Pig-tailed macaques (<Emphasis Type="Italic">Macaca nemestrina</Emphasis>) possess six MHC-E families that are conserved among macaque species: implication for their binding to natural killer receptor variants

MHC loci encode highly polymorphic molecules involved in the presentation of self and non-self peptides to cells of the adaptive and innate immune systems. Although variable, MHC-E genes are well conserved among primates and provide signals to natural killer cells. In this study, we sequenced and analyzed MHC-E alleles of pig-tailed macaque (Macaca nemestrina), a nonhuman primate used for HIV pathogenesis and vaccine studies. Among a group of seven macaques, the characterization of eight Mane-E alleles revealed an increased number of polymorphic sites compared with human HLA-E alleles. Phylogenetic analyses of MHC-E alleles from pig-tailed macaque, rhesus monkey (Macaca mulatta) and cynomolgus macaque (Macaca fascicularis) demonstrated that the three macaque species shared six families of macaque MHC-E alleles and indicated that these families existed in the common ancestor 5.5 million years ago. Polymorphic Mane-E sites were not concentrated within the peptide-binding pockets, but were distributed throughout the entire ORF. The peptide-binding domain of Mane-E is similar to its human analogue, and peptide substrates theoretically capable of binding to Mane-E molecules were found in the leader sequence of classical Mane-A and -B molecules. Additionally, the polymorphic amino acids located in the ₁ and ₂ domains of Mane-E molecules have side chains expected to be oriented toward solvent and away from the peptide-binding groove, suggesting that some of them (positions 19, 73, 79 and 145) might be available for interaction with polymorphic receptors of natural killer cells.     

Characterization of pig-tailed macaque classical MHC class I genes: implications for MHC evolution and antigen presentation in macaques

MHC-dependent CD8(+) T cell responses have been associated with control of viral replication and slower disease progression during lentiviral infections. Pig-tailed macaques (Macaca nemestrina) and rhesus monkeys (Macaca mulatta), two nonhuman primate species commonly used to model HIV infection, can exhibit distinct clinical courses after infection with different primate lentiviruses. As an initial step in assessing the role of MHC class I restricted immune responses to these infections, we have cloned and characterized classical MHC class I genes of pig-tailed macaques and have identified 19 MHC class I alleles (Mane) orthologous to rhesus macaque MHC-A, -B, and -I genes. Both Mane-A and Mane-B loci were found to be duplicated, and no MHC-C locus was detected. Pig-tailed and rhesus macaque MHC-A alleles form two groups, as defined by 14 polymorphisms affecting mainly their B peptide-binding pockets. Furthermore, an analysis of multiple pig-tailed monkeys revealed the existence of three MHC-A haplotypes. The distribution of these haplotypes in various Old World monkeys provides new insights about MHC-A evolution in nonhuman primates. An examination of B and F peptide-binding pockets in rhesus and pig-tailed macaques suggests that their MHC-B molecules present few common peptides to their respective CTLs.     

Development of an integrative database with 499 novel microsatellite markers for Macaca fascicularis

Background

Cynomolgus macaques (Macaca fascicularis) are a valuable resource for linkage studies of genetic disorders, but their microsatellite markers are not sufficient. In genetic studies, a prerequisite for mapping genes is development of a genome-wide set of microsatellite markers in target organisms. A whole genome sequence and its annotation also facilitate identification of markers for causative mutations. The aim of this study is to establish hundreds of microsatellite markers and to develop an integrative cynomolgus macaque genome database with a variety of datasets including marker and gene information that will be useful for further genetic analyses in this species.

Results

We investigated the level of polymorphisms in cynomolgus monkeys for 671 microsatellite markers that are covered by our established Bacterial Artificial Chromosome (BAC) clones. Four hundred and ninety-nine (74.4%) of the markers were found to be polymorphic using standard PCR analysis. The average number of alleles and average expected heterozygosity at these polymorphic loci in ten cynomolgus macaques were 8.20 and 0.75, respectively.

Conclusion

BAC clones and novel microsatellite markers were assigned to the rhesus genome sequence and linked with our cynomolgus macaque cDNA database (QFbase). Our novel microsatellite marker set and genomic database will be valuable integrative resources in analyzing genetic disorders in cynomolgus macaques.     

A Monoclonal Antibody Selection for Immunohistochemical Examination of Lymphoid Tissues From Non-human Primates

Non-human primates (NHPs) offer valuable animal models for basic research into human diseases and for the preclinical validation of new therapeutics. Detailed in situ examination of the involved cell types using immunohistochemistry is often hampered by the lack of cross-reactive antibodies (Abs). In the current study, we have tested a large panel of monoclonal antibodies raised against human leukocyte differentiation and activation markers for cross-reactivity on cryosections of lymphoid tissue from six NHP species. In total, we have tested 130 Abs against 69 antigens expressed in tissues from one great ape species (chimpanzee/Pan troglodytes), two Old World species (rhesus macaque/Macaca mulatta and cynomolgus macaque/Macaca fascicularis), and three New World species (common marmoset/Callithrix jacchus, cotton-top tamarin/Saguinus oedipus, and owl monkey/Aotus triviogatus). We have found a large panel of cross-reactive Abs: 93 of 102 (91%) in chimpanzee, 97 of 125 (78%) in rhesus macaque, 70 of 109 (64%) in cynomolgus macaque, 69 of 116 (60%) in common marmoset, 40 of 81 (49%) in cotton-top tamarin, and 35 of 80 (44%) in owl monkey. The availability of a reliable panel of cross-reactive markers is important to gaining further insight into immunological processes in disease-affected tissues from NHP species. (J Histochem Cytochem 57:1159–1167, 2009)     

Conformational Adaptation of Asian Macaque TRIMCyp Directs Lineage Specific Antiviral Activity

TRIMCyps are anti-retroviral proteins that have arisen independently in New World and Old World primates. All TRIMCyps comprise a CypA domain fused to the tripartite domains of TRIM5α but they have distinct lentiviral specificities, conferring HIV-1 restriction in New World owl monkeys and HIV-2 restriction in Old World rhesus macaques. Here we provide evidence that Asian macaque TRIMCyps have acquired changes that switch restriction specificity between different lentiviral lineages, resulting in species-specific alleles that target different viruses. Structural, thermodynamic and viral restriction analysis suggests that a single mutation in the Cyp domain, R69H, occurred early in macaque TRIMCyp evolution, expanding restriction specificity to the lentiviral lineages found in African green monkeys, sooty mangabeys and chimpanzees. Subsequent mutations have enhanced restriction to particular viruses but at the cost of broad specificity. We reveal how specificity is altered by a scaffold mutation, E143K, that modifies surface electrostatics and propagates conformational changes into the active site. Our results suggest that lentiviruses may have been important pathogens in Asian macaques despite the fact that there are no reported lentiviral infections in current macaque populations.     

Interspecies pair housing of macaques in a research facility

The eighth edition of The Guide for the Care and Use of Laboratory Animals establishes social housing as the 'default' for social species including non-human primates. The advantages of social housing for primates have been well established, but small research facilities housing few primates in indoor cages have struggled with social housing as a result of limitations on appropriate housing and availability of compatible monkeys. Here, we report a novel approach to pair housing macaques - crossing species. We have successfully pair housed an intact male rhesus macaque with an intact male cynomolgus macaque, and an adult female rhesus macaque with numerous subadult female cynomolgus macaques. Monkeys in these pairs established dominant-subordinate relationships similar to same-species pairs. Rhesus and cynomolgus macaques can be successfully paired for the purpose of social housing in facilities with limited numbers of monkeys.     

Species-Specific Activity of SIV Nef and HIV-1 Vpu in Overcoming Restriction by Tetherin/BST2

Tetherin, also known as BST2, CD317 or HM1.24, was recently identified as an interferon-inducible host–cell factor that interferes with the detachment of virus particles from infected cells. HIV-1 overcomes this restriction by expressing an accessory protein, Vpu, which counteracts tetherin. Since lentiviruses of the SIV_smm/mac/HIV-2 lineage do not have a vpu gene, this activity has likely been assumed by other viral gene products. We found that deletion of the SIV_mac239 nef gene significantly impaired virus release in cells expressing rhesus macaque tetherin. Virus release could be restored by expressing Nef in trans. However, Nef was unable to facilitate virus release in the presence of human tetherin. Conversely, Vpu enhanced virus release in the presence of human tetherin, but not in the presence of rhesus tetherin. In accordance with the species-specificity of Nef in mediating virus release, SIV Nef downregulated cell-surface expression of rhesus tetherin, but did not downregulate human tetherin. The specificity of SIV Nef for rhesus tetherin mapped to four amino acids in the cytoplasmic domain of the molecule that are missing from human tetherin, whereas the specificity of Vpu for human tetherin mapped to amino acid differences in the transmembrane domain. Nef alleles of SIV_smm, HIV-2 and HIV-1 were also able to rescue virus release in the presence of both rhesus macaque and sooty mangabey tetherin, but were generally ineffective against human tetherin. Thus, the ability of Nef to antagonize tetherin from these Old World primates appears to be conserved among the primate lentiviruses. These results identify Nef as the viral gene product of SIV that opposes restriction by tetherin in rhesus macaques and sooty mangabeys, and reveal species-specificity in the activities of both Nef and Vpu in overcoming tetherin in their respective hosts.     

Complete characterization of killer Ig-like receptor (KIR) haplotypes in Mauritian cynomolgus macaques: novel insights into nonhuman primate KIR gene content and organization

Killer Ig-like receptors (KIRs) are implicated in protection from multiple pathogens including HIV, human papillomavirus, and malaria. Nonhuman primates such as rhesus and cynomolgus macaques are important models for the study of human pathogens; however, KIR genetics in nonhuman primates are poorly defined. Understanding KIR allelic diversity and genomic organization are essential prerequisites to evaluate NK cell responses in macaques. In this study, we present a complete characterization of KIRs in Mauritian cynomolgus macaques, a geographically isolated population. In this study we demonstrate that only eight KIR haplotypes are present in the entire population and characterize the gene content of each. Using the simplified genetics of this population, we construct a model for macaque KIR genomic organization, defining four putative KIR3DL loci, one KIR3DH, two KIR2DL, and one KIR1D. We further demonstrate that loci defined in Mauritian cynomolgus macaques can be applied to rhesus macaques. The findings from this study fundamentally advance our understanding of KIR genetics in nonhuman primates and establish a foundation from which to study KIR signaling in disease pathogenesis.     

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.     

Functional analysis of frequently expressed Chinese rhesus macaque MHC class I molecules Mamu-A1*02601 and Mamu-B*08301 reveals HLA-A2 and HLA-A3 supertypic specificities

The Simian immunodeficiency virus (SIV)-infected Indian rhesus macaque (Macaca mulatta) is the most established model of HIV infection and AIDS-related research, despite the potential that macaques of Chinese origin is a more relevant model. Ongoing efforts to further characterize the Chinese rhesus macaques?? major histocompatibility complex (MHC) for composition and function should facilitate greater utilization of the species. Previous studies have demonstrated that Chinese-origin M. mulatta (Mamu) class I alleles are more polymorphic than their Indian counterparts, perhaps inferring a model more representative of human MHC, human leukocyte antigen (HLA). Furthermore, the Chinese rhesus macaque class I allele Mamu-A1*02201, the most frequent allele thus far identified, has recently been characterized and shown to be an HLA-B7 supertype analog, the most frequent supertype in human populations. In this study, we have characterized two additional alleles expressed with high frequency in Chinese rhesus macaques, Mamu-A1*02601 and Mamu-B*08301. Upon the development of MHC?Cpeptide-binding assays and definition of their associated motifs, we reveal that these Mamu alleles share peptide-binding characteristics with the HLA-A2 and HLA-A3 supertypes, respectively, the next most frequent human supertypes after HLA-B7. These data suggest that Chinese rhesus macaques may indeed be a more representative model of HLA gene diversity and function as compared to the species of Indian origin and therefore a better model for investigating human immune responses.     

The MHC E locus in macaques is polymorphic and is conserved between macaques and humans

Although the functions of the molecules encoded by the classical MHC class I loci are well defined, no function has been ascribed to the molecules encoded by the non-classical MHC class I loci. To investigate the evolution and conservation of the non-classical loci, we cloned and sequenced HLA-E homologues in macaques. We isolated four E locus alleles from five rhesus monkeys and two E locus alleles from one cynomolgus monkey, which indicated that the E locus in macaques is polymorphic. We also compared the rate of nucleotide substitution in the second intron of the macaque and human E locus alleles with that of exons two and three. The rate of nucleotide substitution was significantly higher in the introns, which suggested that the E locus has evolved under selective pressure. Additionally, comparison of the rates of synonymous and non-synonymous substitutions in the peptide binding region versus the remainder of the molecule suggested that the codons encoding the amino acids in the peptide binding region had been conserved in macaques and humans over the 36 million years since macaques and humans last shared a common ancestor.The nucleotide sequence data reported in this paper have been submitted to the GenBank nucleotide sequence database and have been assigned the accession numbers UO2976–UO2981     

Evolution of the ABO blood group gene in Japanese macaque

We determined 5 sequences of Japanese macaque ABO blood group gene exon 7 (ca. 0.5 kb) and 2 sequences for exon 5 and intron 6 (ca. 1.7 kb). We compared those data with published sequences of other Old World monkey species, and the results suggest that alleles A and B were polymorphic in the ancestral species of macaques, and that B type allele evolved independently in macaque and baboon lineages.     

A shared MHC supertype motif emerges by convergent evolution in macaques and mice, but is totally absent in human MHC molecules

The SIV-infected rhesus macaque (Macaca mulatta) is the most established model of AIDS disease systems, providing insight into pathogenesis and a model system for testing novel vaccines. The understanding of cellular immune responses based on the identification and study of Major Histocompatibility Complex (MHC) molecules, including their MHC:peptide-binding motif, provides valuable information to decipher outcomes of infection and vaccine efficacy. Detailed characterization of Mamu-B*039:01, a common allele expressed in Chinese rhesus macaques, revealed a unique MHC:peptide-binding preference consisting of glycine at the second position. Peptides containing a glycine at the second position were shown to be antigenic from animals positive for Mamu-B*039:01. A similar motif was previously described for the D(d) mouse MHC allele, but for none of the human HLA molecules for which a motif is known. Further investigation showed that one additional macaque allele, present in Indian rhesus macaques, Mamu-B*052:01, shares this same motif. These "G2" alleles were associated with the presence of specific residues in their B pocket. This pocket structure was found in 6% of macaque sequences but none of 950 human HLA class I alleles. Evolutionary studies using the "G2" alleles points to common ancestry for the macaque sequences, while convergent evolution is suggested when murine and macaque sequences are considered. This is the first detailed characterization of the pocket residues yielding this specific motif in nonhuman primates and mice, revealing a new supertype motif not present in humans.     

Pandemic Swine-Origin H1N1 Influenza Virus Replicates to Higher Levels and Induces More Fever and Acute Inflammatory Cytokines in Cynomolgus versus Rhesus Monkeys and Can Replicate in Common Marmosets

The close immunological and physiological resemblance with humans makes non-human primates a valuable model for studying influenza virus pathogenesis and immunity and vaccine efficacy against infection. Although both cynomolgus and rhesus macaques are frequently used in influenza virus research, a direct comparison of susceptibility to infection and disease has not yet been performed. In the current study a head-to-head comparison was made between these species, by using a recently described swine-origin pandemic H1N1 strain, A/Mexico/InDRE4487/2009. In comparison to rhesus macaques, cynomolgus macaques developed significantly higher levels of virus replication in the upper airways and in the lungs, involving both peak level and duration of virus production, as well as higher increases in body temperature. In contrast, clinical symptoms, including respiratory distress, were more easily observed in rhesus macaques. Expression of sialyl-α-2,6-Gal saccharides, the main receptor for human influenza A viruses, was 50 to 73 times more abundant in trachea and bronchus of cynomolgus macaques relative to rhesus macaques. The study also shows that common marmosets, a New World non-human primate species, are susceptible to infection with pandemic H1N1. The study results favor the cynomolgus macaque as model for pandemic H1N1 influenza virus research because of the more uniform and high levels of virus replication, as well as temperature increases, which may be due to a more abundant expression of the main human influenza virus receptor in the trachea and bronchi.     

Comprehensive identification of MHC class II alleles in a cohort of Chinese rhesus macaques

Rhesus macaque is a very important animal model for various human diseases, especially for AIDS and vaccine research. The susceptibility and/or resistance to some of these diseases are related to the major histocompatibility complex (MHC). To gain insight into the MHC background and to facilitate the experimental use of Chinese rhesus macaques, Mamu-DPB1, Mamu-DQB1, and Mamu-DRB alleles were investigated in 30 Chinese rhesus macaques through gene cloning and sequencing. A total of 66 alleles were identified in this study, including 14 Mamu-DPB1, 20 Mamu-DQB1, and 30 Mamu-DRB alleles as well as 2 high-frequency Mamu-DPB1 alleles. Interestingly, one of the high-frequency Mamu-DPB1 alleles had been undocumented in earlier studies. Eleven of the other alleles, including four Mamu-DPB1, three Mamu-DQB1, and four Mamu-DRB alleles were also novel. Importantly, like MHC-DRB, more than two Mamu-DPB1 sequences per animal were detected in 13 monkeys, which suggested that they might represent gene duplication. Our data also indicated quite a few differences in the distribution of MHC class II alleles between the Chinese rhesus macaques and the previously reported Indian rhesus macaques. To our knowledge, our results revealed comprehensively the combination of MHC II alleles. This information will not only promote the understanding of Chinese rhesus macaque MHC polymorphism but will also facilitate the use of Chinese rhesus macaques in studies of human disease.     

Identification of Mamu-DPA1, Mamu-DQA1, and Mamu-DRA alleles in a cohort of Chinese rhesus macaques

Rhesus macaques have long been used as animal models for various human diseases; the susceptibility and/or resistance to some of these diseases are related to the major histocompatibility complex (MHC). To gain insight into the MHC background and to facilitate the experimental use of Chinese rhesus macaques, Mamu-DPA1, Mamu-DQA1, and Mamu-DRA alleles were investigated in 30 Chinese rhesus macaques by gene cloning and sequencing. A total of 14 Mamu-DPA1, 17 Mamu-DQA1, and 9 Mamu-DRA alleles were identified in this study. Of these alleles, 22 novel sequences have not been documented in earlier studies, including nine Mamu-DPA1, ten Mamu-DQA1, and three Mamu-DRA alleles. Interestingly, like Mafa-DQA1 and Mafa-DPA1, more than two Mamu-DQA1 and Mamu-DPA1 alleles were detected in one animal in this study, which suggested that they might represent gene duplication. If our findings can be validated by other studies, it will further increase the number of known Mamu-DPA1 and Mamu-DQA1 polymorphisms. Our data also indicated significant differences in MHC class II allele distribution among the Chinese rhesus macaques, Vietnamese cynomolgus macaques, and the previously reported rhesus macaques, which were mostly of Indian origin. This information will not only promote the understanding of Chinese rhesus macaque MHC diversity and polymorphism but will also facilitate the use of Chinese rhesus macaques in studies of human disease.     

Pathogenicity of simian-human immunodeficiency virus SHIV-89.6P and SIVmac is attenuated in cynomolgus macaques and associated with early T-lymphocyte responses

Because most studies of AIDS pathogenesis in nonhuman primates have been performed in Indian-origin rhesus macaques (Macaca mulatta), little is known about lentiviral pathogenicity and control of virus replication following infection of alternative macaque species. Here, we report the consequences of simian-human immunodeficiency virus SHIV-89.6P and SIVmac251 infection in cynomolgus (Macaca fascicularis) and rhesus macaques of Chinese origin. Compared to the pathogenicity of the same viruses in Indian rhesus macaques, both cynomolgus and Chinese rhesus macaques showed lower levels of plasma virus. By 9 to 10 months after infection, both viruses became undetectable in plasma more frequently in cynomolgus than in either Chinese or Indian rhesus macaques. Furthermore, after SHIV-89.6P infection, CD4+ T-cell numbers declined less and survival was longer in cynomolgus and Chinese rhesus macaques than in Indian rhesus macaques. This attenuated pathogenicity was associated with gamma interferon ELISPOT responses to Gag and Env that were generated earlier and of higher frequency in cynomolgus than in Indian rhesus macaques. Cynomolgus macaques also developed higher titer neutralizing antibodies against SHIV-89.6 at 10 and 20 weeks postinoculation than Indian rhesus macaques. These studies demonstrate that the pathogenicity of nonhuman primate lentiviruses varies markedly based on the species or geographic origin of the macaques infected and suggest that the cellular immune responses may contribute to the control of pathogenicity in cynomolgus macaques. While cynomolgus and Chinese rhesus macaques provide alternative animal models of lentiviral infection, the lower levels of viremia in cynomolgus macaques limit the usefulness of infection of this species for vaccine trials that utilize viral load as an experimental endpoint.     

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.     

Molecular Evidence for Distinct Genotypes of Monkey B Virus (Herpesvirus Simiae) Which Are Related to the Macaque Host Species

Although monkey B virus (herpesvirus simiae; BV) is common in all macaque species, fatal human infections appear to be associated with exposure to rhesus macaques (Macaca mulatta), suggesting that BV isolates from rhesus monkeys may be more lethal to nonmacaques than are BV strains indigenous to other macaque species. To determine if significant differences that would support this supposition exist among BV isolates, we compared multiple BV strains isolated from rhesus, cynomolgus, pigtail, and Japanese macaques. Antigenic analyses indicated that while the isolates were very closely related to one another, there are some antigenic determinants that are specific to BV isolates from different macaque species. Restriction enzyme digest patterns of viral DNA revealed marked similarities between rhesus and Japanese macaque isolates, while pigtail and cynomolgus macaque isolates had distinctive cleavage patterns. To further compare genetic diversity among BV isolates, DNA sequences from two regions of the viral genome containing genes that are conserved (UL27 and US6) and variable (US4 and US5) among primate alphaherpesviruses, as well as from two noncoding intergenic regions, were determined. From these sequence data and a phylogenetic analysis of them it was evident that while all isolates were closely related strains of BV, there were three distinct genotypes. The three BV genotypes were directly related to the macaque species of origin and were composed of (i) isolates from rhesus and Japanese macaques, (ii) cynomolgus monkey isolates, and (iii) isolates from pigtail macaques. This study demonstrates the existence of different BV genotypes which are related to the macaque host species and thus provides a molecular basis for the possible existence of BV isolates which vary in their levels of pathogenicity for nonmacaque species.