To define the cell populations that drive joint inflammation in rheumatoid arthritis (RA), we applied single-cell RNA sequencing (scRNA-seq), mass cytometry, bulk RNA-seq and flow cytometry to T cells, B cells, monocytes and fibroblasts from 51 samples of synovial tissue from patients with RA or osteoarthritis. Utilizing an integrated strategy based on canonical correlation analysis of 5,265 scRNA-seq profiles, we identified 18 unique cell populations. Combining mass cytometry and transcriptomics together revealed cell states expanded in RA synovia: THY1(CD90) + HLA-DRA hi sublining fibroblasts, IL1B + pro-inflammatory monocytes, ITGAX + TBX21 + autoimmune-associated B cells and PDCD1 + T peripheral helper (Tph) and T follicular helper (Tfh). We defined distinct subsets of CD8 + T cells characterized by a GZMK + , GZMB + and GNLY + phenotype. We mapped inflammatory mediators to their source cell populations; for example, we attributed IL6 expression to THY1 + HLA-DRA hi fibroblasts, and IL1B production to pro-inflammatory monocytes. These populations are potentially key mediators of RA pathogenesis.

Wei, Slowikowski, Fonseka, Rao et al A single cell map of the RA joint Abstract 78 To define the cell populations in rheumatoid arthritis (RA) driving joint inflammation, we applied 79 single-cell RNA-seq (scRNA-seq), mass cytometry, bulk RNA-seq, and flow cytometry to sorted 80 T cells, B cells, monocytes, and fibroblasts from 51 synovial tissue RA and osteoarthritis (OA) 81 patient samples. Utilizing an integrated computational strategy based on canonical correlation 82 analysis to 5,452 scRNA-seq profiles, we identified 18 unique cell populations. Combining mass 83 cytometry and transcriptomics together revealed cell states expanded in RA synovia: 84 THY1 + HLA high sublining fibroblasts (OR=33.8), IL1B + pro-inflammatory monocytes (OR=7.8), 85 CD11c + T-bet + autoimmune-associated B cells (OR=5.7), and PD-1 + Tph/Tfh (OR=3.0). We also 86 defined CD8 + T cell subsets characterized by GZMK + , GZMB + , and GNLY + expression. Using 87 bulk and single-cell data, we mapped inflammatory mediators to source cell populations, for 88 example attributing IL6 production to THY1 + HLA high fibroblasts and naïve B cells, and IL1B to 89 pro-inflammatory monocytes. These populations are potentially key mediators of RA 90 pathogenesis. 91 92 93 94 95 96 97 98 99 100

The gross and histologic anatomy of the inferior glenohumeral ligament was studied in 11 fresh frozen cadaver shoulders. Arthroscopic observations of the joint capsule through the normal range of motion revealed that the inferior glenohumeral ligament is actually a complex of structures consisting of an anterior band, a posterior band, and an interposed axillary pouch. While these components of the inferior glenohumeral ligament complex were present in all 11 specimens, they were best demonstrated in some shoulders by placing the humeral head in internal or external rotation in varying degrees of abduction. Histologic examination of the joint capsule revealed that the anterior and posterior bands of the inferior glenohumeral ligament complex were readily identifiable as distinct structures comprised of thickened bands of well-organized collagen bundles. Although slight variations were noted in the attachment sites of the anterior and posterior bands to the glenoid, the inferior glenohumeral ligament complex was observed to attach to the humeral neck in one of two distinct configurations. A collar-like attachment, in which the entire inferior glenohumeral ligament complex attaches just inferior to the articular edge of the humeral head, was observed in six specimens. In the remaining five specimens, the attachment was in the shape of a "V," with the anterior and posterior bands attaching adjacent to the articular edge of the humeral head and the axillary pouch attaching at the apex of the "V" distal to the articular edge. The orientation and design of the inferior glenohumeral ligament complex supports the functional concept of this single structure as an important anterior and posterior stabilizer of the shoulder joint.

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