Allelic diversity at the Mhc-DP locus in rhesus macaques (Macaca mulatta)

Unraveling the architecture of major histocompatibility complex class II haplotypes in rhesus macaques

The regions in the genome that encode components of the immune system are often featured by polymorphism, copy number variation, and segmental duplications. There is a need to thoroughly characterize these complex regions to gain insight into the impact of genomic diversity on health and disease. Here we resolve the organization of complete major histocompatibility complex (MHC) class II regions in rhesus macaques by using a long-read sequencing strategy (Oxford Nanopore Technologies) in concert with adaptive sampling. In particular, the expansion and contraction of the primate DRB-region appear to be a dynamic process that involves the rearrangement of different cassettes of paralogous genes. These chromosomal recombination events are propagated by a conserved pseudogene, DRB6, which features the integration of two retroviral elements. In contrast, the DRA locus appears to be protected from rearrangements, which may be owing to the presence of an adjacently located truncated gene segment, DRB9 With our sequencing strategy, the annotation, evolutionary conservation, and potential function of pseudogenes can be reassessed, an aspect that was neglected by most genome studies in primates. Furthermore, our approach facilitates the characterization and refinement of an animal model essential to study human biology and disease.

A subset of HLA-DP molecules serve as ligands for the natural cytotoxicity receptor NKp44

Natural killer (NK) cells can recognize virus-infected and stressed cells1 using activating and inhibitory receptors, many of which interact with HLA class I. Although early studies also suggested a functional impact of HLA class II on NK cell activity2,3, the NK cell receptors that specifically recognize HLA class II molecules have never been identified. We investigated whether two major families of NK cell receptors, killer-cell immunoglobulin-like receptors (KIRs) and natural cytotoxicity receptors (NCRs), contained receptors that bound to HLA class II, and identified a direct interaction between the NK cell receptor NKp44 and a subset of HLA-DP molecules, including HLA-DP401, one of the most frequent class II allotypes in white populations4. Using NKp44ζ+ reporter cells and primary human NKp44+ NK cells, we demonstrated that interactions between NKp44 and HLA-DP401 trigger functional NK cell responses. This interaction between a subset of HLA-DP molecules and NKp44 implicates HLA class II as a component of the innate immune response, much like HLA class I. It also provides a potential mechanism for the described associations between HLA-DP subtypes and several disease outcomes, including hepatitis B virus infection5-7, graft-versus-host disease8 and inflammatory bowel disease9,10.

The influence of positive selection and trans-species evolution on DPB diversity in the golden snub-nosed monkeys (Rhinopithecus roxellana)

Genetic variation plays a significant role in the adaptive potential of the endangered species. The variation at major histocompatibility complex (MHC) genes can offer valuable information on selective pressure related to natural selection and environmental adaptation, particularly the ability of a host to continuously resist evolving parasites. Thus, the genetic polymorphism on exon 2 of the MHC DPB1 gene in the golden snub-nosed monkeys (Rhinopithecus roxellana) was specifically analyzed. The results show that the 6 Rhro-DPB1 alleles identified from 87 individuals exhibit positive selection and trans-species polymorphism. The results also imply that although the populations of the species have experienced dramatic reduction and severe habitat fragmentation in recent Chinese history, balancing selection still maintains relatively consistent, with moderate DPB1 polymorphism. Thus, the study provides valuable information and evidence in developing effective strategies and tactics for genetic health and population size expansion of the species. It also offers strong genetic background for further studies on other primate species, particularly those in Rhinopithecus-a further endeavor that would result in fully understanding the MHC genetic information of the Asian colobines.

[Polymorphic analysis of Mhc-DPB1 gene exon 2 in Tibetan macaques (Macaca thibetana)]

Major histocompatibility complex (MHC) molecules play an important role in the susceptibility and/or resistance to many diseases. To gain an insight into the MHC background of the Tibetan macaques (Macaca thibetana), and thereby facilitate their protection and application in biomedical research, the second exon of the Mhc-DPB1 genes from 70 Tibetan macaques in Sichuan Province were characterized by PCR, cloning, sequencing, and statistical analysis. A total of 18 Mhc-DPB1 alleles were identified from Tibetan macaques, of which one (Math-DPB1*01:06N) was a pseudogene. Math-DPB1*06:01:01 (67.14%) was the most frequent allele in all the 18 alleles detected, followed by Math-DPB1* 01:03:01 (37.14%), Math-DPB1*09:02 (25.71%), and Math-DPB1*22:01 (15.71%). The alignment of putative amino acid sequences of the 18 Math-DPB1 alleles showed that 5 variable sites were species-specific to Tibetan macaques. A phylogenetic tree constructed using DPB1 alleles in difference species demonstrated that the alleles for Math-DPB1, Mamu-DPB1, and Mafa-DPB1 tended to mix together, rather than cluster into a separate branch in a species-specific fashion, and the Trans-species polymorphism was also observed in the phylogenetic tree. Selection analysis revealed that balancing selection may play an important role in maintaining the polymorphism of Math-DPB1 genes.

Nomenclature report on the major histocompatibility complex genes and alleles of Great Ape, Old and New World monkey species

The major histocompatibility complex (MHC) plays a central role in the adaptive immune response. The MHC region is characterised by a high gene density, and most of these genes display considerable polymorphism. Next to humans, non-human primates (NHP) are well studied for their MHC. The present nomenclature report provides the scientific community with the latest nomenclature guidelines/rules and current implemented nomenclature revisions for Great Ape, Old and New World monkey species. All the currently published MHC data for the different Great Ape, Old and New World monkey species are archived at the Immuno Polymorphism Database (IPD)-MHC NHP database. The curators of the IPD-MHC NHP database are, in addition, responsible for providing official designations for newly detected polymorphisms.

Characterization of the major histocompatibility complex class II DOB, DPB1, and DQB1 alleles in cynomolgus macaques of Vietnamese origin

Major histocompatibility complex (MHC) molecules play an important role in the susceptibility and/or resistance to many diseases. To gain an insight into the MHC background and to facilitate the experimental use of cynomolgus macaques, the second exon of the MhcMafa-DOB, -DPB1, and -DQB1 genes from 143 cynomolgus macaques were characterized by cloning to sequencing. A total of 16 Mafa-DOB, 16 Mafa-DPB1, and 34 Mafa-DQB1 alleles were identified, which revealed limited, moderate, and marked allelic polymorphism at DOB, DPB1, and DQB1, respectively, in a cohort of cynomolgus macaques of Vietnamese origin. In addition, 16 Mafa-DOB, 5 Mafa-DPB1, and 8 Mafa-DQB1 alleles represented novel sequences that had not been reported in earlier studies. Almost of the sequences detected at the DOB and DQB1 locus in the present study belonged to DOB*01 (100%) and DQB1*06 (62%) lineages, respectively. Interestingly, four, three, and one high-frequency alleles were detected at Mafa-DOB, -DPB1, and -DQB1, respectively, in this monkeys. The alleles with the highest frequency among these monkeys were Mafa-DOB*010102, Mafa-DPB1*13, and Mafa-DQB1*0616, and these were found in 33 (25.6%) of 129 monkeys, 32 (31.37%) of 102 monkeys, and 30 (31%) of 143 monkeys, respectively. The high-frequency alleles may represent high priority targets for additional characterization of immune function. We also carried out evolutionary and population analyses using these sequences to reveal population-specific alleles. This information will not only promote the understanding of MHC diversity and polymorphism in the cynomolgus macaque but will also increase the value of this species as a model for biomedical research.

[Polymorphism of MHC-DPB1 gene exon 2 in rhesus macaques (Macaca mulatta)]

Rhesus macaque (Macaca mulatta) has long been used as an experimental model animal for biomedical research and was under the key state protection (class II) from Chinese government. In order to facilitate the use of Chinese rhesus macaques in biomedical research and their protection based on better understanding of the major mistocompability complex (MHC) genes in these macaques, the exon 2 of Mamu-DPB1 genes were determined in 106 wild rhesus macaques using DGGE, cloning and sequencing. A total of 21 Mamu-DPB1 alleles were obtained, of which 15 alleles were novel sequences that had not been documented previously. Mamu-DPB1 30 was the most frequent allele in the whole large population comprising all 106 rhesus macaque individuals (0.1120) and in Xiaojin population (0.1120), Mamu-DPB1 04 in Heishui (0.1702), -DPB1 32 in Bazhong (0.1613), -DPB1 30 in Hanyuan (0.1120), and -DPB1 04 in Jiulong (0.1139). The alignment of the amino acids sequences showed that 12 variable sites were species-specific, of which 9 sites occurred in the putative amino acids sequences of the 15 novel Mamu-DPB1 alleles. Trans-species polymorphism was observed on the phylogenetic tree based on the DPB1 alleles of rhesus macaques and cynomolgus (Macaca fascicularis). In addition, these results also demonstrated that significant genetic differentiation has occurred between Chinese and Indian rhesus macaque population.

Characterisation and comparative analysis of MHC-DPA1 exon 2 in the owl monkey (Aotus nancymaae)

The Aotus nancymaae (owl monkey) is an important animal model in biomedical research, particularly for the preclinical evaluation of vaccine candidates against Plasmodium falciparum and Plasmodium vivax, which require a precisely typed major histocompatibility complex. The exon 2 from A. nancymaae MHC-DPA1 gene was characterised in order to infer its allelic diversity and evolutionary history. Aona-DPA1 shows no polymorphism and is related to other primate DPA alleles (including Catarrhini and Platyrrhini), constituting an ancient trans-specific and strongly supported lineage with different variability and selective patterns when compared to other primate-MHC-DPA1 lineages. A. nancymaae monkeys have thus a smaller MHC-DP polymorphism than MHC-DQ or MHC-DR.

Pinpointing a selective sweep to the chimpanzee MHC class I region by comparative genomics

Chimpanzees experienced a reduction of the allelic repertoire at the major histocompatibility complex (MHC) class I A and B loci, which may have been caused by a retrovirus belonging to the simian immunodeficiency virus (SIV) family. Extended MHC haplotypes were defined in a pedigreed chimpanzee colony. Comparison of genetic variation at microsatellite markers mapping inside and outside the Mhc region was carried out in humans and chimpanzees to investigate the genomic extent of the repertoire reduction. Multilocus demographic analyses underscored that chimpanzees indeed experienced a selective sweep that mainly targeted the chromosomal segment carrying the Mhc class I region. Probably due to genetic linkage, the sweep also affected other polymorphic loci, mapping in the close vicinity of the Mhc class I region genes. Nevertheless, although the allelic repertoire at particular Mhc class I and II loci appears to be limited, naturally occurring recombination events allowed the establishment of haplotype diversity after the sweep. However, recombination did not have sufficient time to erase the signal of the selective sweep.

Comprehensive characterization of MHC class II haplotypes in Mauritian cynomolgus macaques

There are currently no nonhuman primate models with fully defined major histocompatibility complex (MHC) class II genetics. We recently showed that six common MHC haplotypes account for essentially all MHC diversity in cynomolgus macaques (Macaca fascicularis) from the island of Mauritius. In this study, we employ complementary DNA cloning and sequencing to comprehensively characterize full length MHC class II alleles expressed at the Mafa-DPA, -DPB, -DQA, -DQB, -DRA, and -DRB loci on the six common haplotypes. We describe 34 full-length MHC class II alleles, 12 of which are completely novel. Polymorphism was evident at all six loci including DPA, a locus thought to be monomorphic in rhesus macaques. Similar to other Old World monkeys, Mauritian cynomolgus macaques (MCM) share MHC class II allelic lineages with humans at the DQ and DR loci, but not at the DP loci. Additionally, we identified extensive sharing of MHC class II alleles between MCM and other nonhuman primates. The characterization of these full-length-expressed MHC class II alleles will enable researchers to generate MHC class II transferent cell lines, tetramers, and other molecular reagents that can be used to explore CD4+ T lymphocyte responses in MCM.

Novel cynomolgus macaque MHC-DPB1 polymorphisms in three South-East Asian populations

Cynomolgus macaques (Macaca fascicularis, Mafa), alias the crab-eating monkeys or long-tailed macaques, live across a vast range of South-East Asia. These non-human primates have emerged as important animal models in infectious and chronic diseases and transplantation studies, necessitating a more extensive characterization of their major histocompatibility complex polymorphic regions. The current information on the polymorphic variation or diversity of the Mafa-DPB1 locus is largely limited in comparison with the more commonly studied rhesus macaque DPB1 locus. In this article, to better elucidate the degree and types of polymorphisms and genetic differences of Mafa-DPB1 locus among three South-East Asian populations and to investigate how the allele differences between macaques and humans might affect their respective immune responses, we identified 40 alleles within exon 2 of the Mafa-DPB1 locus by DNA sequencing using 217 individuals. We also performed evolutionary and population analyses using these sequences to reveal some population-specific alleles and trans-species allelic conservation between the cynomolgus macaques and the rhesus macaques. Of the 40 new alleles, eight belong to a newly identified lineage group not previously found in the rhesus macaque species. This allele information will be useful for medical researchers using the cynomolgus macaques in disease and immunological studies.

Sequence analysis of the MHC class II DPB1 gene in chimpanzees (Pan troglodytes)

The diversity of the MHC class II region in non-human primates is a focus of biomedical research because this region plays a crucial role in the recognition of antigens in the immune system. In particular, the chimpanzee [Pan troglodytes (Patr)], which belongs to the superfamily Hominoidea, has been used as a human model for the study of diseases such as human hepatitis C virus (HCV), human hepatitis B virus (HBV) and human immunodeficiency virus (HIV) infections, to which only humans and chimpanzees are susceptible. In the present study, polymorphisms of the MHC-DPB1 gene (Patr-DPB1) in a chimpanzee colony in Japan were examined using a stepwise polymerase chain reaction (PCR) technique. In order to design a suitable primer pair which would amplify exon 2 of the Patr-DPB1 gene, a fragment of approximately 8 kb from exon 1 to exon 3 was amplified from chimpanzee genomic DNA. After designing a 500-bp primer pair at the 3' region of intron 1 and the 5' region of intron 2, analysis of DPB1 exon 2 alleles of each chimpanzee was carried out. Twenty-two chimpanzees were used in our study, and we identified seven alleles by sequence analysis on the Patr-DPB1 gene, including one new allele. The obtained nucleotide sequence patterns suggest that Patr-DPB1 alleles emerge by genetic variations such as the exchange of sequence motifs and the accumulation of point mutations.

Comparative genetics of MHC polymorphisms in different primate species: duplications and deletions

Gene products of the major histocompatibility complex (MHC) play a crucial role in the activation of adaptive (antigen-dependent) immune responses. In this paper similarities and dissimilarities among the MHCs of different primate species and their functional implications are reviewed. The human HLA system represents the most thoroughly investigated MHC of any contemporary living primate species, and so it will serve as a reference.

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.

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.

The major histocompatibility complex influences the ethiopathogenesis of MS-like disease in primates at multiple levels

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease primarily affecting the central nervous system. Of the many candidate polymorphic major histocompatibility complex (MHC) and non-MHC genes contributing to disease susceptibility, including those encoding effector (cytokines and chemokines) or receptor molecules within the immune system (MHC, TCR, Ig or FcR), human leukocyte antigen (HLA) class II genes have the most significant influence. In this article we put forward the hypothesis that the influence of HLA genes on the risk to develop MS is actually the sum of multiple antigen presenting cell (APC) and T-cell interactions involving HLA class I and class II molecules. This article will also discuss that, because of the genetic and immunologic similarity to humans, autoimmune models of MS in non-human primates are the experimental models "par excellence" to test this hypothesis.

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 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.

Major histocompatibility genes in cyprinid fishes: theory and practice

The first teleostean MHC sequences were described for carp. Subsequent studies in a number of cyprinid fishes showed that the class I sequences of these fishes are of particular interest. Two distinct lineages (Cyca-Z and Cyca-U) are found in the common and ginbuna crucian carp, but only the U lineage is present in zebrafish and other non-cyprinid species. The presence of the Z lineage is hypothesised to be the result of an allotetraploidisation event. Both phylogenetic analyses and amino acid sequence comparisons suggest that Cyca-Z sequences are non-classical class I sequences, probably similar to CD1. The comprehensive phylogenetic analyses of these sequences revealed different phylogenetic histories of the exons encoding the extracellular domains. The MHC genes were studied in laboratory and natural models. The natural model addressed the evolution of MHC genes in a Barbus species flock. Sequence analysis of class I and class II supported the species designation of the morphotypes present in the lake, and as a consequence the trans-species hypothesis of MHC polymorphism. The laboratory model involves the generation of gynogenetic clones, which can be divergently selected for traits such as high and low antibody response. The role of MHC molecules can be investigated further by producing a panel of isogenic lines.

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.

Rapid allelic diversification and intensified selection at antigen recognition sites of the Mhc class II DPB1 locus during hominoid evolution

The evolution of polymorphism at the Mhc class II DPB1 locus was studied by comparison of chimpanzee (Pan troglodytes), pygmy chimpanzee (Pan paniscus), gorilla (Gorilla gorilla) and human DPB1 alleles. Extensive polymorphism was found in all hominoids. The clustering of sequences in the phylogenetic tree is consistent with rapid generation of the DPB1 polymorphism. Analysis of the substitution pattern for human alleles shows an excess of non-synonymous changes to synonymous changes at antigen recognition sites, indicating that the amino acid polymorphism at these sites is being maintained by selection. By contrast, no excess of nonsynonymous changes was found at the antigen recognition sites of nonhuman hominoid species. Thus, it appears that diversifying selection on the DPB1 polymorphism has intensified in the lineage leading to humans. No evidence was found for the existence of ancient allelic lineages predating the divergence of the hominoid species. The number of synonymous differences among DPB1 alleles is lower than among DQB1 and DRB1 alleles, indicative of a more recent origin for the DPB1 polymorphism and consistent with the more rapid evolution suggested by the phylogenetic tree.

Evolution of the major histocompatibility complex DPA1 locus in primates

The evolutionary relationships among Mhc-DPA1 alleles of various nonhuman primate species was studied by sequence analysis of exon 2. Here we report the nucleotide sequences of 15 Mhc-DPA1 alleles obtained from several great ape and Old and New World monkey species. Comparison with their human homologues reveals that alleles can be grouped into transspecies lineages, indicating that some HLA-DPA1-associated polymorphisms have been maintained for at least 35 million years.