Abstract
Mycobacterium avium subspecies paratuberculosis (MAP), the causative agent of ruminant enteritis, targets intestinal macrophages. During infection, macrophages contribute to mucosal inflammation and development of granulomas in the small intestine which worsens as disease progression occurs. Vitamin D3 is an immunomodulatory steroid hormone with beneficial roles in host-pathogen interactions. Few studies have investigated immunologic roles of 25-hydroxyvitamin D3 (25(OH)D3) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) in cattle, particularly cattle infected with MAP. This study examined the effects of exogenous vitamin D3 on immune responses of monocyte derived macrophages (MDMs) isolated from dairy cattle naturally infected with MAP. MDMs were pre-treated with ± 100 ng/ml 25(OH)D3 or ± 4 ng/ml 1,25(OH)2D3, then incubated 24 hrs with live MAP in the presence of their respective pre-treatment concentrations. Following treatment with either vitamin D3 analog, phagocytosis of MAP by MDMs was significantly greater in clinically infected animals, with a greater amount of live and dead bacteria. Clinical cows had significantly less CD40 surface expression on MDMs compared to subclinical cows and noninfected controls. 1,25(OH)2D3 also significantly increased nitrite production in MAP infected cows. 1,25(OH)2D3 treatment played a key role in upregulating secretion of pro-inflammatory cytokines IL-1β and IL-12 while downregulating IL-10, IL-6, and IFN-γ. 1,25(OH)2D3 also negatively regulated transcripts of CYP24A1, CYP27B1, DEFB7, NOS2, and IL10. Results from this study demonstrate that vitamin D3 compounds, but mainly 1,25(OH)2D3, modulate both pro- and anti-inflammatory immune responses in dairy cattle infected with MAP, impacting the bacterial viability within the macrophage.
Highlights
Johne’s disease in ruminants, caused by the intracellular pathogen Mycobacterium avium subsp. paratuberculosis (MAP), is characterized by a chronic enteritis leading to clinical symptoms of watery diarrhea and wasting due to malabsorption of nutrients by a thickened intestinal wall (Manning and Collins, 2001)
The effects of exogenous vitamin D3 compounds on killing of Mycobacterium avium subspecies paratuberculosis (MAP) were assessed in monocyte derived macrophages (MDMs) cultures by BacLight viability dyes following incubation with MAP (10:1 multiplicity of infection (MOI)) for 24 hrs
The amount of total MAP phagocytized by MDMs was observed to be significantly (P < 0.001) greater in clinical animals, while subclinical cows demonstrated a decrease in MAP uptake compared to noninfected controls (P < 0.001)
Summary
Johne’s disease in ruminants, caused by the intracellular pathogen Mycobacterium avium subsp. paratuberculosis (MAP), is characterized by a chronic enteritis leading to clinical symptoms of watery diarrhea and wasting due to malabsorption of nutrients by a thickened intestinal wall (Manning and Collins, 2001). Macrophages are key reservoirs for MAP and provide a niche microenvironment in which the pathogen can replicate while concealing itself from innate and adaptive immune responses within the infected host. Mutations in TLR1, TLR2, and TLR4 have been found to be associated with increased susceptibility to MAP infection in cattle, possibly as a result in dampened pro-inflammatory cytokine responses such as IFN-g and IL-12 (Bhide et al, 2009; Mucha et al, 2009). Studies have shown MAP’s ability to block signaling of IFNg and TNF-a, which are both cell-activating pro-inflammatory cytokines that play a role in inhibiting intracellular replication of MAP (Stabel, 1995; Arsenault et al, 2012). A delicate balance of both pro-inflammatory and regulatory cytokine action is needed to prevent progression to advanced disease states by maintaining control of the infection while regulating inflammation in the host tissue
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