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This Perspectives article recounts the isolation and sequencing of the first human histocompatibility gene (HLA) in 1980-1981. At the time, general knowledge of the molecules of the immune system was already fairly extensive, and gene rearrangements in the immunoglobulin complex (discovered in 1976) had generated much excitement: HLA was quite obviously the next frontier. The author was able to use a homologous murine H-2 cDNA to identify putative human HLA genomic clones in a [lambda]-phage library and thus to isolate and sequence the first human histocompatibility gene. This personal account relates the steps that led to this result, describes the highly competitive international environment, and highlights the role of location, connections, and sheer luck in such an achievement. It also puts this work in perspective with a short description of the current knowledge of histocompatibility genes and, finally, presents some reflections on the meaning of 'discovery.'

CD4 T cells recognized posttranslationally modified peptides of the protein hen egg-white lysozyme (HEL), consisting of nitration of tyrosines and modifications of tryptophans in the T cell contact residues of the peptides. T cells were directed against modifications of a chemically dominant HEL peptide as well as a minor HEL peptide, bound to the class II histocompatibility molecule I-[A.sup.k]. The modified peptides were generated in vivo after immunization with native HEL molecules or were generated ex vivo by peroxynitrite treatment of HEL. Moreover, antigen-presenting cells (APC), either macrophages or dendritic cells activated in culture or in vivo, generated the modified HEL epitopes that stimulated the T cells. In transgenic mice expressing HEL, the T cells to the modified epitopes escaped negative selection and were found, albeit fewer in number than in normal mice. Infection with Listeria monocytogenes of the transgenic HEL mice generated APC containing the modifications. T cells to modified epitopes induced by activation of APC may be a component of antimicrobial immunity and autoimmune reactions. histocompatability molecules | nitrotyrosine | posttranslational modification

The amount of genetic variation for a class II gene in the major histocompatibility complex has been studied in the Mexican wolf, an endangered species, and related canids. It is thought to be part of the most important genetic basis for pathogen resistance in vertebrates. For Mexican wolves five different alleles were found. One of the Mexican wolf alleles was found in dogs and the allele found in grey and red wolves is found in dogs.

Tumor necrosis factor (TNF) biology and the major histocompatibility complex in humans are discussed relative to linkage, with the TNF (ital) gene within the MHC gene cluster, that can make interpretation of studies in animal models difficult. TNF seems to have a significant role in promotion of inflammation, likely in a mode identified from TNF (ital) gene-targeted mice.

The bare lymphocyte syndrome (BLS), a rare severe combined immunodeficiency that is autosomal recessive, is discussed in relation to molecular clues about major histocompatibility complex (MHC) class II genes and their transcriptional regulation. Complementation group A cells have defects in the class II transactivator (CIITA), deficiencies in the complementation groups B,C, and E exist, and CIITA and the regulatory-factor X (RFX) complex are integral parts of MHC class II expression.

Distant relatives of major histocompatibility complex (MHC) class I molecules, human MICA and MICB, function as stress-induced antigens that are broadly recognized by intestinal epithelial [Gamma][Delta] T cells. They may thus play a central role in the immune surveillance of damaged, infected, or otherwise stressed intestinal epithelial cells. However, the generality of this system in evolution and the mode of recognition of MICA and MICB are undefined. Analysis of cDNA sequences from various primate species defined translation products that are homologous to MICA and MICB. All of the MIC polypeptides have common characteristics, although they are extraordinarily diverse. The most notable alterations are several deletions and frequent amino acid substitutions in the putative [Alpha]-helical regions of the [[Alpha].sub.1][[Alpha].sub.2] domains. However, the primate MIC molecules were expressed on the surfaces of normal and transfected cells. Moreover, despite their sharing of relatively few identical amino acids in potentially accessible regions of their [[Alpha].sub.1][[Alpha].sub.2] domains, they were recognized by diverse human intestinal epithelial [Gamma][Delta] T cells that are restricted by MICA and MICB. Thus, MIC molecules represent a family of MHC proteins that are structurally diverse yet appear to be functionally conserved. The promiscuous mode of [Gamma][Delta] T cell recognition of these antigens may be explained by their sharing of a single conserved interaction site.

HIV Tat, a transactivator of viral transcription, represses transcription of major histocompatibility (MHC) class I genes. Repression depends exclusively on the C-terminal domain of Tat, although the mechanism of this repression has not been known. We now show that repression results from the interaction of Tat with the TAFII250 component of the general transcription factor, TFIID. The C-terminal domain of Tat binds to a site on TAFII250 that overlaps the histone acetyl transferase domain, inhibiting [TAF.sub.II]250 histone acetyl transferase activity. Furthermore, promoters repressed by Tat, including the MHC class I promoter, are dependent on [TAF.sub.II]250 whereas those that are not repressed by Tat, such as SV40 and MuLV promoters, are independent of functional [TAF.sub.II]250. Thus, Tat repression of MHC class I transcription would be one mechanism by which HIV avoids immune surveillance.

Human autoimmune diseases are thought to develop through a complex combination of genetic and environmental factors. Genome-wide linkage searches of autoimmune and inflammatory/immune disorders have identified a large number of non-major histocompatibility complex loci that collectively contribute to disease susceptibility. A comparison was made of the linkage results from 23 published autoimmune or immune-mediated disease genome-wide scans. Human diseases included multiple sclerosis, Crohn's disease, familial psoriasis, asthma, and type-I diabetes (IDDM). Experimental animal disease studies included murine experimental autoimmune encephalomyelitis, rat inflammatory arthritis, rat and murine IDDM, histamine sensitization, immunity to exogenous antigens, and murine lupus (systemic lupus erythematosus; SLE). A majority ([approximately equal to]65%) of the human positive linkages map nonrandomly into 18 distinct clusters. Overlapping of susceptibility loci occurs between different human immune diseases and by comparing conserved regions with experimental autoimmune/immune disease models. This nonrandom clustering supports a hypothesis that, in some cases, clinically distinct autoimmune diseases may be controlled by a common set of susceptibility genes.

We report here the genomic sequence of the centromeric portion of HLA class I, extending 424,015 bp from tumor necrosis factor [Alpha] to a newly identified gene [approximately equal to]20 kb telomeric of Otf-3. As a source of DNA, we used cosmids centromeric of HLA-B that had been mapped previously with conventional restriction digestion and fingerprinting and previously characterized yeast artificial chromosomes subcloned into cosmids and mapped with multiple complete digest methodologies. The data presented provide a description of the gene content of centromeric HLA class I including new data on intron, promoter and flanking sequences of previously described genes, and a description of putative new genes that remain to be characterized beyond the structural information uncovered. A complete accounting of the repeat structure including abundant di-, tri-, and tetranucleotide microsatellite loci yielded access to precisely localized mapping tools for the major histocompatibility complex. Comparative analysis of a highly polymorphic region between HLA-B and -C was carried out by sequencing over 40 kb of overlapping sequence from two haplotypes. The levels of variation observed were much higher than those seen in other regions of the genome and indeed were higher than those observed between allelic HLA class I loci.

Mouse studies, and those of some other vertebrates, have shown that mate choice decisions may be based on individual genotype at the major histocompatibility complex (MHC). That would make sense, given the importance of immunocompetence in some sexual selection theories. Genetic background, sex, and early life experience can be factors in mating preference and both strength and direction of MHC-based mating can vary.

The experiments presented in this report were designed to specifically examine the role of CD4-major histocompatibility complex (MHC) class II interactions during T cell development in vivo. We have generated transgenic mice expressing class II molecules that cannot interact with CD4 but that are otherwise competent to present peptides to the T cell receptor. MHC class II expression was reconstituted in A[Beta] gene knock-out mice by injection of a transgenic construct encoding either the wild-type I-A[[Beta].sup.b] protein or a construct encoding a mutation designed to specifically disrupt binding to the CD4 molecule. We demonstrate that the mutation, EA137 and VA142 in the [Beta]2 domain of I-[A.sup.b], is sufficient to disrupt CD4-MHC class II interactions in vivo. Furthermore, we show that this interaction is critical for the efficient selection of a complete repertoire of mature CD[4.sup.+] T helper cells as evidenced by drastically reduced numbers of conventional CD[4.sup.+] T cells in animals expressing the EA137/VA142 mutant I-[A.sup.b] and by the failure to positively select the transgenic AND T cell receptor on the mutated I-[A.sup.b]. These results underscore the importance of the CD4-class II interaction in the development of mature peripheral CD[4.sup.+] T cells.

The genotypic proportions for major histocompatibility complex loci, HLA-A and HLA-B, of progeny in families in 23 South Amerindian tribes in which segregation for homozygotes and heterozygotes could occur are examined. Overall, there is a large deficiency of homozygotes compared with Mendelian expectations (for HLA.A, 114 observed and 155.50 expected and for HLA-B 110 observed and 144.75 expected), consistent with strong balancing selection favoring heterozygotes. There is no evidence that these deficiencies were associated with particular alleles or with the age of the individuals sampled. When these families were divided into four mating types, there was strong selection against homozygotes, averaging 0.462 for three of the mating types over the two loci. For the other mating type in which the female parent is homozygous and shares one allele with the heterozygous male parent, there was no evidence of selection against homozygotes. A theoretical model incorporating these findings surprisingly does not result in a stable polymorphism for two alleles but does result in an excess of heterozygotes and a minimum fitness at intermediate allele frequencies. However, for more than two alleles, balancing selection does occur and the model approaches the qualities of the symmetrical heterozygote advantage model as the number of alleles increases.

A challenge for subunit vaccines whose goal is to elicit [CD8.sup.+] cytotoxic T lymphocytes (CTLs) is to deliver the antigen to the cytosol of the living cell, where it can be processed for presentation by major histocompatibility complex (MHC) class I molecules. Several bacterial toxins have evolved to efficiently deliver catalytic protein moieties to the cytosol of eukaryotic cells. Anthrax lethal toxin consists of two distinct proteins that combine to form the active toxin. Protective antigen (PA) binds to cells and is instrumental in delivering lethal factor (LF) to the cell cytosol. To test whether the lethal factor protein could be exploited for delivery of exogenous proteins to the MHC class I processing pathway, we constructed a genetic fusion between the amino-terminal 254 aa of LF and the gp120 portion of the HIV-1 envelope protein. Cells treated with this fusion protein (LF254-gp120) in the presence of PA effectively processed gp120 and presented an epitope recognized by HIV-1 gp120 V3-specific CTL. In contrast, when cells were treated with the LF254-gp120 fusion protein and a mutant PA protein defective for translocation, the cells were not able to present the epitope and were not lysed by the specific CTL. The entry into the cytosol and dependence on the classical cytosolic MHC class I pathway were confirmed by showing that antigen presentation by PA + LF254-gp120 was blocked by the proteasome inhibitor lactacystin. These data demonstrate the ability of the LF amino-terminal fragment to deliver antigens to the MHC class I pathway and provide the basis for the development of novel T cell vaccines.

By combining two previously generated null mutations, [Ii.sup.[circle]] and [M.sup.[circle]], we produced mice lacking the invariant chain and H-2M complexes, both required for normal cell-surface expression of major histocompatibility complex class II molecules loaded with the usual diverse array of peptides. As expected, the maturation and transport of class II molecules, their expression at the cell surface, and their capacity to present antigens were quite similar for cells from [Ii.sup.[circle]] [M.sup.[circle]] double-mutant mice and from animals carrying just the [Ii.sup.[circle]] mutation. More surprising were certain features of the CD[4.sup.+] T cell repertoire selected in [Ii.sup.[circle]][M.sup.[circle]] mice: many fewer cells were selected than in [Ii.sup.+][M.sup.[circle]] animals, and these had been purged of self-reactive specificities, unlike their counterparts in [Ii.sup.+][M.sup.[circle]] animals. These findings suggest (i) that the peptides carried by class II molecules on stromal cells lacking H-2M complexes may almost all derive from invariant chain and (ii) that H-2M complexes edit the peptide array displayed on thymic stromal cells in the absence of invariant chain, showing that it can edit, in vivo, peptides other than CLIP.

CIITA is a positive regulator of class II major histocompatibility complex gene transcription that has been found to be defective in one of the five complementation groups of class II major histocompatibility complex-negative cell lines. Its N-terminal region is capable of activating transcription from a reporter gene when fused to a DNA binding domain. We have investigated the mechanism of transactivation mediated by the CIITA activation domain by studying its role in the process of transcription initiation and elongation. Specifically the altered specificity TBP (TATA box binding protein) assay has been used to analyze the response of the CIITA activation domain to mutations in TBP known to disrupt its interaction with its associated general factors. Transactivation by CIITA was extremely sensitive to a mutation in TBP that in yeast is known to abolish VP16-mediated transcription but leaves basal transcription unaffected. A TBP mutant defective in interaction with TBP-associated factor [TAF.sub.[Pi]]250 also failed to mediate transactivation through the CIITA activation domain. Certain interactions between TBP and general factors that are specifically required for acidic activation domains were also required for CIITA-mediated transactivation to reach its full potential. Finally, like VP16, CIITA was able to stimulate elongation of transcription. Overall the mechanism of transactivation by the human B-cell-specific CIITA is very similar to that mediated by the herpes virus transactivator VP16 in the ways that have been tested.

The human cytomegalovirus (HCMV) early glycoprotein products of the US11 and US2 open reading frames cause increased turnover of major histocompatibility complex (MHC) class I heavy chains. Since US2 is homologous to another HCMV gene (US3), we hypothesized that the US3 gene product also may affect MHC class I expression. In cells constitutively expressing the HCMV US3 gene, MHC class I heavy chains formed a stable complex with [[Beta].sub.2]-microglobulin. However, maturation of the N-linked glycan of MHC class I heavy chains was impaired in US3+ cells. The glycoprotein product of US3 (gpUS3) occurs mostly in a high-mannose form and coimmunoprecipitates with [[Beta].sub.2]-microglobulin associated class I heavy chains. Mature class I molecules were detected at steady state on the surface of US3 + cells, as in control cells. Substantial perinuclear accumulation of heavy chains was observed in US3+ cells. The data suggest that gpUS3 impairs egress of MHC class I heavy chains from the endoplasmic reticulum.

Recent advances in DNA-based human leukocyte antigen (HLA) typing may reveal alternative forms of the genes at the HLA loci, which may aid understanding of HLA matching. HLA is any of the four major genetic markers that are used to determine the level of tissue compatibility between potential bone marrow donors and recipients. Highly compatible tissues decrease the risk that the recipient's immune system will attack the marrow. Standard HLA typing tests cannot distinguish all of the alternative forms of the genes at the HLA class I and class II loci and they have a relatively high error rate. As a result, the biological appearance of HLA in unrelated donors and recipients may be identical, although the DNA is mismatched. Polymerase chain reaction (PCR) tests are a method to copy DNA for analysis. The 'reverse blot' PCR method can identify alternative forms of genes at the HLA class I and class II loci and is suitable for clinical laboratory use.

Experimental studies reveal the incapability of interferon-gamma (IFN-gamma) to alter the peptidase activity of purified human multicatalytic proteases (MCP). The aminopeptide associated with lymphoblast MCPs is absent, confirming this theory. The synthesis of peptides is affected by IFN-gamma through a potent activator of MCP.

INTRODUCTION The ability of the immune systems of higher eukaryotes to specifically recognize and respond to most foreign proteins is generally dependent on the activation of a subclass of lymphocytes [...]

The tenascin-X (TN-X) and tenascin-C (TN-C) are reciprocally distributed in the skin and tissues of the digestive system. The TN-x MRNA in the skeletal nd heart muscles undergoes heparin binding and encodes a 40 fibronectin type III with a molecular size of 500 kD. The TN-X gene is located in the histocompatibility complex (MHC) class III region.

Growth dependence of mature CD4 cells, containing the class I-restricted F5 T-cells antigen receptor, on the expression of a CD8 transgene characterized by thymic specificity suggests the involvement of a probabilistic element during the growth of class I major histocomptability complex-restricted cells. Specificity of thymocyte-expressed T-cell antigen receptor determines the selection of either a CD4 or a CD8 lineage. A common derivation expressing both CD4 and CD8 promotes the growth of CD4 helper T cells and CD8 cytotoxic cells.

The hypothesis that the unique evolutionary patterns observed in the b locus of the rabbit immunoglobulin light chain constant region is the result of over dominance-type selection was evaluated by using population genetic data. An excess of heterozygotes of 10% of the b locus is revealed by an analysis of allele correlations in natural populations. The distribution of gene diversity among localities and areas was found to be homogeneous with the patterns in the histocompatibility loci.

Chicken egg ovalbumin (Ova) attached to beads was presented with major histocompatibility complex (MHC) class I molecules by antigen presenting cells (APCs) up to 104-fold better than soluble Ova. This improved presentation was noticed with covalently or noncovalently linked Ova, and with beads of different compositions. A crucial indicator in the activity of conjugates was the bead size. A macrophage is the APC that caused this manner of presentation.

Laboratory studies on chimeras of the tunicate Botryllus schlosseri revealed the phenomenon of 'allogeneic resorption' or 'colony resorption,' the elimination of one partner in a chimera. A hypothesis outlining the genetic basis of the resorption phenomenon is presented here. It proposes that allogeneic resorption in Botryllus is controlled by a polymorphic, ladder-like, tri-level hierarchial system of histocompatibility loci, with codominantly expressed alleles. The relative state of homozygosity at these alleles within each level reflects the state of the hierarchy in the resorption phenomenon. The Fu/HC haplotype of the tunicates serves as the first level, whereas the other two levels are each controlled by specific resorption alleles (Re/HC) that operate only after a response has failed to occur at previous levels. Some morphologically expressed similarities to murine minor histocompatibility loci (Hh-1 and M1s) are discussed.

A modified form of Pseudomonas aeruginosa exotoxin A (PE) was described. The binding and translocating domains were fused to epitopes from influenza A matrix protein and nucleoprotein, respectively. These fusion proteins, processed by class I major histocompatibilty complex (MHC) class I-positive target cells, were capable of sensitizing target cells for lysis by peptide-specific cytotoxic T lymphocytes. Thus, fusion of peptide epitopes with PE provides a useful probe for studying MHC class I-restricted antigen processing.

Defects in promoters of the silent DQA2, DQB2 and DOB genes from the major histocompatibility complex class II region were mapped by placing the Z and X boxes of these genes in a synthetic DRA promoter. The conserved upstream sequences (CUS) confer B-cell-specific and gamma-interferon-inducible expression to the DRA gene. These CUS are implicated in the transcriptional defects of these silent genes.

The major histocompatibility complex class II-deficient mice were used to examine the role of indirect recognition in rejection of skin grafts. Rejection of the class II-deficient skin occurred rapidly on normal recipients and independent of CD4+ function. The results suggest that in the absence of donor class II antigens, indirect recognition is an effective pathway to initiate rapid graft rejection.

The interferon-regulated appearance of proteins on the cell surface was investigated. Cells derived from fibrosarcoma were subjected to mutagenesis, immunoselection, flow cytofluorometry, RNA analysis, cell fusions and band-shift assaying. Results indicate that the expression of major histocompatibility class II and invariant-chain genes in fibrosarcoma cells involve five different gene products.

The genetic polymorphism of one of the subunits of the large cystolic proteasome complex, Lmp-2 gene product, was investigated. Experiments involve the application on 12 inbred mouse strains of polymerase chain reaction, Southern blot analysis and cDNA sequencing. Results indicate that the Lmp-2 gene maintains an autoimmune disease susceptibility with the involvement of its allelic polymorphism with peptide selection.

Changes in early biochemical T-cell activation events and membrane phenomena due to T-cellreceptor antagonism are discussed. A nonstimulatory analogue of the antigenic peptide influenza hemagglutinin was used to characterize synthesized peptide samples. The non-interference of antagonistic peptides in the cellular events leading to stable T-cell conjugate formations and its inhibition of early biochemical events required for T-cell proliferation were demonstrated.

The variability of PSF1 and PSF2, which encode subunits of a transporter involved in antigen processing for presentation of peptide epitopes by major histocompatibility complex class I molecules, was investigated by single-strand conformation polymorphism analysis and DNA sequencing. Several amino acid variants were identified and examined for their association with ankylosing spondylitis, insulin-dependent diabetes mellitus and celiac disease.

Research has been conducted on vertebtrates' major histocompatibility complex. The authors have investigated the effect of balancing selection on this complex which defies neutrality predictions, and have determined that selection is not detectable in major histocompatibility complex datasets in every generation.

Research has been conducted on histocompatibility complex composed of tightly linked gene clusters, called dog leukocyte antigen region in dogs. The authors describe the characterization of different loci in dog leukocyte antigen region carried out via canine bacterial artificial chromosome library used for DNA sequencing.

Research has been conducted on major histocompatibility complex. The authors have investigated the role of pathogen presence and absence variation in genetic variation at multiallelic loci, and they describe the results.

High levels of allelic diversity and strong linkage disequilibrium are found in the major histocompatibility (MHC) system in humans and other vertebrates. This article proposes several descriptive statistics that quantify the extent and pattern of strong linkage disequilibrium between pairs of highly polymorphic loci. It also develops an approximate analytic theory incorporating the effects of balancing selection, mutation, recombination, and genetic drift at two closely linked loci and compares the theoretical predictions with published surveys of the MHC class II loci, DQA1 and DQB1, in humans and nonhuman primates. The descriptive statistics proposed include the fraction of complementary haplotypes (haplotypes with D' = 1), the fraction of excess haplotypes, and the numbers of alleles at each locus in complementary haplotypes with one or more alleles at the other locus. The model assumes the infinite alleles model of mutation and the symmetric overdominance model of selection. Analytic approximations in some cases are obtained in the strong selection, weak mutation (SSWM) limit introduced by J. Gillespie. The predictions of the approximate analysis are confirmed by simulation. Both the analytic theory and simulations show that relatively few haplotypes will be found when selection is strong and recombination is weak relative to genetic drift. The model can reproduce many of the observed patterns at DQA1 and DQB1 provided that the recombination rate is assumed to be very small.

Interferon-gamma (IFNgamma) on the other hand is a cytokine that activates macrophages and induces the killing of intercellular parasites such as Leishmania. Investigators looked at the immunologic processes that occur [...]

Genetic constitutions of the elderly, particularly the centenarians, are homogeneous due to the elimination of detrimental alleles and contribute to death and diseases. Angiotensin-converting enzymes and proteins such as apolipoprotein E, apolipoprotein B decrease in centenarians. Long life is associated with alleles of major histocompatibility. The Centre d'Etude du Polymorphisme Humaine, Paris, is conducting research on French centenarians.