Submitted to: Biomed Central (BMC) Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2008
Publication Date: 9/23/2008
Citation: Wang, Y., Couture, O.P., Qu, L., Uthe, J., Bearson, S.M., Kuhar, D.J., Lunney, J.K., Nettleton, D., Dekkers, J.C., Tuggle, C.K. 2008. Analysis of Porcine Transcriptional Response to Salmonella enterica Serovar Choleraesuis Suggests Novel Targets of NFkappaB are Activated in the Mesenteric Lymph Node. Biomed Central (BMC) Genomics. 9(437). Available: http://biomedcentral.com/1471-2164/9/437. Interpretive Summary: Background: Salmonella enterica serovar Choleraesuis usually causes a systemic disease in swine. As described previously by our research group, the expression of specific immune genes in response to infection with serovar Choleraesuis is delayed compared to Salmonella enterica serovar Typhimurium that only causes enterocolitis. A lag in the host’s immune response may contribute to the ability of serovar Cholerasuis in achieving systemic disease. This project analyzed the global transcriptional response of pigs infected with serovar Choleraesuis to identify pig genes with differences in expression during the acute and chronic stages of infection. Description: The gene expression studies revealed the lack of dendritic cell-mediated antigen presentation in the cells of the gastrointestinal lymph nodes during infection with serovar Choleraesuis. Furthermore, new genes were identified that participate in a critical immune response system (NFkappaB). Impact: This research has identified a possible mechanism by which Salmonella serovar Cholerasuis initiates a systemic infection in swine. The functional pathways for antigen presentation by dendritic cells were not significantly altered during infection, suggesting that serovar Choleraesuis may escape recognition by an important immune cell in the pig. Industry, university and government researchers investigating host-pathogen interactions and specificity should find this research interesting, especially those analyzing systemic Salmonella infections.
Technical Abstract: The Affymetrix GeneChip® porcine genome array was used to identify differentially expressed genes in pig mesenteric lymph nodes (MLN) responding to infection with Salmonella enterica serovar Choleraesuis (S. Choleraesuis) at acute (8 hours (h), 24h and 48h post-inoculation (pi)) and chronic stages (21 days (d) pi). Analysis of variance with false discovery rate control showed that 1,853 genes exhibited significant changes in expression level with analysis of variance p-value<0.01 and estimated fold change >2 (q<0.26). Hierarchical clustering analysis on gene expression revealed several specific features of host response to infection. Down-regulation of translation-related genes at 8 hpi and 24 hpi implied that S. Choleraesuis repressed several steps in host protein translation. Genes involved in the Th1, innate immune/inflammation response and apoptosis pathways were induced significantly. However, the antigen presentation/dendritic cell (DC) function pathways were not affected significantly during infection. We suspect that a lack of strong DC-mediated antigen presentation in the MLN might be the reason that S. Choleraesuis infected pigs can develop a systemic infection. Furthermore, Quantitative-PCR analyses of 22 genes confirmed a strong NFkappaB pathway transcriptional response detected by the microarray results, as 59 known NFkappaB target genes were induced significantly at 8, 24 and/or 48 hpi. These target genes can be classified as an “Early” group (genes induced at either 8 or 24 hpi) and a “Late” group (genes only induced at 48 hpi) based on their expression patterns. Expanded GO-slim annotation revealed that functions for cytokine activity or chemokine activity were enriched within the Early group genes (Fisher exact test p=0.053), while the Late group was predominantly composed of signal transduction and cell metabolism annotated genes. In addition, our analysis suggests a number of putative novel NFkappaB targets, due to these genes having 1) similar expression pattern as known NFkappaB target genes and 2) computationally-identified NFkappaB binding motifs within the promoter region of the orthologous human gene. Our study not only provides novel genome-wide transcriptional profiling data on the porcine response to S. Choleraesuis, but also expands the understanding of NFkappaB signaling in response to Salmonella infection.