Immunoglobulin and peripheral B-lymphocyte concentrations in Fell pony foal syndrome

Genetics of Immune Disease in the Horse

Host defenses against infection by viruses, bacteria, fungi, and parasites are critical to survival. It has been estimated that upwards of 7% of the coding genes of mammals function in immunity and inflammation. This high level of genomic investment in defense has resulted in an immune system characterized by extraordinary complexity and many levels of redundancy. Because so many genes are involved with immunity, there are many opportunities for mutations to arise that have negative effects. However, redundancy in the mammalian defense system and the adaptive nature of key immune mechanisms buffer the untoward outcomes of many such deleterious mutations.

Fell Pony syndrome: characterization of developmental hematopoiesis failure and associated gene expression profiles

Fell Pony syndrome (FPS) is a fatal immunodeficiency that occurs in foals of the Fell Pony breed. Affected foals present with severe anemia, B cell lymphopenia, and opportunistic infections. Our objective was to conduct a prospective study of potential FPS-affected Fell Pony foals to establish clinical, immunological, and molecular parameters at birth and in the first few weeks of life. Complete blood counts, peripheral blood lymphocyte phenotyping, and serum immunoglobulin concentrations were determined for 3 FPS-affected foals, 49 unaffected foals, and 6 adult horses. In addition, cytology of bone marrow aspirates was performed sequentially in a subset of foals. At birth, the FPS-affected foals were not noticeably ill and had hematocrit and circulating B cell counts comparable to those of unaffected foals; however, over 6 weeks, values for both parameters steadily declined. A bone marrow aspirate from a 3-week-old FPS-affected foal revealed erythroid hyperplasia and concurrent erythroid and myeloid dysplasia, which progressed to a severe erythroid hypoplasia at 5 weeks of life. Immunohistochemical staining confirmed the paucity of B cells in primary and secondary lymphoid tissues. The mRNA expression of genes involved in B cell development, signaling, and maturation was investigated using qualitative and quantitative reverse transcriptase PCR (RT-PCR). Several genes, including CREB1, EP300, MYB, PAX5, and SPI1/PU.1, were sequenced from FPS-affected and unaffected foals. Our study presents evidence of fetal erythrocyte and B cell hematopoiesis with rapid postnatal development of anemia and B lymphopenia in FPS-affected foals. The transition between fetal/neonatal and adult-like hematopoiesis may be an important aspect of the pathogenesis of FPS.

Population screening of endangered horse breeds for the foal immunodeficiency syndrome mutation

The Fell and Dales are UK pony breeds that have small populations and may be at risk from in-breeding and inherited diseases. Foal immunodeficiency syndrome (FIS) is a lethal inherited disease caused by the recessive mutation of a single gene, which affects both Fell and Dales ponies and potentially other breeds that have interbred with either of these. FIS, previously known as Fell pony syndrome, is characterised by progressive anaemia and severe B lymphocyte deficiency. The identification of the causal mutation for this disease led to the recent development of a DNA-based carrier test. In this study, the authors used this test to estimate the prevalence of the FIS mutation in the Fell and Dales populations, revealing that approximately 18 per cent of adult Dales ponies and 38 per cent of adult Fell ponies are carriers of the FIS defect. In addition, a study of five potential at-risk breeds was conducted to assess the transfer of the FIS defect into these populations. Of the 192 coloured ponies tested, two were confirmed as FIS carriers: No carriers were found among 210 Clydesdales, 208 Exmoor ponies, 161 Welsh section D, 49 part-bred Welsh section D and 183 Highland ponies.

Identification of a mutation associated with fatal Foal Immunodeficiency Syndrome in the Fell and Dales pony

The Fell and Dales are rare native UK pony breeds at risk due to falling numbers, in-breeding, and inherited disease. Specifically, the lethal Mendelian recessive disease Foal Immunodeficiency Syndrome (FIS), which manifests as B-lymphocyte immunodeficiency and progressive anemia, is a substantial threat. A significant percentage (∼10%) of the Fell ponies born each year dies from FIS, compromising the long-term survival of this breed. Moreover, the likely spread of FIS into other breeds is of major concern. Indeed, FIS was identified in the Dales pony, a related breed, during the course of this work. Using a stepwise approach comprising linkage and homozygosity mapping followed by haplotype analysis, we mapped the mutation using 14 FIS–affected, 17 obligate carriers, and 10 adults of unknown carrier status to a ∼1 Mb region (29.8 – 30.8 Mb) on chromosome (ECA) 26. A subsequent genome-wide association study identified two SNPs on ECA26 that showed genome-wide significance after Bonferroni correction for multiple testing: BIEC2-692674 at 29.804 Mb and BIEC2-693138 at 32.19 Mb. The associated region spanned 2.6 Mb from ∼29.6 Mb to 32.2 Mb on ECA26. Re-sequencing of this region identified a mutation in the sodium/myo-inositol cotransporter gene (SLC5A3); this causes a P446L substitution in the protein. This gene plays a crucial role in the regulatory response to osmotic stress that is essential in many tissues including lymphoid tissues and during early embryonic development. We propose that the amino acid substitution we identify here alters the function of SLC5A3, leading to erythropoiesis failure and compromise of the immune system. FIS is of significant biological interest as it is unique and is caused by a gene not previously associated with a mammalian disease. Having identified the associated gene, we are now able to eradicate FIS from equine populations by informed selective breeding.

Foal Immunodeficiency Syndrome (FIS) is a genetic disease that affects two related British pony breeds, namely the Fell and the Dales. Foals with FIS appear to be normal at birth but within a few weeks develop evidence of infection such as diarrhoea, pneumonia, etc. The infections are resistant to treatment, and the foals die or are euthanized before three months of age. The foals also suffer from a severe progressive anemia. Being a recessive condition, the disease is difficult to control without a diagnostic DNA test to identify symptom-free carrier parents. Within the last few years the horse genome has been sequenced, and this has allowed the development of tools to identify genetic mutations in the horse at high resolution. In this article we demonstrate the use of these new tools to identify the location of the FIS mutation. The presumptive causal lesion was then identified by sequencing this region. This has enabled us to develop a test that can be used to identify carrier ponies, allowing breeders to avoid FIS in their foal crop.

Immunophenotypical characterization in Andalusian horse: variations with age and gender

Assessment of lymphocyte subsets is an effective method for characterizing disorders such as leukemia, lymphomas, autoimmune and infectious diseases. In order to clinically interpret these parameters, normal reference values should be set, estimating age- and gender-related variations. This research aimed to: (1) characterize lymphocyte subpopulations in Andalusian horse, and (2) evaluate age and gender-related variations of lymphocyte subsets. Jugular blood samples were obtained from 159 animals, 77 males and 82 females, belonging to four age groups-1: 1-2 years (N=39; 21 males and 18 females), 2: 2-3 years (N=38; 16 males and 22 females), 3: 3-4 years (N=41; 19 males and 22 females) and 4: 4-7 years (N=41; 21 males and 20 females). T lymphocytes subsets were quantified by flow cytometry with monoclonal antibodies specific for CD2, CD4 and CD8 cell markers. B and NK cell counts were estimated by using a mathematical formula. No variations were found in T, B lymphocytes and NK cells between males and females. Animals of group 1 and 2 had a higher number of CD2, T, CD4+, CD8+, B lymphocytes and NK cells than animals of groups 3 and 4. The percentage of CD2 in group 1 was significantly lower than in group 4. The percentage of T and CD4+ lymphocytes in the group 1 were significantly higher than groups 2 and 3, respectively. Whereas the percentage of B cells calculated by flow cytometry was significantly lower in group 2 compared to group 4, the percentage of B cells calculated by a mathematical formula was higher in group 1. NK cells percentage was significantly lower in group 3 and 4 than in younger animals. In conclusion, in Andalusian horse, gender does not influence absolute numbers and percentages of T, B and NK. There is an age-related decline in absolute number of CD2, T, CD4+ and CD8+ lymphocytes, B lymphocytes and NK cells, with increasing percentage of CD2, T, CD4+ and B lymphocytes, and a decrease in NK with no differences in CD4/CD8 ratio. The decline of lymphocyte population numbers with age is a natural process in many animal species, and could be the origin for immune dysfunction observed in geriatric individuals.

Immunodeficiency disorders in horses

Immunodeficiencies are characterized as primary (genetic) or secondary (acquired). Primary immunodeficiencies are relatively uncommon; however, clinically, they present a significant challenge to the practitioner, especially if the underlying disorder goes unrecognized. Secondary immunodeficiencies may present at any age, but failure of passive transfer in neonatal foals is most commonly encountered. This article provides a general overview of clinical signs and diagnosis of primary and secondary immunodeficiencies currently recognized in horses.

Immunologic Disorders in Neonatal Foals

Foals live in an environment heavily populated by bacteria, many of which are capable of causing disease. Development of infection,however, is the exception rather than the rule. The ability of the foal to prevent infection by most pathogens is the result of a sophisticated set of defense mechanisms. These defense mechanisms can be divided into adaptive and innate immunity. Innate immunity encompasses defense mechanisms that pre-exist or are rapidly induced within hours of exposure to a pathogen. Conversely, adaptive or acquired immunity represents host defenses mediated by T and B lymphocytes, each expressing a highly specific antigen receptor and exhibiting memory during a second encounter with a given antigen. Immunologic disorders are relatively common in foals compared with their occurrence in adult horses. This article summarizes the current understanding of the equine fetal and neonatal immune system and reviews common immunodeficiency disorders as well as disorders resulting from allogenic incompatibilities.