Restricted recognition of beta 2-microglobulin by cytotoxic T lymphocytes

A systematic review of multimodal clinical biomarkers in the management of thyroid eye disease

Thyroid Eye Disease (TED) is an autoimmune disease that affects the extraocular muscles and periorbital fat. It most commonly occurs with Graves' Disease (GD) as an extrathyroidal manifestation, hence, it is also sometimes used interchangeably with Graves' Ophthalmopathy (GO). Well-known autoimmune markers for GD include thyroid stimulating hormone (TSH) receptor antibodies (TSH-R-Ab) which contribute to hyperthyroidism and ocular signs. Currently, apart from radiological investigations, detection of TED is based on clinical signs and symptoms which is largely subjective, with no established biomarkers which could differentiate TED from merely GD. We evaluated a total of 28 studies on potential biomarkers for diagnosis of TED. Articles included were published in English, which investigated clinical markers in tear fluid, orbital adipose-connective tissues, orbital fibroblasts and extraocular muscles, serum, thyroid tissue, as well as imaging biomarkers. Results demonstrated that biomarkers with reported diagnostic power have high sensitivity and specificity for TED, including those using a combination of biomarkers to differentiate between TED and GD, as well as the use of magnetic resonance imaging (MRI). Other biomarkers which were upregulated include cytokines, proinflammatory markers, and acute phase reactants in subjects with TED, which are however, deemed less specific to TED. Further clinical investigations for these biomarkers, scrutinising their specificity and sensitivity on a larger sample of patients, may point towards selection of suitable biomarkers for aiding detection and prognosis of TED in the future.

The Structure of a Peptide-Loaded Shark MHC Class I Molecule Reveals Features of the Binding between β2-Microglobulin and H Chain Conserved in Evolution

Cartilaginous fish are the most primitive extant species with MHC molecules. Using the nurse shark, the current study is, to the best of our knowledge, the first to present a peptide-loaded MHC class I (pMHC-I) structure for this class of animals. The overall structure was found to be similar between cartilaginous fish and bony animals, showing remarkable conservation of interactions between the three pMHC-I components H chain, β₂-microglobulin (β₂-m), and peptide ligand. In most previous studies, relatively little attention was given to the details of binding between the H chain and β₂-m, and our study provides important new insights. A pronounced conserved feature involves the insertion of a large β₂-m F56+W60 hydrophobic knob into a pleat of the β-sheet floor of the H chain α1α2 domain, with the knob being surrounded by conserved residues. Another conserved feature is a hydrogen bond between β₂-m Y10 and a proline in the α3 domain of the H chain. By alanine substitution analysis, we found that the conserved β₂-m residues Y10, D53, F56, and W60-each binding the H chain-are required for stable pMHC-I complex formation. For the β₂-m residues Y10 and F56, such observations have not been reported before. The combined data indicate that for stable pMHC-I complex formation β₂-m should not only bind the α1α2 domain but also the α3 domain. Knowing the conserved structural features of pMHC-I should be helpful for future elucidations of the mechanisms of pMHC-I complex formation and peptide editing.

Effects of Epstein-Barr Virus Infection on the Risk and Prognosis of Primary Laryngeal Squamous Cell Carcinoma: A Hospital-Based Case-Control Study in Taiwan

Mounting molecular evidence supports Epstein-Barr virus (EBV) involvement in the pathogenesis of laryngeal squamous cell carcinoma (LSCC); however, the epidemiological data are inconsistent. In this retrospective case-control study, we aimed to determine whether EBV infection underlies the risk and prognosis of LSCC. The prevalence of EBV infection, as analyzed using an EBV DNA polymerase chain reaction assay, was significantly higher in 42 Taiwanese patients with newly diagnosed primary LSCC, compared to 39 age- and sex-matched control patients without cancer (48% vs. 19%). Furthermore, most of the EBER signals detected using in situ hybridization were localized to the nuclei of tumor-infiltrating lymphocytes. In multivariate analysis, EBV DNA positivity, age ≥ 55 years, cigarette smoking, and high BCL-2, B2M, and CD161 expression (assessed using immunohistochemistry) were identified as independent risk factors for LSCC. Furthermore, five-year local recurrence and disease-free survival rates were 34% and 58%, respectively, with a high EBER signal and low CD3 expression independently predicting five-year local recurrence and disease-free survival. Our comprehensive profiling data accurately identified patients at risk for LSCC development, local recurrence, or disease-free survival. The information obtained in this study improves our understanding of EBV infection in LSCC, and may guide precision medicine for patients with LSCC.

Proteomics of tear fluid in thyroid-associated orbitopathy

BACKGROUND

Proteomics and mass spectrometry are useful tools for peptide screening in body fluids. In thyroid-associated orbitopathy (TAO), evidence for lacrimal gland involvement with altered composition of tears has been reported. Our objective was to detect and evaluate potential changes in the proteomic patterns of tear fluid in TAO.

METHODS

Tear fluid was collected from 45 patients with TAO and 15 healthy controls. Tear proteins were analyzed using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry, and peptides were identified using matrix-assisted laser desorption/ionization time-of-flight technology.

RESULTS

Peptides with molecular weights 3808 Dalton (Da, p=0.004), 3734 Da (p=0.034), and 3837 Da (p=0.042), respectively, were downregulated in patients with TAO versus controls. They were identified as proline-rich protein 4 (PRP4) or as its variant nasopharyngeal carcinoma-associated PRP4. The peptide 3837 Da correlated positively with the basal secretory test (r=0.506, p<0.001) and negatively with the clinical activity score (r = -0.334, p<0.05) and age (r=-0.431, p<0.001). Also, a 12,003-Da peptide was downregulated (p=0.019) in patients and identified as ß2-microglobulin. This peptide decreased in tear fluid with increased clinical severity of TAO (p=0.027). In comparison, a 5815-Da peptide was upregulated (p=0.045) and identified as lysozyme C. When differentiating between treated and untreated patients with TAO, an 11,770-Da peptide (p=0.0072) that was also upregulated was identified as cystatin S.

CONCLUSIONS

Altered regulation of proinflammatory and protective proteins in tears of patients with TAO was demonstrated, reflecting an autoimmune- and/or inflammatory-induced dysfunction of the lacrimal gland.

Xenogeneic beta 2-microglobulin substitution affects functional binding of MHC class I molecules by CD8+ T cells

NK cells and CD8+ T cells bind MHC-I molecules using distinct topological interactions. Specifically, murine NK inhibitory receptors bind MHC-I molecules at both the MHC-I H chain regions and beta2-microglobulin (beta2m) while TCR engages MHC-I molecules at a region defined solely by the class I H chain and bound peptide. As such, alterations in beta2m are not predicted to influence functional recognition of MHC-I by TCR. We have tested this hypothesis by assessing the capability of xenogeneic beta2m to modify the interaction between TCR and MHC-I. Using a human beta2m-transgenic C57BL/6 mouse model, we show that human beta2m supports formation and expression of H-2K(b) and peptide:H-2K(b) complexes at levels nearly equivalent to those in wild-type mice. Despite this finding, the frequencies of CD8+ single-positive thymocytes in the thymus and mature CD8+ T cells in the periphery were significantly reduced and the TCR Vbeta repertoire of peripheral CD8+ T cells was skewed in the human beta2m-transgenic mice. Furthermore, the ability of mouse beta2m-restricted CTL to functionally recognize human beta2m+ target cells was diminished compared with their ability to recognize mouse beta2m+ target cells. Finally, we provide evidence that this effect is achieved through subtle conformational changes occurring in the distal, peptide-binding region of the MHC-I molecule. Our results indicate that alterations in beta2m influence the ability of TCR to engage MHC-I during normal T cell physiology.

The immunogenomics of minor histocompatibility antigens

Minor histocompatibility (H) antigens are a diverse assemblage of major histocompatibility complex (MHC)-bound peptides with the unifying property of acting as alloantigens that induce allogeneic tissue rejection. They are a consequence of any form of accumulated genetic variation that translates to differential MHC-presented peptide epitopes, the most common form of which is simple sequence polymorphisms. The universe of potential minor H antigens is large when transplantation is performed between genetically unrelated, MHC-matched individuals, especially considering the remarkable discriminative sensitivity of T cells. However, the phenomenon of immunodominance greatly simplifies immune responses that ensue. One mouse minor H antigen, H60, stands out in that the preponderance of the CD8 T cell response elicited in a complex alloantigenic setting is directed against this single minor H antigen epitope. Its immunodominance is because mice lacking H60 develop an unusually robust T cell repertoire dedicated to this single minor H antigen. The now well-characterized mouse minor H antigen system should provide a vehicle to assess the degree to which immunodominant alloantigens contribute to transplant rejection.

Skin graft rejection elicited by beta 2-microglobulin as a minor transplantation antigen involves multiple effector pathways: role of Fas-Fas ligand interactions and Th2-dependent graft eosinophil infiltrates

Beta(2)-microglobulin (beta(2)m)-derived peptides are minor transplantation Ags in mice as beta(2)m-positive skin grafts (beta(2)m(+/+)) are rejected by genetically beta(2)m-deficient recipient mice (beta(2)m(-/-)). We studied the effector pathways responsible for the rejection induced by beta(2)-microglobulin-derived minor transplantation Ags. The rejection of beta(2)m(+/+) skin grafts by naive beta(2)m(-/-) mice was dependent on both CD4 and CD8 T cells as shown by administration of depleting mAbs. Experiments performed with beta(2)m(-/-)CD8(-/-) double knockout mice grafted with a beta(2)m(+/+) MHC class I-deficient skin showed that sensitized CD4 T cells directed at beta(2)m peptides-MHC class II complexes are sufficient to trigger rapid rejection. Rejection of beta(2)m(+/+) grafts was associated with the production of IL-5 in vitro, the expression of IL-4 and IL-5 mRNAs in the grafted tissue, and the presence within rejected grafts of a considerable eosinophil infiltrate. Blocking IL-4 and IL-5 in vivo and depleting eosinophils with an anti-CCR3 mAb prevented graft eosinophil infiltration and prolonged beta(2)m(+/+) skin graft survival. Lymphocytes from rejecting beta(2)m(-/-) mice also displayed an increased production of IFN-gamma after culture with beta(2)m(+/+) minor alloantigens. In vivo neutralization of IFN-gamma inhibited skin graft rejection. Finally, beta(2)m(+/+) skin grafts harvested from B6(lpr/lpr) donor mice, which lack a functional Fas molecule, survived longer than wild-type beta(2)m(+/+) skin grafts, showing that Fas-Fas ligand interactions are involved in the rejection process. We conclude that IL-4- and IL-5-dependent eosinophilic rejection, IFN-gamma-dependent mechanisms, and Fas-Fas ligand interactions are effector pathways in the acute rejection of minor transplantation Ags.

Allo-Major Histocompatibility Complex–Restricted Cytotoxic T Lymphocytes Engraft in Bone Marrow Transplant Recipients Without Causing Graft-Versus-Host Disease

Previous experiments in humans and mice have shown that allogeneic donors can serve as a source of cytotoxic T lymphocytes (CTL) specific for proteins, such as cyclin-D1 and mdm-2, expressed at elevated levels in tumor cells. In vitro, allo-major histocompatibility complex (MHC)–restricted CTL against these proteins selectively killed allogeneic tumor cells, including lymphoma, but not normal control cells. This suggested that these CTL may be useful for adoptive tumor immunotherapy, provided that they (1) survive in MHC-disparate hosts, (2) maintain their killing specificity, and (3) do not attack normal host tissues. Here, we used cloned allo-restricted CTL isolated from BALB/c mice (H-2d) that killed H-2b–derived tumor cells expressing elevated levels of the mdm-2 target protein. When these CTL were injected into bone marrow transplanted (BMT) C57BL/6 (H-2b) recipients, they consistently engrafted and were detectable in lymphoid tissues and in the bone marrow (BM). Long-term survival was most efficient in spleen and lymph nodes, where CTL were found up to 14 weeks after injection. The administration of CTL did not cause graft-versus-host disease (GVHD) normally associated with injection of allogeneic T cells. These data show that allo-restricted CTL clones are promising reagents for antigen-specific immunotherapy in BMT hosts, because they engraft and retain their specific killing activity without causing GVHD.

Allo-Major Histocompatibility Complex–Restricted Cytotoxic T Lymphocytes Engraft in Bone Marrow Transplant Recipients Without Causing Graft-Versus-Host Disease

Previous experiments in humans and mice have shown that allogeneic donors can serve as a source of cytotoxic T lymphocytes (CTL) specific for proteins, such as cyclin-D1 and mdm-2, expressed at elevated levels in tumor cells. In vitro, allo-major histocompatibility complex (MHC)–restricted CTL against these proteins selectively killed allogeneic tumor cells, including lymphoma, but not normal control cells. This suggested that these CTL may be useful for adoptive tumor immunotherapy, provided that they (1) survive in MHC-disparate hosts, (2) maintain their killing specificity, and (3) do not attack normal host tissues. Here, we used cloned allo-restricted CTL isolated from BALB/c mice (H-2d) that killed H-2b–derived tumor cells expressing elevated levels of the mdm-2 target protein. When these CTL were injected into bone marrow transplanted (BMT) C57BL/6 (H-2b) recipients, they consistently engrafted and were detectable in lymphoid tissues and in the bone marrow (BM). Long-term survival was most efficient in spleen and lymph nodes, where CTL were found up to 14 weeks after injection. The administration of CTL did not cause graft-versus-host disease (GVHD) normally associated with injection of allogeneic T cells. These data show that allo-restricted CTL clones are promising reagents for antigen-specific immunotherapy in BMT hosts, because they engraft and retain their specific killing activity without causing GVHD.

Alloreactive cytotoxic T cells recognize minor transplantation antigens presented by major histocompatibility complex class Ib molecules

BACKGROUND

Cytotoxic T lymphocytes (CTLs) contribute to the rejection of transplanted tissues through two pathways: first, by direct recognition of foreign graft major histocompatibility complex (MHC) class I molecules; and second, by recognition of foreign graft-derived peptides presented by classical MHC class Ia molecules that are matched between graft and donor. However, a number of observations suggest that additional categories of CTL recognition patterns may exist, but they remain to be defined molecularly.

METHODS

Previous studies showed that the murine nonclassical MHC molecule H2 M3 may be involved in allorecognition. We investigated whether other members of nonclassical MHC class Ib, namely Qa1 and Qa2, may be recognized. Alloreactive CTLs were generated from mice mismatched for non-MHC and/or MHC genetic backgrounds and tested using various target cells, including cells transfected with Qa1 or Qa2. Furthermore, candidate peptides were synthesized and used to generate CTLs specific for peptide presented by Qa1 or Qa2.

RESULTS

The experiments demonstrate that allogeneic and xenogeneic peptides were recognized by CTLs when presented on shared nonclassical MHC class Ib Qa1 and Qa2 molecules.

CONCLUSIONS

The results confirm that MHC class Ib molecules present peptides to CTLs. This potentially important alloreactivity pathway may be functional between most individuals because sharing of MHC class Ib alleles is frequent.

T Cells Specific for a Polymorphic Segment of CD45 Induce Graft-Versus-Host Disease with Predominant Pulmonary Vasculitis

To study the character of graft-vs-host disease (GVHD) induced by T cells specific for hemopoietic cells, T cells specific for a polymorphic segment of CD45 were transferred into CD45 congenic mice. C57BL/6 mice that express the CD45b allele were immunized with a 13 mer peptide representing the polymorphic segment (p257–268) of CD45a protein. Conversely, C57BL/6 mice congenic for CD45a were immunized with the CD45b peptide. CD4+ T cells specific for allelic CD45 peptides were elicited. Importantly, T cells specific for CD45 peptides proliferated specifically and vigorously in response to spleen cells expressing the appropriate polymorphic CD45 protein. T cells specific for CD45 induced a substantial graft-vs-host response (GVHR) with predominant early pulmonary vasculitis and later more widespread interstitial mononuclear cell infiltration and alveolitis. No GVHR was induced in bone marrow chimeras expressing only donor hemopoietic cells. Thus, donor T cell recognition of host hemopoietic cells is sufficient to elicit GVHR, but the classical skin, liver, and gut manifestations of GVHD were not observed. The CD45-specific T cells used secreted Th1 cytokines, but without detectable soluble IL-2. Studies using CD45-specific T cells with different effector functions might allow further dissection of donor cell requirements for GVHD syndromes.

Minor histocompatibility antigens

The existence of transplantation antigens, in addition to those encoded by genes in the MHC, has been known for over half a century. The molecular identification of these additional minor histocompatibility (H) antigens lagged behind that of their MHC counterparts, largely because minor H antigens are recognised by T cells and not by antibodies. In the past year, however, new minor H antigens have been identified at both the genetic and protein level and include Uty, a second novel gene encoding a male-specific epitope in mice, a novel autosomal gene encoding each of the H-13 alleles of mice, and a second male-specific epitope encoded by the SMCY gene.

Human minor histocompatibility antigens: new concepts for marrow transplantation and adoptive immunotherapy

Bone marrow transplantation (BMT) is the present treatment for hematological malignancies. Two major drawbacks of allogeneic BMT are graft-versus-host disease (GVHD) and leukemia relapse. The use of HLA-matched siblings as marrow donors results in the best transplant outcome. Nonetheless, the results of clinical BMT reveal that the selection of MHC-identical donors' bone marrow (BM) is no guarantee for avoiding GVHD or ensuring disease-free survival even when donor and recipient are closely related. It is believed that non-MHC-encoded so-called minor histocompatibility antigens (mHag) are involved in both graft-versus-host and graft-versus-leukemia activities. The recent new insights into the chemical nature of mHag not only reveal their physiological function but, more importantly, provide insights into their role in BMT. Together with the information on the human mHag genetics and tissue distribution gathered in the past, we may now apply this knowledge to the benefit of human BMT. Directly relevant is the utility of mHag molecular typing for diagnostics in BM donor selection. Most promising is the use of mHag-specific cytotoxic T cells for adoptive immunotherapy of leukemia.

Unexpected beta2-microglobulin sequence diversity in individual rainbow trout

For mammals beta2-microglobulin (beta2m), the light chain of major histocompatibility complex (MHC) class I molecules, is invariant (or highly conserved) and is encoded by a single gene unlinked to the MHC. We find that beta2m of a salmonid fish, the rainbow trout (Oncorhynchus mykiss), does not conform to the mammalian paradigm. Ten of 12 randomly selected beta2m cDNA clones from an individual fish have different nucleotide sequences. A complex restriction fragment length polymorphism pattern is observed with rainbow trout, suggesting multiple beta2m genes in the genome, in excess of the two genes expected from the ancestral salmonid tetraploidy. Additional duplication and diversification of the beta2m genes might have occurred subsequently. Variation in the beta2m cDNA sequences is mainly at sites that do not perturb the structure of the mature beta2m protein, showing that the observed diversity of the trout beta2m genes is not primarily a result of pathogen selection.

Acceptance of skin grafts between mice bearing different allelic forms of beta 2-microglobulin

Single amino acid disparities in MHC class I molecules can elicit transplantation responses. Since beta 2 microglobulin (beta 2m) is noncovalently associated with class I antigens on the cell membrane we investigated whether the single amino acid polymorphism at position 85 (Asp-->Ala) in the mouse beta 2m molecule can cause skin graft rejection. A B2mb transgene was introduced into CBA(B2ma) mice which subsequently expressed both forms of beta 2m. Skin from these CBA beta 2mb transgenic mice was not rejected by the parental CBA strain. Previous studies showed that cytotoxic T lymphocyte (CTL) responses directed against beta 2mb use H2Kb as a restriction element. We therefore produced mice expressing H2Kb and H2Ab as well as beta 2mb by crossing CBA.beta 2mb mice with either CBA.Kb (CBK) transgenic mice or C3H.SW mice and used these as skin graft donors for beta 2mb negative littermates. In both cases rejection of transgenic skin only occurred when mice had received both a beta 2mb graft and an H2-disparate allograft lying adjacent in the same site. Introduction of the male specific antigen, H-Y, as a helper determinant did not result in rejection of beta 2mb skin. Neither did two CTL determinants (P91A and beta 2mb) on the same graft complement one another to elicit a transplantation response. Prior immunisation with tissues expressing the beta 2m disparity alone did not generate in vivo or in vitro beta 2mb-specific CTL responses, suggesting that this single amino acid difference is not sufficient to elicit a CTL or helper T cell response.

Identification of a graft versus host disease-associated human minor histocompatibility antigen

Minor histocompatibility antigen disparities between human leukocyte antigen (HLA)-matched bone marrow donors and recipients are a major risk factor for graft versus host disease (GVHD). An HLA-A2.1-restricted cytotoxic T cell clone that recognized the minor histocompatibility antigen HA-2 was previously isolated from a patient with severe GVHD after HLA-identical bone marrow transplantation. The HLA-A2.1-bound peptide representing HA-2 has now been identified. This peptide appears to originate from a member of the non-filament-forming class I myosin family. Because HA-2 has a phenotype frequency of 95 percent in the HLA-A2.1-positive population, it is a candidate for immunotherapeutic intervention in bone marrow transplantation.

Increased beta 2-microglobulin in both parotid and submandibular/sublingual saliva from patients with Sjögren's syndrome

Samples of unstimulated saliva from patients with sialoadenopathy were collected by microcapillary tube (1 microliter), and their beta 2-microglobulin (B2-MG) content determined by a sandwich enzyme immunoassay. A higher than normal (control) concentration of the globulin was present in both parotid and submandibular/sublingual saliva from the patients with Sjögren's syndrome but not in the samples from the patients with sialoadenitis or diabetes mellitus. The increase in B2-MG in saliva from patients with Sjögren's syndrome may reflect that immunolopathological events are important in the degeneration of both glands in this disease. Therefore, the determination of B2-MG in saliva may be a simple, non-invasive technique for confirming the diagnosis of Sjögren's syndrome as an autoimmune disease.

Sequence divergence of B2m alleles of wild Mus musculus and Mus spretus implies positive selection

Mouse beta 2-microglobulin (beta 2m) is polymorphic. Sequences of five allelic wild mouse B2m genes have been determined from the large exons of genomic DNA using the polymerase chain reaction. Relative to the standard B2m(a) allele, the products of four alleles of Mus musculus origin (w2, w3, w4, and w5), differ by only one or two amino acids. w5 has a single nucleotide change, Asp85-->Val, and is identical to the c allele. w3 has two changes, Val(-13)-->Ile and Lys44-->Glu. w2 differs at Arg81-->Thr and w4 at His34-->Gln, and they share the Asp85-->Val change with B2mc and B2mw5. w5 and c cells are lysed by S19.8, a monoclonal antibody specific for beta 2mb (Ala85), in a complement-mediated cytotoxicity assay, whereas w4 cells are not. Thus, distant changes appear to introduce subtle conformational effects on beta 2m structure. Five independent isolates of Mus spretus (w1) differ the most from B2m(a), with 12 amino acid changes and only one silent substitution. Replacements predicted from the nucleotide sequence occur in loops of the molecule facing away from the class I heavy chain and not in regions where beta 2m associates with class I alpha 3 domains. Concordantly, the w1-5 allelic forms of beta 2m associate well with H-2 heavy chains. The many amino acid changes in the spretus sequence and the paucity of silent substitutions suggest that B2m has been subject to positive selection.

A new approach to the cloning of genes encoding T-cell epitopes

The molecular structure of antigens recognized exclusively by T cells, such as minor histocompatibility antigens and some antigens that provoke autoimmune responses, has proved difficult to determine. Recently, several antigens induced on tumor cells by mutagen treatment have been cloned by transfection of genomic DNA libraries into P1.HTR cells, screening for antigen expression using T-cell clones, and subsequent recovery of the integrated DNA by cosmid rescue. We have modified this technique and have stably transfected P1.HTR cell lines with polyoma T antigen, which allows episomal replication of the shuttle vector, pCDM8. Using pCDM8-CAT constructs, we have determined the frequency of transfection and plasmid copies taken up per cell under optimal transfection conditions. Using a pCDM8 construct which expresses the tumor-specific antigen, P91A (pCDM8-tum-), that is recognized by a T-cell clone, we have found that cells transfected with this antigen can be recognized by the T-cell clone when they are present at only 1%-3% of a mixed population. Progeny of a single cell transfected with pCDM8-tum-: pCDM8-CAT at proportions of 1:10, 1:25, and 1:50 are recognized by the T-cell clone. Furthermore, Hirt extracted plasmid DNA from transfectants expressing the tum- antigen can be amplified in bacteria, transfected back into P1.HTR recipients, and recognized by the T-cell clone. This approach should enable reasonably rapid screening of cDNA libraries for even relatively low abundance messages encoding, for example, minor histocompatibility and alloantigens, and allow their subsequent cloning.

What are minor histocompatibility loci? A new look at an old question

In this article, Derry Roopenian relates the traditional view of minor histocompatibility (H) loci to recent advances in understanding of the tissue rejection process and the molecular nature of minor histocompatibility antigens. He proposes that minor H loci can be subdivided by the ability of their products to stimulate different T-cell subsets and discusses the implications of this concept in terms of the origins and behavior of minor H loci and their antigens, tumor immunology and autoimmunity.

Minor histocompatibility antigens

Immune responses against foreign tissue or organs can be directed against alloantigenic differences between donor and host encoded by genes of the major histocompatibility complex (MHC; HLA in man and H-2 in mouse). However, when MHC antigens are matched, as in HLA-identical siblings, or between different mouse strains sharing the same H-2 haplotype, graft rejection still occurs and is then directed against alloantigenic differences termed minor histocompatibility (H) antigens. Their molecular nature is not yet determined but they are recognised by T cells in an MHC-restricted manner, so are assumed to be derived from molecules co-expressed with MHC class I or II glycoproteins, possibly as peptides or as "super-antigens". The genes encoding them are scattered throughout the genome, including the Y chromosome, on which the H-Y antigen gene has been mapped in both man and mouse. One striking feature of minor H antigens is their recognition by T cells but not by antibodies. This made work with them, before our ability to generate T cell responses and maintain T cell clones in vitro, very slow but currently the use of MHC-restricted T cell clones has enabled detailed mapping studies and should eventually allow for their molecular characterisation.

Additional mapping of mouse chromosome 2 genes

The purpose of this work was to elucidate the genetic fine structure of the central portion of mouse chromosome (Chr) 2. Seven Chr 2 congenic mouse strains [B10.PA(L)-pa we un at, B10.PA(L)-pa Aw, B10.PA(L)-we un at, B10.PA(J)-pa a, B10.FS-we Aw, B10.C-we Aw, and B10.YBR-a] were produced. Breeding studies were carried out using strains B10.PA(L)-pa we un at and B10.LP-H-13b to accurately determine the recombination frequencies between marker genes pa and we (1.9% +/- 0.3), we and un (8.8% +/- 0.5), and un and at (4.5% +/- 0.4) of strain B10.PA(L)-pa we un at. These strains and other Chr 2 congenic strains were typed for immunologically defined loci using monoclonal antibody (mAb) C23 reactive with the gene product of B2mb T-lymphocyte clone C1 reactive with the gene product of H-3a and H-3c, and lymphocyte clone H1.8 reactive with the gene product of Hd-1a. B2m and H-3 typing located a recombinational event separating [pa B2m H-3] from we (the order of bracketed genes is not known). Hd-1 typing indicated that Hd-1 maps distal to [H-42, H-44] and proximal to un. The gene order [pa, B2m, H-3], we, [H-42, H-45], Hd-1, un, H-13, at, with H-44 mapping centromeric to Hd-1, is indicated by the data.

Beta 2-microglobulin restriction of antigen presentation

Antigens are generally thought to be recognized by cytotoxic T lymphocytes as peptides in the context of class I major histocompatibility proteins complex, which are heterodimers of heavy chains noncovalently associated with beta 2-microglobulin (beta 2m). The highly polymorphic nature of the heavy chains and their resulting ability to present different sets of peptides has presumably evolved to allow potent immune responses against most pathogens. By contrast, the polymorphism of beta 2m is limited; seven alleles are known in the mouse and only one has been identified in humans. beta 2-Microglobulin was consequently thought to have only structural functions: namely, to ensure correct folding of class I molecules and their transport to the cell surface. Although beta 2m is not implicated directly in the formation of the peptide binding site, we report here that it participates in the selection of MHC class I molecule-associated peptides.

Characterization of naturally occurring minor histocompatibility peptides including H-4 and H-Y

Minor histocompatibility (H) antigens can be peptides derived from cellular proteins that are presented on the cell surface by major histocompatibility complex (MHC) class I molecules. This is similar to viral antigens, because in both cases cytotoxic T lymphocytes (CTLs) recognize artificially produced peptides loaded on target cells. Naturally processed minor H peptides were found to be similar to those artificial CTL-epitopes, as far as size and hydrophobicity is concerned. The peptides studied were isolated from a transfectant that expressed a model CTL-defined antigen, beta-galactosidase, from male cells that express H-Y, which has been known operationally since 1955, and from cells that express H-4, known since 1961.

Limit of T cell tolerance to self proteins by peptide presentation

Cytotoxic T lymphocytes (CTLs) recognize foreign peptides bound to major histocompatibility complex (MHC) class I molecules. MHC molecules can also bind endogenous self peptides, to which T cells are tolerant. Normal mice contained CTLs specific for self peptides that were from proteins of ubiquitous or tissue-restricted expression. In vivo, these endogenous self peptides are not naturally presented in sufficient density by somatic cells expressing MHC class I molecules. They can, however, be presented if added exogenously. Thus, our data imply that CTLs are only tolerant of those endogenous self peptide sequences that are presented by MHC class I-positive cells in a physiological manner.

Nuclear myxovirus-resistance protein Mx is a minor histocompatibility antigen

Minor histocompatibility antigens (MiHAgs) cause slow-to-rapid organ transplant rejection by immunocompetent hosts and mild-to-severe graft-versus-host reactions in immunosuppressed hosts. MiHAgs are allelic forms of major histocompatibility complex (MHC) class I-restricted self-antigens recognized by cytotoxic T cells and usually are defined immunogenetically. Although structurally not identified as yet, it is assumed that MiHAgs are internal cell antigens that are processed and then presented by MHC class I proteins similar to viral antigens. To define a MiHAg both molecularly and functionally, we took advantage of the allelic difference of the structurally characterized intracellular myxovirus-resistance protein (Mx) and investigated its antigenicity. Skin grafts from congenic Mx+ mice carrying the functional Mx1 gene were rejected by mice lacking a functional Mx1 gene (Mx- mice). In parallel, cytotoxic MHC class I-restricted effector T cells specific for Mx protein and the H-2Kk antigen (but not for several other allelic H-2 antigens) were strongly induced in Mx- mice immunized with spleen cells from interferon-treated Mx+ mice. These data show that allelic forms of cell internal proteins presented by MHC class I may act as MiHAgs.

Differences in specificity of "DPw2-specific" cytotoxic T cell clones revealed with HLA-mutant lines: evidence that non-DP HLA genes influence recognition by some clones

Seven allospecific cytotoxic T lymphocyte (CTL) clones derived from DPw2-specific bulk populations were characterized by three approaches to obtain a more detailed understanding of the T cell recognition of the HLA-DPw2 molecule. All seven of the clones were DPw2 specific and indistinguishable in specificity by three approaches: (a) patterns of lysis of panels of targets from normal donors; (b) inhibition of lysis by anti-class II monoclonal antibodies (mAb); (c) lysis of mutant lymphoblastoid B cell lines (LCL) with isolated loss of DP2 alpha or DP2 beta gene expression (as a result of selection for resistance to DPw2-specific CTL). However, only four of the seven CTL clones (which we designate "orthodox") lysed all mutant DPw2+ LCL tested; the other three ("heterodox") CTL clones showed reduced or no lysis of particular LCL which expressed DPw2 but had been mutagenized and selected for loss of DR expression. Cold target blocking experiments with the mutant LCL confirmed differences in: (a) specificity among CTL clones and (b) CTL-defined phenotype among serologically indistinguishable DR-DPw2+ mutant LCL. Differences were not explained by different levels of DP expression by the mutant LCL. Given the nature of the mutagens and mutations, it is highly improbable that point mutations in DP account for differences in recognition. These data suggest that non-DP HLA genes influence recognition by some DP-specific clones, potentially due to corecognition of HLA-DR alpha or another non-DP HLA product in the context of a DPw2 alpha/beta dimer.

Identification of classical minor histocompatibility antigen as cell-derived peptide

Histocompatibility antigens expressed on tissue grafted between individuals are recognized by host T cells, which reject the graft. The major histocompatibility complex (MHC) antigens have been identified on the molecular level, whereas the molecules representing the remaining ones, the minor histocompatibility antigens, are unknown, apart from some exceptions. The cytotoxic T lymphocyte (CTL) response against minor histocompatibility antigens shares many aspects with that against virus-infected cells. Virus-specific CTL recognize peptides derived from viral proteins produced in the infected cell. These peptides are presented by MHC class I molecules, as indicated by functional and crystallographic data. By analogy, minor histocompatibility antigens have been postulated to be peptides derived from normal cellular proteins presented by MHC class I molecules. Here we report that peptides derived from normal cellular proteins can indeed be recognized by CTL raised in the classical minor histoincompatible mouse strain combination, C57BL/6 against BALB.B. Thus, we have proven the above postulate, and isolated one of the minor histocompatibility molecules elusive for several decades.

Responses against antigens encoded by the H-3 histocompatibility locus: antigens stimulating class I MHC- and class II MHC-restricted T cells are encoded by separate genes

The purpose of this work was to study the genetic basis of histocompatibility antigens encoded by the mouse minor histocompatibility (H) locus H-3. Both class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTL) and class II MHC-restricted helper T cells (TH) specific for antigens encoded by genes within the H-3 locus were isolated and analyzed. Typing a number of mouse strains for expression of antigens recognized by these TH and CTL suggested that there was a different strain distribution pattern of expression of the antigens recognized by TH compared with those recognized by CTL. Separation of the genes whose products stimulate TH from those whose products stimulate CTL was suggested by: (1) analysis of the strain B10.FS(92NX)/Grf that has undergone recombination within the H-3 region; (2) genetic segregation studies of (B10.UW-H-3b/Sn x C57BL/10Sn)F2 mice; and (3) F1 complementation studies in which CTL specific for products of the TH-defined gene(s) could not be detected, even in the absence of immune responses to products of the CTL-defined genes. Taken together, these data suggest that in addition to two genes (B2m and Cd-1) within the H-3 region whose products typically stimulate class I MHC-restricted CTL, there is at least one additional gene whose product selectively stimulates class II MHC-restricted TH. This new gene is located telomeric from the CTL-defined genes and between the loci we and un on chromosome 2. These data demonstrate a novel degree of complexity of the H-3 "locus" and suggest selective presentation of minor H gene products in the context of class I or class II MHC proteins.

Protein-specific cytotoxic T lymphocytes. Recognition of transfectants expressing intracellular, membrane-associated or secreted forms of beta-galactosidase

BALB/c-derived tumor cells were transfected with recombinant Escherichia coli beta-galactosidase (beta-gal) genes which were inserted into IgM heavy chain gene derivatives, leading to expression of the resulting fusion protein in different cellular compartments. A beta-gal-specific, major histocompatibility complex (MHC) class I-restricted CD8+CD4- cytotoxic T lymphocyte (CTL) line of BALB/c origin raised against one transfectant expressing cytoplasmic beta-gal also lysed transfectants expressing beta-gal as membrane-inserted fusion protein, as well as transfectants secreting beta-gal. Our data show that MHC class I-restricted CTL can recognize fragments of nonviral cellular proteins, be they expressed as intracellular, membrane-inserted, or secreted products. The findings confirm and extend a hypothesis on the nature of minor histocompatibility (H) antigens formulated earlier.

Beta 2-microglobulin decrease in cerebrospinal fluid from parkinsonian patients

A sandwich enzyme immunoassay (EIA) was established by using purified beta 2-microglobulin (beta 2-MG) as a standard protein and a polyclonal antibody raised against human beta 2-MG. The EIA was applied for the measurement of beta 2-MG levels in human cerebrospinal fluid (CSF) from parkinsonian patients and control patients devoid of neurological diseases. beta 2-MG contents in CSF of the control group and the parkinsonian group were 1.81 +/- 0.11 micrograms/ml CSF and 0.63 +/- 0.09 microgram/ml CSF, respectively. Thus, beta 2-MG content in CSF was reduced in parkinsonian patients to less than 35% of the control value (P less than 0.005). We had previously reported that the activity and content of dopamine beta-hydroxylase (DBH) were decreased in CSF from parkinsonian patients. A significant positive correlation (r = 0.87) was observed between the beta 2-MG content and DBH activity for CSF from 45 patients. These results suggest a probable link between an immunological change and the changes in catecholaminergic neurons in Parkinson's disease.

Restricted tissue distribution of Mlsa determinants. Stimulation of Mlsa-reactive T cells by B cells but not by dendritic cells or macrophages

Evidence was sought on the tissue distribution of Mlsa determinants, a class of cell-associated non-H-2 alloantigens that is highly immunogenic for unprimed T cells. Whereas normal CD4+ T cells and an Mlsa-reactive T hybridoma gave strong responses to Mlsa-positive stimulator populations containing Ig+ B cells, anti-Mlsa responses to B-depleted stimulators were almost undetectable. The B-depleted stimulators tested included Thy-1- spleen cells from mu-suppressed mice (mice treated with anti-mu antibody from birth) and J11d- preparations of spleen dendritic cells (DC) and peritoneal macrophages (M phi) from normal mice. Each of these populations was strongly immunogenic for allo-H-2-reactive T cells. The failure to detect Mlsa determinants on Ig- APC, i.e., M phi and DC, suggests that Mlsa determinants are not typical H-2-associated peptides. The data are more compatible with a model in which Mlsa determinants represent (or form part of) an integral cell membrane molecule expressed largely, and perhaps exclusively, on B cells. T cells might recognize these molecules only in native form, "processed" Mlsa determinants being nonimmunogenic. Consistent with this possibility, no evidence was found that Mlsa-negative B cells could absorb Mlsa determinants from Mlsa-positive B cells in a chimeric environment.

Histocompatibility antigen changes associated with pink-eyed dilute (p) mutations

The tight linkage between the H-4 histocompatibility locus and the pink-eyed dilute (p) locus raises the possibility that a single gene is responsible for both a histocompatibility antigen and coat color phenotype. To examine this possibility, we have investigated the effects of a spontaneous coat color mutation, pink-eyed unstable (pun), which occurred at the p locus in the C57BL/6J inbred strain, on histocompatibility antigen phenotype. Skin grafts were transplanted from two independently maintained B6-pun substrains to coisogenic, wild-type C57BL/6 recipients; graft rejection uniformly commenced at 6-7 weeks but did not culminate in complete graft destruction as observed in other cases of "crisis" rejection. Neither the onset of rejection time nor the intensity of rejection could be accelerated by introducing new H-2 haplotypes into the wild-type recipients. These results suggested that the pun allele was associated with a histocompatibility antigen not shared with C57BL/6. The pun allele is characterized by a relatively high frequency of reversion to wild-type. Therefore, skin grafts from B6-pun donors were transplanted to homozygous, revertant (+/+) recipients which were subline-matched with the donors; these grafts underwent crisis rejection with the same time of onset of rejection as observed with C57BL/6 recipients. These observations indicate that a new histocompatibility antigen is associated with the pun mutation and is lost upon reversion to wild type; this association is the first demonstration of a link between histocompatibility and coat color phenotypes.

SV40 T-antigen is a histocompatibility antigen of SV40-transgenic mice

Although the extensive family of non-H-2 histocompatibility (H) antigens provides a formidable barrier to transplantation, the origin of their encoding genes are unknown. Recent studies have demonstrated both the linkage between H genes and retroviral sequences and the ability of integrated Moloney-murine leukemia virus to encode what is operationally defined as a non-H-2 H antigen. The experiments described in this communication reveal that skin grafts from an SV40 T-antigen transgenic C57BL/6 mouse strain are rejected by coisogenic C57BL/6 recipients with a median survival time of 49 days, which is comparable to those of many previously defined non-H-2 H antigens. The specificity of this response for SV40 T-antigen was demonstrated by the identification of SV40 T-antigen-specific cytolytic T lymphocytes and antibodies in multiply-grafted recipients. Although these cytolytic T lymphocytes could detect SV40 T-antigen on syngeneic SV40-transformed fibroblasts, they neither could be stimulated by splenic lymphocytes from T-antigen transgenics nor could they lyse lymphoblast targets from T-antigen transgenics. These observations suggest a limited tissue distribution of SV40 T-antigen in these transgenics. These results confirm the role of viral genes in the determination of non-H-2 histocompatibility antigens by the strict criteria that such antigens stimulate (1) tissue graft rejection and (2) generation of cytolytic T lymphocytes. Furthermore, they suggest that the SV40 enhancer and promoter region can target expression of SV-40 T-antigen to skin cells of transgenic animals.

Thymocyte clones from 14-day mouse embryos. I. State of T cell receptor genes, surface markers, and growth requirements

We have established in culture 13 clones from the thymus of a 14-d B10.BR mouse embryo and characterized 8 of them. All eight FT clones have the TCR-gamma and -beta genes in germline configuration. They express mRNA for the gamma, but not for the beta nor the alpha genes. All eight FT clones are Thy-1+, Ly-1+, LFA-1+, Pgp-1+, H-2K+, and T3-. Three phenotypes could be distinguished on the basis of Lyt-2, L3T4, and IL-2-R expression: Lyt-2+, L3T4-, IL-2-R+ (I); Lyt-2+, L3T4-, IL-2-R- (II); and Lyt-2+, L3T4+, IL-2-R+ (III) cells. All eight clones grow in rIL-4 and six clones also proliferate in rIL-2. Antibodies specific for IL-2-R inhibit their response to rIL-2 but not to rIL-4. The eight FT clones synthesize mRNA for IL-4 after stimulation in vitro and none of them exhibit cytolytic activity or helper function for B lymphocytes. We conclude that the FT clones are at a very early stage of T cell development, that the expression of Lyt-2 and L3T4 surface molecules can precede that of the antigen receptor, and that the same fetal thymocyte can use both IL-4 and IL-2 as growth factor.

Expression of the W6/32 HLA epitope by cells of rat, mouse, human and other species: critical dependence on the interaction of specific MHC heavy chains with human or bovine beta 2-microglobulin

The HLA class I epitope W6/32 is conformationally dependent on both heavy chain and beta 2-microglobulin (beta 2M). Previously, the W6/32 epitope has been detected in humans and other primates as well as from bovine sources. Two controversial reports suggest the W6/32 epitope is constitutively expressed by either normal or transformed murine cells expressing the Db allele. Here we show that the appearance of the W6/32 epitope in murine cells results from the association of either the Db or Kd gene products with either bovine or human beta 2M. We use congenic mouse strains and hybrid H-2 class I genes between Db and Kb to map the W6/32 epitope to particular amino acid residues in the alpha 2 domain. Subsequently, we show that beta 2M exchange is not confined to murine or human cells in vitro but can be detected after beta 2M injection into a mouse. The data presented suggests that beta 2M exchange takes place at the cell surface under physiological conditions and indicates that MHC class I heavy chains are in an equilibrium between the bound and unbound form of beta 2M.

Endogenous retroviruses lead to the expression of a histocompatibility antigen detectable by skin graft rejection

Mov mouse strains differ from their respective, coisogenic partner strains by the embryonic, germ-line introduction of Moloney murine leukemia virus genomes. The possibility that retroviral insertions into the mouse genome resulted in gain or loss mutations at non-H-2 histocompatibility loci was investigated by reciprocal skin grafting between Mov mice and mice from coisogenic, background strains. Two B6-derived and eight 129-derived Mov strains were analyzed. B6 mice rejected skin from the viremic Mov-3 and Mov-14 strains, indicating that these mice had new histocompatibility antigens. No rejections were observed with reciprocal skin grafts exchanged between mice of the 129 background strain and 129-derived Mov strains, one of which (Mov-9) is viremic. To investigate the potential viral origin of the new histocompatibility antigen in Mov-14, lymphocytes from B6 mice primed in vivo with Mov-14 cells or skin were restimulated in vitro with Mov-14 spleen cells and with two retroviral-induced B6 lymphomas, MBL-2 and RBL-5. All three cell types stimulated cytotoxic lymphocytes that lysed Mov-14 Con A lymphoblasts, MBL-2 and RBL-5. The same cytotoxic lymphocytes lysed only lymphoblasts from the viremic Mov-9 strain when tested on cells from 129 and 129 Mov mice. Thus the insertion and expression of exogenous Moloney murine leukemia virus results in the appearance of a new histocompatibility antigen as defined by its stimulation of skin-graft rejection and cytotoxic effector T-cell generation. The non-H-2 histocompatibility antigen identified in this study has been designated H-43 and is encoded by genes mapping to different loci in different Mov strains. These observations suggest that at least a subgroup of non-H-2 histocompatibility antigens is encoded by endogenous retroviruses; the implications of these results for understanding the origin and the identity of non-H-2 histocompatibility antigens are discussed.