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Blockage of indoleamine 2,3-dioxygenase regulates Japanese encephalitis via enhancement of type I/II IFN innate and adaptive T-cell responses.

Kim SB, Choi JY, Uyangaa E, Patil AM, Hossain FM, Hur J, Park SY, Lee JH, Kim K, Eo SK - J Neuroinflammation (2016)

Bottom Line: Indoleamine 2,3-dioxygenase (IDO) has been identified as an enzyme associated with immunoregulatory function.Furthermore, inhibition of IDO activity enhanced resistance to JE, reduced the viral burden in lymphoid and CNS tissues, and resulted in early and increased CNS infiltration by Ly-6C(hi) monocytes, NK, CD4(+), and CD8(+) T-cells.Therefore, our data provide valuable insight into the use of IDO inhibition by specific inhibitors as a promising tool for therapeutic and prophylactic strategies against viral encephalitis caused by neurotropic viruses.

View Article: PubMed Central - PubMed

Affiliation: College of Veterinary Medicine and Bio-Safety Research Institute, Chonbuk National University, Iksan, 54596, Republic of Korea.

ABSTRACT

Background: Japanese encephalitis (JE), a leading cause of viral encephalitis, is characterized by extensive neuroinflammation following infection with neurotropic JE virus (JEV). Indoleamine 2,3-dioxygenase (IDO) has been identified as an enzyme associated with immunoregulatory function. Although the regulatory role of IDO in viral replication has been postulated, the in vivo role of IDO activity has not been fully addressed in neurotropic virus-caused encephalitis.

Methods: Mice in which IDO activity was inhibited by genetic ablation or using a specific inhibitor were examined for mortality and clinical signs after infection. Neuroinflammation was evaluated by central nervous system (CNS) infiltration of leukocytes and cytokine expression. IDO expression, viral burden, JEV-specific T-cell, and type I/II interferon (IFN-I/II) innate responses were also analyzed.

Results: Elevated expression of IDO activity in myeloid and neuron cells of the lymphoid and CNS tissues was closely associated with clinical signs of JE. Furthermore, inhibition of IDO activity enhanced resistance to JE, reduced the viral burden in lymphoid and CNS tissues, and resulted in early and increased CNS infiltration by Ly-6C(hi) monocytes, NK, CD4(+), and CD8(+) T-cells. JE amelioration in IDO-ablated mice was also associated with enhanced NK and JEV-specific T-cell responses. More interestingly, IDO ablation induced rapid enhancement of type I IFN (IFN-I) innate responses in CD11c(+) dendritic cells (DCs), including conventional and plasmacytoid DCs, following JEV infection. This enhanced IFN-I innate response in IDO-ablated CD11c(+) DCs was coupled with strong induction of PRRs (RIG-I, MDA5), transcription factors (IRF7, STAT1), and antiviral ISG genes (Mx1, Mx2, ISG49, ISG54, ISG56). IDO ablation also enhanced the IFN-I innate response in neuron cells, which may delay the spread of virus in the CNS. Finally, we identified that IDO ablation in myeloid cells derived from hematopoietic stem cells (HSCs) dominantly contributed to JE amelioration and that HSC-derived leukocytes played a key role in the enhanced IFN-I innate responses in the IDO-ablated environment.

Conclusions: Inhibition of IDO activity ameliorated JE via enhancement of antiviral IFN-I/II innate and adaptive T-cell responses and increased CNS infiltration of peripheral leukocytes. Therefore, our data provide valuable insight into the use of IDO inhibition by specific inhibitors as a promising tool for therapeutic and prophylactic strategies against viral encephalitis caused by neurotropic viruses.

No MeSH data available.


Related in: MedlinePlus

Enhancement of NK cell activation by IDO ablation. a NK cell frequency and number. The frequency and absolute number of CD3−NK1.1+DX5+ NK cells in the spleen were determined by flow cytometric analysis 2 dpi. Values in representative dot plots on the left denote the average percentage of splenic NK cells derived from at least four mice per group, after gating on CD3− cells; the bar graph on the right denotes the average ± SD of splenic NK cell numbers derived from at least four mice per group. b, c Activation of NK cells. The activation of CD3−NK1.1+DX5+ NK cells was evaluated by intracellular IFN-γ and granzyme B (GrB) staining upon stimulation with PMA plus ionomycin. Values in the representative dot plots on the left denote the average percentage of IFN-γ- or GrB-producing NK cells derived from at least four mice per group; the bar graphs on the right show the average number ± SD of NK cells producing IFN-γ or GrB in the spleens of at least four mice per group. **p < 0.01; ***p < 0.001 compared with levels in the indicated groups
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Fig4: Enhancement of NK cell activation by IDO ablation. a NK cell frequency and number. The frequency and absolute number of CD3−NK1.1+DX5+ NK cells in the spleen were determined by flow cytometric analysis 2 dpi. Values in representative dot plots on the left denote the average percentage of splenic NK cells derived from at least four mice per group, after gating on CD3− cells; the bar graph on the right denotes the average ± SD of splenic NK cell numbers derived from at least four mice per group. b, c Activation of NK cells. The activation of CD3−NK1.1+DX5+ NK cells was evaluated by intracellular IFN-γ and granzyme B (GrB) staining upon stimulation with PMA plus ionomycin. Values in the representative dot plots on the left denote the average percentage of IFN-γ- or GrB-producing NK cells derived from at least four mice per group; the bar graphs on the right show the average number ± SD of NK cells producing IFN-γ or GrB in the spleens of at least four mice per group. **p < 0.01; ***p < 0.001 compared with levels in the indicated groups

Mentions: Antiviral innate NK cell activation is believed to play an important role in regulating JE progression through the control and clearance of JEV in extraneural and neural tissues [38]. Therefore, in order to characterize the immunological parameters associated with control of JEV replication in IDO KO mice, we examined and compared NK cell responses in both BL/6 and IDO KO mice. Because JEV was administered intraperitoneally, analysis of the spleen provides insight into how IDO modulates the innate immune and inflammatory responses during the early phase of infection. Analysis of splenic NK cells revealed that BL/6 mice exhibited a reduction in CD3−NK1.1+DX5+ NK cells following JEV infection (Fig. 4a), as if wild-type mice previously showed decreased number of NK cells [24]. However, IDO KO mice showed less of a reduction in the number of CD3−NK1.1+DX5+ NK cells. Consequently, an increase in the total number of splenic NK cells was detected in IDO KO mice compared to BL/6 mice. Moreover, when the activation of NK cells was evaluated by the production of IFN-γ and granzyme B from NK cells, the frequency and the total number of CD3−NK1.1+DX5+ NK cells producing IFN-γ and granyzme B were apparently increased in IDO KO mice (Fig. 4b, c). Therefore, this result indicates that increased activation of NK cells plays a role in the early control of JEV replication, thereby resulting in the amelioration of JE progression.Fig. 4


Blockage of indoleamine 2,3-dioxygenase regulates Japanese encephalitis via enhancement of type I/II IFN innate and adaptive T-cell responses.

Kim SB, Choi JY, Uyangaa E, Patil AM, Hossain FM, Hur J, Park SY, Lee JH, Kim K, Eo SK - J Neuroinflammation (2016)

Enhancement of NK cell activation by IDO ablation. a NK cell frequency and number. The frequency and absolute number of CD3−NK1.1+DX5+ NK cells in the spleen were determined by flow cytometric analysis 2 dpi. Values in representative dot plots on the left denote the average percentage of splenic NK cells derived from at least four mice per group, after gating on CD3− cells; the bar graph on the right denotes the average ± SD of splenic NK cell numbers derived from at least four mice per group. b, c Activation of NK cells. The activation of CD3−NK1.1+DX5+ NK cells was evaluated by intracellular IFN-γ and granzyme B (GrB) staining upon stimulation with PMA plus ionomycin. Values in the representative dot plots on the left denote the average percentage of IFN-γ- or GrB-producing NK cells derived from at least four mice per group; the bar graphs on the right show the average number ± SD of NK cells producing IFN-γ or GrB in the spleens of at least four mice per group. **p < 0.01; ***p < 0.001 compared with levels in the indicated groups
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Related In: Results  -  Collection

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Fig4: Enhancement of NK cell activation by IDO ablation. a NK cell frequency and number. The frequency and absolute number of CD3−NK1.1+DX5+ NK cells in the spleen were determined by flow cytometric analysis 2 dpi. Values in representative dot plots on the left denote the average percentage of splenic NK cells derived from at least four mice per group, after gating on CD3− cells; the bar graph on the right denotes the average ± SD of splenic NK cell numbers derived from at least four mice per group. b, c Activation of NK cells. The activation of CD3−NK1.1+DX5+ NK cells was evaluated by intracellular IFN-γ and granzyme B (GrB) staining upon stimulation with PMA plus ionomycin. Values in the representative dot plots on the left denote the average percentage of IFN-γ- or GrB-producing NK cells derived from at least four mice per group; the bar graphs on the right show the average number ± SD of NK cells producing IFN-γ or GrB in the spleens of at least four mice per group. **p < 0.01; ***p < 0.001 compared with levels in the indicated groups
Mentions: Antiviral innate NK cell activation is believed to play an important role in regulating JE progression through the control and clearance of JEV in extraneural and neural tissues [38]. Therefore, in order to characterize the immunological parameters associated with control of JEV replication in IDO KO mice, we examined and compared NK cell responses in both BL/6 and IDO KO mice. Because JEV was administered intraperitoneally, analysis of the spleen provides insight into how IDO modulates the innate immune and inflammatory responses during the early phase of infection. Analysis of splenic NK cells revealed that BL/6 mice exhibited a reduction in CD3−NK1.1+DX5+ NK cells following JEV infection (Fig. 4a), as if wild-type mice previously showed decreased number of NK cells [24]. However, IDO KO mice showed less of a reduction in the number of CD3−NK1.1+DX5+ NK cells. Consequently, an increase in the total number of splenic NK cells was detected in IDO KO mice compared to BL/6 mice. Moreover, when the activation of NK cells was evaluated by the production of IFN-γ and granzyme B from NK cells, the frequency and the total number of CD3−NK1.1+DX5+ NK cells producing IFN-γ and granyzme B were apparently increased in IDO KO mice (Fig. 4b, c). Therefore, this result indicates that increased activation of NK cells plays a role in the early control of JEV replication, thereby resulting in the amelioration of JE progression.Fig. 4

Bottom Line: Indoleamine 2,3-dioxygenase (IDO) has been identified as an enzyme associated with immunoregulatory function.Furthermore, inhibition of IDO activity enhanced resistance to JE, reduced the viral burden in lymphoid and CNS tissues, and resulted in early and increased CNS infiltration by Ly-6C(hi) monocytes, NK, CD4(+), and CD8(+) T-cells.Therefore, our data provide valuable insight into the use of IDO inhibition by specific inhibitors as a promising tool for therapeutic and prophylactic strategies against viral encephalitis caused by neurotropic viruses.

View Article: PubMed Central - PubMed

Affiliation: College of Veterinary Medicine and Bio-Safety Research Institute, Chonbuk National University, Iksan, 54596, Republic of Korea.

ABSTRACT

Background: Japanese encephalitis (JE), a leading cause of viral encephalitis, is characterized by extensive neuroinflammation following infection with neurotropic JE virus (JEV). Indoleamine 2,3-dioxygenase (IDO) has been identified as an enzyme associated with immunoregulatory function. Although the regulatory role of IDO in viral replication has been postulated, the in vivo role of IDO activity has not been fully addressed in neurotropic virus-caused encephalitis.

Methods: Mice in which IDO activity was inhibited by genetic ablation or using a specific inhibitor were examined for mortality and clinical signs after infection. Neuroinflammation was evaluated by central nervous system (CNS) infiltration of leukocytes and cytokine expression. IDO expression, viral burden, JEV-specific T-cell, and type I/II interferon (IFN-I/II) innate responses were also analyzed.

Results: Elevated expression of IDO activity in myeloid and neuron cells of the lymphoid and CNS tissues was closely associated with clinical signs of JE. Furthermore, inhibition of IDO activity enhanced resistance to JE, reduced the viral burden in lymphoid and CNS tissues, and resulted in early and increased CNS infiltration by Ly-6C(hi) monocytes, NK, CD4(+), and CD8(+) T-cells. JE amelioration in IDO-ablated mice was also associated with enhanced NK and JEV-specific T-cell responses. More interestingly, IDO ablation induced rapid enhancement of type I IFN (IFN-I) innate responses in CD11c(+) dendritic cells (DCs), including conventional and plasmacytoid DCs, following JEV infection. This enhanced IFN-I innate response in IDO-ablated CD11c(+) DCs was coupled with strong induction of PRRs (RIG-I, MDA5), transcription factors (IRF7, STAT1), and antiviral ISG genes (Mx1, Mx2, ISG49, ISG54, ISG56). IDO ablation also enhanced the IFN-I innate response in neuron cells, which may delay the spread of virus in the CNS. Finally, we identified that IDO ablation in myeloid cells derived from hematopoietic stem cells (HSCs) dominantly contributed to JE amelioration and that HSC-derived leukocytes played a key role in the enhanced IFN-I innate responses in the IDO-ablated environment.

Conclusions: Inhibition of IDO activity ameliorated JE via enhancement of antiviral IFN-I/II innate and adaptive T-cell responses and increased CNS infiltration of peripheral leukocytes. Therefore, our data provide valuable insight into the use of IDO inhibition by specific inhibitors as a promising tool for therapeutic and prophylactic strategies against viral encephalitis caused by neurotropic viruses.

No MeSH data available.


Related in: MedlinePlus