Genes controlling vaccine responses and disease resistance to respiratory viral pathogens in cattle

AbstractFarm animals remain at risk of endemic, exotic and newly emerging viruses. Vaccination is often promoted as the best possible solution, and yet for many pathogens, either there are no appropriate vaccines or those that are available are far from ideal. A complementary approach to disease control may be to identify genes and chromosomal regions that underlie genetic variation in disease resistance and response to vaccination. However, identification of the causal polymorphisms is not straightforward as it generally requires large numbers of animals with linked phenotypes and genotypes. Investigation of genes underlying complex traits such as resistance or response to viral pathogens requires several genetic approaches including candidate genes deduced from knowledge about the cellular pathways leading to protection or pathology, or unbiased whole genome scans using markers spread across the genome.Evidence for host genetic variation exists for a number of viral diseases in cattle including bovine respiratory disease and anecdotally, foot and mouth disease virus (FMDV). We immunised and vaccinated a cattle cross herd with a 40-mer peptide derived from FMDV and a vaccine against bovine respiratory syncytial virus (BRSV). Genetic variation has been quantified. A candidate gene approach has grouped high and low antibody and T cell responders by common motifs in the peptide binding pockets of the bovine major histocompatibility complex (BoLA) DRB3 gene. This suggests that vaccines with a minimal number of epitopes that are recognised by most cattle could be designed. Whole genome scans using microsatellite and single nucleotide polymorphism (SNP) markers has revealed many novel quantitative trait loci (QTL) and SNP markers controlling both humoral and cell-mediated immunity, some of which are in genes of known immunological relevance including the toll-like receptors (TLRs).The sequencing, assembly and annotation of livestock genomes and is continuing apace. In addition, provision of high-density SNP chips should make it possible to link phenotypes with genotypes in field populations without the need for structured populations or pedigree information. This will hopefully enable fine mapping of QTL and ultimate identification of the causal gene(s). The research could lead to selection of animals that are more resistant to disease and new ways to improve vaccine efficacy

Quantitative Trait Loci Associated with the Immune Response to a Bovine Respiratory Syncytial Virus Vaccine

Infectious disease is an important problem for animal breeders, farmers and governments worldwide. One approach to reducing disease is to breed for resistance. This linkage study used a Charolais-Holstein F2 cattle cross population (n = 501) which was genotyped for 165 microsatellite markers (covering all autosomes) to search for associations with phenotypes for Bovine Respiratory Syncytial Virus (BRSV) specific total-IgG, IgG1 and IgG2 concentrations at several time-points pre- and post-BRSV vaccination. Regions of the bovine genome which influenced the immune response induced by BRSV vaccination were identified, as well as regions associated with the clearance of maternally derived BRSV specific antibodies. Significant positive correlations were detected within traits across time, with negative correlations between the pre- and post-vaccination time points. The whole genome scan identified 27 Quantitative Trait Loci (QTL) on 13 autosomes. Many QTL were associated with the Thymus Helper 1 linked IgG2 response, especially at week 2 following vaccination. However the most significant QTL, which reached 5% genome-wide significance, was on BTA 17 for IgG1, also 2 weeks following vaccination. All animals had declining maternally derived BRSV specific antibodies prior to vaccination and the levels of BRSV specific antibody prior to vaccination were found to be under polygenic control with several QTL detected

Expression of the Bovine NK-Lysin Gene Family and Activity against Respiratory Pathogens

Unlike the genomes of many mammals that have a single NK-lysin gene, the cattle genome contains a family of four genes, one of which is expressed preferentially in the lung. In this study, we compared the expression of the four bovine NK-lysin genes in healthy animals to animals challenged with pathogens known to be associated with bovine respiratory disease (BRD) using transcriptome sequencing (RNA-seq). The expression of several NK-lysins, especially NK2C, was elevated in challenged relative to control animals. The effects of synthetic peptides corresponding to functional region helices 2 and 3 of each gene product were tested on both model membranes and bio-membranes. Circular dichroism spectroscopy indicated that these peptides adopted a more helical secondary structure upon binding to an anionic model membrane and liposome leakage assays suggested that these peptides disrupt membranes. Bacterial killing assays further confirmed the antimicrobial effects of these peptides on BRD-associated bacteria, including both Pasteurella multocida and Mannhemia haemolytica and an ultrastructural examination of NK-lysin-treated P. multocida cells by transmission electron microscopy revealed the lysis of target membranes. These studies demonstrate that the expanded bovine NK-lysin gene family is potentially important in host defense against pathogens involved in bovine respiratory disease

Genes of the Major Histocompatibility Complex in Cattle

The search for simple genetic traits that can be used as markers to predict variation in more complex genetic traits has been ongoing for several decades. For a given gene to be useful as a marker, it must have multiple forms, alleles, that are readily identifiable. Also, the frequency for the different alleles of the gene in a population must be such that most animals have two forms of the gene instead of one, otherwise statistical analysis is difficult. Only a few relationships between markers and production traits reported thus far have been utilized in production practices, presumably because of economic considerations. However, inexpensive tests to predict the genetic potential of individual breeding animals for multiple traits having strong genetic influence would likely gain acceptance and benefit the livestock industry. Initial studies in this area attempted to use blood types or blood protein variants as markers. These markers (proteins) had no apparent relationship to the variation in economic traits themselves, nor was there any knowledge of their proximity or linkage to other genes controlling economically important traits. Recombinant DNA technology has made the idea of marker assisted selection more feasible because it is now possible to isolate and study target genes that are known to, or are likely to, impact important traits such as disease resistance, reproduction, or growth. Also, as a result this technology it is possible to identify short stretches of DNA that are inherited in many allelic forms and are distributed randomly over the entire genome. This new kind of marker will allow for the identification of additional target genes through mapping studies and may be useful as tags to follow the inheritance of alleles of target genes which have limited numbers of allelic forms. Important advances in the statistical analysis of this type of genetic data have been made recently. All things considered, there is reason to be optimistic that in the next few years genetic markers can be useful as tools in selection programs. In the past few years, we have concentrated on a complex cluster of genes that are known to be involved in the immune response. These genes are the major histocompatibility complex (MHC) which are referred to as BoLA in cattle. The MHC genes produce two types of protein products. The class I proteins are present on the surface of most cells and function in the rejection of foreign cells such as transplants, tumors, or virus-infected cells. The class II proteins occur in cells of the immune system and are important in antibody formation. Antibody formation is initiated when specialized cells in the immune system take up foreign proteins, antigens, and cleave them into small fragments that are bound by the class II proteins. The binding of antigen fragments from vaccines or pathogens is a critical step in antibody formation which makes the class II genes good candidates to be markers for disease resistance or overall immunity. There are several class II genes and most of these genes have many variants, alleles. Experiments utilizing inbred strains of mice have shown that different class II alleles recognize different fragments of an antigen with differing efficiencies. Some alleles did not recognize any fragments of a rather large antigen which leads to a lack of antibody production. This result may provide an experimental basis for individual variations in antibody production observed in laboratory and domestic animals. We have isolated and characterized some of these class II genes from cattle and have used parts of these genes as probes to follow the inheritance of their allelic forms. We have also analyzed the association of several alleles with growth traits and antibody titers to vaccines