to specific entities of pediatric noninfectious uveitis, yet genetic predisposition encoded by the HLA super-locus across the patient population remains understudied. Methods: We performed next-generation full-length sequencing of HLA-A, HLA-B, HLA-C, HLA-DPB1, HLA-DQB1, and HLA-DRB1 in 280 cases. Dense genotype data from 499 Dutch controls from Genome of the Netherlands were imputed using an HLA-specific reference panel (n = 5225 samples from European ancestry). Cases and controls were compared using logistic regression models adjusting for sex. Results: In total, 179 common and rare alleles were detected. Considering all cases and controls, HLA-DQB1*04:02 and HLA-DRB1*08:01 were identified as the principal HLA association, which was mainly driven by 92 cases with juvenile idiopathic arthritis-associated uveitis (JIA-U). The HLA-DQB1*04:02-HLA-DRB1*08:01 haplotype was also the primary association for the phenotypically similar idiopathic chronic anterior uveitis without arthritis (CAU). Also, HLA-DQB1*05:03 was an independent risk allele for CAU, but not in JIA-U. Analysis of 185 cases with other forms of uveitis revealed HLA-wide associations (P < 2.79 × 10-4) for HLA-DRB1*01:02, HLA-DRB1*04:03, and HLA-DQB1*05:03, which could be primarily attributed to cases with panuveitis. Finally, amino acid substitution modeling revealed that aspartic acid at position 57 that distinguishes the risk allele HLA-DQB1*05:03 (for CAU and panuveitis) from nonrisk alleles, significantly increased the binding capacity of naturally presented ligands to HLA-DQ. Conclusions: These results uncovered novel shared HLA associations among clinically distinct phenotypes of pediatric uveitis and highlight genetic predisposition affecting the antigen presentation pathway.

ERAP2 Increases the Abundance of a Peptide Submotif Highly Selective for the Birdshot Uveitis-Associated HLA-A29.

Birdshot Uveitis (BU) is a blinding inflammatory eye condition that only affects HLA-A29-positive individuals. Genetic association studies linked ERAP2 with BU, an aminopeptidase which trims peptides before their presentation by HLA class I at the cell surface, which suggests that ERAP2-dependent peptide presentation by HLA-A29 drives the pathogenesis of BU. However, it remains poorly understood whether the effects of ERAP2 on the HLA-A29 peptidome are distinct from its effect on other HLA allotypes. To address this, we focused on the effects of ERAP2 on the immunopeptidome in patient-derived antigen presenting cells. Using complementary HLA-A29-based and pan-class I immunopurifications, isotope-labeled naturally processed and presented HLA-bound peptides were sequenced by mass spectrometry. We show that the effects of ERAP2 on the N-terminus of ligands of HLA-A29 are shared across endogenous HLA allotypes, but discover and replicate that one peptide motif generated in the presence of ERAP2 is specifically bound by HLA-A29. This motif can be found in the amino acid sequence of putative autoantigens. We further show evidence for internal sequence specificity for ERAP2 imprinted in the immunopeptidome. These results reveal that ERAP2 can generate an HLA-A29-specific antigen repertoire, which supports that antigen presentation is a key disease pathway in BU.

Common allotypes of ER aminopeptidase 1 have substrate-dependent and highly variable enzymatic properties.

Polymorphic variation of immune system proteins can drive variability of individual immune responses. Endoplasmic reticulum aminopeptidase 1 (ERAP1) generates antigenic peptides for presentation by major histocompatibility complex class I molecules. Coding SNPs in ERAP1 have been associated with predisposition to inflammatory rheumatic disease and shown to affect functional properties of the enzyme, but the interplay between combinations of these SNPs as they exist in allotypes has not been thoroughly explored. We used phased genotype data to estimate ERAP1 allotype frequency in 2504 individuals across five major human populations, generated highly pure recombinant enzymes corresponding to the ten most common ERAP1 allotypes, and systematically characterized their in vitro enzymatic properties. We find that ERAP1 allotypes possess a wide range of enzymatic activities, up to 60-fold, whose ranking is substrate dependent. Strikingly, allotype 10, previously associated with Behçet's disease, is consistently a low-activity outlier, suggesting that a significant percentage of individuals carry a subactive ERAP1 gene. Enzymatic analysis revealed that ERAP1 allotypes can differ in both catalytic efficiency and substrate affinity, differences that can change intermediate accumulation in multistep trimming reactions. Alterations in efficacy of an allosteric inhibitor that targets the regulatory site suggest that allotypic variation influences the communication between the regulatory and the active site. Our work defines the wide landscape of ERAP1 activity in human populations and demonstrates how common allotypes can induce substrate-dependent variability in antigen processing, thus contributing, in synergy with major histocompatibility complex haplotypes, to immune response variability and predisposition to chronic inflammatory conditions.

Central Multifocal Choroiditis: Platelet Granularity as a Potential Marker for Treatment With Steroid-Sparing Immunomodulatory Therapy.

Purpose: We aimed to evaluate the blood cell composition in patients with central multifocal choroiditis (cMFC), a rare form of posterior uveitis predominantly affecting young myopic women. Methods: In this retrospective observational case-control study, a 104-parameter automated hematocytometry was conducted by the Cell-Dyn Sapphire hematology analyzer for 122 cases and 364 age- and sex-matched controls. Cox proportional regression analysis was used to assess the relation between the blood cell composition and the time between disease onset (first visit) and the start of systemic corticosteroid-sparing immunomodulatory therapy (IMT). Results: At a false discovery rate of 5% (Padj), we identified a decrease of blood monocytes in cases with cMFC, which could be attributed to disease activity. Cox proportional hazard analysis including age and sex revealed that increased platelet granularity (measured by mean intermediate angle scatter) was an independent risk factor for treatment with IMT (hazard ratio = 2.3 [95% confidence interval = 1.28 - 4.14], Padj = 0.049). The time between the first presentation and the start of IMT was 0.3 years in the group with an increased platelet granularity and 3.4 years in the group without increased platelet granularity. Conclusions: Patients with cMFC demonstrated a decrease in blood monocytes. Moreover, platelet granularity could potentially be used as a marker for treatment with IMT.