Expression of inflammatory cytokine and inducible nitric oxide synthase genes in the small intestine and mesenteric lymph node tissues of pauci- and multibacillary sheep naturally infected with Mycobacterium avium ssp. paratuberculosis.

OBJECTIVE/BACKGROUND: Paratuberculosis (Johne's disease) is a chronic infectious granulomatous enteritis, primarily affecting ruminants, and caused by Mycobacterium avium ssp. paratuberculosis (MAP). The disease is widely prevalent throughout the world with significant economic losses. MAP has also been implicated with human Crohn's disease. There exists a strong correlation between the immune response and development of various types of pathologies in ruminants. The polarization of the immune response, which is critical to clinical outcome of the paratuberculosis infection, is controlled by the differential expression of certain cytokines and inducible nitric oxide synthase (iNOS) in Johne's disease. In previous studies, the role of different cytokines (Th1 and Th2) has been occasionally studied in sheep paratuberculosis. In the present study, we studied differential expression of interferon (IFN)-γ, interleukin (IL)-1α, IL-10, transforming growth factor (TGF)-β, iNOS, and TRAF1 genes in MAP-infected sheep and established relationship with distinct pathologies.

METHODS: Tissue sections (small intestine, ileocecal junction, and mesenteric lymph nodes) were collected from sheep suspected for Johne's disease and appropriately preserved for RNA extraction, polymerase chain reaction (PCR) analysis, and histopathology. Pathologic grading was done on the basis of nature and extent of cellular infiltration, granuloma formation and abundance of acid-fast bacilli. Six sheep each with pauci (PB)- and multibacillary (MB) lesions and six healthy control sheep were selected for cytokine studies. MAP in tissue extracted genomic DNA of sheep was quantified by a quantitative PCR assay. Tissue extracted RNA was reversed transcribed to prepare c-DNA from which quantitative reverse transcription PCR (qRT-PCR) was performed to amplify IFN-γ, IL-1β, IL-10, TGF-β, β-actin, TRAF1, and iNOS with Quantitect SYBR Green Master Mix. qRT-PCR data were analyzed using 2(-ΔΔCT) method using β-actin gene as a control. All qRT-PCR results were compared by using one-way analysis of variance (least significance difference and Duncan tests) for p-value using SPSS (version 7.5) for expression of each gene in tissues from infected and control sheep.

RESULTS: In the small intestine, PB sheep showed significant enhancements in the expression of IL-10, TGF-β, iNOS, and IFN-γ in comparison to similar tissues from uninfected control sheep. IL-1α expression was significantly reduced (p<0.01). The expression of IL-10 in the mesenteric lymph node (MLN) tissue of PB sheep was significantly increased (p<0.01) as compared with the control sheep. MB sheep revealed significantly enhanced expression of TGF-β mRNA and reduction in the expression of IL-1α in comparison to control sheep. In the MLN of MB sheep, the expressions of IL-10 and TGF-β were significantly (p<0.01) increased, and IFN-γ was significantly downregulated in comparison to uninfected control sheep. When the cytokine expression was compared between two distinctly infected groups, the MB sheep showed highly significant decrease (p<0.01) in the expression of iNOS and IFN-γ in the small intestine and IFN-γ in the MLN tissues.

CONCLUSION: The present study indicated that IFN-γ and iNOS were found to play important role in the induction of Th1 type immune response in PB sheep. MB sheep had significant reduction in expression of IFN-γ and iNOS and elevation of IL-10 and TGF-β, which was typical of Th2 cytokine pattern. Elevated expression of IL-10 and TGF-β in PB cases possibly suggests the role of T-regulatory cells and may follow an independent mechanism not typical of Th1 pattern. In view of significantly reduced expression in both forms of the disease, IL-1α may not be an important cytokine in ovine paratuberculosis.