Rapid evolution of NK cell receptor systems demonstrated by comparison of chimpanzees and humans.

ABSTRACT

That NK cell receptors engage fast-evolving MHC class I ligands suggests that they, too, evolve rapidly. To test this hypothesis, the structure and class I specificity of chimpanzee KIR and CD94NKG2 receptors were determined and compared to their human counterparts. The KIR families are divergent, with only three KIR conserved between chimpanzees and humans. By contrast, CD94NKG2 receptors are conserved. Whereas receptors for polymorphic class I are divergent, those for nonpolymorphic class I are conserved. Although chimpanzee and human NK cells exhibit identical receptor specificities for MHC-C, they are mediated by nonorthologous KIR. These results demonstrate the rapid evolution of NK cell receptor systems and imply that "catching up" with class I is not the only force driving this evolution.