Characterization of class II alpha genes and DLA-D region allelic associations in the dog

Use of multigeneration-family molecular dog leukocyte antigen typing to select a hematopoietic cell transplant donor for a dog with T-cell lymphoma

CASE DESCRIPTION

A 7-year-old Golden Retriever was examined because of anorexia, lethargy, vomiting, and gradual weight loss.

CLINICAL FINDINGS

Splenomegaly, pancytopenia, high serum calcium concentration, and high alkaline phosphatase activity were detected. Magnetic resonance imaging revealed an enlarged mesenteric lymph node and increased signals from the bone marrow of the ilium and vertebral bodies. Histologic examination and immunophenotyping of biopsy specimens confirmed a stage V (b) T-cell malignant lymphoma.

TREATMENT AND OUTCOME

Clinical remission was attained by use of 2 chemotherapy cycles, followed by an allogeneic hematopoietic cell transplant performed at 18 weeks after diagnosis. A donor was identified by molecular dog leukocyte antigen typing methods. The patient was conditioned with 2 fractions of 4 Gy total body irradiation delivered 3 hours apart at 7 cGy/min, followed by an IV infusion of recombinant canine granulocyte colony-stimulating factor mobilized leukapheresis product and postgrafting immunosuppression with cyclosporine. Chimerism analyses revealed full donor engraftment that has been maintained for at least 58 weeks after transplant. Remission has been confirmed by normal results of serum thymidine kinase assays and the absence of peripheral blood clonal T-cell receptor gene rearrangements.

CLINICAL RELEVANCE

Systemic chemotherapy induces remissions; however, most dogs succumb to disease recurrence because of multidrug resistance. Outcome of allogeneic hematopoietic cell transplantation in dogs can be excellent because of improved donor-recipient selection by use of molecular dog leukocyte antigen typing, compared with early attempts, and better prevention of graft versus host disease, better supportive care, and substitution of peripheral blood mononuclear cells for bone marrow.

Cellular, serological, and molecular polymorphism of the class I and class II loci of the canine Major Histocompatibility Complex

This study was undertaken to determine the relationships between canine cellular and serological determinants and more recently described genes. Such relationships might reveal information about immunological reactivity or function of various proteins. To do this we studied the haplotypic associations of dog leukocyte antigen (DLA) class I and class II alleles determined from a panel of 14 DLA-D homozygous dogs. This panel of dogs was typed for the serological determinants DLA-A, DLA-B and DLA-C. Polymorphisms for DLA-DQA1, DLA-DQB1, DLA-DRB1 and DLA-88 were also determined. The number of alleles (one or two) for two microsatellite markers in the DLA region were also determined. Analyses of the nucleotide sequences and of the serological and cellular typing data revealed that phenotypic homozygosity, as defined by the DLA-D type in mixed leukocyte culture (MLC), tended to correlate with homozygosity at the DLA-DRB1 locus but not necessarily at the DLA-DQB1 locus. Furthermore, MLC specificity was determined by other loci besides DLA-DRB1 and DLA-DQB1. The amino acid at position 63 of the DR beta chain could contribute to the DLA-B serological specificity. DLA-88, the most polymorphic class I gene characterized to date, did not have an easily identifiable association with either the DLA-A or DLA-C class I serological specificities. Homozygosity or heterozygosity of each of two microsatellite markers, FH 2200 and FH 2202, located in the class I or class II region, respectively, did not correlate with homozygosity or heterozygosity of the most polymorphic known class I (DLA-88) or class II (DLA-DRB1) genes.

Extensive interbreed, but minimal intrabreed, variation of DLA class II alleles and haplotypes in dogs

The DLA class II genes in the dog major histocompatibility complex are highly polymorphic. To date, 52 DLA-DRB1, 16 DLA-DQA1 and 41 DLA-DQB1 allelic sequences have been assigned. The aim of this study was to examine the intrabreed and interbreed variation of DLA allele and haplotype frequencies in dogs, and to ascertain whether conserved DLA class II haplotypes occur within and between different breeds. One thousand and 25 DNA samples from over 80 different breeds were DLA class II genotyped, the number of dogs per breed ranging from 1 to 61. DNA sequence based typing and sequence specific oligonucleotide probing were used to characterize dogs for their DLA-DRB1, DQA1 and DQB1 alleles. The high frequency of DLA class II homozygous animals (35%), allowed the assignment of many haplotypes despite the absence of family data. Four new DLA alleles were identified during the course of this study. Analysis of the data revealed considerable interbreed variation, not only in allele frequency, but also in the numbers of alleles found per breed. There was also considerable variation in the number of breeds in which particular alleles were found. These interbreed variations were found in all three DLA class II loci tested, and also applied to the three-locus haplotypes identified. Within this data set, 58 different DLA-DRB1/DQA1/DQB1 three-locus haplotypes were identified, which were all found in at least two different animals. Some of the haplotypes appeared to be characteristic of certain breeds. The high interbreed, and relatively low intrabreed, variation of MHC alleles and haplotypes found in this study could provide an explanation for reports of interbreed variation of immune responses to vaccines, viruses and other infections.

Nomenclature for factors of the dog major histocompatibility system (DLA), 2000: second report of the ISAG DLA Nomenclature Committee

The International Society for Animal Genetics (ISAG) Dog Leukocyte Antigen (DLA) Nomenclature Committee met during the "Comparative Evolution of the Mammalian major Histocompatibility Complex (MHC)" meeting in Manchester, UK on 10 September 2000. The main points discussed were the naming of class I genes and alleles, and the inclusion of alleles from other canidae.

Nomenclature for factors of the dog major histocompatibility system (DLA), 2000: Second report of the ISAG DLA Nomenclature Committee

The ISAG DLA Nomenclature Committee met during the "Comparative Evolution of the Mammalian MHC" meeting in Manchester, England on 10th September 2000. The main points discussed were the naming of class I genes and alleles, and the inclusion of alleles from other canidae.

DLA-DQB1 alleles and bone marrow transplantation experiments in narcoleptic dogs

Human narcolepsy is a neurological disorder known to be tightly associated with HLA-DQB1*0602. A clinically similar disorder has been described in various dog breeds. The canine form of the disease is inherited as an autosomal recessive disorder in Labrador retrievers and Doberman pinschers (canarc-1) but occurs sporadically in other breeds, most typically dachshunds and poodles. In this study, we have examined if there is a relationship between the development of narcolepsy and specific dog leukocyte antigen (DLA)-DQB1 alleles. Ninety-nine dogs were typed for DLA-DQB1-31 with narcolepsy and 68 control animals. Recent studies have linked the development of autosomal recessive canine narcolepsy to a disruption of the hypocretin receptor 2 (Hcrtr2) gene on the same chromosome as the canine MHC region (CFA12), but not close to the DLA. Four Hcrtr2-positive families (two Doberman pinscher families, one Labrador retriever family, one dachshund family) were analyzed at the DLA-DQ level. No relationship was found between narcolepsy and DLA in Hcrtr2-mediated narcolepsy but loose genetic linkage was observed (Zmax=2.3 at theta=25%, m= 40). Bone marrow transplantation between two DLA identical affected (Hcrtr2-/-) and unaffected (Hcrtr2+/-) siblings was also performed and found not to be successful neither in transmitting narcolepsy nor in relieving the symptoms in Doberman pinschers. DLA-DQB1 was next studied in 11 dogs with sporadic (non-familial) narcolepsy and in unrelated control animals of the same and different breeds. The allelic and carrier frequencies of various DLA-DQB1 alleles were analyzed. There was no strong positive or negative correlation between the development of narcolepsy and specific DLA-DQB1 alleles. These results do not support the involvement of DLA-DQ in canine narcolepsy, whether of sporadic or familial origin.

DLA-DQA1 polymorphisms in dogs defined by sequence-specific oligonucleotide probes (SSOP)

Several recent studies have identified DNA sequences for alleles of the DLA-DQA1 locus in the dog. To date, 10 DQA1 alleles have been reported. No data exists on the frequencies of these alleles within the general dog population, nor is there any indication of whether alleles are breed specific. We have addressed this issue by establishing a molecular-based sequence-specific oligonucleotide probing (SSOP) method to identify all published DQA1 alleles and have used these methods to type a large number of dogs. Oligonucleotide probes were designed to detect all the polymorphic sites in exon 2. This allowed assignment at the allele level. Three hundred and thirty dogs were typed for DQA1. All but two of the published DQA1 alleles were identified in these animals. One new allele was identified, and confirmed by DNA cloning and sequencing. This typing method provides a powerful tool for generating data that will be essential for studies investigating the genetic relationships between different breeds.

Nomenclature for factors of the dog major histocompatibility system (DLA), 1998: first report of the ISAG DLA Nomenclature Committee

A Nomenclature committee for Factors of the Dog Major Histocompatibility System or Dog Leukocyte Antigen (DLA) has been convened under the auspices of the International Society for Animal Genetics (ISAG) to define a sequence based nomenclature for the genes of the DLA system. The remit of this committee includes: assignment of gene names rules for naming alleles assignment of names to published alleles assignment of names to new alleles rules for acceptance of new alleles DLA Nomenclature Committee, rules for acceptance, DLA genes and alleles, sequence based nomenclature.

Nomenclature for factors of the dog major histocompatibility system (DLA), 1998. First report of the ISAG DLA Nomenclature Committee. International Society for Animals Genetics

A Nomenclature Committee for factors of the dog major histocompatibility system or dog leukocyte antigen (DLA) has been convened under the auspices of the International Society for Animal Genetics (ISAG) to define a sequence-based nomenclature for the genes of the DLA system. The remit of this committee includes: i) assignment of gene names; ii) rules for naming alleles; iii) assignment of names to published alleles; iv) assignment of names to new alleles; and v) rules for acceptance of new alleles.

DLA-DRB1 polymorphisms in dogs defined by sequence-specific oligonucleotide probes (SSOP)

To date, DNA sequences for 29 dog DLA-DRB1 alleles have been reported. However, no data exists on the frequencies of these alleles within the general dog population, nor is there any indication of whether there is interbreed variation of allele distribution. We have addressed this by establishing a molecular based sequence-specific oligonucleotide probing (SSOP) method to identify all of the known broad DRB1 types and we have used this to type a random panel of dogs. A series of oligonucleotide probes were designed to detect known polymorphisms in the three DRB1 hypervariable regions, together with two distinctive motifs in other regions of exon 2. This set of probes enabled us to assign broad DRB1 types. Two hundred and eighteen dogs were SSOP typed for DRB1. All but 4 of the published DLA-DRB1 alleles were identified in these animals. Interbreed variation in both allele distributions and allele frequencies were observed, which may be useful in the study of genetic variation between breeds. This variation also has implications for the selection of control groups for studies aimed at identifying MHC associations with disease susceptibility in the dog.

Canine major histocompatibility complex genes DQA and DQB in Irish setter dogs

Information about genetic variation within the canine major histocompatibility complex (MHC) class II genes is limited. In common with most other vertebrate species the canine MHC, or DLA, includes genes which are homologous to human DR, DQ, and DP. Recently, at least one functional DLA DQ gene-pair has been characterized, but so far systematic screening efforts have been lacking. In the present study, we sequenced both cDNA and genomic clones derived from DLA DQ genes of Irish setter dogs. This breed was of interest, since it shows a high prevalence of gluten sensitive enteropathy (GSE), which may be a useful animal model for celiac disease (CD) of man. Interestingly, few of the alleles found in Irish setters were identical to those previously detected in other breeds. Three novel DLA DQA and four novel DLA DQB alleles were discovered in 19 unrelated dogs. Strong association between certain HLA DQ alleles and CD of man prompted us to screen the DQ alleles of members of a family of gluten-sensitive Irish setter dogs. No haplotypes or alleles were shared by all affected dogs, but one frequent haplotype in this family was also detected in an unrelated gluten-sensitive Irish setter; this haplotype was absent in the healthy dogs. This observation warrants further investigation by screening the DQ alleles of a large population of unrelated gluten-sensitive Irish setters.

Molecular analysis of the DLA DR region

The dog is an important model for studying organ transplantation. In order to develop a DNA-based typing system, a genomic analysis of the canine DR region of the MHC was undertaken. Southern analysis suggests the presence of two DRB genes in most dogs and all have one DRA gene. One dog out of 200 examined contains only one DRB gene. The DRA gene was mapped in one lambda phage clone. One DRB gene (DRBB1) was localized to two overlapping phage clones. Another DRB gene (DRBB2) was localized to two overlapping phage clones. Sequence analysis of the two DRB genes suggests that one gene is intact (DRBB1) and one gene is a pseudogene (DRBB2) because it lacks a splice acceptor signal for exon 3 and lacks exons 2 and exon 4. Intron 1 and 2 sequence data from DRBB1 allow amplification of the polymorphic exon 2 which, in turn, can serve as a basis for developing a typing system for DRB.

Molecular analysis and polymorphism of the DLA-DQA gene

A full-length cDNA clone and two overlapping genomic clones corresponding to the canine DQA class II gene were isolated and sequenced. Restriction mapping and sequence data allow identification and orientation of the five exons corresponding to the alpha (alpha) chain. Sequence analysis of exon 2 amplified from 17 unrelated dogs of various breeds identified seven alleles. The structure of the canine DQA gene is similar to HLA-DQA1 and other mammalian DQA genes. This study will serve as a reference for developing a typing system for the DLA-DQA gene for donor and recipient matching in the canine model for organ and bone marrow transplantation.

Immunological characterization of canine hematopoietic progenitor cells

Canine hematopoietic progenitor cells were characterized by separation with monoclonal antibodies. Depleted and enriched fractions were studied for growth of CFU-GM in semisolid agar and for repopulating capacity of lethally irradiated dogs. CFU growth was not reduced by depletion of marrow using monoclonal antibodies F 3-20-7 (anti-dog Thy-1), MT606 (anti-human CD 6), and IOT2a (anti-human DR). CFU growth was variable following treatment with the anti-canine T-cell antibody MdT-P 1 and immunomagnetic bead separation. It was regularly enriched when MdT-P 1 treatment was followed by immunorosetting with staphylococcal protein A-loaded sheep red blood cells and density gradient separation. Lethally irradiated dogs were reconstituted by autologous marrow depleted of MdT-P 1-positive cells using immunorosetting and density gradient centrifugation, whereas immunomagnetic bead-depleted marrow was ineffective. Fluorescence-activated cell sorting showed enrichment of hematopoietic progenitor cells in the weakly MdT-P 1-positive fraction.

Functional characterization of canine lymphocyte subsets

Functional characterization of subsets of T lymphocytes is essential for transplantation studies in dogs, as it is in other species. We studied the function of T cells separated by two mouse monoclonal antibodies recognizing complementary subsets--an antibody directed to canine T cells (MdT-P1) with an up-regulating function, and an antibody directed to human CD 8 (MT811) that cross-reacts with down-regulating canine T cells. Immunorosetting with sheep red blood cells and Percoll gradient allowed us to study depleted and enriched fractions. Their function was tested in mixed lymphocyte culture (MLC), cell-mediated cytotoxicity (CML), and coculture with B cells in a hemolytic plaque assay (PFC). In MLC, MdT-P1-positive cells showed a high proliferative response, and MT811-positive cells responded poorly to allogeneic cells. Vice versa, MT811- negative cells responded strongly, and MdT-P1-negative cells were poor responders but strong stimulators. Effector cells of CML were separated following 8 days of culture and prior to mixing with target cells. Enriched and depleted fractions with either antibody showed low cytotoxic activity as compared with unseparated cells. When added to unseparated effector cells MT 811-positive cells suppressed cytotoxicity. B cells were obtained by rosetting with staphylococcal protein A (SPA). Their immunoglobulin production was studied following 6 days of culture stimulated by pokeweed mitogen in a reverse hemolytic plaque assay. Again, MT 811-positive cells added to the culture suppressed, and MT 811-negative cells enhanced immunoglobulin production. In conclusion, immunorosetting with two monoclonal antibodies allowed us to distinguish subpopulations of canine T cells with up-regulating (helper/inducer) from those with down-regulating (suppressor) activity.

Correlation of RFLP typing and MLC reactivity in dogs

The human recombinant HLA-DRB1 gene probe was used for histocompatibility typing of two families of beagles for the DLA-D equivalent by using restriction fragment length polymorphisms (RFLP). This method was able to determine the segregation of these genes from the parental animals to the individual F1 offspring. Mixed lymphocyte culture (MLC) reactivity as well as serological typing for class I histocompatibility antigens were also performed for comparison. It was found that there was a high correlation between these three methods. We therefore conclude that RFLP typing is an effective procedure for predicting MLC reactivity in dogs and propose that it is a suitable genotyping method for assignment of class II antigen compatibility for donor-recipient pairs in conjunction with organ transplant studies.

Allelic variation in the DR subregion of the canine major histocompatibility complex

Allelic variation in the DR subregion of the canine major histocompatibility complex (DLA) has been analyzed by nucleic acid sequencing of cDNA clones of DRB genes amplified in vitro by the reverse transcriptase-polymerase chain reaction (RT-PCR). Sequence analysis of a panel of 19 homozygous typing cell dogs representing 12 different DLA-D types (defined by mixed leucocyte reaction) demonstrated the presence of one expressed DRB locus with at least nine distinct alleles in the dog. Unique DLA-DRB alleles were found in the DLA-D types Dw1, Dw3, Dw4, Dw8 (workshop assignments) and D4, D6, D7, D8, and D9 (Seattle assignments). In contrast, the DRB genes of the remaining three DLA-D types (D1, D10, and D16) were identical to those of Dw3/Dw4 (for D1), Dw8 (for D10), and D6 (for D16). The nucleotide sequences of all nine DLA-DRB alleles were typical of functional major histocompatibility complex (MHC) class II beta chains and contained three allelic hypervariable regions (HVRs) in the beta 1 domain at positions 8-16, 26-39, and 57-74. At each variable residue, two to five amino acid substitutions were found. The most polymorphic residues were located at positions 37 (with five amino acid substitutions), 11, 13, 28, and 71 (each with four substitutions). The DLA-DRB alleles had 96%-99% overall nucleotide sequence similarity and 93%-99% amino acid sequence similarity with each other. Cluster analysis of the nucleotide and predicted amino acid sequences subdivided the DLA-DRB alleles into three major allelic groups which may represent the canine counterparts of the supertypic groups described in man.

RFLP analysis of DLA class I genes in the dog

Human major histocompatibility complex (HLA) cDNA probes for class I genes HLA-A,B and HLA-E were used to analyze the Restriction Fragment Length Polymorphism (RFLP) of the class I region of the canine major histocompatibility complex (DLA) in 40 dogs. The Southern blot analysis demonstrated that the dog genome contains at least eight class I genes, including the canine homologues of HLA-A,B and HLA-E genes. The DNA polymorphism detected by the HLA-B7 probe corresponded to the serologically defined DLA-A allelic series. Restriction fragments that correlated with the DLA-A2, -A7 and -A9 antigenic specificities were identified in PstI digests of genomic DNA. The RFLP analysis was particularly useful in genotyping dogs which were not clearly DLA-A typable by serology. This technique can be used as a supplement to serotyping and as a genotyping tool for DLA antigenic specificities for which specific antisera are not available.