Activating natural killer cell receptors (NKC, NKG2C/E, NKG2D, NKG2DL) downregulated in old males in this study are thought to regulate the innate and adaptive immune response through cytokine production and MMP expression leading to the development of inflammatory conditions such as rheumatoid arthritis (RA)39. Here, KLRC2 is linked to rheumatoid arthritis.