Donor-versus-recipient natural killer (NK) cell alloreactivity.

Individuals who express Group 2 HLA-C alleles and possess NK cells that express killer cell immunoglobulin-like receptors (KIRs) specific for Group 2 HLA-C alleles (KIR2DL1) are alloreactive against cells from individuals who do not express Group 2 HLA-C alleles (who are homozygous for Group 1 HLA-C alleles) (top). Individuals who express Group 1 HLA-C alleles possess NK cells with KIRs specific for Group 1 HLA-C alleles (KIR2DL2 and/or KIR2DL3) and are alloreactive against cells from individuals who do not express Group 1 HLA-C alleles (who are homozygous for Group 2 HLA-C alleles) (bottom).