Advanced Cases of Birdshot HLA-A29 Retinochoroiditis: Prevalence and Characteristics

HLA-A29 Birdshot Retinochoroiditis in Its 5th Decade: Selected Glimpses into the Intellectual Meanderings and Progresses in the Knowledge of a Long-Time Misunderstood Disease

The appraisal of HLA-A29 birdshot retinochoroiditis (BRC) was fraught with pitfalls and misunderstandings. Progress in investigational methods has led to better knowledge and management of the disease. Our aim was to assess some of the steps that have led to better characterisation of the clinical entity of BRC. We performed a literature search analysing the relevant progress in disease origin, investigational and imaging methods, clinicopathology and classification, diagnostic criteria and management. Following developments were judged essential in the better appraisal and understanding of the disease: (1) new immunopathological hypotheses regarding the role of endoplasmic reticulum peptidases, (2) the essential importance of HLA testing, (3) relevant imaging modalities among which indocyanine green angiography is crucial, (4) diagnostic criteria that allow early diagnosis and (5) need of an early prolonged, as well as aggressive treatment combining more than one immunosuppressive agent. Based on these findings it is now possible to better define BRC, an indolent however severe disease, unlike thought before, involving the choroidal stroma and the retina independently and concomitantly that can be diagnosed early thanks to indocyanine green angiography and should be treated early and relentlessly.

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.