Organization and evolution of D region class I genes in the mouse major histocompatibility complex

A BAC contig of approximately 400 kb contains the classical class I major histocompatibility complex (MHC) genes of cattle

A cattle BAC library derived from an MHC homozygous animal was screened for MHC class I genes. This revealed at least nine class I-related genes in a contig spanning approximately 400 kb, and several additional genes on other clones. The three classical class I genes expressed on this haplotype (A14) were shown to be distributed over a region at most 212 kb apart.

H-2D end confers dominant protection from IL-10-mediated acceleration of autoimmune diabetes in the nonobese diabetic mouse

BALB/c mice that express IL-10 as a transgene in their pancreatic beta cells (Ins-IL-10 mice) do not develop diabetes, even after crossing to nonobese diabetic (NOD) mice ((Ins-IL-10 x NOD)F(1) mice). However, backcross of F(1) mice to NOD mice (NOD.Ins-IL-10 mice) results in N2 and N3 generations that develop accelerated diabetes. In this study, we found that NOD.Ins-IL-10 mice that expressed BALB/c-derived MHC molecules (NOD.Ins-IL-10(H-2(g7/d)) mice) were protected from diabetes. This protection associated with peri-islet infiltration and preserved beta cell function. Moreover, expression of I-A(d) and I-E(d) MHC class II molecules of BALB/c origin was not responsible for protection, but NOD.Ins-IL-10 mice that expressed BALB/c MHC class I D(d) molecules (NOD.Ins-IL-10(H-2(g7/d)) mice) did not develop diabetes. To directly test the possibility of a protective role of H-2D(d) in the development of accelerated diabetes, we generated transgenic mice expressing D(d) under the control of the MHC class I promoter. We found that double transgenic NOD.Ins-IL-10-D(d) mice developed accelerated diabetes in a fashion similar to NOD.Ins-IL-10 mice that were D(d) negative. Microsatellite analysis of H-2D(d)-linked loci confirmed association between BALB/c-derived alleles and protection of NOD.Ins-IL-10(H-2(g7/d)) mice. These results suggest a control of H-2D(d)-linked gene(s) on IL-10-mediated acceleration of autoimmune diabetes and dominant protection of the D(d) region in NOD.Ins-IL-10 mice.

The mouse as a model for the effects of MHC genes on human disease

As mice are often used to model human major histocompatibility complex (MHC)-associated diseases, it is important to understand how their MHC regions differ at the DNA level. The sequencing of the mouse MHC (H2 region) has enabled a detailed map of this region to be assembled for comparison with the human MHC. Here, Richard Allcock and colleagues outline the similarities between the human and mouse MHC regions and discuss notable differences that might affect disease models.

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.

The Alloreactive T Cell Response Against the Class Ib Molecule H2-M3 Is Specific for High Affinity Peptides

MHC class Ib molecule H2-M3 presents N-formylated peptides to CD8+ CTLs. Endogenous formylated peptides can come from the N-terminus of each of the 13 proteins encoded by the mitochondrial genome. In peptide competition assays, two of these peptides bind with high affinity, six bind with intermediate affinity, three bind with low affinity, and two do not bind measurably. Alloreactive CTLs from M3-specific, mixed lymphocyte cultures responded strongly against the two peptides with high affinity for M3, occasionally to peptides with intermediate affinity, and not at all to the rest. Long term lines and CTL clones reacted with only the high affinity peptides, demonstrating that alloreactive CTLs depend on specific peptides and that peptide affinity for class I correlates with alloantigenicity.

Uncovering subdominant cytotoxic T-lymphocyte responses in lymphocytic choriomeningitis virus-infected BALB/c mice

The cytotoxic T-lymphocyte response against lymphocytic choriomeningitis virus (LCMV) in BALB/c mice is predominantly directed against a single, Ld-restricted epitope in the viral nucleoprotein (residues 118 to 126). To investigate whether any Kd/Dd-restricted responses were activated but did not expand during the primary response, we used a BALB/c mutant, BALB/c-H-2dm2, which does not express the Ld molecule. Splenocytes from LCMV-infected BALB/c mice were transferred into irradiated BALB/c-H-2dm2 mice and rechallenged with LCMV. Thus, they were exposed to an antigenic stimulus without the involvement of the immunodominant Ld-restricted epitope. In this adoptive transfer model, the donor splenocytes protected the recipient mice against chronic LCMV infection by mounting a potent Kd- and/or Dd-restricted secondary antiviral response. Analysis of a panel of Kd binding LCMV peptides revealed that residues 283 to 291 from the viral glycoprotein (GP(283-291)) comprise a major new epitope in the adoptive transfer model. Because the donor splenocytes were first activated during the primary infection in BALB/c mice, the GP(283-291) epitope is a subdominant epitope in BALB/c mice that becomes dominant after rechallenge in BALB/c-H-2dm2 mice. This study makes two points. First, it shows that subdominant CTL responses can be protective, and second, it provides a general experimental approach for uncovering subdominant CTL responses in vivo. This strategy can be used to identify subdominant T-cell responses in other systems.

In vivo administration of interleukin-2 protects susceptible mice from Theiler's virus persistence

In vivo administration of interleukin-2 (IL-2)-secreting tumor cells results in complete protection against persistent infection by Theiler's murine encephalomyelitis virus (TMEV) in susceptible DBA/2 mice. The IL-2-mediated protection was found to depend on the inoculum size as well as the timing of IL-2 administration. IL-2-treated and TMEV-infected mice displayed a three- to fourfold relative increase in virus-specific cytotoxic T-lymphocyte (CTL) precursors. Thus, we postulate that the persistence of TMEV infection in susceptible mice reflects limited numbers of relevant CTL precursors and their time course of induction and activation.

Two distinct populations of primary cytotoxic cells infiltrating into allografted tumor rejection sites: infiltration of macrophages cytotoxic against allografted tumor precedes that of multiple sets of cytotoxic T lymphocytes with distinct specificity to alloantigens

It has been reported that the rejection of tumor allografts is mainly mediated by cytotoxic T lymphocytes (CTLs). Here, we characterized the cytotoxic effector cells of C57BL/6 (B6; H-2b) mice infiltrating into the rejection site of the i.p. allografted Meth A fibrosarcoma (or P815 mastocytoma) cells of H-2d origin. Two types of cytotoxic cells (i.e., CD8+ CTLs and macrophages (M phi s)) were identified by flow cytometric fractionation of the infiltrates or by specific in vitro elimination of cells either with antibody (Ab)-coated beads or with an Ab-plus complement. Of particular interest, these effector cells showed distinct and unique target specificities. First, the CTLs were inactive against transplanted tumor (e.g., Meth A) cells, whereas they were cytotoxic against donor-related concanavalin A (Con A) blasts as well as CTLL-2 (H-2b) cells transfected with a class I gene of H-2d origin. A cold target competition assay suggested that the CTLs were composed of multiple sets of T cells, each of which specifically recognized different allo-antigens. Second, the M phi s lysed the allografted tumor cells but were inert toward the Con A blasts and the CTLL-2 transfectants. Unexpectedly, the infiltration of M phi s preceded the infiltration of CTLs by several days during the course of rejection. These results indicate that two distinct populations of unique cytotoxic cells (i.e., CTLs and M phi s) are induced in the allografted tumor rejection site, and that the infiltration of cytotoxic M phi s responsible for rejection precedes that of the CTLs cytotoxic against cells expressing donor-related allo-antigens.

A physical map of the Q region of B1O.P

The murine class I MHC Q region is part of a large complex multigene family whose members have various peptide binding functions. The structure of the Q region is complex, varying extensively in the b, d, k, and q haplotypes so far examined. To better understand the structural heterogeneity, we examined the Q region of B 10.P, a strain whose immunological characteristics are distinct from other haplotypes. A total of 89 cosmids were isolated from genomic DNA. The B 10.P Q region was found to contain seven genes in a 190-kb cluster linked to DP and two additional Q genes in a separate 55-kb cluster. The gene arrangement in this haplotype was unique and did not correspond to any other haplotype; this underscores the complexity of chromosomal structure in this region. In addition to the Q region clusters, Tla region was tentatively aligned in five clusters spanning approximately 300 kb. One 37-kb M region cosmid was also identified.

CD4+ T cells are essential in overcoming experimental murine measles encephalitis

Clinical observations and experimental animal models have stressed the importance of the cellular immune response in the recovery from measles virus infection. However, the relative contribution of different T-cell subsets to viral elimination is controversial. The aim of the present study was to define the components of the immune system which contribute to the control of measles virus infection. For this purpose the effect of in vivo depletion of CD4+ and/or CD8+ T lymphocytes in the murine model of experimental acute measles encephalitis was monitored with respect to disease manifestation, survival, neuropathological changes, virus elimination from brain, and antiviral antibody titre. In measles virus-resistant BALB/c mice removal of the CD8+ T-cell subset did not interfere with the clearance of virus from the brain. In contrast, depletion of CD4+ T cells rendered BALB/c mice susceptible to infection. Also, in measles virus-susceptible C3H mice CD4+ T cells played a role in recovery from measles infection, but seemed not to be as effective as CD4+ T cells from resistant BALB/c mice. The data indicate that CD4+ T cells are essential for protection against measles virus-infection of the central nervous system.

An intracisternal A-particle sequence codes for an antigen recognized by syngeneic cytolytic T lymphocytes on a mouse spontaneous leukemia

Cytolytic T lymphocyte (CTL) clones directed against spontaneous mouse leukemia LEC have been obtained. By transfecting a cosmid library into cells which were then tested for their ability to stimulate the CTL, we identified the gene coding for the antigen recognized by one of these CTL clones. It is the gag gene of an endogenous defective retrovirus that belongs to the intracisternal A particle (IAP) family. A gag-encoded nonapeptide presented by the H-2 Dk molecule caused recognition by the anti-LEC CTL clone. Southern blot and polymerase chain reaction analyses indicated that the expression of the antigen by the LEC tumor cell line resulted from the transposition of an IAP sequence into a new genomic location.

Metastasis of mouse T lymphoma cells is controlled by the level of major histocompatibility complex class I H-2Dk antigens

In vivo inoculation of a low metastatic BW 5147 derived T-cell lymphoma variant into syngeneic mice, had led to the generation of a highly metastatic variant. The shift towards a more metastatic phenotype is accompanied by an increase in major histocompatibility class I H-2Dk antigen expression. This suggests that H-2Dk antigens may control the metastatic potential of BW T lymphoma cells. Our present findings indicate that H-2Dk expression is directly correlated with the metastatic potential of BW cells. We have confirmed such correlation by specifically altering the level of H-2Dk expression by: 1) FACS analysis, 2) IFN-gamma treatment, 3) H-2Dk gene transfection. Cells sorted for low H-2Dk expression had a significantly reduced metastatic potential. Induction of H-2Dk expression on these cells by either IFN-gamma treatment or H-2Dk gene transfection concomitantly led to increased metastasis. We also assessed metastatic potential of BW cells in irradiated, immunocompromised recipients. Our results show that the immune system is implicated and we further tested which immune effectors are involved. In vivo depletion of natural killer (NK) and CD8+ T-cells revealed that the difference in metastatic potential of the H-2Dk variants relies upon an NK-dependent mechanism, whereas CD8+ T-cells are not implicated. Our observations suggest that highly metastatic cells, expressing a high level of H-2Dk antigens are more resistant to NK-cell-mediated cytotoxicity in vivo. We have confirmed our in vivo results by in vitro cytotoxicity assays using poly I:C induced NK and IL-2 activated LAK cells. We conclude that a NK-dependent mechanism accounts for the association between differential H-2Dk antigen expression and metastasis.

A second lineage of mammalian major histocompatibility complex class I genes

Major histocompatibility complex (MHC) class I genes typically encode polymorphic peptide-binding chains which are ubiquitously expressed and mediate the recognition of intracellular antigens by cytotoxic T cells. They constitute diverse gene families in different species and include the numerous so-called nonclassical genes in the mouse H-2 complex, of which some have been adapted to variously modified functions. We have identified a distinct family of five related sequences in the human MHC which are distantly homologous to class I chains. These MIC genes (MHC class I chain-related genes) evolved in parallel with the human class I genes and with those of most if not all mammalian orders. The MICA gene in this family is located near HLA-B and is by far the most divergent mammalian MHC class I gene known. It is further distinguished by its unusual exon-intron organization and preferential expression in fibroblasts and epithelial cells. However, the presence of diagnostic residues in the MICA amino acid sequence translated from cDNA suggests that the putative MICA chain folds similarly to typical class I chains and may have the capacity to bind peptide or other short ligands. These results define a second lineage of evolutionarily conserved MHC class I genes. This implies that MICA and possibly other members in this family have been selected for specialized functions that are either ancient or derived from those of typical MHC class I genes, in analogy to some of the nonclassical mouse H-2 genes.

P1 and cosmid clones define the organization of 280 kb of the mouse H-2 complex containing the Cps-1 and Hsp70 loci

A 280 kilobase (kb) contig was isolated from mouse genomic P1 and cosmid libraries, using as probes human cDNA and genomic DNA fragments that map in the interval between the second component of complement and tumor necrosis factor genes of the HLA complex. The clone contig demonstrates synteny of eleven mouse genes that are homologous to genes initially mapped within the human major histocompatibility complex. These include the mouse homologs of BAT2 (HLA-B-associated transcript 2) through BAT9 and also three HSP70-related genes. Five P1 clones form a contig of 240 kb that spans from BAT9 through BAT3. Twelve cosmid clones are arranged in three contigs that confirm most of the structure of the P1 contig and link the mouse BAT3 homolog to the BAT2 homolog approximately 15 kb farther telomeric. Polymorphic DNA markers within the cloned region were used to map the cleft palate susceptibility-1 (Cps-1) locus to the interval between Hsp70.1 and BAT6 (valyl-tRNA synthetase). This refines the location of the Cps-1 locus to a 45 kb region contained in the H2-124 P1 insert.

Hierarchy in the assembly of HLA-B27 and HLA-Cw3 molecules in transgenic mice

Cell surface expression of human class I molecules in transgenic mice is dependent upon the available pool of beta 2-microglobulin (beta 2m) and the affinity between mouse beta 2m and human class I molecules. HLA-B27 and HLA-Cw3 transgenes can be expressed in mouse strains of the H-2 haplotypes b, f, k, and s which encode two endogenous class I genes mapping to H-2K and H-2D. The human class I genes cannot be expressed on H-2d and H-2q haplotypes which encode three endogenous class I molecules (K,D,L). This suggests that there may be only enough mouse beta 2m molecules to support three class I molecules. When both the HLA-B27 and HLA-Cw3 genes are introduced into H-2b mice, only HLA-Cw3 reaches the cell surface. This suggests that HLA-Cw3 has a higher affinity than HLA-B27 for mouse beta 2m. The possible implications of our findings regarding the assembly, transport, and expression of class I MHC molecules in vivo are discussed.

The immunogenetics of bone marrow transplantation

It is now clear that it is not necessary to use an HLA genotypically identical donor to have a successful marrow transplant. However, it is equally clear that the likelihood of complications increases with each increment in histoincompatibility. The implication is that histocompatibility testing must be of the highest possible precision to choose the optimal donor, and to predict the risk of adverse alloreactivity. Most clinicians would seriously consider transplantation from a one locus-mismatched relative or an HLA-matched unrelated donor in virtually any situation in which transplantation from a matched sibling would be felt to be the standard of care. More thought would need to go into transplantation from a two or three locus-mismatched relative or a mismatched unrelated donor.

Distinct H-2 complex control of mortality, and immune responses to tuberculosis infection in virgin and BCG-vaccinated mice

We have studied the impact of distinct haplotypes and of different alleles at specific H-2 loci on: (i) the susceptibility to lethal form of experimental tuberculosis; (ii) the level of DTH to mycobacterial antigens; (iii) the efficacy of vaccination with bacille Calmette-Guérin (BCG); and (iv) the IgG production and T cell proliferative response to H37Rv antigens. On the basis of median survival time (MST) following primary inoculation with lethal dose of Mycobacterium tuberculosis, susceptibility to infection associated with I-Ab and Db alleles, host resistance associated with I-Ak and Dd alleles. Mice bearing a disease-resistant phenotype also developed a vigorous DTH response. Vaccination with BCG before H37Rv infection significantly prolonged the survival time of both resistant and susceptible animals, except in B10.M (H-2f) mice. The latter exhibited intermediate resistance to infection before but slight decrease in the MST following a high-dose BCG vaccination. Distinct H-2 regulation of susceptibility to lethal infection and of BCG vaccination efficacy was confirmed in another relatively resistant H-2f-bearing strain A.CA, in which mortality occurred more rapidly in vaccinated compared with primarily infected animals. The expression of the H-2f haplotype was associated with a low DTH response to tuberculin following vaccination and subsequent lethal infection. The lack of BCG protection against Myco, tuberculosis challenge in B10.M mice associated with the high titre of specific IgG. In addition, these mice exhibited a unique ability to respond to 65-kD antigen by both IgG synthesis and T cell proliferation.

HMT, encoded by H-2M3, is a neoclassical major histocompatibility class I antigen

H-2M3 encodes HMT, the major histocompatibility complex (MHC) class I heavy chain of the maternally transmitted antigen (Mta). Like classical MHC class I genes, the expression of M3 can be stimulated by gamma-interferon and its message can be detected from mid-gestational embryos (day 8) through adulthood. HMTb, a nonimmunogenic allelic form of HMT, differs from the common HMTa molecule by four amino acids, of which only two (residues 31 and 95) are located in the alpha 1 and alpha 2 domains that form the peptide-binding groove. Recognition of site-directed mutants by Mta-specific cytotoxic T lymphocytes was hardly affected by the substitution of Met for Val31 but was abolished by the substitution of Gln for Leu95, which is located in the beta-sheet floor of the peptide-binding groove. Thus a single amino acid difference is responsible for the immunological silence of HMTb.

Class I gene contraction within the HLA-A subregion of the human MHC

Individuals expressing either the HLA-A24 or the HLA-A23 histocompatibility antigens have been found to possess an HLA-A class I subregion approximately 50 kb smaller in size than those studied from individuals expressing other HLA-A haplotypes. This originally manifested itself as a haplotype-associated size variation in the NotI and MluI megabase fragments observed on pulsed-field electrophoresis gels after blotting and probing with HLA-A subregion-specific genomic probes. The contracted region falls between the HLA-A and the HLA-G class I genes and specifically includes the novel HLA-A-related pseudogene, HLA-H, as well as the adjacent deteriorated class I pseudogene, 7.0 p. The intactness of locus D6S128, defined by probe pMC6.7 located telomeric to the HLA-H gene, demonstrates that the distal rearrangement point falls within a 20-kb stretch of DNA separating HLA-H from pMC6.7. This extends a previous report regarding variation in class I gene number within the human major histocompatibility complex and precisely localizes the genomic residence of sequences that may define a recombination hot spot. Because the size variation maps to a recombinogenic area, its characterization may ultimately reveal important biological information relevant to the events that shaped the organization of the human HLA class I multigene family.

Temporal order of DNA replication in the H-2 major histocompatibility complex of the mouse

As an approach to mapping replicons in an extended chromosomal region, the temporal order of DNA replication was analyzed in the murine major histocompatibility gene complex (MHC). Replicating DNA from T-lymphoma and myelomonocyte cell lines was density labeled with bromodeoxyuridine and extracted from cells which had been fractionated into different stages of S phase by centrifugal elutriation. The replicating DNA from each fraction of S phase was separated from nonreplicating DNA on density gradients, blotted, and hybridized with 34 specific MHC probes. The earliest replication occurred in the vicinity of transcribed genes K, HAM1 and HAM2, RD, B144, D, L, T18, and T3. The temporal order of replication of groups of DNA segments suggests the location of five or six replicons within the H-2 complex, some of which appear to be either unidirectional or markedly asymmetric. The rates of replication through each of these apparent replicons appear to be similar. The TL region of the S49.1 T-lymphoma cells, which contains at least three transcribed genes, replicates earlier than the inactive TL region of WEHI-3 myelomonocytic cells. These results provide further evidence of a relationship between transcription and the initiation of DNA replication in mammalian cells. The mouse MHC examined in this study is the largest chromosomal region (> 2,000 kb) measured for timing of replication to date.

Temporal order of DNA replication in the H-2 major histocompatibility complex of the mouse

As an approach to mapping replicons in an extended chromosomal region, the temporal order of DNA replication was analyzed in the murine major histocompatibility gene complex (MHC). Replicating DNA from T-lymphoma and myelomonocyte cell lines was density labeled with bromodeoxyuridine and extracted from cells which had been fractionated into different stages of S phase by centrifugal elutriation. The replicating DNA from each fraction of S phase was separated from nonreplicating DNA on density gradients, blotted, and hybridized with 34 specific MHC probes. The earliest replication occurred in the vicinity of transcribed genes K, HAM1 and HAM2, RD, B144, D, L, T18, and T3. The temporal order of replication of groups of DNA segments suggests the location of five or six replicons within the H-2 complex, some of which appear to be either unidirectional or markedly asymmetric. The rates of replication through each of these apparent replicons appear to be similar. The TL region of the S49.1 T-lymphoma cells, which contains at least three transcribed genes, replicates earlier than the inactive TL region of WEHI-3 myelomonocytic cells. These results provide further evidence of a relationship between transcription and the initiation of DNA replication in mammalian cells. The mouse MHC examined in this study is the largest chromosomal region (> 2,000 kb) measured for timing of replication to date.

PFGE mapping and RFLP analysis of the S/D region of the mouse H-2 complex

We have constructed a long range restriction map of the S/D segment of the mouse H-2 complex by pulsed field gel electrophoresis and hybridization with mouse cDNA probes to Bf and Tnfa genes and human cDNA probes to BAT2, BAT3, BAT4, BAT5, and BAT6 genes which have recently been mapped to the human HLA complex between C2 and HLA-B. The distance between the mouse C2 and Tnfa genes was found to be approximately 350 kilobases. The position of the mouse Bat genes in this map were found to be comparable to the position of the BAT genes in the human HLA complex. A panel of recombinant mouse strains was also examined by restriction fragment analysis with probes detecting the Hsp70, Bat5, and Tnfa genes. The results indicate that recombination in this segment is not random. No recombinants were found with crossovers between the C2 and Hsp70 genes and only one recombinant was found with a crossover between Tnfa and H-2D. In contrast, the crossover sites of 16 recombinants were mapped between the Hsp70 and Tnfa genes. Seven of these recombinants were found to have crossovers between Hsp70 and Bat5 and three recombinants were found to have crossover sites between Bat5 and Tnfa.

Structural and functional analysis of three D/L-like class I molecules from H-2v: indications of an ancestral family of D/L genes

Three cDNA with D region gene features have been identified from the H- 2v haplotype. Provisionally, the sequences have been designated as D/Lv1, D/Lv2, and D/Lv3. The coding segments for the antigen binding domain (ABD) of all three D/Lv genes were engineered into a class I genomic expression vector and expressed in L cells. FACS analysis of the three D/Lv-Ld gene transfectants revealed that the D/Lv1 molecules were recognized by both monoclonal antibodies (mAbs) 141 and 142, and the D/Lv2 molecules were recognized by mAb 143. In addition to the D/Lv1 molecules, the mAb 141 also recognized the D/Lv3 molecules. Both the D/Lv1-Ld and D/Lv2-Ld transfectants were killed efficiently by H- 2Dv region-specific alloreactive CTL. The D/Lv3 gene is the first identified D region gene other than D and L that is transcribed abundantly in spleen and the D/Lv3 RNA is present as two alternatively spliced forms. Structural analysis of the D/Lv3 hybrid molecules showed that it was susceptible to proteolysis and thermolabile at 37 degrees C, suggesting D/Lv3 is a transcribed pseudogene. A parsimony tree analysis of three D/Lv sequences with a set of class I gene sequences revealed that the H-2v sequences clustered with D region genes. The presence of a third gene with D/L-like features in H-2v, yet structurally different from the known D/L alleles, raises the possibility that the current D/L genes evolved from a family of D/L- like genes, some of which are no longer represented among many of the mouse major histocompatibility complex haplotypes. The observation that D region alleles cluster into subgroups suggests that the alleles are not all related to each other by linear descent through a single locus. We propose that current alleles are derived from more than one ancestral locus in a manner similar to the origin of the gamma 2 a immunoglobulin constant region alleles.

Physical mapping of the MHC and grc by pulse field electrophoresis

The development of the physical map of the major histocompatibility complex of the rat was undertaken using pulse field gel electrophoresis of fragments of genomic DNA from the BIL/2 (grc+) and BIL/1 (grc-) strains obtained primarily from single and double digests with the enzymes Mlu I, Not I, and Sfi I and hybridized with a variety of mouse, rat, and human probes. Both strains are maintained by inbreeding the BIL heterozygote (forced heterozygosity; F31); hence, their differences lie almost entirely in the MHC-grc regions. The MHC-grc region was contained in five fragments of DNA comprising 3000-3200 kilobases (kb); thus, its size appears to be closer to that of the human MHC than to that of the mouse MHC. This distance may be an underestimate of the size of the entire region, however, because the cluster of class I loci in the RT1. A region could not be defined in detail in this study. The most striking difference between the BIL/2 strain, which has normal growth and reproductive characteristics, and the BIL/1 strain, which has growth and reproductive defects and an enhanced susceptibility to chemical carcinogens, is a deletion of approximately 70 kb in the latter strain. The studies on grc+ and grc- strains suggest that the phenotypic defects of the grc- strains may be due to the loss of genes that are normally present in this deleted region.

Suppression of H-2b-associated resistance to Friend erythroleukemia virus by a class I gene from the H-2d major histocompatibility complex haplotype

Mice homozygous for the H-2d haplotype at the major histocompatibility complex are markedly more susceptible to erythroleukemia induction by the Friend isolate of murine leukemia retrovirus (FV) than are congenic mice homozygous for the H-2b haplotype. The resistance conferred by the H-2b haplotype is recessive in this cross, since heterozygous F1 mice are as susceptible as parental strain H-2d homozygotes. However, H-2b-associated resistance is not an intrinsically recessive trait, since H-2b/H-2dm1 heterozygotes resemble H-2b homozygotes in their relative resistance to FV; the mutant H-2dm1 haplotype lacks the entire D region of the parental haplotype except for a single class I gene formed by the fusion of its terminal D-region genes to produce a class I gene differing from both parental genes, and thus this finding indicates that one or more D-region genes of the H-2d haplotype can actively suppress H-2b-associated resistance. Unlike H-2dm1, the mutant H-2dm2 haplotype, which retains only the class IDd gene in the D region of the H-2d haplotype, strongly suppresses resistance in H-2b/H-2dm2 heterozygotes, and the presence of Dd as a transgene significantly reduces the resistance of H-2b homozygotes. Since H-2b-associated resistance to FV appears to be due mainly to the capacity of Lb (also called Db), the only class I molecule encoded in the D region of the H-2b haplotype, to present viral epitopes for recognition by FV-specific cytotoxic T lymphocytes, suppression of resistance to FV by the Dd molecule implies that the presence of one class I molecule of the major histocompatibility complex can interfere with either the presentation of viral epitopes by another class I molecule or the generation of T cells that recognize viral epitopes so presented.

Murine infection by vesicular stomatitis virus: initial characterization of the H-2d system

BALB/c mice and congenic H-2Ld-deficient BALB/c-H-2dm2 (dm2) mice were experimentally infected intranasally with isolates of vesicular stomatitis virus (VSV). The survival of infected hosts, viral replication in lungs and brains, and histopathologic in the two mouse strains were compared. In both strains of mice, mortality occurred during the period 7 to 10 days postinfection. However, dm2 mice were relatively resistant to lethal infections. Viral replication occurred at low levels in the lungs of both strains and did not evoke significant pathologic changes. In contrast, viral replication in the brains was much greater; in the BALB/c strain, this was accompanied by more frequent and more severe pathologic changes. In general, mice surviving at day 10 had effectively cleared virus from central nervous system but not respiratory sites. Evidence is presented that viral replication occurs first in the nasal cavity and is transmitted both to the lungs and to the olfactory bulb where focal cytopathology occurs. Virus enters the ventricles, causing encephalitis; necrosis occurs around the ventricles and in the lumbosacral region of the spinal cord. Necrotic lesions were accompanied by mononuclear infiltration. Mice immunized with virus of the same serotype or with a vaccinia virus hybrid encoding the VSV glycoprotein were protected from lethal infection; in contrast, mice immunized with heterotypic virus were susceptible to challenge.

A physical linkage map of HLA-A, -G, -7.5p, and -F

The class I region of the human leukocyte antigen (HLA) complex includes genes encoding the classical transplantation antigens (HLA-A, -B, -C), at least three nonclassical class I genes (HLA-E, -F, and -G), and many class I pseudogenes (including HLA-7.5p). We have used probes from DNA within or flanking the HLA -A, -F, -G, and -7.5p genes to construct a physical linkage map that places the HLA-F, -G, and -7.5p loci in order with respect to HLA-A. The map was constructed using clamped homogeneous electric field pulsed-field gel electrophoresis. DNA was isolated from LCL 721 (A1:B8, A2:B5), a human Epstein-Barr virus-transformed lymphoblastoid cell line (LCL), and from two gamma-irradiation-induced mutants of LCL 721 lacking complementary class I haplotypes. The physical linkage data place HLA-G closest to HLA-A and place HLA-7.5p between HLA-G and HLA-F. The map constructed supports a maximum distance of 490 kilobases between HLA-A and HLA-F.

Transmembrane domain length variation in the evolution of major histocompatibility complex class I genes

The fifth exons of major histocompatibility complex (MHC) class I genes encode a transmembrane domain (TM) that is largely responsible for class I antigen cell-surface expression usually through conventional hydrophobic amino acid-membrane interactions or, less often, through phosphatidylinositol linkage. In this report we show that Peromyscus leucopus, a Cricetidae rodent, has MHC class I genes (Pele-A genes) encoding three distinct sizes of TMs. Increases in TM lengths were due to tandem duplications of sequences similar to human hypervariable minisatellite repeats and the lambda chi site. We discerned remnants of a similar duplication event in comparable rodent and primate MHC class I genes. Furthermore, several duplications and deletions appear to have occurred independently in H-2, RT1, Pele-A, and ChLA genes in near-identical positions. Accumulated data suggests that sequences in the fifth exon of MHC class I genes may, therefore, constitute a mutational or recombinational hot spot that is mediated by minisatellite- and chi-like sequences imbedded within the coding region. The MHC class I genes may thus have recruited "selfish" DNA in their evolution to encode cell surface proteins. Expression of Pele-A genes was examined by the polymerase chain reaction (PCR) using oligonucleotide primers specific for exon 4 and 5 sequences. The PCR product sizes indicated that genes encoding each TM domain length are ubiquitously transcribed.

A novel MHC class I-related molecule expressed on mouse thymic stroma cells and mature lymphocytes

A monoclonal antibody (mAb) TP-3 has been established by immunizing rats with the BALB/c mouse thymic epithelial cell line TEL-2. The TP-3 antigen is expressed on stroma cells of thymus, spleen, and lymph node in syngeneic BALB/c mice (H-2d). This antigen is also expressed at a low level on the cell surface of immature thymocytes, and at a high level on mature T and B cells. In allogeneic mice such as C57BL/6 (H-2b) or C3H (H-2k), no cells expressed the TP-3 antigen. Using H-2 congenic mice, reactivity with mAb TP-3 was found to map to a region of H-2DdLd or between Dd and Qa, suggesting that TP-3 is a major histocompatibility complex (MHC) class I antigen. However, immunoprecipitation analysis indicated that this antigen is not identical to the classical mouse class I molecules in terms of molecular size, antigenicity, and tissue distribution.

Mapping of the SLA complex of miniature swine: mapping of the SLA gene complex by pulsed field gel electrophoresis

The overall order of the regions of the swine major histocompatibility complex (MHC), the SLA complex, was determined by pulsed field gel electrophoresis (PFGE). It was found that the order of the regions is class II-class III-class I. A class I probe hybridized to a 420 kb Mlu I and a 420 kb Not I fragment as did a class III probe for C2. None of the class II probes hybridized to these fragments. Thus, linkage of class I to class III was shown. The class III C2, Bf, and C4 genes were found to residue in a 190 kb Not I fragment. Linkage of class III and class II genes was shown when both the class III C4 and the class II DR probes hybridized to the same 195 kb Sac II and 340 kb Not I fragments. The class I probe did not hybridize to these fragments. The order of the regions, class II-class III-class I, is similar to that of human MHC genes and may have been conserved in evolution so that coordinated expression of MHC genes could be achieved.

Major histocompatibility complex class I genes of Peromyscus leucopus

Class I genes of the Peromyscus leucopus major histocompatibility complex (MhcPele) were examined by Southern blot hybridization, genomic cloning, and DNA sequencing. At least three distinct subtypes of Pele class I genes were discerned, which we have designated Pele-A, B, and C. The nucleotide sequences of exon 5-containing regions (encoding the transmembrane domain) suggested that Pele-A genes are homologs of mouse H-2K, D, L, and Q genes and that Pele-B genes correspond to mouse Tla genes. The Pele-C genes appeared similar to mouse M1 genes. The number of unique genes in each subtype cloned from an individual P. leucopus were 20 for Pele-A, 13 for Pele-B, and 2 for Pele-C. Three genomic clones showed cross-hybridization to both Pele-A and Pele-B gene-specific probes. Six genomic clones remained unclassified as they did not cross-hybridize to exon 5-containing probes from Pele-A, B, or C genes. The homology between the transmembrane domains of Pele class I gene subtypes was found to be similar to that observed between the transmembrane domains of H-2 subtypes (or groups). Interspecific similarity of exon 5 was found to be 81%-88% between Pele class I genes and their H-2 counterparts.

Molecular evidence that the H-2D and H-2L genes arose by duplication. Differences between the evolution of the class I genes in mice and humans

To resolve issues regarding the evolution of D region class I MHC genes and their relationship to other class I-encoding regions of the mouse, as well as man, we characterized the class I genes from the Dq region of the B10.AKM mouse strain. The Dq region was selected because it was known to express multiple gene products, yet two of the products previously characterized have structural features in common with the Ld molecule. Since DNA hybridization data defined similarities between the Dd and Dq regions, we used low-copy genomic or oligonucleotide probes derived from the Dd region of BALB/c (H-2d) to screen a B10.AKM cosmid library. Cosmid clones containing Dq, D2q, D3q, D4q, Lq, and Q1q genes have been isolated and aligned with the corresponding genes of the BALB/c MHC, thus demonstrating a similar gene organization. The two classical transplantation genes, Dq and Lq were found to be strikingly similar to each other such that exons 1-3 of Dq and Lq, are approximately 97% homologous, and exons 4-8 are identical. Furthermore, the implied amino acid sequences of both Lq and Dq molecules show considerable homology to Ld, particularly in regions presumed to be involved in ligand binding. These comparisons suggest not only that the Dq and Lq genes arose from the duplication of an Ld-like progenitor, but also that there is a selective advantage for the maintenance of an Ld-like structure. In addition, the 5' portion of the D4q gene was sequenced and found to have a 13-bp deletion and a 4-bp insertion within the alpha 2 exon. These result in a frame shift that creates a premature termination codon and potential polyadenylation site, respectively. Thus, D4q does not encode a typical class I molecule. Sequence comparisons suggest that the D4q gene did not arise from a duplication event involving an Ld-like gene such as Dq and Lq. Interestingly, the D4q molecule, if produced, would have amino acid residues in common with K and/or Q molecules that differ from those observed in D/L molecules. These findings, in conjunction with hybridization data, provide evidence that the D2, D3, and D4 genes were derived from Q genes by an unequal crossover event. Additional hybridization data using low-copy D region probes suggest that several different D region gene organizations exist among mice of different haplotypes. These and other recent molecular studies provide multiple examples of expansion and contraction of the class I genes in the D region.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular analysis of two recombinant mouse strains with crossovers in the E alpha recombination hot spot

Recombination in the E alpha gene of the mouse major histocompatibility complex has been found to occur only in mice derived from crosses between strains with the k and p haplotypes. In the present paper the crossover sites of six additional strains were examined by RFLP analysis. These recombinant strains were derived from crosses between strains (B10.RPD1, B10.RPD2) with crossovers in the E alpha gene and B10.M (H-2f). Four have crossover sites between the E alpha gene and the S region. One recombinant (B10.RFD7) also crossed over within the E alpha gene and a second (B10.RPF1) crossed over within a segment located to the left of the E alpha gene. This study suggests that the DNA sequence responsible for recombination in the E alpha gene is also present in the B10.RPD1 and B10.RPD2 recombinant strains.

H-2 class I loci determine sensitivity to MCMV in macrophages and fibroblasts

Peritoneal (PM) and bone marrow-derived (BMM) macrophages and lung fibroblasts (LF) from inbred, intra-H-2 recombinant, H-2 mutant, and hybrid mice were infected with murine cytomegalovirus (MCMV) under centrifugal enhancement. At the concentration of virus employed, peritoneal macrophages from strains carrying Kd, Kb, Dd, Ks and/or Ds, Kq and/or Dq alleles could be infected to a level of 80%-100%, as assessed by viral antigen expression or loss of Fc receptors. Cells lacking these haplotypes and carrying Kk, Kj, Dk, Dj, or Db were resistant, yielding levels of infection below 20%. The background (non-H-2) and class II genotype and the S allele did not influence the proportions of cells infected. Furthermore, sensitivity was dominant in the F1 progeny of H-2b X H-2k and H-2d X H-2k crosses, and was not compromised by the bm1, bm3, bm10, or bm14 mutations in the alpha 1 or alpha 2 regions of Kb or Db. The proportions of cells able to release infectious virus were low, but paralleled the frequencies of viral antigen expression. The class I genotype also determined susceptibility to MCMV infection in BMM and LF, although up to 35% of H-2k BMM and 46% of H-2k LF could be infected. The findings are consistent with an association between K and D antigens and a cellular receptor for MCMV on all three cell types.

Comparison of exon 5 sequences from 35 class I genes of the BALB/c mouse

DNA sequences of the fifth exon, which encodes the transmembrane domain, were determined for the BALB/c mouse class I MHC genes and used to study the relationships between them. Based on nucleotide sequence similarity, the exon 5 sequences can be divided into seven groups. Although most members within each group are at least 80% similar to each other, comparison between groups reveals that the groups share little similarity. However, in spite of the extensive variation of the fifth exon sequences, analysis of their predicted amino acid translations reveals that only four class I gene fifth exons have frameshifts or stop codons that terminate their translation and prevent them from encoding a domain that is both hydrophobic and long enough to span a lipid bilayer. Exactly 27 of the remaining fifth exons could encode a domain that is similar to those of the transplantation antigens in that it consists of a proline-rich connecting peptide, a transmembrane segment, and a cytoplasmic portion with membrane-anchoring basic residues. The conservation of this motif in the majority of the fifth exon translations in spite of extensive variation suggests that selective pressure exists for these exons to maintain their ability to encode a functional transmembrane domain, raising the possibility that many of the nonclassical class I genes encode functionally important products.

Major histocompatibility complex class I genes in murine fibrosarcoma IC9 are down regulated at the level of the chromatin structure

The fibrosarcoma IC9 is deficient in the expression of the major histocompatibility complex class I genes Kb, Kk, and Dk and expresses only the Db molecule. Because class I deficiency may enable tumor cells to escape the immune response by cytotoxic T lymphocytes, we investigated why the class I genes are not expressed. Expression of the silent class I genes could not be induced, but all known DNA-binding factors specific for class I genes could be detected in nuclear extracts of IC9 cells. After cloning of the silent Kb gene from the IC9 cells and subsequent transfection of this cloned Kb gene into LTK- and IC9 cells, normal Kb antigens were expressed on the cell surface of both cell lines. Digestion of the chromatin of IC9 cells with micrococcal nuclease and DNase I showed a decreased nuclease sensitivity of the silent class I genes in comparison with active genes and the absence of DNase I hypersensitive sites in the promoter region of the silent Dk gene. These findings demonstrate that class I expression is turned off by a cis-acting regulatory mechanism at the level of the chromatin structure.

Organization of the AKR Qa region: structure of a divergent class I sequence, Q5k

We established the organization of the AKR Qa region and determined the sequence of the Q4 and Q5 genes. Restriction mapping and genomic Southern blot analysis revealed that the AKR strain codes for only three H-2K homologous genes in this region. The AKR Q5 gene is not homologous to the Q5 gene of the C57BL strain, but is presumably allelic to the Q5 gene isolated from Balb/c. The organization and structure of the AKR Qa family is virtually identical to the Qa genes of the C3H mouse. The AKR Q5 gene, in contrast to other H-2K homologous Qa region genes, codes for a typical transmembrane region, and upon transfection into BHK cells, a 1.6 kb Q5 transcript is detected.

NK sensitivity, H-2 expression and metastatic potential: analysis of H-2Dk gene transfected fibrosarcoma cells

We have used the 3-Methylcholanthrene induced T-10 fibrosarcoma tumour cell system (H-2b xH-2k)F1 to elucidate the possible correlation between metastatic potential, expression of individual H-2 antigens and susceptibility to NK cells. Transfection of the non-metastatic and NK sensitive IC9 cells (Db+, Dk-, Kb-, Kk-) with the H-2Dk gene, altered the metastatic phenotype of the parental cells, yet had no effect on the susceptibility of these tumour cells to lysis by NK and did not elicit a specific CTL response in syngeneic hosts. Variants of the metastatic and NK resistant IE7 clone (Db+, Dk+, Kb-, Kk-), lacking H-2Dk, were selected by treatment with monoclonal anti H-2Dk antibodies and complement. These variants were sensitive to NK and poorly or non metastatic. Retransfection of 'Dk' 'loss' variants with the H-2Dk gene, resulted in the isolation of several clones expressing a wide range of metastatic phenotypes but maintained sensitivity to NK. These results indicate that the H-2D region of the MHC and or closely linked genes may be involved in the complex interrelationship between target susceptibility to NK and metastasis.

Major histocompatibility complex class I genes in murine fibrosarcoma IC9 are down regulated at the level of the chromatin structure

The fibrosarcoma IC9 is deficient in the expression of the major histocompatibility complex class I genes Kb, Kk, and Dk and expresses only the Db molecule. Because class I deficiency may enable tumor cells to escape the immune response by cytotoxic T lymphocytes, we investigated why the class I genes are not expressed. Expression of the silent class I genes could not be induced, but all known DNA-binding factors specific for class I genes could be detected in nuclear extracts of IC9 cells. After cloning of the silent Kb gene from the IC9 cells and subsequent transfection of this cloned Kb gene into LTK- and IC9 cells, normal Kb antigens were expressed on the cell surface of both cell lines. Digestion of the chromatin of IC9 cells with micrococcal nuclease and DNase I showed a decreased nuclease sensitivity of the silent class I genes in comparison with active genes and the absence of DNase I hypersensitive sites in the promoter region of the silent Dk gene. These findings demonstrate that class I expression is turned off by a cis-acting regulatory mechanism at the level of the chromatin structure.

A monoclonal antibody recognizes a subset of the H-2Dd mouse major class I antigens

Binding studies and competition experiments have shown that a monoclonal antibody (mAb) named 28-8-6 recognizes only 5 to 10% of the cell surface Dd molecules. The molecules detected by 28-8-6 mAb appear to be genuine H-2Dd antigens on the basis of their MW and isolectric points. In addition, the detectability of the subset of cell surface Dd molecules by 28-8-6 does not depend on their degree of glycosylation nor on the presence of mouse beta-2-microglobulin. Several interpretations are discussed. mAb 28-8-6 might detect a particular conformation or a particular chemical derivatization of otherwise normal H-2Dd molecules. Also, because the epitope recognized by 28-8-6 lies close to the peptide binding site, it is possible that mAb 28-8-6 recognizes a subset of Dd molecules bearing a certain category of self peptides.

Analysis of D2d: a D-region class I gene

The mouse major histocompatibility complex is composed of several genes arranged into the K, D, Qa, and Tla regions. The D region of the BALB/c mouse includes genes D2d, D3d, and D4d, in addition to H-2Dd and H-2Ld. We have determined the DNA sequence of the D2d gene and compared it with the known sequences of several class I genes. The exon/intron structure of the D2d gene is similar to other class I genes. It also contains similar 5' regulatory elements. A frameshift occurs in exon seven, resulting in a gene product with a truncated cytoplasmic tail. To examine the surface expression of the D2d molecule, we generated an exon-shuffled construct containing the promoter and exons 1-3, encoding the signal peptide, alpha 1, and alpha 2 external domains of the D2d gene linked to exons 4-8, encoding the alpha 3, transmembrane and cytoplasmic domains, of the H-2Dd gene. The construct was transfected into mouse L cells, and a protein was detected at the cell surface by a monoclonal antibody (mAb) specific for the alpha 3 domain of H-2Dd, as well as by other class I-specific mAbs. Although D2d is expressed at low levels, it may be a functional class I gene that most probably evolved from a Qa region gene.