Objectives of the Presentation
Explain the function of the Major Histocompatibility Complex (MHC) in the cat
Explain why we are interested in the feline MHC
Describe the feline MHC
Characterization of the feline MHC
Overview of the Issue
All higher species examined to date have within their genome a Major Histocompatibility Complex containing three regions of tightly linked genes (class I, II and III), the first two of which are involved in regulation and the presentation of self and non-self antigens to the immune system. The MHC genes are central to the control of the immune response and influence susceptibility/resistance to disease and vaccine response. They are also important to the success (or otherwise) of transplants.
There is great interest in characterizing the domestic cat MHC (which is known as FLA) both as a marker of population genetic variability and to explore genetic variation in response to infectious disease. Recently, renal transplantation has also been used for the treatment of chronic renal failure in the cat. Transplants are currently performed without tissue matching donors and recipients, but with further characterization of the MHC, it may be possible to improve transplant prognosis. The MHC will also be important when studying the impact of genetic polymorphisms on many conditions including feline infectious peritonitis and other immune mediated diseases.
There has been some characterization of the feline MHC in terms of both genomic organization1-3 and polymorphism.4-6 More recently BAC sequencing of the entire DR region has revealed that there are three apparently full coding DRB genes plus one DRB gene fragment.7 Genes within the class II region appear to be highly polymorphic with good evidence for 34 FLA-DRB alleles but the full extent of this polymorphism has not yet been determined.8 Whilst considerable progress has been made in characterizing this crucial locus in the cat, the current techniques (DNA cloning and sequence analysis) used to generate these results are extremely labour intensive and very costly so as to preclude full characterization of this locus and routine FLA typing of cats. We have previously shown that Reference Strand-mediated Conformation Analysis (RSCA)9 can be used to characterize FLA. However, while RSCA is technically challenging to use for FLA typing, it is ideal for screening populations for their MHC diversity, as demonstrated in a small study of cheetahs.10
Variation within the highly polymorphic MHC genes, particularly class II alleles and haplotypes, is pivotal in the adaptive immune response. Maintaining or increasing the diversity of the MHC in endangered populations should increase the genetic fitness of such populations. Therefore assessing the MHC diversity within these populations can provide valuable insights.
Many felid species in the world are classified as endangered, and each species is often found in small geographically isolated populations. Most of these isolated groups will have been through some kind of bottleneck, which will have reduced the genetic variability within the group.
While genetic diversity is often measured using microsatellites, this may not be the most useful measure of diversity, since most microsatellites are considered to be neutral, i.e. not under selection. There is, however, in all mammalian species, a group of genes that are not only some of the most polymorphic markers in any genome, but are also subject to selection. These genes are called the Major Histocompatibility Complex (MHC), and are involved in the regulation of the immune response. MHC genes are involved in susceptibility and resistance to infection, response to vaccination and in the development of immune-mediated diseases. It is widely accepted that lack of diversity at the MHC results in a reduced fitness of both a population and the individuals within that population.
There is a published method for screening the MHC diversity of felid populations, based on Reference Strand-mediated Conformation Analysis (RSCA),4 which has already been used to assess the diversity of the MHC in cheetahs.10
While it is possible to use RSCA to assign MHC variants or alleles to individual cats, (i.e. genotype them for their MHC), in order to do so in many different felid species, this would involve a large amount of DNA cloning and sequencing to identify the alleles. This would be very expensive.
However, RSCA is ideal for screening populations to assess how much sharing of alleles there is, and how many different alleles are present. This would be a simple way of assessing the MHC diversity in populations.
RSCA could also be used to identify mismatched individuals that would be suitable to use in a breeding program that was aimed at increasing MHC and genetic diversity in a species. This has particular relevance when reintroducing animals to autochthonous groups.
RSCA could also identify matched samples for transplantation.
The feline MHC is important in determining outcome of disease.
Variation within a breed or species of cat can have implications for the fitness of the population
Characterization of the feline MHC is currently technically difficult.
1. Yuhki N, Beck T, Stephens RM, et al. Comparative genome organization of human, murine and feline major histocompatibility complex class II region. Genome Research 2003; 13:1169-1179.
2. Yuhki N, Heidecker GF, O'Brien SJ. Characterization of MHC cDNA clones in the domestic cat. Diversity and evolution of class I genes. J Immunol 1989; 142:3676-3682.
3. Yuhki N, O'Brien SJ. Molecular characterization and genetic mapping of class I and class II MHC genes of the domestic cat. Immunogenetics 1988; 27:414-425.
4. Kennedy LJ, Ryvar R, Brown JJ, et al. Resolution of complex feline leucocyte antigen DRB loci by reference strand-mediated conformational analysis (RSCA). Tissue Antigens 2003; 62:313-323.
5. Kennedy LJ, Ryvar R, Gaskell RM, et al. Sequence analysis of MHC DRB alleles in domestic cats from the United Kingdom. Immunogenetics 2002; 54:348-352.
6. Yuhki N, O'Brien SJ. Nature and origin of polymorphism in feline MHC class II DRA and DRB genes. Journal Of Immunology 1997; 158:2822-2833.
7. Yuhki N, Beck T, Stephens R, et al. Comparative genomic structure of human, dog, and cat MHC: HLA, DLA, and FLA. J Hered 2007;98:390-399.
8. Kennedy LJ, Ryvar R, Gaskell RM, et al. Sequence analysis of MHC DRB alleles in domestic cats from the United Kingdom. Immunogenetics 2002;54:348-352.
9. Arguello JR, Pay AL, McDermott A, et al. Complementary strand analysis: a new approach for allelic separation in complex polyallelic genetic systems. Nucleic Acids Research 1997; 25:2236-2238.
10. Drake GJ, Kennedy LJ, Auty HK, et al. The use of reference strand-mediated conformational analysis for the study of cheetah (Acinonyx jubatus) feline leucocyte antigen class II DRB polymorphisms. Mol Ecol 2004; 13:221-229.
11. Kuwahara Y, Kitoh K, Kobayashi R, et al. Genotyping of feline MHC (FLA) class II DRB by PCR-RFLP method using group-specific primers. J Vet Med Sci 2000; 62:1283-1289.