Abstract
BackgroundHaemophilus parasuis is the causative agent of Glässer's disease in pigs. Currently, little is known about the molecular mechanisms that contribute to disease susceptibility. This study used a porcine oligonucleotide microarray to identify genes that were differentially expressed (DE) in the lungs of colostrum-deprived animals previously characterized as being either 'Fully Resistant' (FR) or 'Susceptible' to infection by H. parasuis in a bacterial challenge experiment.ResultsGene expression profiles of 'FR' and 'Susceptible' animals were obtained by the identification of genes that were differentially expressed between each of these groups and mock-inoculated 'Control' animals. At 24 hours post-inoculation, a total of 21 and 58 DE genes were identified in 'FR' and 'Susceptible' animals respectively. At 72 hours, the numbers of genes were 20 and 347 respectively. 'FR' animals at 24 hours exhibited an increased expression of genes encoding extracellular matrix and TGF-β signalling components, possibly indicative of tissue repair following the successful early resolution of infection. The gene expression profile of 'FR' animals at 72 hours supported the hypothesis that higher levels of antibacterial activity were responsible for the 'FR' phenotype, possibly due to an increase in natural immunoglobulin A and decrease in signalling by the immunoregulatory transcription factor peroxisome proliferator-activated receptor gamma (PPAR-γ). The expression profile of 'Susceptible' animals at both time-points was characterized by an imbalance in signalling between pro and anti-inflammatory cytokines and an increased expression of genes involved in biological processes associated with inflammation. These include the pro-inflammatory cytokine genes resistin (RETN) and interleukin 1-beta (IL1B). At 72 hours, a reduction in the expression of genes involved in antigen presentation by both MHC class I and II molecules was observed, which could have contributed to the inability of 'Susceptible' animals to clear infection.ConclusionsThis study is the first to have identified discrete sets of DE genes in pigs of differing susceptibility to H. parasuis infection. Consequently, several candidate genes and pathways for disease resistance or susceptibility phenotypes have been identified. In addition, the findings have shed light on the molecular pathology associated with Glässer's disease.
Highlights
Haemophilus parasuis is the causative agent of Glässer’s disease in pigs
This is not the case for the ‘Fully Resistant’ (FR) v S/S v FR’ comparison, and as the expression profiles described in the Results section only contain genes that were differentially expressed between the group of interest and both other groups, genes whose differential expression is attributable to such a ‘day effect’ should be absent from the expression profiles
This study has identified gene expression profiles associated with host resistance and susceptibility to infection by H. parasuis in CD piglets
Summary
Haemophilus parasuis is the causative agent of Glässer’s disease in pigs. Glässer’s disease in swine is caused by the bacterium Haemophilus parasuis. This bacterium is commonly isolated from the upper respiratory tract of healthy pigs. In some animals the bacterium can breach the mucosal epithelium and spread systemically to cause disease, by means that are poorly understood [1]. Glässer’s disease is characterized by polyserositis, arthritis and meningitis. It can be fatal and typically affects pigs 6-8 weeks of age. Approximately 30% of field strains are untypable by this method, and there is no absolute correlation between virulence and serotype, an indication of the high heterogeneity of H. parasuis isolates [3]. There is a need to investigate other methods of controlling the disease such as improving the disease resistance of pig populations through marker assisted selection
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