Dog leukocyte antigen

Last updated October 04, 2019

The dog leukocyte antigen (DLA) is a part of the major histocompatibility complex (MHC) in dogs, encoding genes in the MHC. The DLA and MHC system are interchangeable terms in canines. The MHC plays a critical role in the immune response system and consists of three regions: class I, class II and class III. DLA genes belong to the first two classes, which are involved in the regulation of antigens in the immune system. The class II genes are highly polymorphic, with many different alleles/haplotypes that have been linked to diseases, allergies, and autoimmune conditions such as diabetes, polyarthritus, and hypothyroidism in canines.

The major histocompatibility complex (MHC) is a set of genes that code for cell surface proteins essential for the acquired immune system to recognize foreign molecules in vertebrates, which in turn determines histocompatibility. The main function of MHC molecules is to bind to antigens derived from pathogens and display them on the cell surface for recognition by the appropriate T-cells. MHC molecules mediate interactions of leukocytes, also called white blood cells (WBCs), which are immune cells, with other leukocytes or with body cells. The MHC determines compatibility of donors for organ transplant, as well as one's susceptibility to an autoimmune disease via crossreacting immunization. The human MHC is also called the HLA complex. The MHC in mice is called the H-2 complex or H-2.

Diabetes mellitus (DM), commonly known as diabetes, is a group of metabolic disorders characterized by high blood sugar levels over a prolonged period. Symptoms of high blood sugar include frequent urination, increased thirst, and increased hunger. If left untreated, diabetes can cause many complications. Acute complications can include diabetic ketoacidosis, hyperosmolar hyperglycemic state, or death. Serious long-term complications include cardiovascular disease, stroke, chronic kidney disease, foot ulcers, and damage to the eyes.

Hypothyroidism, also called underactive thyroid or low thyroid, is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as poor ability to tolerate cold, a feeling of tiredness, constipation, depression, and weight gain. Occasionally there may be swelling of the front part of the neck due to goiter. Untreated hypothyroidism during pregnancy can lead to delays in growth and intellectual development in the baby or congenital iodine deficiency syndrome.

There are likely hundreds of immunologically relevant genes making up the DLA region in the canine genome; as of the present date the complete characteristics of the gene is unknown. MHC genes represent candidates for disease susceptibility in canines; some alleles promote protection against immune-mediated diseases and some increase susceptibility. For example, certain combinations of the DLA-DRB1 and DQ alleles are most favorable for good immune regulation. These alleles help balance immune surveillance and immune response without increasing the risk of developing an autoimmune condition. Different canine breeds have MHC/DLA allele association; these genes exhibit more inter-breed differentiation than intra-breed differentiation. Dogs have been selectively bred for different phenotypes, so the underlying genotypes and linked regions also differ among breeds. Selection on the DLA can lead to an increase in the prevalence of immune-mediated diseases. Due to selective breeding some breeds have become restricted in their DLA genes, with a limited subset of DLA alleles occurring within the breed. This explains some of the variation in immune responses among breeds. This occurs because there is a strong linkage disequilibrium that exists between DLA class II loci. The pattern displayed by the genetic differences among human ethnic groups is analogous to the pattern displayed by the distribution of DLA types in different canine breeds. MHC genes in humans are also known to be major contributors to autoimmune condition development.

In the fields of molecular biology and genetics, a genome is the genetic material of an organism. It consists of DNA. The genome includes both the genes and the noncoding DNA, as well as mitochondrial DNA and chloroplast DNA. The study of the genome is called genomics.

An allele is a variant form of a given gene. Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation. A notable example of this trait of color variation is Gregor Mendel's discovery that the white and purple flower colors in pea plants were the result of "pure line" traits which could be used as a control for future experiments. However, most alleles result in little or no observable phenotypic variation.

In population genetics, linkage disequilibrium is the non-random association of alleles at different loci in a given population. Loci are said to be in linkage disequilibrium when the frequency of association of their different alleles is higher or lower than what would be expected if the loci were independent and associated randomly.

Canine diabetes and DLA

In 1974 J. Nerup and others discovered that there is a link between diabetes and MHC genes. Dog leukocyte antigen has been found to be the genetic component associated with canine diabetes. The common alleles/haplotypes found in diabetes prone breeds (Samoyed, Carin Terrier, and Tibetan Terrier) are DLA DBR1*009, DQA1*001, and DQB1*008. The DLA DQA1 alleles code for an arginine amino acid at position 55 in region two, this increases the risk of developing diabetes in dog as arginine is a positive amino acid which can impair antigen binding. This allele is also associated with hypothyroidism which implies that this allele increases susceptibility for endocrinopathic immune-mediated diseases. It is possible that the link discovered between DLA associations and diabetes could be due to "makers" of susceptibility and that the true reason for susceptibility lies elsewhere in the genome. It could be associated with particular DLA alleles/haplotypes or caused by the strong linkage disequilibrium.

Arginine, also known as l-arginine (symbol Arg or R), is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group, an α-carboxylic acid group, and a side chain consisting of a 3-carbon aliphatic straight chain ending in a guanidino group. At physiological pH, the carboxylic acid is deprotonated (−COO⁻), the amino group is protonated (−NH₃⁺), and the guanidino group is also protonated to give the guanidinium form (-C-(NH₂)₂⁺), making arginine a charged, aliphatic amino acid. It is the precursor for the biosynthesis of nitric oxide. It is encoded by the codons CGU, CGC, CGA, CGG, AGA, and AGG.

Amino acid Organic compounds containing amine and carboxylic groups

Amino acids are organic compounds that contain amine (-NH₂) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), and nitrogen (N), although other elements are found in the side chains of certain amino acids. About 500 naturally occurring amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways. They can be classified according to the core structural functional groups' locations as alpha- (α-), beta- (β-), gamma- (γ-) or delta- (δ-) amino acids; other categories relate to polarity, pH level, and side chain group type (aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.). In the form of proteins, amino acid residues form the second-largest component (water is the largest) of human muscles and other tissues. Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis.

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Histocompatibility, or tissue compatibility, is the property of having the same, or sufficiently similar, alleles of a set of genes called human leukocyte antigens (HLA), or major histocompatibility complex (MHC). Each individual expresses many unique HLA proteins on the surface of their cells, which signal to the immune system whether a cell is part of the self or an invading organism. T cells recognize foreign HLA molecules and trigger an immune response to destroy the foreign cells. Histocompatibility testing is most relevant for topics related to whole organ, tissue, or stem cell transplants, where the similarity or difference between the donor's HLA alleles and the recipient's triggers the immune system to reject the transplant. The wide variety of potential HLA alleles lead to unique combinations in individuals and make matching difficult.

The human leukocyte antigen (HLA) system or complex is a gene complex encoding the major histocompatibility complex (MHC) proteins in humans. These cell-surface proteins are responsible for the regulation of the immune system in humans. The HLA gene complex resides on a 3 Mbp stretch within chromosome 6p21. HLA genes are highly polymorphic, which means that they have many different alleles, allowing them to fine-tune the adaptive immune system. The proteins encoded by certain genes are also known as antigens, as a result of their historic discovery as factors in organ transplants. Different classes have different functions:

HLA-DQ (DQ) is a cell surface receptor protein found on antigen presenting cells. It is an αβ heterodimer of type MHC class II. The α and β chains are encoded by two loci, HLA-DQA1 and HLA-DQB1, that are adjacent to each other on chromosome band 6p21.3. Both α-chain and β-chain vary greatly. A person often produces two α-chain and two β-chain variants and thus 4 isoforms of DQ. The DQ loci are in close genetic linkage to HLA-DR, and less closely linked to HLA-DP, HLA-A, HLA-B and HLA-C.

HLA DR3-DQ2 is double serotype that specifically recognizes cells from individuals who carry a multigene HLA DR, DQ haplotype. Certain HLA DR and DQ genes have known involvement in autoimmune diseases. DR3-DQ2, a multigene haplotype, stands out in prominence because it is a factor in several prominent diseases, namely coeliac disease and juvenile diabetes. In coeliac disease, the DR3-DQ2 haplotype is associated with highest risk for disease in first degree relatives, highest risk is conferred by DQA1*0501:DQB1*0201 homozygotes and semihomozygotes of DQ2, and represents the overwhelming majority of risk. HLA DR3-DQ2 encodes DQ2.5cis isoform of HLA-DQ, this isoform is described frequently as 'the DQ2 isoform', but in actuality there are two major DQ2 isoform. The DQ2.5 isoform, however, is many times more frequently associated with autoimmune disease, and as a result to contribution of DQ2.2 is often ignored.

HLA-DQ8 (DQ8) is a human leukocyte antigen serotype within the HLA-DQ (DQ) serotype group. DQ8 is a split antigen of the DQ3 broad antigen. DQ8 is determined by the antibody recognition of β⁸ and this generally detects the gene product of DQB1*0302.

HLA-A is a group of human leukocyte antigens (HLA) that are coded for by the HLA-A locus, which is located at human chromosome 6p21.3. HLA is a major histocompatibility complex (MHC) antigen specific to humans. HLA-A is one of three major types of human MHC class I cell surface receptors. The others are HLA-B and HLA-C. The receptor is a heterodimer, and is composed of a heavy α chain and smaller β chain. The α chain is encoded by a variant HLA-A gene, and the β chain (β₂-microglobulin) is an invariant β₂ microglobulin molecule. The β₂ microglobulin protein is coded for by a separate region of the human genome.

HLA-DQ2 (DQ2) is a serotype group within HLA-DQ (DQ) serotyping system. The serotype is determined by the antibody recognition of β² subset of DQ β-chains. The β-chain of DQ is encoded by HLA-DQB1 locus and DQ2 are encoded by the HLA-DQB1*02 allele group. This group currently contains two common alleles, DQB1*0201 and DQB1*0202. HLA-DQ2 and HLA-DQB1*02 are almost synonymous in meaning. DQ2 β-chains combine with α-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ2.2 and DQ2.5, are also encoded by the DQA1*0201 and DQA1*0501 genes, respectively.

HLA-DQ4 (DQ4) is a serotype subgroup within HLA-DQ(DQ) serotypes. The serotype is determined by the antibody recognition of β⁴ subset of DQ β-chains. The β-chain of DQ is encoded by HLA-DQB1 locus and DQ4 are encoded by the HLA-DQB1*04 allele group. This group currently contains 2 common alleles, DQB1*0401 and DQB1*0402. HLA-DQ4 and HLA-DQB1*04 are almost synonymous in meaning. DQ4 β-chains combine with α-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. These isoforms, nicknamed DQ4.3 and DQ4.4, are also encoded by the DQA1*0303 and DQA1*0401 genes, respectively.

HLA-DQ6 (DQ6) is a human leukocyte antigen serotype within HLA-DQ (DQ) serotype group. The serotype is determined by the antibody recognition of β⁶ subset of DQ β-chains. The β-chain of DQ isoforms are encoded by HLA-DQB1 locus and DQ6 are encoded by the HLA-DQB1*06 allele group. This group currently contains many common alleles, DQB1*0602 is the most common. HLA-DQ6 and DQB1*06 are almost synonymous in meaning. DQ6 β-chains combine with α-chains, encoded by genetically linked HLA-DQA1 alleles, to form the cis-haplotype isoforms. For DQ6, however, cis-isoform pairing only occurs with DQ1 α-chains. There are many haplotypes of DQ6.

HLA-DQ9 (DQ9) is a human leukocyte antigen serotype within the HLA-DQ (DQ) serotype group. DQ9 is a split antigen of the DQ3 broad antigen. DQ9 is determined by the antibody recognition of β⁹ and this generally detects the gene product of DQB1*0303.

HLA-DQ7 (DQ7) is an HLA-DQ serotype that recognizes the common HLA DQB1*0301 and the less common HLA DQB1*0304 gene products. DQ7 is a form of 'split antigen' of the broad antigen group DQ3 which also contains DQ8 and DQ9.

HLA-DQ1 is a serotype that covers a broad range of HLA-DQ haplotypes. Historically it was identified as a DR-like alpha chain called DC1; later, it was among 3 types DQw1, DQw2 and DQw3. Of these three serotyping specificities only DQw1 recognized DQ alpha chain. The serotype is positive in individuals who bear the DQA1*01 alleles. The most frequently found within this group are: DQA1*0101, *0102, *0103, and *0104. In the illustration on the right, DQ1 serotyping antibodies recognizes the DQ α (magenta), where antibodies to DQA1* gene products bind variable regions close to the peptide binding pocket.

HLA-DR17 (DR17) is an HLA-DR serotype that recognizes the DRB1*0301 and *0304 gene products. DR17 is found at high frequency in Western Europe. DR17 is part of the broader antigen group HLA-DR3 and is very similar to the group HLA-DR18.

HLA-DR3 is composed of the HLA-DR17 and HLA-DR18 split 'antigens' serotypes. DR3 is a component gene-allele of the AH8.1 haplotype in Northern and Western Europeans. Genes between B8 and DR3 on this haplotype are frequently associated with autoimmune disease. Type 1 diabetes mellitus is strongly associated with HLA-DR3 or HLA-DR4.

HLA-DR4 (DR4) is an HLA-DR serotype that recognizes the DRB1*04 gene products. The DR4 serogroup is large and has a number of moderate frequency alleles spread over large regions of the world.

HLA-A1 (A1) is a human leukocyte antigen serotype within HLA-A "A" serotype group. The serotype is determined by the antibody recognition of α¹ subset of HLA-A α-chains. For A1, the alpha "A" chain are encoded by the HLA-A*01 allele group and the β-chain are encoded by B2M locus. This group currently is dominated by A*0101. A1 and A*01 are almost synonymous in meaning. A1 is more common in Europe than elsewhere, it is part of a long haplotype that appears to have been frequent in the ancient peoples of Northwestern Europe. A1 is a frequent component of the AH8.1 haplotype. A1 serotype positivity is roughly linked to a large number of inflammatory diseases and conditions believed to have immune system involvement. Because of its linkage within the AH8.1 haplotype many studies showed association with A1 or A1,B8 only later to show the association drift toward the class II region gene alleles, DR3 and DQ2.5. While it is not clear what role A1 has in infectious disease, some linkage with infection rates in HIV remain associated within the A1 region of the haplotype.

HLA-A*02 (A*02) is a human leukocyte antigen serotype within the HLA-A serotype group. The serotype is determined by the antibody recognition of the α2 domain of the HLA-A α-chain. For A*02, the α chain is encoded by the HLA-A*02 gene and the β chain is encoded by the B2M locus. In 2010 the World Health Organization Naming Committee for Factors of the HLA System revised the nomenclature for HLAs. Before this revision, HLA-A*02 was also referred to as HLA-A2, HLA-A02, and HLA-A*2.

Major histocompatibility complex, class II, DQ alpha 1 protein-coding gene in the species Homo sapiens

Major histocompatibility complex, class II, DQ alpha 1, also known as HLA-DQA1, is a human gene present on short arm of chromosome 6 (6p21.3) and also denotes the genetic locus which contains this gene. The protein encoded by this gene is one of two proteins that are required to form the DQ heterodimer, a cell surface receptor essential to the function of the immune system.

HLA A1-B8-DR3-DQ2 haplotype is a multigene haplotype that covers a majority of the human major histocompatibility complex on chromosome 6. A multigene haplotype is set of inherited alleles covering several genes, or gene-alleles; common multigene haplotypes are generally the result of descent by common ancestry. Chromosomal recombination fragments multigene haplotypes as the distance to that ancestor increases in number of generations.

References

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