Axl and MerTK regulate synovial inflammation and are modulated by IL-6 inhibition in rheumatoid arthritis.

The TAM tyrosine kinases, Axl and MerTK, play an important role in rheumatoid arthritis (RA). Here, using a unique synovial tissue bioresource of patients with RA matched for disease stage and treatment exposure, we assessed how Axl and MerTK relate to synovial histopathology and disease activity, and their topographical expression and longitudinal modulation by targeted treatments. We show that in treatment-naive patients, high AXL levels are associated with pauci-immune histology and low disease activity and inversely correlate with the expression levels of pro-inflammatory genes. We define the location of Axl/MerTK in rheumatoid synovium using immunohistochemistry/fluorescence and digital spatial profiling and show that Axl is preferentially expressed in the lining layer. Moreover, its ectodomain, released in the synovial fluid, is associated with synovial histopathology. We also show that Toll-like-receptor 4-stimulated synovial fibroblasts from patients with RA modulate MerTK shedding by macrophages. Lastly, Axl/MerTK synovial expression is influenced by disease stage and therapeutic intervention, notably by IL-6 inhibition. These findings suggest that Axl/MerTK are a dynamic axis modulated by synovial cellular features, disease stage and treatment.

High-throughput sequencing of IgH gene in minor salivary glands from Sjögren's syndrome patients reveals dynamic B cell recirculation between ectopic lymphoid structures.

OBJECTIVES: B cells play a central role in Sjögren's syndrome (SS) whereby autoreactive B-cells populate ectopic germinal centres (GC) in SS salivary glands (SG) and undergo somatic hypermutation (SHM) and class-switch recombination of the immunoglobulin genes. However, the capacity of specific B cell clones to seed ectopic GC in different SG and undergo clonal diversification is unclear. To unravel the dynamics of B cell recirculation among minor SG biopsies, we investigated the immunoglobulin heavy chain (IgH) gene usage and the pattern of SHM using a high-throughput sequencing approach. METHODS: We generated ~166,000 reads longer than 350bp and detected 1631 clonotypes across eight samples from four different SS patients, all characterised by the presence of functional ectopic GC as demonstrated by the expression of activation-induced cytidine deaminase. RESULTS: A large number of shared clonotypes were observed among paired mSG biopsies from each patient but not across different patients. Lineage tree analysis revealed significant clonal expansion within the mSG with the identification of shared dominant B cell clones suggestive of extensive recirculation across different SG. Several shared clonotypes with high proliferating capacity displayed IgH-VH gene usage common in autoreactive B cells, including VH1-69, which is typical of rheumatoid factor+ B cells representing potential lymphoma precursors. CONCLUSIONS: The complex dynamic recirculation of B cells that we observed within ectopic GC responses linked with their ability to independently proliferate, undergo ongoing SHM and Ig class-switching within individual glands may explain the difficulty in achieving consistent eradication of ectopic GCs following B cell depleting agents reported in different studies.