Gaby G. M. Doxiadis

Major histocompatibility complex class II polymorphisms in primates

Summary: 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.

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.

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.

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.

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.

Metastable Tolerance to Rhesus Monkey Renal Transplants Is Correlated with Allograft TGF-β1+CD4+ T Regulatory Cell Infiltrates

Approaches that prevent acute rejection of renal transplants in a rhesus monkey model were studied to determine a common mechanism of acceptance. After withdrawal of immunosuppression, all 14 monkeys retained normal allograft function for >6 mo. Of these, nine rejected their renal allograft during the study, and five maintained normal function throughout the study period. The appearance of TGF-β1+ interstitial mononuclear cells in the graft coincided with a nonrejection histology, whereas the absence/disappearance of these cells was observed with the onset of rejection. Analysis with a variety of TGF-β1-reactive Abs indicated that the tolerance-associated infiltrates expressed the large latent complex form of TGF-β1. Peripheral leukocytes from rejecting monkeys lacking TGF-β1+ allograft infiltrates responded strongly to donor Ags in delayed-type hypersensitivity trans-vivo assays. In contrast, allograft acceptors with TGF-β1+ infiltrates demonstrated a much weaker peripheral delayed-type hypersensitivity response to donor alloantigens (p < 0.01 vs rejectors), which could be restored by Abs that either neutralized active TGF-β1 or blocked its conversion from latent to active form. Anti-IL-10 Abs had no restorative effect. Accepted allografts had CD8+ and CD4+ interstitial T cell infiltrates, but only the CD4+ subset included cells costaining for TGF-β1. Our data support the hypothesis that the recruitment of CD4+ T regulatory cells to the allograft interstitium is a final common pathway for metastable renal transplant tolerance in a non-human primate model.

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

Summary: 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.

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.

A Non-Human Primate Model for Gluten Sensitivity

Background and Aims Gluten sensitivity is widespread among humans. For example, in celiac disease patients, an inflammatory response to dietary gluten leads to enteropathy, malabsorption, circulating antibodies against gluten and transglutaminase 2, and clinical symptoms such as diarrhea. There is a growing need in fundamental and translational research for animal models that exhibit aspects of human gluten sensitivity. Methods Using ELISA-based antibody assays, we screened a population of captive rhesus macaques with chronic diarrhea of non-infectious origin to estimate the incidence of gluten sensitivity. A selected animal with elevated anti-gliadin antibodies and a matched control were extensively studied through alternating periods of gluten-free diet and gluten challenge. Blinded clinical and histological evaluations were conducted to seek evidence for gluten sensitivity. Results When fed with a gluten-containing diet, gluten-sensitive macaques showed signs and symptoms of celiac disease including chronic diarrhea, malabsorptive steatorrhea, intestinal lesions and anti-gliadin antibodies. A gluten-free diet reversed these clinical, histological and serological features, while reintroduction of dietary gluten caused rapid relapse. Conclusions Gluten-sensitive rhesus macaques may be an attractive resource for investigating both the pathogenesis and the treatment of celiac disease.

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

Abstract Human immunodefiency 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.