Non-invasive biomarkers for close activity monitoring in birdshot chorioretinitis: Optical coherence tomography angiography and beyond

PURPOSE

The purpose of the study was to identify non-invasive imaging biomarkers potentially useful for close activity monitoring in birdshot chorioretinitis (BSCR).

METHODS

Cross-sectional study of BSCR eyes included as per Levinson's and/or SUN criteria. Eyes were blindly classified into active or inactive groups per clinical inflammatory parameters, ultra-widefield (UWF) pseudocolour images, UWF fluorescein angiography (FA) and macular optical coherence tomography (OCT) cube. Qualitative and quantitative OCT and OCT-angiography (OCT-A) parameters at the fundus, superonasal and inferonasal fields were compared between active and inactive eyes.

RESULTS

Thirty consecutive BSCR patients (60 eyes) were analysed. 28 eyes (46.66%) were from women and the overall mean age was 59.7 ± 12.3 years. Active eyes showed an abnormal retinal thickening at inferonasal field (nasal retinal thickness) and a higher averaged thickened retinal index (ATRI) (72.36 active vs. 20.12 inactive, p < 0.0001). A significant moderate correlation was observed between ATRI and FA scores (r = 0.259, p = 0.022). Macular vascular loops were more frequent in the superficial vascular plexus of OCT-A in the active eyes (p = 0.028). The vascular perfusion index tended to be higher in all subfields of active eyes but did not reach statistical significance.

CONCLUSION

Multimodal imaging could be key to discerning activity in BSCR eyes. Higher ATRI and the presence of vascular loops in the superficial plexus are potential non-invasive activity biomarkers for the close monitoring of BSCR.

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.

HLA-A29 and Birdshot Uveitis: Further Down the Rabbit Hole

HLA class I alleles constitute established risk factors for non-infectious uveitis and preemptive genotyping of HLA class I alleles is standard practice in the diagnostic work-up. The HLA-A29 serotype is indispensable to Birdshot Uveitis (BU) and renders this enigmatic eye condition a unique model to better understand how the antigen processing and presentation machinery contributes to non-infectious uveitis or chronic inflammatory conditions in general. This review will discuss salient points regarding the protein structure of HLA-A29 and how key amino acid positions impact the peptide binding preference and interaction with T cells. We discuss to what extent the risk genes ERAP1 and ERAP2 uniquely affect HLA-A29 and how the discovery of a HLA-A29-specific submotif may impact autoantigen discovery. We further provide a compelling argument to solve the long-standing question why BU only affects HLA-A29-positive individuals from Western-European ancestry by exploiting data from the 1000 Genomes Project. We combine novel insights from structural and immunopeptidomic studies and discuss the functional implications of genetic associations across the HLA class I antigen presentation pathway to refine the etiological basis of Birdshot Uveitis.

Retinal vasculitis: A framework and proposal for a classification system

Retinal vasculitis, a poorly understood process involving inflammation or ischemia of the retinal vessel wall, may occur in association with a systemic process, although it can also be isolated to the retina. Because of the limited ability to perform histopathological studies on retinal vessels, there is no gold standard for diagnosis. Thus, there is utility in creating a classification system for retinal vasculitis and improving diagnostic strategies for this disease. We provide a framework for understanding retinal vasculitis based on size, location, and etiology. We hope that this information can be implemented in the clinical setting to provide some diagnostic strategies for this often confusing entity.