MIC gene polymorphism and haplotype diversity in rhesus macaques

Rhesus macaques (Macaca mulatta) mainly originating from India were analysed for their major histocompatibility complex class I-related (MIC) gene repertoire. Thus far, three distinct genes, designated MIC1, MIC2 and MIC3, have been identified in the rhesus macaque. In addition, an MICD pseudogene has been described mapping apart from the other loci in a telomeric direction. Genomic comparisons and the presence of a characteristic microsatellite in exon 5 suggest that the MIC1 gene is the equivalent of the human MICA gene. Hence, the MIC2 gene, lacking the microsatellite - as do humans -, is considered to be the equivalent of human MICB. The MIC3 gene, a hybrid of MICA and MICB, seems to be generated by a crossing-over event with one breakpoint in intron 3 and accordingly is named MICA/B. Apart from their human counterparts, MICA, MICB and MICA/B cluster in separate branches in the phylogenetic tree, confirming the hybrid character of the MICA/B gene. Population analyses have shown that the various genes display polymorphism, and six MICA, five MICB and three MICA/B alleles have been identified. In the panel of homozygous typing cells, two distinct haplotype configurations have been defined by segregation analyses. Each haplotype comprises an MICB gene in conjunction with either an MICA or an MICA/B gene. Furthermore, the presence of a polymorphic microsatellite in the MICA and MICA/B alleles facilitates speedy and accurate haplotyping.

MHC class I A region diversity and polymorphism in macaque species

The HLA-A locus represents a single copy gene that displays abundant allelic polymorphism in the human population, whereas, in contrast, a nonhuman primate species such as the rhesus macaque (Macaca mulatta) possesses multiple HLA-A-like (Mamu-A) genes, which parade varying degrees of polymorphism. The number and combination of transcribed Mamu-A genes present per chromosome display diversity in a population of Indian animals. At present, it is not clearly understood whether these different A region configurations are evolutionarily stable entities. To shed light on this issue, rhesus macaques from a Chinese population and a panel of cynomolgus monkeys (Macaca fascicularis) were screened for various A region-linked variations. Comparisons demonstrated that most A region configurations are old entities predating macaque speciation, whereas most allelic variation (>95%) is of more recent origin. The latter situation contrasts the observations of the major histocompatibility complex class II genes in rhesus and cynomolgus macaques, which share a high number of identical alleles (>30%) as defined by exon 2 sequencing.

Reactivation by exon shuffling of a conserved HLA-DR3-like pseudogene segment in a New World primate species

The common marmoset (Callithrix jacchus), a New World monkey species with a limited MHC class II repertoire, is highly susceptible to certain bacterial infections. Genomic analysis of exon 2 sequences documented the existence of only one DRB region configuration harboring three loci. Two of these loci display moderate levels of allelic polymorphism, whereas the -DRB*W12 gene appears to be monomorphic. This study shows that only the Caja-DRB*W16 and -DRB*W12 loci produce functional transcripts. The Caja-DRB1*03 locus is occupied by a pseudogene, given that most of the transcripts, if detected at all, show imperfections and are present at low levels. Moreover, two hybrid transcripts were identified that feature the evolutionarily conserved peptide-binding motif characteristic for the Caja-DRB1*03 gene. Thus, the severely reduced MHC class II repertoire in common marmosets has been expanded by reactivation of a pseudogene segment as a result of exon shuffling.

Extensive sharing of MHC class II alleles between rhesus and cynomolgus macaques

In contrast to rhesus monkeys, substantial knowledge on cynomolgus monkey major histocompatibility complex (MHC) class II haplotypes is lacking. Therefore, 17 animals, including one pedigreed family, were thoroughly characterized for polymorphic Mhc class II region genes as well as their mitochondrial DNA (mtDNA) sequences. Different cynomolgus macaque populations appear to exhibit unique mtDNA profiles reflecting their geographic origin. Within the present panel, 10 Mafa-DPB1, 14 Mafa-DQA1, 12 Mafa-DQB1, and 35 Mafa-DRB exon 2 sequences were identified. All of these alleles cluster into lineages that were previously described for rhesus macaques. Moreover, about half of the Mafa-DPB1, Mafa-DQA1, and Mafa-DQB1 alleles and one third of the Mafa-DRB exon 2 sequences are identical to rhesus macaque orthologues. Such a high level of Mhc class II allele sharing has not been reported for primate species. Pedigree analysis allowed the characterization of nine distinct Mafa class II haplotypes, and seven additional ones could be deduced. Two of these haplotypes harbor a duplication of the Mafa-DQB1 locus. Despite extensive allele sharing, rhesus and cynomolgus monkeys do not appear to possess identical Mhc class II haplotypes, thus illustrating that new haplotypes were generated after speciation by recombination-like processes.

Microsatellite typing of the rhesus macaque MHC region

To improve the results gained by serotyping rhesus macaque major histocompatibility complex (MHC) antigens, molecular typing techniques have been established for class I and II genes. Like the rhesus macaque Mamu-DRB loci, the Mamu-A and -B are not only polymorphic but also polygenic. As a consequence, sequence-based typing of these genes is time-consuming. Therefore, eight MHC-linked microsatellites, or short tandem repeats (STRs), were evaluated for their use in haplotype characterization. Polymorphism analyses in rhesus macaques of Indian and Chinese origin showed high STR allelic diversity in both populations but different patterns of allele frequency distribution between the groups. Pedigree data for class I and II loci and the eight STRs allowed us to determine extended MHC haplotypes in rhesus macaque breeding groups. STR sequencing and comparisons with the complete rhesus macaque MHC genomic map allowed the exact positioning of the markers. Strong linkage disequilibria were observed between Mamu-DR and -DQ loci and adjacent STRs. Microsatellite typing provides an efficient, robust, and quick method of genotyping and deriving MHC haplotypes for rhesus macaques regardless of their geographical origin. The incorporation of MHC-linked STRs into routine genetic tests will contribute to efforts to improve the genetic characterization of the rhesus macaque for biomedical research and can provide comparative information about the evolution of the MHC region.

Reduced MIC gene repertoire variation in West African chimpanzees as compared to humans

The human major histocompatibility complex class I chain-related (MIC) genes are members of a multicopy family showing similarity to the classical HLA-A, HLA-B, and HLA-C genes. Only the MICA and MICB genes produce functional transcripts. In chimpanzees, however, only one MIC gene is expressed, showing an intermediate character, resulting from a deletion fusing the MICA and MICB gene segments together. The present population study illustrates that all chimpanzee haplotypes sampled possess the hybrid MICA/B gene. In contrast to the human situation this gene displays reduced allelic variation. The observed repertoire reduction of the chimpanzee MICA/B gene is in conformity with the severe repertoire condensation documented for Patr-B locus lineages, probably due to the close proximity of both genes.

Unparalleled complexity of the MHC class I region in rhesus macaques

The highly polymorphic gene products of the classical MHC class I genes in humans (HLA-A, HLA-B, and HLA-C) play a critical role in the immune defense against intracellular infections. Because non-human primates are important models for AIDS vaccine research, rhesus monkeys from a thoroughly pedigreed and serotyped colony were subjected to full-length cDNA analysis of MHC class I gene transcripts. Rhesus macaques express multiple dominant Mamu-A and Mamu-B transcripts (majors) per chromosome, which are characterized by high expression levels. The presence of additional cDNAs with low levels of expression (minors) suggests evidence for transcriptional control of MHC class I genes. Moreover, phylogenetic analyses illustrate that most of the Mamu-A and Mamu-B loci/lineages identified display no or only limited levels of allelic polymorphism. Thus, MHC class I diversity in rhesus macaques is typified by the existence of an unmatched high number of Mamu-A and Mamu-B region configurations that exhibit polymorphism with regard to the number and combination of transcribed loci present per chromosome.

Genetic makeup of the DR region in rhesus macaques: gene content, transcripts, and pseudogenes

In the human population, five major HLA-DRB haplotypes have been identified, whereas the situation in rhesus macaques (Macaca mulatta) is radically different. At least 30 Mamu-DRB region configurations, displaying polymorphism with regard to number and combination of DRB loci present per haplotype, have been characterized. Until now, Mamu-DRB region genes have been studied mainly by genomic sequencing of polymorphic exon 2 segments. However, relatively little is known about the expression status of these genes. To understand which exon 2 segments may represent functional genes, full-length cDNA analyses of -DRA and -DRB were initiated. In the course of the study, 11 cDRA alleles were identified, representing four distinct gene products. Amino acid replacements are confined to the leader peptide and cytoplasmatic tail, whereas residues of the alpha1 domain involved in peptide binding, are conserved between humans, chimpanzees, and rhesus macaques. Furthermore, from the 11 Mamu-DRB region configurations present in this panel, 28 cDRB alleles were isolated, constituting 12 distinct cDRA/cDRB configurations. Evidence is presented that a single configuration expresses maximally up to three -DRB genes. For some exon 2 DRB sequences, the corresponding transcripts could not be detected, rendering such alleles as probable pseudogenes. The full-length cDRA and cDRB sequences are necessary to construct Mhc class II tetramers, as well as transfectant cell lines. As the rhesus macaque is an important animal model in AIDS vaccine studies, the information provided in this communication is essential to define restriction elements and to monitor immune responses in SIV/simian human immunodeficiency virus-infected rhesus macaques.

A prevalent POLG CAG microsatellite length allele in humans and African great apes

The human nuclear gene for the catalytic subunit of mitochondrial DNA polymerase gamma ( POLG) contains within its coding region a CAG microsatellite encoding a polyglutamine repeat. Previous studies demonstrated an association between length variation at this repeat and male infertility, suggesting a mechanism whereby the prevalent (CAG)(10) allele, which occurs at a frequency of >80% in different populations, could be maintained by selection. Sequence analysis of the POLG CAG microsatellite region of more than 1000 human chromosomes reveals that virtually all allelic variation at the locus is accounted for by length variation of the CAG repeat. Analysis of POLG from African great apes shows that a prevalent length allele is present in each species, although its exact length is species-specific. In common chimpanzee ( Pan troglodytes) a number of different sequence variants contribute to the prevalent length allele, strongly supporting the idea that the length of the POLG microsatellite region, rather than its exact nucleotide or amino acid sequence, is what is maintained. Analysis of POLG in other primates indicates that the repeat has expanded from a shorter, glutamine-rich sequence, present in the common ancestor of Old and New World monkeys.

Evolutionary stability of MHC class II haplotypes in diverse rhesus macaque populations

A thoroughly characterized breeding colony of 172 pedigreed rhesus macaques was used to analyze exon 2 of the polymorphic Mamu- DPB1, -DQA1, -DQB1, and - DRB loci. Most of the monkeys or their ancestors originated in India, though the panel also included animals from Burma and China, as well as some of unknown origin and mixed breeds. In these animals, mtDNA appears to correlate with the aforementioned geographic origin, and a large number of Mamu class II alleles were observed. The different Mamu- DPB1 alleles were largely shared between monkeys of different origin, whereas in humans particular alleles appear to be unique for ethnic populations. In contrast to Mamu-DPB1, the highly polymorphic - DQA1/DQB1 alleles form tightly linked pairs that appear to be about two-thirds population specific. For most of the DQA1/DQB1 pairs, Mamu- DRB region configurations present on the same chromosome have been ascertained, resulting in 41 different -DQ/DRB haplotypes. These distinct DQ/DRB haplotypes seem to be specific for monkeys of a determined origin. Thus, in evolutionary terms, the Mamu-DP, -DQ, and -DR regions show increasing instability with regard to allelic polymorphism, such as for -DP/DQ, or gene content and allelic polymorphism, such as for -DR, resulting in population-specific class II haplotypes. Furthermore, novel haplotypes are generated by recombination-like events. The results imply that mtDNA analysis in combination with Mhc typing is a helpful tool for selecting animals for biomedical experiments.

Evidence for an ancient selective sweep in the MHC class I gene repertoire of chimpanzees

MHC class I molecules play an essential role in the immune defense against intracellular infections. The hallmark of the MHC is its extensive degree of polymorphism at the population level. However, the present comparison of MHC class I gene intron variation revealed that chimpanzees have experienced a severe repertoire reduction at the orthologues of the HLA-A, -B, and -C loci. The loss of variability predates the (sub)speciation of chimpanzees and did not effect other known gene systems. Therefore the selective sweep in the MHC class I gene may have resulted from a widespread viral infection. Based on the present results and the fact that chimpanzees have a natural resistance to the development of AIDS, we hypothesize that the selective sweep was caused by the chimpanzee-derived simian immunodeficiency virus (SIVcpz), the closest relative of HIV-1, or a closely related retrovirus. Hence, the contemporary chimpanzee populations represent the offspring of AIDS-resistant animals, the survivors of a HIV-like pandemic that took place in the distant past.

Extensive Mhc-DQB variation in humans and non-human primate species

Non-human primates are often used in biomedical research, and the application of these animals as a model in immune-related diseases necessitates the characterisation of their MHC system. In particular, the MHC class II regions of the chimpanzee (Pan troglodytes), the rhesus macaque (Macaca mulatta)and the common marmoset (Callithrix jacchus) have been subject of molecular biological studies in recent years. In this study the emphasis was on MHC class II genes of another macaque species, Macaca fascicularis(crab eating macaque or cynomolgous monkey). The exon 2 of the Mhc-DQB gene (Mafa-DQB) was sequenced in each of a random panel of 60 non-pedigreed cynomolgous monkeys. This resulted in the detection of 23 Mafa-DQB1alleles that had not previously been published. In addition, unreported alleles were found in chimpanzees, rhesus macaques, orang-utans (Pongo pygmaeus) and stump-tailed macaques (Macaca arctoides), of which a few individuals were included in this study. Phylogenetic analyses confirm the trans-species model of evolution of the MHC-DQBlineages, in which a group of major alleles is passed on in the phylogeny, and has led to the sharing of allelic lineages by different species of non-human primates. The sharing of alleles is observed only for closely related macaque species. Furthermore, this manuscript provides an overview of all published, and whenever necessary corrected, non-human primate Mhc-DQB exon 2 alleles.

Differential evolutionary MHC class II strategies in humans and rhesus macaques: relevance for biomedical studies

The rhesus macaque is an important preclinical model in transplantation research and in investigations of chronic and infectious diseases that need a well-characterised major histocompatibility complex (MHC-Mamu). In a large population of pedigreed rhesus macaques, 70 Mamu-DRB, 18 -DQA1, 24 -DQB1, and 14 -DPB1 alleles were detected. In humans, five HLA-DRB region configurations are present, displaying diversity with regard to number and combinations of loci. The HLA-DRB1 gene of each of these configurations is highly polymorphic. For rhesus monkeys, at least 31 Mamu-DRB region configurations have been determined. In contrast to humans, most Mamu-DRB region configurations display no or only limited allelic polymorphism. Segregation analyses revealed 28 Mamu-DQA1/DQB1 pairs, each pair linked to a limited number of Mamu-DRB region configurations and vice versa. In comparison with humans, the degree of freedom of recombination between Mamu-DQA1 and -DQB1 is extremely low and equivalents of HLA-DQA2/DQB2 are absent. The Mamu-DPA1 gene is invariant and -DPB1 manifests only moderate allelic variation, whereas the HLA-DPA1 gene is oligomorphic and HLA-DPB1 highly polymorphic. Thus, both species used different evolutionary strategies to create polymorphism and diversity at the MHC class II loci in order to cope with pathogens.

Allelic diversity of Mhc-DRB alleles in rhesus macaques

The Biomedical Primate Research Centre (BPRC) rhesus macaque colony was started with a large number of wild-caught animals originating mainly from the Indian subcontinent. The contemporary self-sustaining colony comprises approximately 800 individuals. We screened a large section of the colony for Mamu-DRB polymorphisms by applying the denaturing gradient gel electrophoresis (DGGE) technique. Based on disparate DGGE profiles, animals were selected for nucleotide sequence analysis. This approach allowed the detection of 25 unreported Mamu-DRB alleles, bringing to 126 the total number of alleles documented in the literature. This communication demonstrates that rhesus macaques, like humans, display extensive allelic polymorphism at the DRB region. Phylogenetic analyses illustrate that humans and rhesus macaques share several Mhc-DRB loci and lineages. Identical exon 2 sequences, however, which are shared between humans and rhesus macaques, were not observed. This indicates that most primate Mhc-DRB alleles are of post-speciation origin.

Major histocompatibility complex class I diversity in a West African chimpanzee population: implications for HIV research

Human immunodeficiency virus (HIV) poses a major threat to humankind. And though, like humans, chimpanzees are susceptible to HIV infection, they are considered to be resistant to the development of the acquired immune deficiency syndrome (AIDS). Little is known about major histocompatibility complex (MHC) class I diversity in chimpanzee populations and, moreover, whether qualitative aspects of Patr class I molecules may control resistance to AIDS. To address these questions, we assayed MHC class I diversity in a West African chimpanzee population and in some animals from other subspecies of chimpanzee. Application of different techniques allowed the detection of 17 full-length Patr-A, 19 Patr-B, and 10 Patr-C alleles. All Patr-A alleles cluster only into the HLA-A1/A3/A11 family, which supports the idea that chimpanzees have experienced a reduction in their repertoire of A locus alleles. The Patr-B alleles do not cluster in the same lineages as their human equivalents, due to frequent exchange of polymorphic sequence motifs. Furthermore, polymorphic motifs may have been exchanged between Patr-A and Patr-B loci, resulting in convergence. With regard to evolutionary stability, the Patr-C locus is more similar to the Patr-A locus than it is to the Patr-B locus. Despite the relatively low number of animals analyzed, humans and chimpanzees were ascertained as sharing similar degrees of diversity at the contact residues constituting the B and F pockets in the peptide-binding side of MHC class I molecules. Our results indicate that within a small sample of a West African chimpanzee population, a high degree of Patr class I diversity is encountered. This is in agreement with the fact that chimpanzees display more mitochondrial DNA variation than humans. In addition, population analyses demonstrated that particular Patr-B molecules, with the capacity to bind conserved HIV-1 epitopes, are characterized by high gene frequencies. These findings have important implications for evaluating immune responses in HIV vaccine studies and, more importantly, may help in understanding the relative resistance of chimpanzees to AIDS.

Unprecedented polymorphism of Mhc-DRB region configurations in rhesus macaques

The rhesus macaque is an important model in preclinical transplantation research and for the study of chronic and infectious diseases, and so extensive knowledge of its MHC (MhcMamu) is needed. Nucleotide sequencing of exon 2 allowed the detection of 68 Mamu-DRB alleles. Although most alleles belong to loci/lineages that have human equivalents, identical Mhc-DRB alleles are not shared between humans and rhesus macaques. The number of -DRB genes present per haplotype can vary from two to seven in the rhesus macaque, whereas it ranges from one to four in humans. Within a panel of 210 rhesus macaques, 24 Mamu-DRB region configurations can be distinguished differing in the number and composition of loci. None of the Mamu-DRB region configurations has been described for any other species, and only one of them displays major allelic variation giving rise to a total of 33 Mamu-DRB haplotypes. In the human population, only five HLA-DRB region configurations were defined, which in contrast to the rhesus macaque exhibit extensive allelic polymorphism. In comparison with humans, the unprecedented polymorphism of the Mamu-DRB region configurations may reflect an alternative strategy of this primate species to cope with pathogens. Because of the Mamu-DRB diversity, nonhuman primate colonies used for immunological research should be thoroughly typed to facilitate proper interpretation of results. This approach will minimize as well the number of animals necessary to conduct experiments.

Mamu-I: a novel primate MHC class I B-related locus with unusually low variability

The rhesus macaque is an important animal model for several human diseases and organ transplantation. Therefore, definition of the MHC of this species is crucial to the development of these models. Unfortunately, unlike humans, lymphocytes from a single rhesus macaque express up to 12 different MHC class I cDNAs. From which locus these various alleles are derived is unclear. In our attempts to define the MHC class I loci of the rhesus macaque, we have identified an unusual MHC class I locus, Mamu-I. We isolated 26 I locus alleles from three different macaque species but not from three other Cercopithecine genera, suggesting that the I locus is the result of a recent duplication of the B locus occurring after the divergence of macaques from the ancestor of the other extant Cercopithecine genera. Mamu-I mRNA transcripts were detected in all tissues examined and Mamu-I protein was produced in rhesus B lymphoblastoid cell lines. Furthermore, Mamu-I protein was detected by flow cytometry on the surface of human 721.221 cells transfected with Mamu-I. In contrast to the polymorphism present at this locus, there is unusually low sequence variability, with the mean number of nucleotide differences between alleles being only 3.6 nt. Therefore, Mamu-I is less variable than any other polymorphic MHC class I locus described to date. Additionally, no evidence for positive selection on the peptide binding region was observed. Together, these results suggest that Mamu-I is an MHC class I locus in primates that has features of both classical and nonclassical loci.

Major histocompatibility complex class II polymorphisms in primates

In the past decade, the major histocompatibility complex (MHC) class II region of several primate species has been investigated extensively. Here we will discuss the similarities and differences found in the MHC class II repertoires of primate species including humans, chimpanzees, rhesus macaques, cotton-top tamarins and common marmosets. Such types of comparisons shed light on the evolutionary stability of MHC class II alleles, lineages and loci as well as on the evolutionary origin and biological significance of haplotype configurations.

Complete withdrawal of immunosuppression in kidney allograft recipients: a prospective study in rhesus monkeys

BACKGROUND

We previously reported the successful withdrawal of immunosuppression in kidney-allografted rhesus monkeys. Recipients had received pretransplant blood transfusions and cyclosporine (CsA) immunosuppression for 6 to 12 months. One animal is still alive at more than 15 years after transplantation. Our hypothesis was that the sharing of a single DR antigen between blood donor and recipient, and the sharing of the same DR antigen with the kidney donor, may be beneficial to allograft survival. We now report on the results from a prospective study.

METHODS

The animals received three pretransplant blood transfusions from a single donor sharing one DR antigen with the recipient. Subsequently, a life-supporting kidney from a donor sharing the same DR antigen was transplanted. CsA was given for at least 6 months after transplantation.

RESULTS

Two animals rejected their graft at 5-8 weeks after cessation of CsA treatment. One animal is still alive at 700 days after transplantation. This animal showed MLR nonreactivity to its kidney donor, similar to the animal at more than 15 years after transplantation.

CONCLUSION

These results demonstrate that withdrawal of immunosuppression may be a realistic option in kidney graft patients under careful immunological monitoring of donor-specific immunity.

Characterization and distribution of Mhc-DPB1 alleles in chimpanzee and rhesus macaque populations

Allelic diversity at the nonhuman primate Mhc-DPB1 locus was studied by determining exon 2 nucleotide sequences. This resulted in the detection of 17 chimpanzee (Pan troglodytes), 2 orangutan (Pongo pygmaeus) and 16 rhesus macaque (Macaca mulatta) alleles. These were compiled with primate Mhc-DPB1 nucleotide sequences that were published previously. Based upon the results, a sequence specific oligotyping method was developed allowing us to investigate the distribution of Mhc-DPB1 alleles in distinct chimpanzee and rhesus macaque colonies. Like found in humans, chimpanzee and rhesus macaque populations originating from different geographic backgrounds appear to be characterized by the presence of a few dominant Mhc-DPB1 alleles.

The common marmoset: a new world primate species with limited Mhc class II variability

The common marmoset (Callithrix jacchus) is a New World primate species that is highly susceptible to fatal infections caused by various strains of bacteria. We present here a first step in the molecular characterization of the common marmoset's Mhc class II genes by nucleotide sequence analysis of the polymorphic exon 2 segments. For this study, genetic material was obtained from animals bred in captivity as well as in the wild. The results demonstrate that the common marmoset has, like other primates, apparently functional Mhc-DR and -DQ regions, but the Mhc-DP region has been inactivated. At the -DR and -DQ loci, only a limited number of lineages were detected. On the basis of the number of alleles found, the -DQA and -B loci appear to be oligomorphic, whereas only a moderate degree of polymorphism was observed for two of three Mhc-DRB loci. The contact residues in the peptide-binding site of the Caja-DRB1*03 lineage members are highly conserved, whereas the -DRB*W16 lineage members show more divergence in that respect. The latter locus encodes five oligomorphic lineages whose members are not observed in any other primate species studied, suggesting rapid evolution, as illustrated by frequent exchange of polymorphic motifs. All common marmosets tested were found to share one monomorphic type of Caja-DRB*W12 allele probably encoded by a separate locus. Common marmosets apparently lack haplotype polymorphism because the number of Caja-DRB loci present per haplotype appears to be constant. Despite this, however, an unexpectedly high number of allelic combinations are observed at the haplotypic level, suggesting that Caja-DRB alleles are exchanged frequently between chromosomes by recombination, promoting an optimal distribution of limited Mhc polymorphisms among individuals of a given population. This peculiar genetic make up, in combination with the limited variability of the major histocompatability complex class II repertoire, may contribute to the common marmoset's susceptibility to particular bacterial infections.

Characterization of the ABO blood group genes in macaques: evidence for convergent evolution

The ABO blood group system is known to act as a major transplantation barrier in primates. Different primate species share the presence of A and B antigens. The polymorphism of the macaque ABO blood group genes was analyzed by cloning and sequencing the exon 7 region. In the case of the rhesus macaque (Macaca mulatta) and cynomolgus monkey (Macaca fascicularis) we were able to identify ABO blood group gene segments which cluster into two lineages, namely: *A/*O1 and *B. In addition allelic variation was observed. The 2 amino acid replacements at positions 266 and 268, which are thought to be crucial for A or B transferase activity, could be confirmed for both macaque species. Comparison of primate sequences shows that A and B reactivity was generated independently from each other in the hominoids and Old World monkey lineages. Hence, the primate A and B blood group genes are subject to convergent evolution.