Major histocompatibility complex class II-restricted antigen presentation across a species barrier: conservation of restriction determinants in evolution

Reactivity of HLADR antibody manifests expression of surface MHC II molecules on peripheral blood T lymphocytes in new world monkeys

BACKGROUND

Major histocompatibility complex (MHC) class II molecules expressed on B cells, monocytes and dendritic cells present processed peptides to CD4+ T cells as one of the mechanisms to combat infection and inflammation.

AIM

To study MHC II expression in a variety of nonhuman primate species, including New World (NWM) squirrel monkeys (Saimiri boliviensis boliviensis), owl monkeys (Aotus nancymae), common marmosets (Callithrix spp.), and Old World (OWM) rhesus (Macaca mulatta), baboons (Papio anubis).

METHODS

Two clones of cross-reactive mouse anti-human HLADR monoclonal antibodies (mAb) binding were analyzed by flow cytometry to evaluate MHC II expression on NHP immune cells, including T lymphocytes in whole blood (WB) and peripheral blood mononuclear cells (PBMC).

RESULTS

MHC class II antibody reactivity is seen with CD20+ B cells, CD14+ monocytes and CD3+ T lymphocytes. Specific reactivity with both clones was demonstrated in T lymphocytes: this reactivity was not inhibited by purified CD16 antibody but was completely inhibited when pre-blocked with purified unconjugated MHC II antibody. Freshly prepared PBMC also showed reactivity with T lymphocytes without any stimulation. Interestingly, peripheral blood from rhesus macaques and olive baboons (OWM) showed no such T lymphocyte associated MHCII antibody reactivity.

DISCUSSION & CONCLUSION

Our results from antibody (MHC II) reactivity clearly show the potential existence of constitutively expressed (with no stimulation) MHC II molecules on T lymphocytes in new world monkeys. These results suggest that additional study is warranted to evaluate the functional and evolutionary significance of these finding and to better understand MHC II expression on T lymphocytes in new world monkeys.

Ligandomes obtained from different HLA-class II-molecules are homologous for N- and C-terminal residues outside the peptide-binding cleft

Human CD4+ T lymphocytes play an important role in inducing potent immune responses. T cells are activated and stimulated by peptides presented in human leucocyte antigen (HLA)-class II molecules. These HLA-class II molecules typically present peptides of between 12 and 20 amino acids in length. The region that interacts with the HLA molecule, designated as the peptide-binding core, is highly conserved in the residues which anchor the peptide to the molecule. In addition, as these peptides are the product of proteolytic cleavages, certain conserved residues may be expected at the N- and C-termini outside the binding core. To study whether similar conserved residues are present in different cell types, potentially harbouring different proteolytic enzymes, the ligandomes of HLA-DRB1*03:01/HLA-DRB > 1 derived from two different cell types (dendritic cells and EBV-transformed B cells) were identified with mass spectrometry and the binding core and N- and C-terminal residues of a total of 16,568 peptides were analysed using the frequencies of the amino acids in the human proteome. Similar binding motifs were found as well as comparable conservations in the N- and C-terminal residues. Furthermore, the terminal conservations of these ligandomes were compared to the N- and C-terminal conservations of the ligandome acquired from dendritic cells homozygous for HLA-DRB1*04:01. Again, comparable conservations were evident with only minor differences. Taken together, these data show that there are conservations in the terminal residues of peptides, presumably the result of the activity of proteases involved in antigen processing.

Using DR52c/Ni2+ mimotope tetramers to detect Ni2+ reactive CD4+ T cells in patients with joint replacement failure

T cell mediated hypersensitivity to nickel (Ni²⁺) is one of the most common causes of allergic contact dermatitis. Ni²⁺ sensitization may also contribute to the failure of Ni²⁺ containing joint implants, and revision to non-Ni²⁺ containing hardware can be costly and debilitating. Previously, we identified Ni²⁺ mimotope peptides, which are reactive to a CD4⁺ T cell clone, ANi2.3 (Vα1, Vβ17), isolated from a Ni²⁺ hypersensitive patient with contact dermatitis. This T cell is restricted to the major histocompatibility complex class II (MHCII) molecule, Human Leukocyte Antigen (HLA)-DR52c (DRA, DRB3*0301). However, it is not known if Ni²⁺ induced T cell responses in sensitized joint replacement failure patients are similar to subjects with Ni²⁺ induced contact dermatitis. Here, we generated DR52c/Ni²⁺ mimotope tetramers, and used them to test if the same Ni²⁺ T cell activation mechanism could be generalized to Ni²⁺ sensitized patients with associated joint implant failure. We confirmed the specificity of these tetramers by staining of ANi2.3T cell transfectomas. The DR52c/Ni²⁺ mimotope tetramer detected Ni²⁺ reactive CD4⁺ T cells in the peripheral blood mononuclear cells (PBMC) of patients identified as Ni²⁺ sensitized by patch testing and a positive Ni²⁺ LPT. When HLA-typed by a DR52 specific antibody, three out of four patients were DR52 positive. In one patient, Ni²⁺ stimulation induced the expansion of Vβ17 positive CD4⁺ T cells from 0.8% to 13.3%. We found that the percentage of DR52 positivity and Vβ17 usage in Ni²⁺ sensitized joint failure patients are similar to Ni sensitized skin allergy patients. Ni²⁺ independent mimotope tetramers may be a useful tool to identify the Ni²⁺ reactive CD4⁺ T cells.

The extracellular domain of myelin oligodendrocyte glycoprotein elicits atypical experimental autoimmune encephalomyelitis in rat and Macaque species

Atypical models of experimental autoimmune encephalomyelitis (EAE) are advantageous in that the heterogeneity of clinical signs appears more reflective of those in multiple sclerosis (MS). Conversely, models of classical EAE feature stereotypic progression of an ascending flaccid paralysis that is not a characteristic of MS. The study of atypical EAE however has been limited due to the relative lack of suitable models that feature reliable disease incidence and severity, excepting mice deficient in gamma-interferon signaling pathways. In this study, atypical EAE was induced in Lewis rats, and a related approach was effective for induction of an unusual neurologic syndrome in a cynomolgus macaque. Lewis rats were immunized with the rat immunoglobulin variable (IgV)-related extracellular domain of myelin oligodendrocyte glycoprotein (IgV-MOG) in complete Freund’s adjuvant (CFA) followed by one or more injections of rat IgV-MOG in incomplete Freund’s adjuvant (IFA). The resulting disease was marked by torticollis, unilateral rigid paralysis, forelimb weakness, and high titers of anti-MOG antibody against conformational epitopes of MOG, as well as other signs of atypical EAE. A similar strategy elicited a distinct atypical form of EAE in a cynomolgus macaque. By day 36 in the monkey, titers of IgG against conformational epitopes of extracellular MOG were evident, and on day 201, the macaque had an abrupt onset of an unusual form of EAE that included a pronounced arousal-dependent, transient myotonia. The disease persisted for 6–7 weeks and was marked by a gradual, consistent improvement and an eventual full recovery without recurrence. These data indicate that one or more boosters of IgV-MOG in IFA represent a key variable for induction of atypical or unusual forms of EAE in rat and Macaca species. These studies also reveal a close correlation between humoral immunity against conformational epitopes of MOG, extended confluent demyelinating plaques in spinal cord and brainstem, and atypical disease induction.

The significance of non-human primates as preclinical models of human arthritic disease

BACKGROUND

The broad immunological gap between inbred SPF-raised strains of mice and rats and the diverse rheumatoid arthritis (RA) patient population limits the predictive value of the existing disease models for clinical success of new therapies, in particular for those using highly specific biologicals.

OBJECTIVE

This review argues that because of their closer immunological and physiological proximity to patients, disease models in non-human primates (NHPs) may bridge this gap and help reduce the failure of many (± 80%) new therapies in clinical trials. In various research areas, NHPs are an accepted intermediate between disease models in rodents and the ultimate introduction for clinical use in patients. However, with the exception of transplantation, this is not the case for immune-mediated inflammatory disorders, such as RA, although useful preclinical models are being developed.

METHOD

The validity and use of the rhesus monkey model of collagen-induced arthritis as a preclinical RA model is reviewed. The discussion comprises present genetic and immunological aspects, biomarkers, and an overview of published preclinical therapy evaluations.

CONCLUSION

It is time to consider the use of NHPs with a greater evolutionary proximity to humans as models for preclinical evaluation of new human-specific drugs for arthritic disease.

Reassessing the role of HLA-DRB3 T-cell responses: evidence for significant expression and complementary antigen presentation

In humans, several HLA-DRB loci (DRB1/3/4/5) encode diverse beta-chains that pair with alpha-chains to form DR molecules on the surface of APC. While DRB1 and DRB5 have been extensively studied, the role of DRB3/4 products of DR52/DR53 haplotypes has been largely neglected. To clarify the relative expression of DRB3, we quantified DRB3 mRNA levels in comparison with DRB1 mRNA from the same haplotype in both B cells and monocytes, observing quantitatively significant DRB3 synthesis. In CD19+ cells, DRB1*03/11/13 was 3.5-fold more abundant than DRB3, but in CD14+ this difference was only two-fold. Monocytes also had lower overall levels of DR mRNA compared with B cells, which was confirmed by cell surface staining of DRB1 and DRB3. To evaluate the functional role of DRB3, tetramer-guided epitope mapping was used to detect T cells against tetanus toxin and several influenza antigens presented by DRB3*0101/0202 or DRB1*03/11/13. None of the epitopes discovered were shared among any of the DR molecules. Quantitative assessment of DRB3-tetanus toxin specific T cells revealed that they are present at similar frequencies as those observed for DRB1. These results suggest that DRB3 plays a significant role in antigen presentation with different epitopic preferences to DRB1. Therefore, DRB3, like DRB5, serves to extend and complement the peptide repertoire of DRB1 in antigen presentation.

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.

Modeling human arthritic diseases in nonhuman primates

Models of rheumatoid arthritis (RA) in laboratory animals are important tools for research into pathogenic mechanisms and the development of effective, safe therapies. Rodent models (rats and mice) have provided important information about the pathogenic mechanisms. However, the evolutionary distance between rodents and humans hampers the translation of scientific principles into effective therapies. The impact of the genetic distance between the species is especially seen with treatments based on biological molecules, which are usually species-specific. The outbred nature and the closer anatomical, genetic, microbiological, physiological, and immunological similarity of nonhuman primates to humans may help to bridge the wide gap between inbred rodent strain models and the heterogeneous RA patient population. Here we review clinical, immunological and pathological aspects of the rhesus monkey model of collagen-induced arthritis, which has emerged as a reproducible model of human RA in nonhuman primates.

Lung restricted T cell receptor AV2S3+ CD4+ T cell expansions in sarcoidosis patients with a shared HLA-DRbeta chain conformation

BACKGROUND

Sarcoidosis is a systemic disease of unknown aetiology frequently affecting the lungs. CD4+ T cells, in particular, accumulate in the lungs, implicating them in the pathogenesis of the disease.

METHODS

T cell receptor (TCR) variable (V) gene expression on bronchoalveolar lavage (BAL) fluid T cells and the HLA DR alleles of 121 Scandinavian patients with sarcoidosis was determined.

RESULTS

As expected from our previous results, almost every DRB1*0301 (i.e. DR17) positive patient (67/69) had significantly increased numbers of AV2S3+ CD4+ T cells in the BAL fluid but normal levels in peripheral blood (that is, lung restricted expansions) compared with only six of 52 DRB1*0301 negative patients. Detailed genotypic HLA analysis showed that these six DRB1*0301 negative patients with lung restricted AV2S3+ T cell expansions had another HLA allele in common-the HLA-DRB3*0101 allele (also called DR52a)-which was not found in any other DRB1*0301 negative patient. A new group of sarcoidosis patients was therefore identified, characterised by a strict correlation between a distinct HLA allele and lung accumulated T cells expressing a particular TCR V segment. Furthermore, the HLA-DRB1*0301 and HLA-DRB3*0101 encoded molecules showed similarities, with identical amino acid sequences in regions important for antigen binding which may enable them to bind and present the same or similar antigenic peptides.

CONCLUSIONS

HLA-DRB3*0101 as well as DRB1*0301 positive sarcoidosis patients may have the capacity to present specific sarcoidosis associated antigens in such a way that AV2S3+ CD4+ T cells are stimulated preferentially, generating lung restricted AV2S3+ T cell expansions.

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.

Identification of DRB alleles in rhesus monkeys using polymerase chain reaction-sequence-specific primers (PCR-SSP) amplification

Major histocompatibility complex (MHC) class In molecules play a vital role in the regulation of T-cell functions in the mammalian immune system. Two key features characterize the polymorphism of MHC haplotypes in humans and non-human primates: the existence of a large number of alleles, and the high degree of genetic diversity between those alleles. Rhesus monkeys and Chimpanzees have been extensively used as relevant models for human diseases and transplantation We have investigated DRB genes in 19 macaques, members of 3 families, using polymerase chain reaction with sequence-specific primers (PCR-SSP) and denaturing gradient gel electrophoresis (DGGE). After amplification PCR products were purified and subjected direct sequencing. Seven animals (Madison #1) were typed by DDGE also. We report that the DRB haplotypes defined by PCR-SSP exhibit a high degree of concordance with the data obtained by DGGE and direct sequening. Our data show prominent variability in the number of DRB1 alleles ranging from 1-4 per genotype within these families. This analysis demonstrated that most of the amplicons were identical to Mamu-DRB alleles that our PCR primers were to amplify. However, 98-99% similarity was noticed in the case of Mamu-DRB1*0303, Mamu-DRB6*0103 and Mamu-DRB*W201 alleles. The observed mismatches were located in non-polymorphic regions. Thus, family studies in rhesus macaques performed by molecular methods confirmed the multiplicity of Mamu-DRB1 alleles per haplotype and the existence of allelic associations published earlier. In addition, we propose 3 more DRB allele associations (haplotypes): Mamu-DRB1*04-DRB5*03; Mamu-DRB1*04-*DRB*W5; Mamu-DRB1*04*W2. The proposed medium-resolution PCR-SSP technique appears to be a highly reproducible and discriminatory typing method for detecting polymorphisms of DRB genes in rhesus monkeys.

Scanning a DRB3*0101 (DR52a)-Restricted Epitope Cross-Presented by DR3: Overlapping Natural and Artificial Determinants in the Human Acetylcholine Receptor

A recurring epitope in the human acetylcholine receptor (AChR) α subunit (α146–160) is presented to specific T cells from myasthenia gravis patients by HLA-DRB3*0101—“DR52a”—or by DR4. Here we first map residues critical for DR52a in this epitope by serial Ala substitution. For two somewhat similar T cells, this confirms the recently deduced importance of hydrophobic “anchor” residues at peptide p1 and p9; also of Asp at p4, which complements this allele’s distinctive Arg74 in DRβ. Surprisingly, despite the 9 sequence differences in DRβ between DR52a and DR3, merely reducing the bulk of the peptide’s p1 anchor residue (Trp149→Phe) allowed maximal cross-presentation to both T cells by DR3 (which has Val86 instead of Gly). The shared K71G73R74N77 motif in the α helices of DR52a and DR3 thus outweighs the five differences in the floor of the peptide-binding groove. A second issue is that T cells selected in vitro with synthetic AChR peptides rarely respond to longer Ag preparations, whereas those raised with recombinant subunits consistently recognize epitopes processed naturally even from whole AChR. Here we compared one T cell of each kind, which both respond to many overlapping α140–160 region peptides (in proliferation assays). Even though both use Vβ2 to recognize peptides bound to the same HLA-DR52a in the same register, the peptide-selected line nevertheless proved to depend on a recurring synthetic artifact—a widely underestimated problem. Unlike these contaminant-responsive T cells, those that are truly specific for natural AChR epitopes appear less heterogeneous and therefore more suitable targets for selective immunotherapy.

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.

Rejection of wild-type and genetically engineered major histocompatibility complex-deficient glial cell xenografts in the central nervous system results in bystander demyelination and Wallerian degeneration

Mixed glial cell cultures prepared from neonatal wild type and mutant male mice lacking either major histocompatibility complex class I, class II or both class I and II molecules (major histocompatibility complex class I(o/o)II(o/o)), and from syngeneic male rats were transplanted into female rat spinal cord white matter. Graft survival was monitored using DNA probes specific to the Y chromosome. Survival of major histocompatibility complex class-deficient grafts was not prolonged compared to wild-type grafts and in most cases grafts could not be detected at 28 days post-transplantation, at which time syngeneic grafts were still present. However, rejection of xenografts resulted in significant bystander damage to host tissue. In recipients of wild-type and major histocompatibility complex class I(o/o) xenografts the predominant pathology was demyelination. Demyelination was also observed in recipients of major histocompatibility complex class II(o/o) and major histocompatibility complex class I(o/o)II(o/o) xenografts, however in addition there was marked collagen deposition and meningeal cell invasion. Significantly more axons had undergone Wallerian degeneration in recipients of major histocompatibility complex class II(o/o) and major histocompatibility complex class I(o/o)II(o/o) xenografts than recipients of wild-type and major histocompatibility complex class I(o/o) xenografts. These findings were interpreted as evidence of a more destructive immune response associated with rejection of grafts lacking major histocompatibility complex class II molecules. It was proposed that the difference in the severity of bystander damage may be related to the previously demonstrated ability of xenogeneic major histocompatibility complex class II molecules to activate host T cells directly, whereas xenografts lacking major histocompatibility complex class II molecules were capable of activating host T cells only by the indirect pathway.

Liposome-mediated peptide loading of MHC-DR molecules in vivo

Amino acid residues 3-15 of mycobacterial HSP60 define a dominant T-cell epitope for HLA-DR3+ve humans and Mamu-DR3+ve rhesus monkeys. Our results show that Mamu-DR3 molecules on PBMC can be efficiently loaded in vivo with the above-mentioned peptides when they are intravenously injected encapsulated in liposomes, but not in the free form. Mamu-DR3 loading is abolished by encapsulation of a nonstimulatory peptide. These results have implications for the delivery of therapeutic peptides in vivo.

A single residue polymorphism at DR beta 37 affects recognition of peptides by T cells

Single amino acid polymorphism at residue 37 of the HLA-DR beta chain (DR beta 37) between DRB1*0406 and 0403 markedly influences susceptibility to the insulin autoimmune syndrome. We investigated the effects of DR beta 37 polymorphism regarding recognition of nonself peptides by a T-cell clone, YN5-32, specific to a streptococcal peptide (M12p54-68) presented by the DRB1*0406 molecule. YN5-32 responded better to M12p54-68 presented by allogeneic DRB1*0403 with a single Tyr-substitution at DR beta 37-Ser of the DRB1*0406 molecule. One hundred and fifty-four peptides carrying single residue substitutions at each of the core residues 57-65 of M12p54-68, were tested for full agonistic and TCR antagonistic activities. Forty-six peptides showed full agonism, 34 analogues exhibited TCR antagonism, and 45 analogues exhibited neither full agonism nor TCR antagonism, irrespective of the presenting molecules (DRB1*0406 or 0403). On the other hand, 29 analogue peptides substituted at each of residues 57-63 of M12p54-68 were recognized differently by YN5-32, depending on the presenting molecules. These observations indicate that 1) single amino acid polymorphism (Ser-Tyr) at the DR beta 37 residue induced a conformational change distinguished by TCR in some but not all peptides; and 2) these conformational changes were observed even in analogue peptides carrying single residue substitutions at residues far from a putative DR beta 37 contact site. These findings provide further evidence for altered human T-cell responses induced by TCR ligands with minor modifications.

Differences in peptide binding of DR11 and DR13 microvariants demonstrate the power of minor variation in generating DR functional diversity

The influence of subtle HLA diversification on antigen binding was explored using murine L-cell transfectants expressing alleles in the DR11/DR13 family and a panel of peptides. The levels of binding among this family of DR microvariants were as diverse as the levels of binding among distantly related DR molecules. Even a single amino acid difference between allelic products had a profound effect on peptide binding. Specific amino acid substitutions, generated using site-directed mutagenesis to alter polymorphic residues at DR beta 32, 37, 57, 58, 67, 71, 86, demonstrated that a specific change within the context of a single DR molecule differed in its effect on the binding of specific peptides. In addition, a specific amino acid substitution had a differential effect on the binding level of a peptide to different DR molecules. Each polymorphic amino acid appeared to play a role in the binding of some peptide. Studies using the amino-terminal portion of the invariant chain CLIP peptide suggested that this peptide may offer varying degrees of competition in the binding of the cellular peptide pool in cells expressing different DR molecules. Finally, the results obtained with two strain-specific peptides from an immunodominant region of a malarial parasite show differential binding to two DR13 molecules, suggesting that immune pressure may promote parasite diversity. A dynamic interaction may exist between pathogens and the immune system shaping the HLA profile in a population. Thus even subtle diversification of the HLA molecules, possibly pathogen driven, can have a substantial effect on peptide binding and immune recognition.

A novel mode of immunoprotection of neural xenotransplants: masking of donor major histocompatibility complex class I enhances transplant survival in the central nervous system

To determine the role of major histocompatibility complex (MHC) class I in immunological rejection of neural xenotransplants, F(ab')2 fragments of a monoclonal antibody to porcine MHC class I were used to mask this complex on porcine fetal striatal cells transplanted into rat striata previously lesioned with quinolinic acid. Presence of MHC class I on the surface of porcine striatal cells was confirmed by fluorescence-activated cell sorting prior to F(ab')2 treatment. At three to four months post-transplantation, survival of F(ab')2-treated xenografts was assessed by means of donor-specific immunostaining and compared to that of untreated xenografts in non-immunosuppressed rats and in rats immunosuppressed with cyclosporine A. In this study, masking of donor MHC class I by F(ab')2 treatment resulted in enhanced xenografts survival compared to the non-immunosuppressed controls (graft survival rates, 52% and 7%, respectively; P < 0.005) at survival times up to four months. While xenograft survival in F(ab')2-treated animals was not significantly different from that in cyclosporine-treated rats (74% graft survival), mean graft volume in F(ab')2-treated animals was smaller than that in cyclosporine-treated animals (1.07 +/- 0.30 mm3 versus 3.14 +/- 0.51 mm3; P < 0.005). The cytoarchitectonic organization of the xenografts was similar in F(ab')2- and cyclosporine-treated animals, and grafts in both groups exhibited long distance target-directed axonal outgrowth. The pattern of immunoreactivity to porcine MHC class I in the xenografts corresponded to the regional distribution of donor glia. In xenografts undergoing rejection, infiltration with host inflammatory cells was restricted to necrotic graft remnants and spared the nearby host structures. We conclude that MHC class-I-restricted immune mechanisms play an important role in neural xenograft rejection and that masking of this complex on donor cells may provide a useful strategy for immunoprotection of neural xenografts.

Neural xenotransplantation: reconstruction of neuronal circuitry across species barriers

Selective replacement of degenerated neurons in the adult brain with allogeneic fetal neuroblasts is a promising therapeutic modality for human neurodegenerative diseases, but is confounded with practical and potential ethical problems. To evaluate the potential of xenogeneic donors as a cell source for neural transplantation, we have critically examined the available experimental evidence in animal models pertaining to the survival, integration and function of xenogeneic fetal neuroblasts in the host brain. A statistical meta-analysis across multiple studies revealed that immunologically-related transplantation parameters (immunosuppression and donor-host phylogenetic distance) were the main determinants of neural xenograft survival. The immunological basis for xenograft rejection is reviewed in the context of novel immunoprotection strategies designed to enhance xenograft survival. Furthermore, the evidence for behavioral recovery based on anatomical and functional integration of neural xenografts in the host brain is examined with an awareness of developmental considerations. It is concluded that neural xenotransplantation offers a unique opportunity for effective neuronal replacement with significant potential for clinical use.

Gel electrophoretic analysis of rhesus macaque major histocompatibility complex class II DR molecules

Rhesus macaque MHC class II DR molecules were isolated from radiolabeled B-cell line extracts by immunoprecipitation with the mAbs 7.3.19.1 and B8.11.2 and subsequently analyzed by 2D-gel electrophoresis. The B-cell lines used for this study were obtained from monkeys that are homozygous for the Mamu-DR region as defined by serologic techniques. Some of these animals have been selectively bred and originate from consanguineous matings. These analyses show that monkeys with the same allotyping may express different types of DR molecules. As in humans, the number of DR molecules expressed per haplotype is not constant and varies from 1 to 3, depending on the serologically defined Mamu-DR specificity, whereas it has been shown that the number of Mamu-DRB genes present per haplotype varies from 2 to 6. Therefore the present study also demonstrates that some of the rhesus macaque DR regions contain one or more pseudogenes.

Primary in vitro sensitization of human T-helper lymphocytes by peptides derived from the V3 loop of human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein

To generate CD4+ T-helper cell lines, lymphocytes from HIV-seronegative subjects were primed in vitro with peptides derived from the V3 loop of HIV-1 gp120. Antigen-specific reactivity was inhibited by an anti-DR monoclonal antibody, indicating HLA-class II dependency, but peptides could be recognized in different HLA-class II contexts. Three sites on V3LAI and two on V3MN were identified as targets of the respective V3LAI- and V3MN-specific lines. Recognition of V3 peptides was isolate-specific. The lines did not react against whole gp160, which suggests that V3 may be differently presented when used as such rather than as part of the entire glycoprotein. Similar results were obtained in chimpanzees immunized in vivo against V3LAI.

The biologic importance of conserved major histocompatibility complex class II motifs in primates

Phylogenetic comparisons of polymorphic second-exon sequences of MHC class II DRB genes showed that equivalents of the HLA-DRB1*03 alleles are present in various nonhuman primate species such as chimpanzees, gorillas, and rhesus macaques. These alleles must root from ancestral structure(s) that were once present in a progenitor species that lived about 35 million years ago. Due to accumulation of genetic variation, however, sequences that cluster into a lineage are generally unique to a species. To investigate the biologic importance of such conservation and variation, the peptide-binding capacity of various Mhc-DRB1*03 lineage members was studied. Primate Mhc-DRB1*03 lineage members successfully binding the p3-13 peptide of the 65-kD heat-shock protein of Mycobacterium tuberculosis/leprae share a motif that maps to the floor of the peptide-binding site. Apart from that, some rhesus macaque MHC class-II-positive cells were able to present the p3-13 peptide to HLA-DR17-restricted T cells whereas cells obtained from great ape species failed to do so. Therefore, these studies open ways to understand which MHC polymorphisms have been maintained in evolution and which MHC residues are essential for peptide binding and T-cell recognition.

Evolutionary conservation of major histocompatibility complex-DR/peptide/T cell interactions in primates

Many major histocompatibility complex (MHC) polymorphisms originate from ancient structures that predate speciation. As a consequence, members of the Mhc-DRB1*03 allelic lineage are not only present in humans but in chimpanzees and rhesus macaques as well. This emphasizes that Mhc-DRB1*03 members must have been present in a common ancestor of these primate species that lived about 30 million years ago. Due to the accumulation of genetic variation, however, alleles of the Mhc-DRB1*03 lineage exhibit species-unique sequences. To investigate the biological importance of such conservation and variation, we have studied both the binding and antigen presentation capacity of various trans-species Mhc-DRB1*03 lineage members. Here we show that p3-13 of the 65-kD heat-shock protein (hsp65) of Mycobacterium leprae and M. tuberculosis binds not only to HLA-DR17(3) but also to some chimpanzee and rhesus macaque class II-positive cells. Comparison of the corresponding human, chimpanzee, and rhesus macaque Mhc-DRB1*03 lineage members revealed the presence of uniquely shared amino acid residues, at positions 9-13 and 26-31, of the antigen-binding site that are critical for p3-13 binding. In addition it is shown that several nonhuman primate antigen-presenting cells that bind p3-13 can activate HLA-DR17-restricted T cells. Certain amino acid replacements, however, in Mhc-DRB1*03 lineage members did not influence peptide binding or T cell recognition. Therefore, these studies demonstrate that some polymorphic amino acid residues (motifs) within the antigen-binding site of MHC class II molecules that are crucial for peptide binding and recognition by the T cell receptor have been conserved for over 30 million years.

T-cell receptor gamma/delta: comparison of gene configurations and function between humans and chimpanzees

The human and chimpanzee T-cell receptor gamma-delta (TCR gamma delta) bearing cells represent a minor subset (3-8%) of T lymphocytes. In the periphery, the TCR gamma delta population has a restricted combinatorial repertoire. The TCRD-V1 and -V2 gene products are expressed in a mutually exclusive fashion, whereas, the TCRD-V2 and the TCRG-V9 encoded proteins show, in general, a coordinated expression. Restriction fragment length polymorphism analysis showed conservation of the restriction sites that identify the TCRG-V9 and TCRD-V2 rearrangements. The human TCRG-V9 locus has two alleles, TCRG-V9A1 and TCRG-V9A2 differing at codon position 31. The chimpanzee TCRG-V9 gene product differs from the products of the human TCRG-V9A1 and TCRG-V9A2 allele by two and three amino acid replacements, respectively. The human and the chimpanzee TCRG-V9-TCRD-V2 lymphocytes show a similar specific proliferative and cytolytic response to human Daudi Burkitt's lymphoma cells. Therefore, the amino acid replacements found in the chimpanzee TCRG-V9 gene product do not change the superantigen specificity across this species barrier.

Binding of a major T cell epitope of mycobacteria to a specific pocket within HLA-DRw17(DR3) molecules

CD4+ T cells recognize antigenic peptides bound to the polymorphic peptide-binding site of major histocompatibility complex (MHC) class II molecules. The polymorphism of this site is thought to dictate which peptides can be bound and thus presented to the T cell receptor. The mycobacterial 65-kDa heat-shock protein (hsp65) peptide 3-13 is an important T cell epitope: it is immunodominant in the mycobacterium-specific T cell response of HLA-DR3+ individuals but, interestingly cannot be recognized in the context of any other HLA-DR molecules. We, therefore, have tested whether the hsp65 epitope p3-13 is selected for T cell recognition in the context of only HLA-DR3 molecules by an unique binding specificity for HLA-DR3. Using biotinylated peptides and EBV-transformed BLCL comprising all known HLA class II specificities, we find that p3-13 binds to HLA-DRw17(DR3) but not to any other HLA-DR molecule. Conversely, a control peptide p307-319 influenza hemagglutinin binds to all known HLA-DR molecules but only weakly to HLA-DRw17 and HLA-DR9. Peptide binding could be inhibited by excess unbiotinylated competitor analogue as well as by anti-DR monoclonal antibodies but not by anti-class I-, anti-DP- or anti-DQ monoclonal antibodies. The amino acid sequence of DRw17 molecules differs uniquely at five positions from the other DR beta 1 sequences. Three of these five residues (positions 26, 71 and 74) are potential peptide contacting residues. These residues map closely together in the hypothetical three-dimensional model of the DR molecule and, thus, most probably form a positively charged pocket, critical for the binding of p3-13. Interestingly, p3-13 does not bind to a DR3 variant, the DRw18 molecule. The DRw18 beta 1 chain differs from DRw17 at two major positions, close to or within the DRw17-specific pocket. These substitutions drastically change the structure and charge of the pocket and thus presumably abrogate its ability to bind p3-13.

Leukocyte infiltration and glial reactions in xenografts of mouse brain tissue undergoing rejection in the adult rat brain. A light and electron microscopical immunocytochemical study

Neural mouse xenografts undergoing rejection in the adult recipient rat brain were characterized with regard to infiltrating host leukocytes and reactions of graft and host astro- and microglial cells. Rejection occurred within 35 days with infiltration of the grafts by in particular macrophages and T-cells as well as blood-brain barrier (BBB) leakage for IgG. In the surrounding host brain microglial cells showed increased histochemical staining for nucleoside diphosphatase (NDPase) and increased immunocytochemical expression of complement receptor type 3 (CR3), while astroglial cells displayed an increased immunoreactivity for glial fibrillary acidic protein (GFAP). Light microscopic findings of rat major histocompatibility complex (MHC) antigen class I on microglial cells, endothelial cells and leukocytes were confirmed at the ultrastructural level and extended to include a few astrocytes. Rat and mouse MHC antigen class II was only detected on leukocytes and activated microglia. We suggest that host macrophages and activated host and xenograft microglial cells act in situ as immunostimulatory cells on T-helper cells, and that increased levels of donor MHC antigen class I may further enhance the killer activity exerted by host T-cytotoxic cells.

The chimpanzee major histocompatibility complex class II DR subregion contains an unexpectedly high number of beta-chain genes

The major histocompatibility complex (MHC) class II DR subregion of the chimpanzee was studied by restriction fragment length polymorphism (RFLP) analysis. Genomic DNA obtained from a panel of 94 chimpanzees was digested with the restriction enzyme Taq I and hybridized with an HLA-DR beta probe specific for the 3' untranslated (UT) region. Such a screening revealed the existence of 14 distinct DRB/Taq I gene-associated fragments allowing the definition of 11 haplotypes. Segregation studies proved that the number of chimpanzee class II DRB/Taq I fragments is not constant and varies from three to six depending on the haplotype. Comparison of these data with a human reference panel manifested that some MHC DRB/Taq I fragments are shared by man and chimpanzee. Moreover, the number of HLA-DRB/Taq I gene-associated fragments detected in a panel of homozygous typing cells varies from one to three and corresponds with the number of HLA-DRB genes present for most haplotypes. However, a discrepancy is observed for the HLA-DR4, -DR7, and -DR9 haplotypes since a fourth HLA-DRB pseudogene present within these haplotypes lacks its 3' UT region and thus is not detected with the probe used. These results suggest that chimpanzees have a higher maximum number of DRB genes per haplotype than man. As a consequence, some chimpanzee haplotypes must show a dissimilar organization of the MHC DR subregion compared to their human equivalents. The implications of these findings are discussed in the context of the trans-species theory of MHC polymorphism.