Genes of the major histocompatibility complex in mouse and man

Genetics of antigen processing and presentation

Immune response to disease requires coordinated expression of an army of molecules. The highly polymorphic MHC class I and class II molecules are key to control of specificity of antigen presentation. Processing of the antigen, to peptides or other moieties, requires other sets of molecules. For classical class I, this includes TAP peptide transporters, proteasome components and Tapasin, genes which are encoded within the MHC. Similarly, HLA-DO and -DM, which influence presentation by HLA class II molecules, are encoded in the MHC region. Analysis of MHC mutants, including point mutations and large deletions, has been central to understanding the roles of these genes. Mouse genetics has also played a major role. Many other genes have been identified including those controlling expression of HLA class I and class II at the transcriptional level. Another genetic approach that has provided insight has been the analysis of microorganisms, including viruses and bacteria that escape immune recognition by blocking these antigen processing and presentation pathways. Here, we provide a brief history of the genetic approaches, both traditional and modern, that have been used in the quest to understand antigen processing and presentation.

Enrichment of cells with TALEN-induced mutations using surrogate reporters

Targeted gene knockout using engineered nucleases such as transcription activator like-effector nucleases (TALENs) is a gold standard for investigating the functions of a gene of interest. Although most TALENs can cleave chromosomal DNA efficiently, the activities of designed TALENs are not always high enough to allow the efficient derivation of cells containing TALEN-driven mutations. Thus, simple methods to enrich cells containing TALEN-directed mutations would facilitate the use of TALENs. Here we describe the enrichment of such cells using surrogate episomal reporters coupled with flow cytometric sorting, magnetic separation, or hygromycin selection.

The neck as a preferred recipient site for vascularized composite allotransplantation in the mouse

BACKGROUND

The mouse is still considered the premier model in basic immunologic and transplant-related research. However, because of its much smaller size, the mouse has proven to be a technically difficult and physiologically fragile model from a surgical standpoint. That is why only a few studies currently use mouse models in vascularized composite allotransplantation. The purpose of this study therefore was to develop a reproducible and reliable surgical technique in the mouse for future vascularized composite allotransplantation studies.

METHODS

Forty DBA/2 (H2-D) hindlimb osteomyocutanous flaps were transplanted into the right cervical region of C57BL/6 (H2-D) mice using a nonsuture cuff technique. The donor iliac artery and femoral vein were mounted with polyimide cuffs (inner diameter, 0.404 mm; wall thickness, 0.025 mm) and subsequently anastomosed to the recipient common carotid artery and external jugular vein. Immunosuppressant drugs were used postoperatively.

RESULTS

The overall success rate was 85.0 percent (34 of 40). The mortality rate was 12.5 percent (five of 40); all deaths resulted from perioperative bleeding. Only one arterial insufficiency was encountered after transplantation. The operative time was approximately 2 hours. Indefinite allograft survival (>120 days) could be achieved using a specific immunosuppressant regimen.

CONCLUSIONS

This novel mouse model allows performing vascularized composite allotransplantation with very high success and survival rates. The advantages over conventional models are multifold. A high-flow common carotid artery keeps the anastomosis patent, and diastolic suction of the heart reduces the risk of venous stasis and thrombus formation. Less destruction because of the heterotopic positioning of the hindlimb graft further reduces the associated mortality and morbidity in this fragile model.

Magnetic separation and antibiotics selection enable enrichment of cells with ZFN/TALEN-induced mutations

The ability to enrich cells with targeted mutations greatly facilitates the process of using engineered nucleases, including zinc-finger nucleases and transcription activator-like effector nucleases, to construct such cells. We previously used surrogate reporters to enrich cells containing nuclease-induced mutations via flow cytometry. This method is, however, limited by the availability of flow cytometers. Furthermore, sorted cells occasionally fail to form colonies after exposure to a strong laser and hydrostatic pressure. Here we describe two different types of novel reporters that enable mutant cell enrichment without the use of flow cytometers. We designed reporters that express H-2K^k, a surface antigen, and the hygromycin resistance protein (Hygro^R), respectively, when insertions or deletions are generated at the target sequences by the activity of engineered nucleases. After cotransfection of these reporters and the engineered nuclease-encoding plasmids, H-2K^k- and Hygro^R-expressing cells were isolated using magnetic separation and hygromycin treatment, respectively. We found that mutant cells were drastically enriched in the isolated cells, suggesting that these two reporters enable efficient enrichment of mutants. We propose that these two reporters will greatly facilitate the use of engineered nucleases in a wider range of biomedical research.

Global major histocompatibility class II β (mh-IIβ)-polymorphism in Arctic charr Salvelinus alpinus

This study explored the use of the gene encoding the β subunit of the major histocompatibility (MH) receptor as a population marker in Arctic charr Salvelinus alpinus. The use of this polymorphic marker allowed differentiation of the S. alpinus lineages previously defined using mitochondrial DNA (mtDNA) but also allowed differentiation between the populations studied within those lineages. The majority of the variation observed here occurred prior to the last glaciation event. Nevertheless, all S. alpinus populations were differentiated using both MH Class II β (mh-IIβ) sequences and allelic frequencies. The fact that all the populations studied presented high rates of non-synonymous: synonymous substitutions and high levels of interpopulation variation, suggested mh-IIβ as an ideal marker to assess differentiation among S. alpinus populations in ways that may represent divergence both by genetic drift and natural adaptation to the local environment.

MHC evolution in three salmonid species: a comparison between class II alpha and beta genes

The genes of the major histocompatibility complex (MHC) are amongst the most variable in vertebrates and represent some of the best candidates to study processes of adaptive evolution. However, despite the number of studies available, most of the information on the structure and function of these genes come from studies in mammals and birds in which the MHC class I and II genes are tightly linked and class II alpha exhibits low variability in many cases. Teleost fishes are among the most primitive vertebrates with MHC and represent good organisms for the study of MHC evolution because their class I and class II loci are not physically linked, allowing for independent evolution of both classes of genes. We have compared the diversity and molecular mechanisms of evolution of classical MH class II alpha and class II beta loci in farm populations of three salmonid species: Oncorhynchus kisutch, Oncorhynchus mykiss and Salmo salar. We found single classical class II loci and high polymorphism at both class II alpha and beta genes in the three species. Mechanisms of evolution were common for both class II genes, with recombination and point mutation involved in generating diversity and positive selection acting on the peptide-binding residues. These results suggest that the maintenance of variability at the class IIalpha gene could be a mechanism to increase diversity in the MHC class II in salmonids in order to compensate for the expression of one single classical locus and to respond to a wider array of parasites.

Tentative chromosomal localization of the bovine major histocompatibility complex by in situ hybridization

A genetic region, most likely the major histocompatibility complex, was assigned to bands q13-23 of cattle chromosome 23 by in situ hybridization using a cloned DNA sequence of a class I gene of the pig major histocompatibility complex.

MH class IIalpha polymorphism in local and global adaptation of Arctic charr (Salvelinus alpinus L.)

Arctic charr, a highly plastic salmonid that inhabits the circumpolar region, colonized its current environment after the last glaciation. Recent colonization limits the capacity of many techniques to define and characterize constituent populations. As a novel approach, we used the major histocompatibility (MH) class IIalpha gene polymorphism as a marker that would characterize the genetic divergence of global Arctic charr populations caused by drift and by local adaptation to pathogens. We were able to detect significant isolation of all the lineages previously defined by mitochondrial DNA sequencing and also isolation of some populations within those groups. We found that most of the polymorphism of the class IIalpha gene was distributed globally, which indicates ancestral selection; however, in most cases, distinctive allele frequencies and specific haplotypes distinguished each population suggesting that recent selection has also occurred. Although all studied populations showed similar MH class IIalpha polymorphisms, we also found variation in which particular amino acid positions were polymorphic and which were constant in the different populations studied. This variation provides a greater adaptive capacity for the MH class IIalpha receptors in Arctic charr and is yet another illustration of the extraordinary plasticity of the species.

MHC Class I Antigens and Immune Surveillance in Transformed Cells

MHC class I antigens play a crucial role in the interaction of tumor cells with the host immune system, in particular, in the presentation of peptides as tumor-associated antigens to cytotoxic lymphocytes (CTLs) and in the regulation of cytolytic activity of natural killer (NK) cells. In this review we discuss the role of MHC class I antigens in the recognition and elimination of transformed cells and in the generation of tumor immune escape routes when MHC class I losses occur in tumors. The different altered MHC class I phenotypes and their distribution in different human tumors are the main topic of this review. In addition, molecular defects that underlie MHC alterations in transformed cells are also described in detail. Future research directions in this field are also discussed, including the laboratory analysis of tumor MHC class I-negative variants and the possible restoration of MHC class I expression.

Temporary assisting suspension suture technique for successful microvascular anastomosis of extremely small and thin walled vessels for mice transplantation surgery

Dissection and microsurgical anastomosis in small and thin-walled vessels is challenging. Temporary assisting suspension suture technique was developed to overcome those difficulties in establishing successful composite tissue allotransplantation in mice. The operations were performed in 12- to 16-week-old Balb/c mice weighing 25 to 30 grams as both donor and recipient animals. Extended vascularized groin cutaneous flaps based on the superficial epigastric vessels were used. A total of 10 groin cutaneous flaps were transplanted. Three temporary assisting suspension sutures of 11-0 nylon were placed at the 12-, 4-, and 8-o'clock positions to donor and recipient artery and vein before the anastomosis. This technique allowed atraumatic dissection of delicate and thin vessels, prevented vessel wall collapse, and facilitated adequate exposure of the lumen during placement of the permanent microvascular sutures. Thus, the microvascular anastomosis was performed in an unusual manner. The temporary assisting suspension sutures were removed just before the permanent suture was tied down. The mean operation time was 1 hour and 45 minutes with an ischemia time of 1 hour. Ninety-percent success in immediate and late-term patency rates was achieved, which was confirmed by transplant survival. This technique was proven to be useful for microvascular anastomosis in thin-walled vessels and is recommended.

MHC-congenic mice (C57BL/6J and B6-H-2K) show differences in speed but not accuracy in learning the Hebb-Williams Maze

We compared spatial learning and memory in male and female mice of two MHC-congenic strains (C57BL/6J and B6-H-2K) in two versions of the Hebb-Williams Maze. In the food-reward paradigm, males required fewer sessions to learn than females, but there were no strain differences in acquisition. There were no strain or sex differences in the number of errors during the test phase, but the B6-H-2K mice reached the goal box faster than the C57BL/6J mice. In the water-escape paradigm, the C57BL/6J mice required more sessions than the B6-H-2K mice during acquisition. There were no strain or sex differences in the number of errors or in the latency to swim to the goal box in the test phase of the water-escape task. There were no significant correlations between the number of sessions to learn the two mazes; the number of errors made or the latencies to reach the goal box in each maze. These results indicate that these two strains show differences in performance in the Hebb-Williams Maze, but do not differ in cognitive ability.

The mouse major histocompatibility complex: some assembly required

We have assembled a contig of 81 yeast artificial chromosome clones that spans 8 Mb and contains the entire major histocompatibility complex (Mhc) from mouse strain C57BL/6 (H2b), and we are in the process of assembling an Mhc contig of bacterial artificial chromosome (BAC) clones from strain 129 (H2bc), which differs from C57BL/6 in the H2-Q and H2-T regions. The current BAC contig extends from Tapasin to D17Leh89 with gaps in the class II, H2-Q, and distal H2-M regions. Only four BAC clones were required to link the class I genes of the H2-Q and H2-T regions, and no new class I gene was found in the previous gap. The proximal 1 Mb of the H2-M region has been analyzed in detail and is ready for sequencing; it includes 21 class I genes or fragments, at least 14 olfactory receptor-like genes, and a number of non-class I genes that clearly establish a conserved synteny with the class I regions of the human and rat Mhc.

An alternative promoter in the mouse major histocompatibility complex class II I-Abeta gene: implications for the origin of CpG islands

Nonmethylated CpG islands are generally located at the 5' ends of genes, but a CpG island in the mouse major histocompatibility complex class II I-Abeta gene is remote from the promoter and covers exon 2. We have found that this CpG island includes a novel intronic promoter that is active in embryonic and germ cells. The resulting transcript potentially encodes a severely truncated protein which would lack the signal peptide and external beta1 domains. The functional significance of the internal CpG island may be to facilitate gene conversion, thereby sustaining the high level of polymorphism seen at exon 2. Deletions of the I-Abeta CpG island promoter reduce transcription and frequently lead to methylation of the CpG island in a transgenic mouse assay. These and other results support the idea that all CpG islands arise at promoters that are active in early embryonic cells.

Two distinct forms of soluble MHC class I molecules synthesized by different mechanisms in normal rat cells in vitro

Rat soluble MHC class I synthesis was studied at both RNA and protein levels to determine whether multiple forms of soluble MHC class I molecules are produced by different mechanisms. RT-PCR and sequencing of MHC class I transcripts identified an alternatively spliced nonclassical MHC class I gene product, lacking both exon 5 and 6, in both spleen and liver. Immunoprecipitation and SDS-PAGE identified two distinct soluble MHC class I proteins in both splenocyte- and hepatocyte-culture supernatants. The 36Kd classical soluble MHC class I protein (RT1.Aa) was precipitated by both allele-specific (MN4.91.6, R3/13, R2/15S) and pan-reactive (OX18) mAbs. The 39Kd non-RT1.A soluble MHC class I protein was precipitated only by OX18. The production of soluble RT1.Aa was inhibited by a metalloproteinase inhibitor, but not by serine/thiol protease inhibitors. None of these protease inhibitors interfered with the soluble non-RT1.A production, suggesting that it might be derived from an alternatively spliced MHC class I transcript. The soluble non-RT1.A was always associated with beta2m. However, soluble RT1.Aa molecule was cleaved in beta2m-free form and was reassociated with beta2m in culture supernatants. Thus two soluble MHC class I molecules, classical (36Kd RT1.Aa) and nonclassical (the alternatively spliced transcript), were produced from rat cells. Alternative splicing led to the nonclassical soluble MHC class I synthesis. Proteolytic cleavage by metalloproteinase led to the classical soluble MHC class I synthesis.

Major histocompatibility complex class I expression in oligodendrocytes induces hypomyelination in transgenic mice

Increased expression of MHC Class I occurs in the central nervous system in association with demyelinating diseases such as multiple sclerosis and experimental allergic encephalomyelitis. To determine if MHC Class I expression by oligodendrocytes induces white matter pathology, the MHC Class I gene was expressed in transgenic mice under the control of the myelin basic protein (MBP) promoter. These mice display a neurological phenotype at 21 days-of-age. We examined these mice at 1,3, and 12 weeks-of-age. MHC Class I was detected in the brains and spinal cords of transgenic mice but not in control mice. Class I was located in oligodendrocyte perikarya but not in myelin sheaths. The central nervous system of these transgenic mice was hypomyelinated and contained hypertrophic microglia and astrocytes. These observations establish that Class I expression by oligodendrocytes delays normal myelination but does not cause inflammatory demyelination. This hypomyelinating animal model is of potential use in studying the interactions between immunologically active molecules and remyelination in disorders of myelin.

Dysmyelination in class I MHC transgenic mice

Why is it that oligodendrocytes do not normally express major histocompatibility complex (MHC) molecules? To examine the effect of aberrant MHC expression in oligodendrocytes, transgenic mice have been produced which expressed the class I MHC gene, H-2Kb, under direction of the MBP promoter [Turnley et al. (1991b) Nature, 353:566-569; Yoshioka et al. (1991) Mol. Cell. Biol., 11:5479-5486]. A proportion of these mice exhibited a shivering phenotype, with tonic seizures and early death. Oligodendrocyte function and viability was shown to be affected, resulting in severe dysmyelination of the CNS. Is this phenomenon of cell damage due to aberrant expression of MHC molecules restricted to oligodendrocytes, and could other, non-MHC molecules, when aberrantly expressed, result in similar cell damage? This paper discusses these questions and examines possible mechanisms for the oligodendrocyte damage and hypomyelination observed in these transgenic mice. Finally, the implications of aberrant MHC expression in oligodendrocytes for demyelinating diseases such as multiple sclerosis are discussed.

Targeted amplification of alternatively spliced transcripts of major histocompatibility complex class I heavy chain

The RPMI1788 cell line was found to produce soluble form of HLA class I molecules (sHLA) constitutively, due at least in part to an alternative splicing mechanism in which exon 5 of HLA class I heavy chain transcripts is deleted. Reverse transcription-polymerase chain reaction (RT-PCR) of cytoplasmic RNA of RPMI1788 cells using a pair of primers (A,B) complementary to the conserved sequences of HLA class I exon 4 and 6 yielded almost exclusively the full-length class I heavy chain cDNA. In order to amplify the alternatively spliced transcripts, primer C corresponding to the 5' boundary conserved region of exon 6 juxtaposed with three conserved nucleotides in 3' boundary region of exon 4 was synthesized. Using the primers A and C the spliced transcripts of RPMI1788 cells can be selectively or preferentially amplified by RT-PCR with three different DNA polymerases. Cloning and sequencing of the resulting cDNA confirmed that the spliced transcript lacks exon 5. The targeted amplification method may be useful and important for studies with respect to the regulation of class I sHLA expression and the mechanism by which alternative splicing of HLA class I heavy chain mRNA is induced.

Neuronal progenitors identified by their inability to express class I histocompatibility antigens in response to interferon-gamma

Interferon-gamma (IFN-gamma) can induce class I major histocompatibility complex (MHC) antigen (H-2) expression on virtually all neuroepithelial cells isolated from embryonic day 9 (E9) mice. However, a subpopulation of cells become refractory to H-2 induction (H-21-) by E10 and the percentage of H-2 noninducible cells increases during development. Cell sorting, by flow cytometry or magnetic bead immunoselection, has shown that H-21- cells give rise exclusively to neuronal cells, and by E12, the majority of the neuronal progenitors are found within this population. It has also been found that 98% of the H-21- also express the neuron-associated marker, A2B5. Cells of the glial cell lineage retain the ability to express class I antigens throughout development. From these studies, it is clear that the neuroepithelium contains cells committed to the neuronal cell lineage as early as E10 in the mouse.

Bioengineered soluble HLA-B7. Genesis, characterization, and occurrence of dimerization

A soluble, secreted form of HLA-B7 was engineered by replacing the exons encoding the transmembrane and cytoplasmic domains of the B7 gene with a CI. The modified gene, gsB7, transfected into J27.2 or C1R cell lines, produced a secreted protein, sB7, serologically recognized as B7. Size fractionation showed one species of sB7 at the approximately 55 kD expected for an sB7 alpha-chain-beta 2m heteroduplex, and another at approximately 120 kD which had the same constituent chains and was a dimer of the 55-kD species. Dimer formation appeared to be related to protein concentration but not to disulfide bridging. The sB7 heavy chain on SDS-PAGE showed a doublet at approximately 39 and approximately 42 kD; enzyme analysis indicated that the two bands differed only by a carboxyl terminal polypeptide. Analysis of gsB7 transfectants' mRNA by Northern blots and PCR revealed message fully spliced or with retained CI, accounting for the 39- and 42-kD bands, respectively, and apparently untranslated message with I3 retained. sB7 was not detectable on the surface of gsB7 transfectants by CTLs, nor did it inhibit those CTLs. Production of the sB7 protein provides a ready, consistent source of soluble class I antigen for further study, including test materials for tolerogenicity studies in animal models.

The presence of messenger RNA for HLA class I in human platelets and its capability for protein biosynthesis

In order to determine whether platelets contain specific messenger RNA encoding for HLA class I molecules, polymerase chain reaction (PCR) was performed with RNA from different platelet donors. Two amplified 300 bp and 279 bp cDNA fragments were obtained which encompassed sequences from 321 to 620 and from 795 to 1073. The 300 bp fragment encodes exon 2 and exon 3, the 279 bp encodes a portion of exon 4, exon 5, exon 6 and a portion of exon 7. A 300 bp nested PCR product from one donor, that encoded for the highly polymorphic region alpha 2, was cloned and sequenced. The resulting nucleotide sequences fitted to the expected sequence for HLA B*3801 of this donor. Sequence analysis of the 279 bp PCR product demonstrated the presence of exon 5 encoding for the 117 bp transmembrane domain. In addition, de novo protein biosynthesis was studied by radioimmunoprecipitation of HLA class I molecules from 35S-methionine metabolically labelled platelet lysates with a monoclonal antibody (mab) w6/32 specific for a monomorphic epitope on the heavy chain of HLA class I antigens. Analysis of the immunoprecipitates on SDS polyacrylamide gel electrophoresis showed a specific band with apparent molecular weight (M(r)) of 44 kD corresponding to integral membrane HLA protein. On the basis of these results, we conclude that platelets contain specific messenger RNA encoding for HLA class I molecules and have the capability to synthesize the integral HLA membrane protein.

Organization and structure of the H-2M4-M8 class I genes in the mouse major histocompatibility complex

We have cloned and characterized five new class I genes from the M region at the distal end of the H-2 complex of the BALB/c mouse. M4, M5, and M6 are clustered on two overlapping cosmids, and M7 and M8 are located on another cosmid together with the previously cloned M1 gene, to which they are most closely related. M4, M6, and M7 are full-length class I genes (exons 1 through 5 were identified) but with stop codons or frameshifts that mark them as pseudogenes, and only exons 4 and 5 remain of M8. M5 has complete open reading frames in exons 1 through 5 and intact splice signals; it has the potential to encode a divergent class I major histocompatibility molecule, but no transcripts were found. These genes provide probes for studying the evolution of class I genes in rodents and for the mapping and cloning of genes at the end of the distal inversion in t haplotype chromosomes.

Major histocompatibility complex genes have an increased brain expression after scrapie infection

We have examined the expression of the major histocompatibility complex (MHC) antigens and related genes in scrapie-infected hamster brain. Both the class I and the class II MHC genes as well as the class II-associated invariant chain were found to have an increased brain expression after scrapie infection. The increased expression of the class I complex was immunohistochemically localized primarily to neurons, though some astrocytes contained much smaller amounts of the class I complex. While there is no detectable immune response to scrapie infection, the possibility that increased MHC expression affords some defense against the scrapie agent is discussed.

Long-range chromosomal mapping of the carcinoembryonic antigen (CEA) gene family cluster

A long-range physical map of the carcinoembryonic antigen (CEA) gene family cluster, which is located on the long arm of chromosome 19, has been constructed. This was achieved by hybridization analysis of large DNA fragments separated by pulse-field gel electrophoresis and of DNA from human/rodent somatic cell hybrids, as well as the assembly of ordered sets of cosmids for this gene region into contigs. The different approaches yielded very similar results and indicate that the entire gene family is contained within a region located at position 19q13.1-q13.2 between the CYP2A and the D19S15/D19S8 markers. The physical linkage of nine genes belonging to the CEA subgroup and their location with respect to the pregnancy-specific glycoprotein (PSG) subgroup genes have been determined, and the latter are located closer to the telomere. From large groups of ordered cosmid clones, the identity of all known CEA subgroup genes has been confirmed either by hybridization using gene-specific probes or by DNA sequencing. These studies have identified a new member of the CEA subgroup (CGM8), which probably represents a pseudogene due to the existence of two stop codons, one in the leader and one in the N-terminal domain exons. The gene order and orientation, which were determined by hybridization with probes from the 5' and 3' regions of the genes, are as follows: cen/3'-CGM7-5'/3'-CGM2-5'/5'-CEA-3'/5'-NCA-3'/5'-CGM1- 3'/3'-BGP-5'/3'- CGM9-5'/3'-CGM6-5'/5'-CGM8-3'/PSGcluster/qter.

Role of the transmembrane and cytoplasmic domains of surface IgM in endocytosis and signal transduction

The cross-linking of membrane IgM (mIgM) triggers the activation and differentiation of B lymphocytes. One very rapid result of the cross-linking is the activation of phospholipase C, the subsequent mobilization of free calcium from internal stores and the activation of protein kinase C. This is followed by a redistribution of the receptor-ligand complexes to a small cap on the B cell surface, the first step in endocytosis and antigen processing. Cross-linking of major histocompatibility complex (MHC) class I neither stimulates the release of intracellular calcium nor does it induce capping and endocytosis of the cell surface receptors. In this study, we sought to determine the role of the two carboxyterminal domains of the mu heavy chain in signal transduction, capping and endocytosis of mIgM. We took advantage of the clear differences between MHC class I molecules and mIgM, replacing the transmembrane and cytoplasmic domains of mu by their MHC class I equivalents. Our results show that the hybrid heavy chain could still associate with light chains and assemble into a tetramer on the cell surface. However, cross-linking of the hybrid cell receptor produced neither release of calcium from internal stores, nor capping and endocytosis. These observations demonstrate that the two carboxy-terminal domains of mu are critical to both signal transduction and modulation of the mIgM-ligand complexes from the surface of B lymphocytes.

Adenovirus infection inhibits the phosphorylation of major histocompatibility complex class I proteins

Major histocompatibility complex (MHC) class I molecules act as peptide receptors to direct the recognition of foreign antigens by cytolytic T cells. The cell surface expression and trafficking of these peptide receptors is thought to be controlled by the conformation of the MHC molecule and possibly by the phosphorylation of the cytoplasmic portion of the heavy chain protein. It is of some interest that adenoviruses (Ads) have evolved proteins that interfere with the expression of MHC molecules. One of these proteins, called E3/19k, binds to newly synthesized MHC molecules in the rough endoplasmic reticulum (RER) and inhibits their trafficking to the cell surface. Here we show that during the infection of a human cell line with Ad2, the phosphorylation of the endogenous MHC molecules is inhibited. We also observe that the phosphorylation of the endogenous HLA molecules is grossly impaired in a human cell line transfected with the Ad2 EcoRI D fragment containing the E3/19k gene. We conclude that the E3/19k protein inhibits the phosphorylation of the MHC heavy chains and that this may be one of the important functions of this protein in infected cells. In addition, we show that a mutant of the E3/19k protein, which lacks an RER retention signal but which retains its ability to bind to HLA molecules, does not inhibit the phosphorylation of HLA molecules and that phosphorylated molecules are not Endo H sensitive. This suggests that HLA molecules are phosphorylated after leaving the medial-Golgi compartment, thus providing the most compelling evidence yet that HLA molecules are phosphorylated at or near the cell surface. Finally, to our knowledge, this is the first study under which the phosphorylation of MHC molecules is shown to be altered and may have some relevance for other pathogenic conditions.

Nucleotide sequence, polymorphism, and evolution of ovine MHC class II DQA genes

The nucleotide sequence of all exons and introns, excluding exon 1, of the ovine major histocompatibility complex (MhcOvar) genes analogous to the HLA-DQA1 and -DQA2 genes has been determined and the gene structure found to be similar to that reported for other species. The predicted amino acid sequences of the Ovar-DQA genes have been compared with the equivalent DQA genes in man, mouse, rat, rabbit, and cattle and used to determine the evolutionary relationships of the sheep class II genes to these other species. Northern blot analysis of sheep mRNA using exon specific probes for each of the two Ovar-DQA genes show that both genes are transcribed, whereas in humans there is no evidence that HLA-DQA2 is transcriptionally active. Restriction fragment length polymorphisms (RFLPs) have been used to define a polymorphic series of alleles in both Ovar-DQA genes and have indicated that the number of DQA genes is not constant in sheep as it is in humans, but varies with the haplotype.

Molecular comparisons of the beta 2-microglobulin-binding site in class I major-histocompatibility-complex alpha-chains and proteins of related sequences

beta 2-Microglobulin (beta 2m) binds non-covalently to the alpha 1, alpha 2 and alpha 3 domains of the alpha-chain of Class I major-histocompatibility-complex (MHC) molecules. On the basis of the crystal structures of human leucocyte antigens HLA-A2.1 and HLA-Aw68.1, we have used molecular-graphics analyses to define 44 contact points between 19 alpha-chain residues and 18 beta 2m residues. In 88 other alpha-chain sequences from the HLA-A, HLA-B, HLA-C, HLA-D, HLA-E, HLA-F and HLA-G locus products in man and the H-2, Qa and Tla loci in mouse, 37 contact sites were conserved to 90% or more, and in beta 2m sequences from seven other species 40% of contact sites were totally conserved. Four distinct regions form the contact points between the alpha-chain and beta 2m, one on each of the alpha 1 and alpha 2 domains and two on the alpha 3 domain. We have further studied the alpha-chain sequences of three non-MHC molecules, human CD1 and rat Fc receptor (FcRn), known to bind to beta 2m, and a third molecule, the putative product of the H301 (UL18) gene of human cytomegalovirus (CMV). CMV has been shown to bind beta 2m, and it has been postulated that the H301-gene product, which has sequence similarity to Class I HLA, is the protein responsible. These sequences exhibited much lower residue conservation with the MHC-linked group, although the alpha 3 domain was the most highly conserved, and gaps and insertions were required for optimal alignments with the 90 alpha-chain sequences. Of the 44 beta 2m-alpha-chain contacts defined for Class I HLA, 24 alpha-chain contact sites were conserved in CD1, 25 in FcRn and 17 in the H301-gene product. For CD1 and FcRn, the majority of the conserved beta 2m contacts were found in the alpha 2 domain and the major contact region in the alpha 3 domain. Together with the use of secondary-structure predictions, it was concluded that the binding of beta 2m in CD1 and FcRn was MHC-like at the alpha 3 domain, and probably also at the alpha 2 domain for FcRn, but non-MHC-like for the alpha 1 domain of both molecules and the alpha 2 domain of CD1. In the H301-gene product sequence, only the beta 2m contacts with the main region of the alpha 3 domain were noticeably conserved.(ABSTRACT TRUNCATED AT 400 WORDS)

Unexpected behavior of H2Kb mutant DNAs in denaturing gradient gel electrophoresis

Denaturing gradient gel electrophoresis (DGGE) is based upon the different melting behaviors of DNA molecules in a chemical denaturant gradient according to their sequences. This technique has recently become a widespread tool to detect mutations. The introduction of a GC-clamp enables the detection of most single base differences between two DNA molecules. As a test system we have applied the polymerase chain reaction (PCR) in combination with DGGE to detect a number of mutations in the mouse H2Kb DNA sequence. A wide variety of spontaneous in vivo mutations of this haplotype have been reported in the C57BL/6J mouse strain and are clustered in the alpha 1 and alpha 2 domains. The combination of PCR and DGGE revealed almost all base changes present in the H2Kb mutants used. However, most of the PCR products of these mutants showed melting behavior which is not easily predicted. We suggest that in addition to current simple theory, which considers that the migration of a DNA molecule in a denaturing gradient depends primarily on its initial melting behavior, additional factors such as secondary structure in partially melted molecules may play a role and can be used to detect mutations.

Structure of class II genes in wild mouse Mus saxicola: functional and evolutionary implications

Class II beta genes have been characterized from Mus saxicola, a wild mouse which diverged five millions years ago from the house mouse. The nucleotide sequences of the exons 2 and 3 of E beta 1, A beta 2 and E beta 2 genes have been determined in order to define the molecular mechanisms of interspecies variability. The E beta 1 and A beta 1 (J. X. She, personal communication) genes from Mus saxicola display extensive sequence variability in exon 2 when compared to those of the house mouse, in association with the variability of residues probably involved in antigen binding. On the other hand, most putative T cell contact residues from the I-E beta chain, and to a lesser extent from the I-A beta chain, were found conserved in mice. T cell contact residues from Mus saxicola I-A beta and I-E beta chains are identical to those of the b and q, and of the k haplotypes of the house mouse, respectively. Comparisons performed with A beta 2 and E beta 2 genes revealed that both are highly conserved and, in contrast to A beta 1 and E beta 1 genes, that a strong selective pressure for conservation occurs in the A beta 2 second exon. The different aspects of A beta 2 and E beta 2 genes evolution may correlate with the original function of their products. Comparisons of the intervening sequences revealed that the repeated motifs of the hotspot region present in the E beta 1b gene are also conserved in Mus saxicola. Recombinations may have occurred, in some cases in association with chi-like sequences.

Recombinational hotspot specific to female meiosis in the mouse major histocompatibility complex

The wm7 haplotype of the major histocompatibility complex (MHC), derived from the Japanese wild mouse Mus musculus molossinus, enhances recombination specific to female meiosis in the K/A beta interval of the MHC. We have mapped crossover points of fifteen independent recombinants from genetic crosses of the wm7 and laboratory haplotypes. Most of them were confined to a short segment of approximately 1 kilobase (kb) of DNA between the A beta 3 and A beta 2 genes, indicating the presence of a female-specific recombinational hotspot. Its location overlaps with a sex-independent hotspot previously identified in the Mus musculus castaneus CAS3 haplotype. We have cloned and sequenced DNA fragments surrounding the hotspot from the wm7 haplotype and the corresponding regions from the hotspot-negative B10.A and C57BL/10 strains. There is no significant difference between the sequences of these three strains, or between these and the published sequences of the CAS3 and C57BL/6 strains. However, a comparison of this A beta 3/A beta 2 hotspot with a previously characterized hotspot in the E beta gene revealed that they have a very similar molecular organization. Each hotspot consists of two elements, the consensus sequence of the mouse middle repetitive MT family and the tetrameric repeated sequences, which are separated by 1 kb of DNA.

Altered actin and immunoglobulin C mu expression in nitrogen mustard-resistant human Burkitt lymphoma cells

Raji-HN2 is a B cell lymphoma (Burkitt lymphoma) line that was made resistant to nitrogen mustard. The drug-resistant phenotype was accompanied by changes in gene expression. The expression of four unrelated genes was examined by Northern blot analysis. Raji-HN2 cells were found to contain about twice the number of actin mRNA found in Raji cells. Both cell lines were found to contain equivalent amounts of beta 2-microglobulin, c-myc oncogene, and immunoglobulin C mu mRNAs. The C mu mRNA was, however, larger in size in Raji-HN2 cells. Alterations in actin and C mu mRNAs in Raji-HN2 cells were not due to gene amplification or rearrangement because Southern blot analysis revealed no changes in the genomic organization of these genes. The increased actin mRNA content was correlated with an increased actin content of Raji-HN2 cells. The F-actin (stained with 7-nitrobenz-2-oxa-1,3-diazolylphallacidin) content of single cells was quantitated in a meridian interactive laser cytometer. Raji-HN2 cells contained about twice the amount of F-actin present in the parental Raji cells. Similar results were obtained when large populations, 10(6) cells each, were examined in a flow cytometer.

Secretion of genetically engineered human/mouse class I antigens

Two soluble, secreted forms of HLA-B7 were engineered by the creation of hybrid human/mouse molecules containing the polymorphic 5' region of the HLA-B7 gene and the secretory 3' region of the mouse Q10d gene. The hybrid, designated F1, is the first construct with only human extracytoplasmic domains, consisting of exons for the leader peptide and the three extracellular domains (alpha 1, alpha 2, alpha 3) of B7 spliced to the exons for the Q10d truncated transmembrane and 3' untranslated (3'UT) sequences. The second construct, designated C2, is similar but has the human alpha 3 replaced by the Q10 alpha 3 domain. Protein product from each construct was best demonstrated after gene transfection into the J27.2 cell line. In particular, secretion of the F1 product proves that the Q10 alpha 3 domain is not necessary for secretion of class I/Q10 hybrids. Moreover, the two soluble B7 forms, which differ only in their alpha 3 domain, are similarly recognized by monoclonal antibodies W6/32 (anti-HLA-ABC), BBM.1 (anti-human beta 2 microglobulin), and allo-B7-antibody, but differentially recognized by monoclonal antibody Q1/28 (anti-HLA class I heavy chain). Production of such soluble hybrid class I molecules in large amounts should allow critical structural and functional studies of these proteins.

The tissue distribution of Ia- and IgM-positive cells in adult and newborn miniature pigs

Distribution of Ia- and IgM-positive cells was compared in tissues of adult and newborn miniature pigs, using indirect immunoperoxidase and immunofluorescent techniques with monoclonal antibodies. The different distribution patterns were found mainly in adult jejunum and kidney. Both IgM- and Ia-staining were ascertained in the lamina propria between the Lieberkühn crypts and in the lymphoid follicles of the jejunum. Moreover, IgM-positive cells were demonstrated in the crypts while Ia-reaction was seen in the lamina propria of the villi. In the kidney, IgM-staining was limited to the glomeruli. On the contrary, a distinct Ia-reaction was found mainly in intertubular structures. Small differences in IgM- and Ia-positive cell distribution were also noted in the mesenteric lymph nodes and in the spleen. Developmental changes of the adult distribution patterns (chiefly that of IgM-positive cells) were found in all tissues studied at 2 days of age.

Splice of life: toward understanding genetic determinants of oral diseases

The introduction of recombinant DNA technology has led to a rapid advancement of our knowledge of genes and genomic structure. Such technology, applied to the human genome, has provided valuable information concerning the nature and possible treatment of inherited disorders throughout the human life span. A number of oral diseases can be attacked by use of molecular biological techniques in conjunction with genetic linkage analysis. It will be possible to identify carriers of inherited diseases, to utilize prenatal and antenatal diagnosis when appropriate, and to pursue studies on the mode of inheritance of specific oral diseases. Present and projected advances in this dimension of dental research provide the knowledge and strategies for approaching and solving a number of major problems as we continue to pave the way for improvements in the diagnosis, treatment, and prevention of many oral and craniofacial diseases. This position paper examines a few of the promising areas and suggests future goals toward establishing a knowledge of the genetic determinants for oral diseases.

Inherited immunodeficiency with a defect in a major histocompatibility complex class II promoter-binding protein differs in the chromatin structure of the HLA-DRA gene

A defect in a trans-regulatory factor which controls major histocompatibility complex class II gene expression is responsible for an inherited form of immunodeficiency with a lack of expression of human leukocyte antigen (HLA) class II antigens. We have recently described and cloned an HLA class II promoter DNA-binding protein, RF-X, present in normal B cells and absent in these class II-deficient regulatory mutants. Here we report that these in vitro results correlate with a specific change in the chromatin structure of the class II promoter: two prominent DNase I-hypersensitive sites were identified in the promoter of the HLA-DRA gene in normal B lymphocytes and found to be absent in the class II-deficient mutant cells. The same two prominent DNase I-hypersensitive sites were observed in normal fibroblastic cells induced by gamma interferon to express class II genes. Interestingly, they were also observed in the uninduced class II-negative fibroblastic cells, which have also been shown to have a normal RF-X binding pattern. We conclude that the two DNase I-hypersensitive sites in the HLA-DRA promoter reflect features in chromatin structure which correlate with the binding of the trans-acting factor RF-X and which are necessary but not sufficient for the expression of class II genes.

Inherited immunodeficiency with a defect in a major histocompatibility complex class II promoter-binding protein differs in the chromatin structure of the HLA-DRA gene

A defect in a trans-regulatory factor which controls major histocompatibility complex class II gene expression is responsible for an inherited form of immunodeficiency with a lack of expression of human leukocyte antigen (HLA) class II antigens. We have recently described and cloned an HLA class II promoter DNA-binding protein, RF-X, present in normal B cells and absent in these class II-deficient regulatory mutants. Here we report that these in vitro results correlate with a specific change in the chromatin structure of the class II promoter: two prominent DNase I-hypersensitive sites were identified in the promoter of the HLA-DRA gene in normal B lymphocytes and found to be absent in the class II-deficient mutant cells. The same two prominent DNase I-hypersensitive sites were observed in normal fibroblastic cells induced by gamma interferon to express class II genes. Interestingly, they were also observed in the uninduced class II-negative fibroblastic cells, which have also been shown to have a normal RF-X binding pattern. We conclude that the two DNase I-hypersensitive sites in the HLA-DRA promoter reflect features in chromatin structure which correlate with the binding of the trans-acting factor RF-X and which are necessary but not sufficient for the expression of class II genes.

Microrecombinations generate sequence diversity in the murine major histocompatibility complex: analysis of the Kbm3, Kbm4, Kbm10, and Kbm11 mutants

The mechanism that generates spontaneous mutants of the Kb histocompatibility gene was analyzed. Nucleotide sequence analysis of four mutant genes (Kbm3, Kbm4, Kbm10, and Kbm11) revealed that each mutant K gene contains clustered, multiple nucleotide substitutions. Hybridization analyses of parental B6 genomic DNA and cloned class I genes with mutant-specific oligonucleotide probes, followed by sequence analyses, have identified major histocompatibility complex class I genes in the K, D, and Tla regions (K1, Db, and T5, respectively) that contain the exact sequences as substituted into mutant Kb genes. These data provide evidence for the hypothesis that the mutant Kb genes are generated by a microrecombination (gene conversion) mechanism that results in the transfer of small DNA segments from class I genes of all four regions of the major histocompatibility complex (K, D, Qa, and Tla) to Kb. Many of the nucleotides substituted into the mutant Kb genes were identical to those found in other naturally occurring K alleles such as Kd. Thus, we propose that the accumulation of microrecombination products within the K genes of a mouse population is responsible for the high sequence diversity among H-2 alleles.