Associations between the presence of specific antibodies to the West Nile Virus infection and candidate genes in Romanian horses from the Danube delta

Twelve toll-like receptor (TLR) genes in the family Equidae - comparative genomics, selection and evolution

Toll-like receptors (TLRs) represent an important part of the innate immune system. While human and murine TLRs have been intensively studied, little is known about TLRs in non-model species. The order Perissodactyla comprises a variety of free-living and domesticated species exposed to different pathogens in different habitats and is therefore suitable for analyzing the diversity and evolution of immunity-related genes. We analyzed TLR genes in the order Perissodactyla with a focus on the family Equidae. Twelve TLRs were identified by bioinformatic analyses of online genomic resources; their sequences were confirmed in equids by genomic DNA re-sequencing of a panel of nine species. The expression of TLR11 and TLR12 was confirmed in the domestic horse by cDNA sequencing. Phylogenetic reconstruction of the TLR gene family in Perissodactyla identified six sub-families. TLR4 clustered together with TLR5; the TLR1-6-10 subfamily showed a high degree of sequence identity. The average estimated evolutionary divergence of all twelve TLRs studied was 0.3% among the Equidae; the most divergent CDS were those of Equus caballus and Equus hemionus kulan (1.34%) in the TLR3, and Equus africanus somaliensis and Equus quagga antiquorum (2.1%) in the TLR1 protein. In each TLR gene, there were haplotypes shared between equid species, most extensively in TLR3 and TLR9 CDS, and TLR6 amino acid sequence. All twelve TLR genes were under strong negative overall selection. Signatures of diversifying selection in specific codon sites were detected in all TLRs except TLR8. Differences in the selection patterns between virus-sensing and non-viral TLRs were observed.

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.

Associations between the presence of specific antibodies to the West Nile Virus infection and candidate genes in Romanian horses from the Danube delta

The West Nile virus (WNV) is a mosquito-borne flavivirus causing meningoencephalitis in humans and animals. Due to their particular susceptibility to WNV infection, horses serve as a sentinel species. In a population of Romanian semi-feral horses living in the Danube delta region, we have analyzed the distribution of candidate polymorphic genetic markers between anti WNV-IgG seropositive and seronegative horses. Thirty-six SNPs located in 28 immunity-related genes and 26 microsatellites located in the MHC and LY49 complex genomic regions were genotyped in 57 seropositive and 32 seronegative horses. The most significant association (p_corr < 0.0002) was found for genotypes composed of markers of the SLC11A1 and TLR4 genes. Markers of five other candidate genes (ADAM17, CXCR3, IL12A, MAVS, TNFA), along with 5 MHC class I and LY49-linked microsatellites were also associated with the WNV antibody status in this model horse population. The OAS1 gene, previously associated with WNV-induced clinical disease, was not associated with the presence of anti-WNV antibodies.