AXL and rheumatoid arthritis: This is likely due to post-translational modifications linked to the RA tissue environment, including the cleavage of Axl ectodomain, as we demonstrated in this paper, and/or the epigenetic-driven down-regulation of Axl protein in cell-subsets of the sublining (e.g., Thy-1+ FLS or sublining macrophages), as previously demonstrated by Kurowska-Stolarska and colleagues in RA DCs4.