Mannan oligosaccharide modulates gene expression profile in pigs experimentally infected with porcine reproductive and respiratory syndrome virus.

This study characterized gene expression in peripheral blood mononuclear cells (PBMC) and bronchoalveolar lavage fluid (BALF) cells from control- or mannan oligosaccharide (MOS)-fed pigs with or without porcine reproductive and respiratory syndrome virus (PRRSV) at d 7 postinfection (PI). Weaned pigs (3 wk old) fed 0 or 0.2% MOS (Bio-Mos) diets were intranasally inoculated with PRRSV or a sterile medium at 5 wk of age. Total RNA (3 pigs/treatment) was extracted from cells. Double-stranded cDNA was amplified, labeled, and further hybridized to the Affymetrix GeneChip Porcine Genome Array consisting of 23,937 probe sets representing 20,201 genes. Microarray data were analyzed in R using packages from the Bioconductor project. Differential gene expression was tested by fitting a mixed linear model equivalent to a 2 × 2 factorial ANOVA using the limma package. Dietary MOS and PRRSV changed the expression of thousands of probe sets in PBMC and BALF cells (P < 0.05). The MOS × PRRSV interaction altered the expression of more nonimmune probe sets in PBMC (977 up, 1,128 down) than in BALF cells (117 up, 78 down). The MOS × PRRSV interaction (P < 0.05) for immune probe sets in PBMC affected genes encoding key inflammatory mediators. In uninfected pigs, gene expression of IL-1α, IL-6, myeloid differentiation factor 88, Toll-like receptor (TLR) 4, major histocompatibility complex (MHC) II, and dead box polypeptide 58 increased in PBMC of MOS-fed pigs (P < 0.05). This suggests that MOS enhances disease resistance in pigs and supports the fact that MOS induced a rapid increase in leukocytes at d 3 and 7 PI. Within infected pigs, however, MOS reduced the expression of IL-1β, IL-6, IL-8, macrophage inflammatory protein (MIP)-1α, MIP-1β, monocyte chemotactic protein (MCP)-1, and TLR4 genes in PBMC (P < 0.05). This finding may explain why fever was ameliorated in infected pigs fed MOS by d 7 PI. The expression of IL-1β, IL-6, MIP-1β, MCP-1, and TLR4 genes was confirmed by quantitative real-time reverse-transcription PCR. In BALF cells of infected pigs, MOS reduced the gene expression of TLR4, MHCII, and molecules associated with the complement system, but increased the gene expression of MHCI. In short, MOS regulated the expression of nonimmune and immune genes in pig leukocytes, perhaps providing benefits by enhancing the immune responses of the pigs to an infection, while preventing overstimulation of the immune system.