NGFR and rheumatoid arthritis: Among different synovial fibroblast clusters, in treatment-naïve RA synovial tissues, lining layer PRG4pos cluster and sublining THY1posCOL1A1pos fibroblast cluster are enriched of p75NTR compared to other FLS clusters as well as to other resident and inflammatory synovial cells such as macrophages or T and B lymphocytes (Figure 1B).