In rheumatoid arthritis an increased percentage of NKG2Dpos CD4pos T cells has been reported in blood and synovial fluid (22), while patients affected by systemic lupus erythematosus (SLE) showed an increase in the percentage of NKG2Dpos T cells and a decrease of NKG2D in NK cells in terms of expression, percentage, and relative number (23–25). Here, KLRK1 is linked to rheumatoid arthritis.