Interferon-γ and Tumor Necrosis Factor-α Mediate the Upregulation of Indoleamine 2,3-Dioxygenase and the Induction of Depressive-Like Behavior in Mice in Response to Bacillus Calmette-Guérin
Jason C. O'Connor, Caroline André, Yunxia Wang, Marcus A. Lawson, Sandra S. Szegedi et al.
behavioralmouseWild-type (WT) control mice and IFN-γR−− mice
Objective: Demonstrate the essential role of interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) in the induction of indoleamine 2,3-dioxygenase (IDO) and depressive-like behaviors in response to chronic immune activation via BCG infection
Materials & Equipment Checklist
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Equipment2
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Protocol Steps
View Abstract
Although the tryptophan-degrading enzyme, indoleamine 2,3-dioxygenase (IDO), is a pivotal mediator of inflammation-induced depression, its mechanism of regulation has not yet been investigated in this context. Here, we demonstrate an essential role for interferon (IFN)γ and tumor necrosis factor (TNF)α in the induction of IDO and depressive-like behaviors in response to chronic immune activation. Wild-type (WT) control mice and IFNγR −− mice were inoculated with an attenuated form of Mycobacterium bovis , bacille Calmette-Guérin (BCG). Infection with BCG induced an acute episode of sickness that was similar in WT and IFNγR −− mice. Increased immobility during the forced swim and tail suspension tests occurred in WT mice 7 d after BCG inoculation but was entirely absent in IFNγR −− mice. In WT mice, these indices of depressive-like behavior were associated with chronic upregulation of IFNγ, interleukin(IL)-1β, TNFα, and IDO. Proinflammatory cytokine expression was elevated in BCG-infected IFNγR −− mice as well, but upregulation of lung and brain IDO mRNA was completely abolished. This was accompanied by an attenuation of BCG-induced TNFα mRNA and the lack of an increase in plasma kynurenine/tryptophan ratio in the BCG-inoculated IFNγR −− mice compared with WT controls. Pretreatment of mice with the TNFα antagonist, etanercept, partially blunted BCG-induced IDO activation and depressive-like behavior. In accordance with these in vivo data, IFNγ and TNFα synergized to induce IDO in primary microglia. Together, these data demonstrate that IFNγ, with TNFα, is necessary for induction of IDO and depressive-like behavior in mice after BCG infection.
1
BCG Inoculation
Inoculate wild-type control mice and IFN-γR−− mice with attenuated Mycobacterium bovis bacille Calmette-Guérin
Not specifiedNot specified
Note: Two genotypes of mice were used for comparison
View evidence from paper
“Wild-type (WT) control mice and IFN-γR−− mice were inoculated with an attenuated form of Mycobacterium bovis, bacille Calmette-Guérin (BCG)”
2
Acute Sickness Observation
Monitor for acute sickness episode following BCG inoculation in both WT and IFN-γR−− mice
Not specifiedNot specified
Note: Acute sickness was similar in both WT and IFN-γR−− mice
View evidence from paper
“Infection with BCG induced an acute episode of sickness that was similar in WT and IFN-γR−− mice”
3
Forced Swim Test
Conduct forced swim test to measure depressive-like behavior by assessing immobility
Note: Increased immobility occurred in WT mice but was entirely absent in IFN-γR−− mice
View evidence from paper
“Increased immobility during the forced swim and tail suspension tests occurred in WT mice 7 d after BCG inoculation but was entirely absent in IFN-γR−− mice”
4
Tail Suspension Test
Conduct tail suspension test to measure depressive-like behavior by assessing immobility
Note: Increased immobility occurred in WT mice but was entirely absent in IFN-γR−− mice
View evidence from paper
“Increased immobility during the forced swim and tail suspension tests occurred in WT mice 7 d after BCG inoculation but was entirely absent in IFN-γR−− mice”
5
Cytokine and IDO mRNA Analysis
Measure chronic upregulation of IFN-γ, interleukin-1β, TNF-α, and IDO mRNA in WT mice following BCG infection
Not specifiedNot specified
Note: In WT mice, depressive-like behavior indices were associated with chronic upregulation of these markers
View evidence from paper
“In WT mice, these indices of depressive-like behavior were associated with chronic upregulation of IFN-γ, interleukin(IL)-1β, TNF-α, and IDO”
6
IDO mRNA Analysis in IFN-γR−− Mice
Measure lung and brain IDO mRNA upregulation in BCG-infected IFN-γR−− mice
Not specifiedNot specified
Note: Upregulation of lung and brain IDO mRNA was completely abolished in IFN-γR−− mice despite elevated proinflammatory cytokine expression
View evidence from paper
“Proinflammatory cytokine expression was elevated in BCG-infected IFN-γR−− mice as well, but upregulation of lung and brain IDO mRNA was completely abolished”
7
TNF-α mRNA and Kynurenine/Tryptophan Ratio Analysis
Measure BCG-induced TNF-α mRNA and plasma kynurenine/tryptophan ratio in IFN-γR−− mice compared with WT controls
Not specifiedNot specified
Note: IFN-γR−− mice showed attenuation of BCG-induced TNF-α mRNA and lack of increase in plasma kynurenine/tryptophan ratio
View evidence from paper
“This was accompanied by an attenuation of BCG-induced TNF-α mRNA and the lack of an increase in plasma kynurenine/tryptophan ratio in the BCG-inoculated IFN-γR−− mice compared with WT controls”
8
Etanercept Pretreatment Study
Pretreat mice with TNF-α antagonist etanercept and assess effects on BCG-induced IDO activation and depressive-like behavior
Not specifiedNot specified
Note: Etanercept partially blunted BCG-induced IDO activation and depressive-like behavior
View evidence from paper
“Pretreatment of mice with the TNF-α antagonist, etanercept, partially blunted BCG-induced IDO activation and depressive-like behavior”
9
Primary Microglia Culture Study
Assess IFN-γ and TNF-α synergistic effects on IDO induction in primary microglia in vitro
Not specifiedNot specified
Note: In vitro data confirmed that IFN-γ and TNF-α synergize to induce IDO
View evidence from paper
“In accordance with these in vivo data, IFN-γ and TNF-α synergized to induce IDO in primary microglia”
Subjects / Specimens
Species
mouse
Strain
Wild-type (WT) control mice and IFN-γR−− mice
Age
Not specified
Sex
unknown
Weight
Not specified
Two genotypes compared: WT control and IFN-γR knockout mice
