KIR3DL1 and COVID-19: In particular, some conserved extended haplotypes of the major histocompatibility complex (MHC) and the presence of the killer cell immunoglobulin-like receptor (KIR) gene KIR2DS2 in combination with HLA-C alleles of the C1 group (HLA-C1) significantly counteract the risk of developing severe clinical manifestations in Sardinian COVID-19 patients (12, 22).