Short KIR haplotypes in pygmy chimpanzee (Bonobo) resemble the conserved framework of diverse human KIR haplotypes

Some pygmy chimpanzees (also called Bonobos) give much simpler patterns of hybridization on Southern blotting with killer cell immunoglobulin-like rec eptor (KIR) cDNA probes than do either humans or common chimpanzees. Charac terization of KIRs from pygmy chimpanzees having simple and complex banding patterns identified nine different KIRs, representing seven genes. Five of these genes have orthologs in the common chimpanzee, and three of them (KI RCI, KIR2DL4, and KIR2DL5) also have human orthologs. The remaining two gen es are KIR3D paralogous to the human and common chimpanzee major histocompa tibility complex A- and /or -B-specific KIRs. Within a pygmy chimpanzee fam ily, KIR haplotypes were defined. Simple patterns on Southern blot were due to inheritance of "short" KIR haplotypes containing only three KIR genes, KIRCI, KIR2DL4, and KIR3D, each of which represents one of the three major KIR lineages. These three genes in pygmy chimpanzees or their corresponding genes in humans and common chimpanzees form the conserved "framework" comm on to all KIR haplotypes in these species and upon which haplotypic diversi ty is built. The fecundity and health of individual pygmy chimpanzees who a re homozygotes for shot KIR haplotypes attest to the viability of short KIR haplotypes, indicating that they can provide minimal, essential KIRs for t he natural killer and T cells of the hominoid immune system.