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Temporal effects of tumor necrosis factor-alpha on intracellular survival of Mycobacterium paratuberculosis
1Leptospirosis and Mycobacteriosis Research Unit, National Animal Disease Center, USDA-ARS, Ames, IA 50010, USA.
Abstract:
The causative agent in Johne's disease is Mycobacterium paratuberculosis, an intracellular pathogen which causes enteritis in ruminants. Little is known about interactions between the host cell (macrophage) and M. paratuberculosis; however, this bacterium is able to evade normal host immune defenses and cause a chronic infective state. In the present study, we evaluated whether activation of a murine macrophage cell line (J774.16) by pretreatment with recombinant murine tumor necrosis factor alpha (TNF) prior to infection with M. paratuberculosis would affect their ability to restrict growth and kill the ingested bacteria. A murine cell line was utilized owing to difficulty in obtaining bovine reagents and lack of a continuous bovine macrophage cell line for repeated experimentation. After 4 h of infection, numbers of viable bacteria in cell lysates were significantly lower for macrophages pretreated with 1000 IU TNF ml-1. The rate of bacterial growth as assessed by BACTEC radiometric culture system was also reduced at this time point. Upon further extension of the infection period to 72 h, we observed that moderate doses of TNF (10-1000 IU ml-1) significantly increased the number of viable M. paratuberculosis recovered whereas the highest dose of TNF (4000 IU ml-1) effectively reduced bacterial numbers. These data indicate that TNF can either enhance or reduce macrophage mycobactericidal and mycobacteriostatic activity depending upon both the level of TNF to which cells are exposed and the duration of infection.
Insights
Tumor necrosis factor alpha (TNF) influences Mycobacterium paratuberculosis infection in macrophages. TNF can either enhance or reduce bacterial growth depending on dose and infection duration, impacting Johne
Area of Science:
- Immunology
- Microbiology
- Veterinary Science
Background:
- Johne's disease in ruminants is caused by Mycobacterium paratuberculosis, an intracellular pathogen.
- Host cell (macrophage) interactions with M. paratuberculosis are poorly understood, yet the bacterium evades immune defenses.
- Understanding these interactions is crucial for developing effective treatments for Johne's disease.
Purpose of the Study:
- To investigate the effect of tumor necrosis factor alpha (TNF) activation on murine macrophages infected with M. paratuberculosis.
- To determine if pre-treating macrophages with TNF enhances their ability to restrict M. paratuberculosis growth and viability.
- To assess the dose- and time-dependent effects of TNF on macrophage anti-mycobacterial activity.
Main Methods:
- Utilized a murine macrophage cell line (J774.16) for experimental consistency and reagent availability.
- Pretreated macrophages with varying doses of recombinant murine TNF alpha before infection with M. paratuberculosis.
- Quantified viable M. paratuberculosis within cell lysates at 4 and 72 hours post-infection using BACTEC radiometric culture.
Main Results:
- At 4 hours post-infection, 1000 IU/ml TNF significantly reduced viable M. paratuberculosis numbers and bacterial growth rate.
- At 72 hours, moderate TNF doses (10-1000 IU/ml) increased viable M. paratuberculosis, while a high dose (4000 IU/ml) effectively reduced bacterial numbers.
- TNF exhibited dual effects on macrophage anti-mycobacterial activity, dependent on concentration and infection duration.
Conclusions:
- TNF's impact on macrophage control of M. paratuberculosis is complex and context-dependent.
- Both the dose of TNF and the duration of infection are critical factors influencing bacterial survival.
- These findings highlight the intricate interplay between host immune mediators and intracellular pathogens like M. paratuberculosis.
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