FAP and rheumatoid arthritis: Furthermore, DSP revealed specific upregulation of genes in the sublining of refractory patients encoding for the fibroblast marker FAP, which has been linked with RA pathogenesis16, while other markers consistently modulated across all regions included CCL13 encoding for the monocyte-attracting chemokine MCP-4, which has been shown to activate synovial fibroblasts32.