Orientation of loci in the major histocompatibility complex of the rat and its comparison to man and the mouse

Swine composite tissue allotransplant model for preclinical hand transplant studies

Our laboratory previously developed and used an orthotopic radial forelimb osteomyocutaneous flap in the pig as a preclinical composite tissue allograft (CTA) model. To ensure that it mimicked the clinical situation as closely as possible we developed this model taking many immunologic and reconstructive considerations into account. While our original pig CTA model was ideal for studying the methods of preventing skin, muscle, bone, vessel and nerve rejection, and systemic toxicity, it did not include specialized tissues/structures of a joint and digit. Therefore, we were unable to evaluate rejection of these specialized tissues and their functional properties. Recognizing the importance of assessing joint rejection and function in hand transplantation research we developed a new swine forelimb CTA model that included the animal's medial digit. The present study describes the anatomy and the transplantation technique used in this new preclinical CTA model. We transplanted a radial osteomyocutaneous flap that included the medial digit between two size- (17-21 kg) and age- (6-8-week) matched farm pigs. We removed the digit from the recipient pig's forelimb in continuity with a section of the radial bone and replaced it with the same structure transplanted from a donor pig. After transplantation, a full-length cast was placed on the recipient pig's operated limb and changes in flap color, temperature and the presence of edema were monitored continuously for 6 h, and then regularly at predetermined intervals over 4 days. No weight bearing restrictions were placed on the animal's operated limb. After 4 days, the animal was euthanized. Direct visual monitoring of the allograft during 4 days revealed it was viable with no signs of graft failure due to technical complications associated with the transplant procedure. Upon waking from anesthesia, the animal stood and wandered freely about its cage with no apparent difficulty. Based on the animal's high level of activity at this time, we concluded that the procedure caused it minimal morbidity. At 4 days after the operation, early signs of rejection (skin erythema and edema) were observed. By incorporating a digit into our original CTA pig forelimb model we have made it a better model for performing preclinical hand transplant studies. The added advantage of being able to assess methods of preventing rejection in the specialized joint/digital tissues (articular cartilage, digital flexor and extensor systems, the nail complex) and assess long-term function of these structures is important. The fact that the procedure does not cause major morbidity to the animal makes it possible to conduct long-term graft survival and functional studies.

Physical mapping of the E/C and grc regions of the rat major histocompatibility complex

Alignment of class I-hybridizing cosmids from an R21 (AlBlDlEugrc+) genomic DNA library gave two contigs: one [150 kilobases (kb)] encompassed the E/C region, or a large part thereof, and the other (110 kb) contained the grc region which has genes influencing resistance to chemical carcinogens (rcc), fertility (ft), and growth (dw-3). Amplification of gene sequences in the four cosmids in the E/C region using Eu-specific and LW2 (RT1.C)-specific primers showed that each cosmid contained both Eu-like and C-like genes. They are clearly different but closely associated, and they show some variation from the prototypic E (Eu) and C (LW2) genes, respectively. Comparison of DNA from grc+ and grc- strains of rats showed that the deletion in the grc- strains was approximately 50 kb, and that it was located on two of the three cosmids in the grc-region contig. The use of specific class I probes showed that the grc region contained tandemly duplicated RT1.O-RT1.N genes and that the RT.BM1 loci lay outside of the grc region. Neither contig reacted with probes specific for class II, TNFA, Hsp70, or RT1.M genes. The data presented here and the previous data in the literature (summarized in Gill et al. 1995) suggest that the gene order in the major histocompatibility complex (MHC) and MHC-linked region of the rat is: A-E/C-grc-M.

Multiple TL-like loci in the grc-G/C region of the rat

The grc-G/C region of the rat is homologous to the Q/TL region of the mouse, and deletions in this region are associated with fetal mortality, developmental defects, and decreased resistance to cancer. Several cosmids spanning approximately 45 kilobases of this region were analyzed for their class I loci, using a mouse general class I probe (pAG64c), grc-specific probes (pGRC1.4, pGRC1.7), and four probes derived from the TL-like locus RT1.N1. The results showed that TL-like genes other than RT1.N1 exist in the rat: a duplicated gene, RT1.N2, was identified, sequenced, and shown to be 99.3% similar to RT1.N1; and a third TL-like gene, RT1.N3, was isolated from a cDNA library, sequenced, and shown to be 92.8% similar to RT1.N1. These observations suggest that the rat TL-like loci are duplicated and that there is more than one cluster of these duplicated genes. The TL-like genes are transcribed predominantly in the thymus, except in grc- strains, and their level of transcription increases during fetal life and reaches its maximum at birth. Finally, a cosmid that appears to identify the end of the deletion in grc- strains was identified.

The gene map of the Norway rat (Rattus norvegicus) and comparative mapping with mouse and man

The current status of the rat gene map is presented. Mapping information is now available for a total of 214 loci and the number of mapped genes is increasing steadily. The corresponding number of loci quoted at HGM10 was 128. Genes have been assigned to 20 of the 22 chromosomes in the rat. Some aspects of comparative mapping with mouse and man are also discussed. It was found that there is a good correlation between the morphological homologies detectable in rat and mouse chromosomes, on the one hand, and homology at the gene level on the other. For 10 rat synteny groups all the genes so far mapped are syntenic also in the mouse. For the remaining rat synteny groups it appears that the majority of the genes will be syntenic on specific (homologous) mouse chromosomes, with only a few genes dispersed to other members of the mouse karyotype. Furthermore, the data indicate that mouse chromosome 1 genetically corresponds to two rat chromosomes, viz., 9 and 13, equalizing the difference in chromosome number between the two species. Further mappings will show whether the genetic homology will prove to be as extensive as these preliminary results indicate. As might be expected from evolutionary considerations, rat synteny groups are much more dispersed in the human genome. It is clear, however, that many groups of genes have remained syntenic during the period since man and rat shared a common ancestor. One further point was noted. In two cases groups of genes were syntenic in the mouse but dispersed to two chromosomes in rat and man, whereas in a third case a group of genes was syntenic in the rat but dispersed to two chromosomes in mouse and man. This finding argues in favor of the notion that the original gene groups were on separate ancestral chromosomes, which have fused in one rodent species but remained separate in the other and in man.

Biochemical characteristics and subcellular localizations of rat liver neuraminidase isozymes: a paradox resolved

A striking discrepancy in the abilities of two analytical approaches (fluorometric and electrophoretic) to detect the effect of a gene, Neu-2, on rat liver neuraminidase phenotypes led us to examine the biochemical and physical properties of the liver isozymes NEU-1 and NEU-2 that might be responsible for this difference. Cell fractionation via Percoll gradient centrifugation revealed NEU-1 activity almost exclusively in the lysosomal cell fraction, while NEU-2 was strictly cytosolic in distribution. The two isozymes were also found to differ in pH activity curves and optima (optima: 4.6-4.8 and 5.4-5.8 for NEU-1 and NEU-2, respectively) and in solubility characteristics (NEU-2 highly soluble; NEU-1 relatively insoluble but solubilized by freezing/thawing). Both isozymes were found to be freeze-thaw stable in crude, whole-cell extracts, but NEU-1 was destabilized in the enriched (partially purified) lysosomal subcellular fraction. Consideration of these properties relative to those described previously for unidentified cytosolic and membrane bound (lysosomal) rat liver neuraminidases (Tulsiani, D. R. P., and Carubelli, R., J. Biol. Chem. 245:1821, 1970) leads us to believe that NEU-2 also is destabilized by partial purification and that NEU-1 and NEU-2 have very different relative abundances within the cell. The biochemical and physical differences between NEU-1 and NEU-2 can account for the discrepant abilities of the fluorometric and electrophoretic approaches to detect the effects of Neu-2. Ways to increase the sensitivity of the fluorometric approach for quantitative assays of specific NEU-1 and NEU-2 activity are discussed.

Genetic linkage in the Norway rat

The present status of research on genetic linkage is reviewed. Where possible, the data are statistically combined to give consolidated estimates of the recombination value. Ten groups of linked genes have been determined. The first assignments of linkage groups to specific chromosomes have been facilitated by inter-species cell hybridisation.

Class I and class II restriction pattern polymorphisms associated with independently derived RT1 haplotypes in inbred rats

This communication reports the DNA level identification of class I and class II sequences associated with 20 RT1 haplotypes which have been assigned previously to eight RT1 groups. Sixteen to 22 bands in genomic blots hybridized with the mouse pH-2III class I cDNA probe. Only the three RT1k haplotypes associated with identical class I restriction fragment patterns. Differences in restriction bands between putatively identical RT1 haplotypes were either less than or equal to 6%, or greater than 50%, suggesting a relatively high level of recombination between serologically identified RT1.A genes and the majority of class I sequences. Restriction fragment patterns associated with three RT1u haplotypes differed by less than 6%. However, intra-RT1a, intra-RT1b, and intra-RT1l restriction fragment differences were between 50 and 64%. In specific cases, different RT1 haplotypes associated with identical class I restriction patterns, e.g., RT1m (MNR) and RT1d (MR); higher resolution confirmed the difference (two bands) between RT1m and RT1d. Results of hybridization with the human DC1 beta probe confirmed that the AVN RT1a and NSD RT1b haplotypes were generated by recombinations within the vicinity of the RT1.B:RT1.D regions. These results demonstrate that a previous classification of RT1 haplotypes was incomplete and did not include the majority of class I and class II sequences which distinguish RT1 haplotypes.

Analysis of neuraminidase isozyme phenotypes in mammalian tissues: an electrophoretic approach

A simple cellulose acetate electrophoretic method for visualizing mammalian neuraminidase isozymes has been developed. Application of the method with rat and mouse liver extracts reveals the presence of two distinct isozymes in each species. Each isozyme exhibits tremendous variation in activity between inbred strains. The two isozymes vary independently of one another suggesting that their activities are controlled by different genes. The neuraminidase phenotypes detected in these inbred strains via electrophoresis are consistent with published accounts of neuraminidase phenotypes determined fluorometrically in whole liver homogenates, but also indicate the presence of a second isozyme not perceived by this other procedure.

Evidence for extensive polymorphism of class I genes in the rat major histocompatibility complex (RT1)

The major histocompatibility complex of the rat (RT1) has been poorly characterized with respect to the number, linkage, and polymorphism of class I genes. To estimate the number of class I RT1 genes and the relative extent of their polymorphism, we performed Southern blot analysis with liver DNA from rat strains expressing eight RT1 haplotypes. After digestion with EcoRI and BamHI, the DNA was separated on agarose gels, blotted onto nitrocellulose, and hybridized with mouse H-2 cDNA probes, pH-2III and pH-2IIa. Ten to 20 EcoRI and 13 to 20 BamHI bands hybridized with pH-2III and pH-2IIa; restriction fragment length patterns were observed to be highly polymorphic. The restriction fragments associated with different RT1 haplotypes differed by 17-70%; this range is similar to the differences observed between mouse H-2 haplotypes. The same restriction fragment pattern was observed in DNA from three different rat strains sharing the same RT1 allele, confirming that the patterns were RT1-associated. Further, the RT1l and RT1lvl haplotypes, which differ at a single previously identified RT1-linked locus, were associated with EcoRI restriction pattern differences of 39-50%, confirming the supposition that RT1 class I genes identified by previous serological and T-cell-mediated assays have identified only a minority of the actual number of RT1-linked class I genes. In summary, the results reported in this communication demonstrate that the RT1 complex encompasses a large family of highly polymorphic class I genes similar to the H-2 and HL-A complexes of mouse and man.

Major histocompatibility complex (MHC)-linked genes affecting development

Genes affecting growth and development which are linked to the major histocompatibility complex have been found in the mouse (t-complex) and in the rat (growth and reproduction complex, grc), and there is some evidence that they also exist in humans. The genes of the t-complex have different effects depending upon the specific combinations involved: skeletal and fertility abnormalities, complete or partial embryonic mortality, high transmission ratios (segregation distortion) in males, high level of linkage disequilibrium with H-2, and suppression of recombination over the adjacent portion of the chromosome. The grc in the homozygous state causes small body size, sterility in the male and reduced fertility in the female, partial embryonic mortality, and a high level of linkage disequilibrium with RT1. It also interacts epistatically with the heterozygous Tal (tail anomaly lethal) gene to cause complete embryonic death. Mice carrying t-haplotypes and rats carrying the grc have an antigen in the male germ cells which cross-reacts very strongly (t-antigen). Suggestive evidence for such genes in humans comes from (1) studies on the relationship between skeletal defects and HLA haplotypes; (2) the association of specific HLA and complement haplotypes with a high transmission ratio in males, linkage disequilibrium among certain HLA and complement specificities and suppression of recombination in some MHC haplotypes; and (3) the lack of homozygotes in an isolated inbreeding population of desert nomads (Kel Kummer Tuaregs). In addition, immunogenetic studies on couples having chronic spontaneous abortions suggest that there is an unusually high incidence of homozygosity for the HLA-D/DR and HLA-A loci in these couples, and this finding is consistent with the presence of linked loci which behave like t or grc.

Immunochemical evidence for multiple class I antigens coded by the MHC of the rat (RT1) and their differential expression on red blood cells and lymphocytes

Five monoclonal antibodies reacting with class I MHC antigens were produced by fusing lymphocytes from WF (RT1u) rats immunized against DA (RT1a) rats with P3-X63-Ag8.653 myeloma cells. Sequential immunoprecipitation studies with the mAb and the WF anti-DA alloantiserum demonstrated the presence of four different class I molecules: all four molecules were reactive with the alloantiserum; three of them contained the determinant for mAb 155; two of the latter three molecules shared the determinants for mAb 3, 56 and 60, and one of these two molecules also contained the determinant for mAb 118. The four molecules could be isolated from the antigen preparation by sequential immunodepletion first with 118, next with 3, then with 115 and finally with the alloantiserum or by sequential absorption with affinity columns of Sepharose 4B coupled to the antibodies. The three antigens which were sequentially isolated with the mAb 118, 3, and 155, respectively, were analysed by SDS-PAGE after digestion with Staphylococcus aureus V8 protease, and they showed differences in peptide patterns. The relative amounts of the antigens expressed on red blood cells and on lymphocytes were different based on the results of sequential isolation and indirect cellular radioimmunoassay: the antigen which reacted with both mAb 3 (and 56 or 60) and 155 was the major class I antigen on red blood cells, and the antigen which reacted with mAb 118, 3 (and 56 or 60) and 155 was the major class I antigen on lymphocytes.

Biochemical characterization of Ia antigens encoded by the RT1.B and RT1.D loci in the rat MHC

Ia antigens in rats are genetically associated with typical MHC-linked immune response (Ir) genes. One rat Ir gene (IR-GLT) has recently been mapped to the RT1.D locus in a rat MHC recombinant, WRC. We have studied the expression of Ia antigenic determinants in WRC and its parental strains BN and WRA using a panel of monoclonal antibodies. Our results suggest that the inheritance of IR-GLT corresponds with the inheritance of I-E-like, but not I-A-like, antigens in the WRC rat. These observations were confirmed when WRC I-E-like antigens were analyzed by two-dimensional gel electrophoresis. We propose that RT1.D shares both functional and antigenic homologies with the mouse I-E subregion.

The major histocompatibility complex of the rat: a partial review

The major histocompatibility complex of the rat is now called RT1, and this name is becoming widely accepted. In the past five years many recombinants have been reported within RT1 that enable distinct functional regions to be identified and located relative to each other. RT1 does not at present look particularly like its closest known relative, H-2. No doubt the genetic relationship will become apparent at the DNA level. The spontaneous diabetes mellitus of the BB rat line is associated with RT1. The data so far suggest that RT1u supplies a dominant susceptibility that becomes apparent only if protection conferred by a dominant gene mapping outside the MHC is withdrawn. It seems likely that the BB rat carries a recessive mutation at this "protective" locus.

Genetic control of cell-mediated immunity in the rat. III. T cells restricted by the RT1.A locus recognize viable Listeria but not isolated bacterial antigens

This study investigates the discordance between the restriction criteria required for the transfer of cellular resistance to Listeria monocytogenes (LM) and those for the transfer of delayed type hypersensitivity to Listeria antigens. Infective bacteria elicit both RT1.A-restricted T cells and RT1.B-restricted T cells. Both populations of T cells mediate lymphoblast localization and macrophage accumulation, which are reactions characteristic of delayed type hypersensitivity (DTH), and cause macrophage activation with rapid and efficient bacterial elimination, which is an expression of cellular resistance. If alcohol-killed Listeria organisms (pLMA) are injected, only the RT1.B-restricted T cell subset is triggered. Direct comparison of lymphoblast localization in LM infection sites and the expression of resistance revealed that efficient resistance may be mediated by small numbers of lymphoblasts and that below a certain threshold there is no correlation between lymphoblast localization and the level of resistance.

Genetic control of cell-mediated immunity in the rat. II. Sharing of either the RT1.A or RT1.B locus is sufficient for transfer of antimicrobial resistance

The MHC restriction criteria for T cells activating macrophages in vivo and mediating antimicrobial resistance to Listeria monocytogenes were determined. Antimicrobial resistance could be transferred by T cells in order of decreasing efficiency from syngeneic, RT1.A compatible, RT1.B compatible and RT1 incompatible donors. Alloreactive T cells responding to either A locus or B locus encoded antigens in a graft-versus-host reaction were also able to activate macrophages. Approximately five times as many MLC-reactive precursors responded to B locus alloantigens as to A locus alloantigens, but A-restricted Listeria-specific T cells were considerably more numerous (or more efficient) in Listeria-infected hosts than were B-restricted, Listeria-specific T cells. This was unexpected, since A-restricted, Listeria-specific T cells failed to transfer delayed type hypersensitivity (DTH) to soluble bacterial antigens.

CML characterization of a product of a second class I locus in the rat MHC

In the rat, genes that control the expression of target antigens detected by cell-mediated lympholysis (CML) are present in the major histocompatibility complex (MHC). The relationship of these loci, CT and Ag-L, to each other and to other loci within the MHC is unknown. In this report, we demonstrate the existence of a CML target antigen in the (DA X BN)F1 anti-DA.1I(BI) strain combination. The gene coding for this antigen is linked to the RT1 complex as indicated by the CML reactivity of targets from backcross and congenic animals. Inhibition studies demonstrated that this antigen has the widespread tissue distribution characteristic of class I antigens, and the gene coding for this CML antigen maps coincident with the RT1.E class I locus as indicated by the lysis of targets from the recombinant strains r10 and r11. The CML can be blocked by antisera directed against a product of the RT1.E locus. The locus controlling this CML reactivity, like CT and Ag-L, has been separated from RT1.A by recombination; unlike CT and Ag-L, the produce of this CML locus appears to be identical with an RT1.E allelic product that has been serologically identified and biochemically characterized.