Divergent B cell and cytotoxic TNK cell activation signatures in HLA-B27-associated ankylosing spondylitis and acute anterior uveitis

Eisa Mahyari ¹ Sean Davin ² Kimberly Ogle ² Emma Fale-Olsen ² Carley Shaut ² Tammy M. Martin ² Jasvinder Ahuja ² Eric Suhler ² Atul Deodhar ² James Rosenbaum ³ Tejpal Gill ^2*

• ¹ Oregon National Primate Research Center, Oregon Health & Science University, Beaverton, Oregon, United States
• ² Oregon Health and Science University, Portland, United States
• ³ Legacy Health, Portland, Oregon, United States

Ankylosing spondylitis (AS), or radiographic axial spondyloarthritis (r-axSpA), is an immune-mediated inflammatory disorder frequently associated with acute anterior uveitis (AAU). Both these diseases share a strong association with the genetic risk factor, human leukocyte antigen (HLA)-B27. However, the immunophenotype underlying HLA-B27-associated AS and/or AAU pathophysiology is not known. Using cellular indexing of transcriptomes and epitopes (CITE-Seq) on a well-characterized cohort of 25 subjects (AS (HLA-B27 pos ), AS+AAU (HLA-B27 pos ), AAU (HLA-B27 pos ), HCs (HLA-B27 pos ) and HCs (HLA-B27 neg ); N=5/group) to identify transcriptomic differences at the single-cell level, along with differentially expressed cell surface markers, our study elucidates shared and distinct immune alterations linked to HLA-B27 and disease.Further, we employed Sparse decomposition of arrays (SDA) analysis, an unsupervised machine learning method, to examine high-dimensional transcriptional landscape of our data, to identify complex and non-linear relationships. Our study identified HLA-B27 and disease-specific transcriptomic differences in AS and AAU.AS+AAU showed immune profiles similar to AS, indicating AS's dominant role in immune dysregulation. SDA analysis revealed a dysregulated B-cell maturation and activation response in AS subjects, while AAU subjects had an enrichment of cytotoxic effector function in T and NK cells. However, both AS and AAU showed myeloid cell activation, which is crucial for initiating and sustaining inflammation. Furthermore, both AS and AAU subjects exhibit a dampening of homeostatic function, i.e. the balance between identification and active elimination of foreign pathogens while preventing response to self-antigens, suggesting that inflammation may be resulting as an imbalance in the immune function. In conclusion, our results reveal the overlapping myeloid effectors in addition to specific immunophenotypic responses such as decreased naive B cells in AS subjects and CD8/NK cell population in AAU subjects. These results highlight a distinct set of immune mediators underlying AS versus AAU pathogenesis. Future studies including HLA-B27 negative AS and AAU patients and validation of B-cell and myeloid dysfunction in AS and AAU have the potential to yield novel biomarkers and therapeutic targets.