Inflammatory TH17 responses to infection with Mycobacterium avium subspecies paratuberculosis (MAP) in cattle and their potential role in the development of Johne's disease
Mycobacterium avium subspecies paratuberculosis (MAP) causes a chronic inflammatory gastrointestinal disease of ruminants known as Johne’s disease (JD). MAP primarily colonizes the ileum of ruminants, leading to reduced nutrient absorption, chronic diarrhea, and eventually death. The percentage of dairy operations infected MAP in the US may have risen to as much as 91% from earlier reports of 68%. In correspondence, an estimated dairy industry loss has increased from $200 million to $1.5 billion was due to JD. Control of JD is difficult largely due to insensitive diagnostic tools, a long subclinical stage of infection, and lack of effective vaccines. Correlates of protection are lacking in model systems of JD and the sources of inflammation due to JD are not well characterized. Inside macrophages, MAP survives and replicates. Monocyte-derived macrophages (MDMs), peripheral blood mononuclear cells (PBMCs), and various T-cells interact with MAP. Commonly studied immune responses, such as the Th1/Th2 paradigm, do not adequately explain host responses to MAP. The major remaining knowledge gaps in MAP immunopathogenesis include key inflammatory responders in the ileum, and how naïve T-cell responsive choice (Th1, Th2, Th17) is influenced. A potential role for non-classical immune responses to MAP, such as that mediated by Th17 cells, has been suggested. Indeed, MAP antigens induce mRNAs encoding the cytokines IL-23 and IL-17A in bovine PBMCs. IL-23 and IL-17A production are both associated with Th17-like immune responses. Th17 cells are also defined by surface expression of the IL-23 receptor (IL-23R). The mean relative percent (MRP) of T cell subtypes expressing IL-23R was determined by flow cytometry and indicated an increase in mean relative percent (MRP) of T cells (CD4+, CD8+, and TCR1+) in peripheral blood mononuclear cells (PBMCs) of JD+ cows with high and low expression of IL-23R (IL-23RHigh and IL-23RLow) when compared to JD- cows. Although MAP stimulates PBMCs to secrete IL-17A in-vitro, there were no differences in IL-17A levels between subclinical JD+ and JD- cows when analyzed by ELISA. Plasma with low JD+ score values had significantly more IL-17A when compared to plasma with high JD+ score values, establishing a moderate correlation between JD+ score and IL-17A. However, overall plasma from JD+ cows had significantly less IL-17A than plasma from JD- cows. Unlike IL-17A, IL-23 was greater in plasma from JD+ cows than in JD- cows. Evaluating the relationship that MAP is having on APCs and CD3+ in relation to Th17 cytokines (IL-23, IL-17A, IL-17F, IL-22, IL-27) as well as Th1 cytokine IFNγ, CD3+ were stimulated with MAP in the presence of APCs (MDMs or B cells) or alone and evaluated by RT-qPCR. MAP stimulation significantly increased production of mRNA encoding Th17 cytokines and IFNγ in CD3+ T cells regardless of APCs. However, the presence of MDMs significantly increase the quantity of mRNA. Lastly, we observed that αβ T cells (mostly CD4+) are responsible for production of Th17 cytokines as an early response to MAP in the absence of APCs. Our data suggests that Th17-like cells may indeed play a role in early immune responses to MAP infection and development or control of JD. Understanding the influences and potential novel mechanisms of an inflammatory pathway during MAP infection could be exploited for treatment, prevention, or diagnosis of JD.
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- In Collections
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Electronic Theses & Dissertations
- Copyright Status
- In Copyright
- Material Type
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Theses
- Authors
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DeKuiper, Justin Lee
- Thesis Advisors
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Coussens, Paul M.
Steibel, Juan
- Committee Members
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Petroff, Peggy
Norby, Bo
- Date
- 2019
- Program of Study
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Animal Science- Doctor of Philosophy
- Degree Level
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Doctoral
- Language
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English
- Pages
- xiii, 145 pages
- ISBN
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9781392508428
1392508428