TREM2 and rheumatoid arthritis: Confocal images of RA synovial compartments showed that SLC16A1 and SLC16A3 were expressed by both sub-lining (CD90) and lining (CLIC5 and PRG4) fibroblast subsets, while SLC16A3 was mainly expressed by CD68+TREM2+ lining macrophages (Figures 1C, D).