Moreover, we found that activating KIR2DS1 alone or in combination with the HLA-C1C1 genotype (which indicates the absence of the HLA ligands for their homologous inhibitory receptor KIR2DL1) is associated with susceptibility to ReA (p = .039 and p = .011, respectively), whereas KIR2DL2 in combination with the HLA-C1 ligand is associated with protection against ReA (p = .039).