Natural killer group 2A (NKG2A) receptor is an inhibitory receptor expressed by NK cells that recognizes histocompatibility antigen, alpha chain E (HLA-E), also known as major histocompatibility complex (MHC) class I antigen E. NKG2A + NK cells have previously been reported to be decreased in PD patients compared to controls24. This evidence concerns the gene KLRC1 and Parkinson disease.