Because there were no differences in expression of MHC class I genes (HLA-A, HLA-B, HLA-C) or NK/cytotoxic lymphocyte markers (CD56 [NCAM1], KLRF1 [NKp80], PRF1, GZMA/B/K, KLRD1 [CD94], IL2RB [CD122], TBX2) between IgAV skin biopsies with and without nephritis (Supplemental Table), individuals with IgAV who develop nephritis likely have reduced KIR gene content and/or transcription compared with those with IgAV without nephritis. The gene discussed is KLRD1; the disease is nephritis.