KLRK1 and rheumatoid arthritis: A study of the interactions between fibroblast-like synovial cells (FLS) and NK cell lines (Nishi) in RA found that FLS express many ligands of NK cells and stimulate the degranulation of Nishi cells, and NKG2D is one of the key activating receptors involved in Nishi’s degranulation of FLS [66].