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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

Blockage of IDO enhances resistance to JE and reduces viral burden. a Levels of l-kynurenine in the sera and brain of BL/6 and IDO KO mice. Following JEV infection, levels of l-kynurenine in the sera and brain homogenates were estimated by HPLC at different time points. b Susceptibility of IDO-ablated mice to JE. BL/6 and IDO KO mice (4 to 5 weeks old, n = 25–30) were inoculated i.p. with JEV (3.0 × 107 PFU) and examined over 15 days for their survival. c Enhanced resistance to JE by IDO inhibition. BL/6 mice were infected i.p. with JEV and administered an IDO inhibitor (1-MT, 1 and 2 mg per mouse) every day. Left graph, curve showing survival rates; middle graph, proportion of mice showing neurological disorders during JE progression every 6 h from 4 to 11 dpi; right graph, changes in body weight. Changes in body weight were expressed as the mean percentage ± SD of body weight relative to the time of challenge. d Viral burden in lymphoid and inflammatory tissues during JE. Viral burden in the spleen and brain of infected mice was assessed by real-time qRT-PCR at the indicated time points post-infection. The viral RNA load was expressed as viral RNA copy number per microgram of total RNA (n = 5–7). *p < 0.05; **p < 0.01; ***p < 0.001 compared with levels in the indicated groups or in BL/6 control mice
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Fig2: Blockage of IDO enhances resistance to JE and reduces viral burden. a Levels of l-kynurenine in the sera and brain of BL/6 and IDO KO mice. Following JEV infection, levels of l-kynurenine in the sera and brain homogenates were estimated by HPLC at different time points. b Susceptibility of IDO-ablated mice to JE. BL/6 and IDO KO mice (4 to 5 weeks old, n = 25–30) were inoculated i.p. with JEV (3.0 × 107 PFU) and examined over 15 days for their survival. c Enhanced resistance to JE by IDO inhibition. BL/6 mice were infected i.p. with JEV and administered an IDO inhibitor (1-MT, 1 and 2 mg per mouse) every day. Left graph, curve showing survival rates; middle graph, proportion of mice showing neurological disorders during JE progression every 6 h from 4 to 11 dpi; right graph, changes in body weight. Changes in body weight were expressed as the mean percentage ± SD of body weight relative to the time of challenge. d Viral burden in lymphoid and inflammatory tissues during JE. Viral burden in the spleen and brain of infected mice was assessed by real-time qRT-PCR at the indicated time points post-infection. The viral RNA load was expressed as viral RNA copy number per microgram of total RNA (n = 5–7). *p < 0.05; **p < 0.01; ***p < 0.001 compared with levels in the indicated groups or in BL/6 control mice

Mentions: Because IDO expression in lymphoid and neural tissues was closely associated with JE progression, we were interested in investigating the role of IDO during JE progression. BL/6 mice infected with JEV showed gradually elevated release of the tryptophan catabolite l-kynurenine by cells expressing functional IDO enzyme activity in the sera and brain homogenates relative to basal levels in IDO KO mice (Fig. 2a), which suggests that IDO expression increases during JE progression. Also, we examined and compared the susceptibility of IDO-deficient (KO) mice to JE caused by neurotropic JEV infection with that of wild-type BL/6 mice (Fig. 2b). The ablation of IDO resulted in a markedly increased survival rate of 55 % in IDO KO mice vs. 18 % in BL/6 mice after JEV infection (3.0 × 107 PFU) (left curve in Fig. 2b), thereby signifying significantly enhanced resistance to JE. Likewise, IDO KO mice showed delayed signs of neurological disorder starting 5–6 dpi compared to BL/6 mice, which displayed signs of neurological disorder sooner and in a higher proportion of animals (middle graph in Fig. 2b), and IDO ablation resulted in less change in body weight (right graph in Fig. 2b). These results indicate that IDO ablation ameliorates JE progression. Furthermore, we tested the effect of the IDO-specific inhibitor 1-methyl-[d]-tryptophan (1-MT) on JE progression. As suggested by our other results, oral treatment with 1-MT resulted in reduced mortality, delayed neurological disorder, and less change in body weight compared to untreated BL/6 mice (Fig. 2c). Therefore, this result strengthens our finding that IDO ablation provides enhanced resistance to JE. To better understand JE progression in IDO-ablated mice, we examined viral burden in peripheral lymphoid and CNS tissues after JEV infection. IDO KO mice were observed to contain less amount of virus, with around a tenfold decrease in the spleen and brain compared to levels in BL/6 mice (Fig. 2d). Ultimately, these results suggest that IDO ablation ameliorates JE progression by regulating the viral burden in peripheral lymphoid and CNS tissues.Fig. 2


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)

Blockage of IDO enhances resistance to JE and reduces viral burden. a Levels of l-kynurenine in the sera and brain of BL/6 and IDO KO mice. Following JEV infection, levels of l-kynurenine in the sera and brain homogenates were estimated by HPLC at different time points. b Susceptibility of IDO-ablated mice to JE. BL/6 and IDO KO mice (4 to 5 weeks old, n = 25–30) were inoculated i.p. with JEV (3.0 × 107 PFU) and examined over 15 days for their survival. c Enhanced resistance to JE by IDO inhibition. BL/6 mice were infected i.p. with JEV and administered an IDO inhibitor (1-MT, 1 and 2 mg per mouse) every day. Left graph, curve showing survival rates; middle graph, proportion of mice showing neurological disorders during JE progression every 6 h from 4 to 11 dpi; right graph, changes in body weight. Changes in body weight were expressed as the mean percentage ± SD of body weight relative to the time of challenge. d Viral burden in lymphoid and inflammatory tissues during JE. Viral burden in the spleen and brain of infected mice was assessed by real-time qRT-PCR at the indicated time points post-infection. The viral RNA load was expressed as viral RNA copy number per microgram of total RNA (n = 5–7). *p < 0.05; **p < 0.01; ***p < 0.001 compared with levels in the indicated groups or in BL/6 control mice
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Related In: Results  -  Collection

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Fig2: Blockage of IDO enhances resistance to JE and reduces viral burden. a Levels of l-kynurenine in the sera and brain of BL/6 and IDO KO mice. Following JEV infection, levels of l-kynurenine in the sera and brain homogenates were estimated by HPLC at different time points. b Susceptibility of IDO-ablated mice to JE. BL/6 and IDO KO mice (4 to 5 weeks old, n = 25–30) were inoculated i.p. with JEV (3.0 × 107 PFU) and examined over 15 days for their survival. c Enhanced resistance to JE by IDO inhibition. BL/6 mice were infected i.p. with JEV and administered an IDO inhibitor (1-MT, 1 and 2 mg per mouse) every day. Left graph, curve showing survival rates; middle graph, proportion of mice showing neurological disorders during JE progression every 6 h from 4 to 11 dpi; right graph, changes in body weight. Changes in body weight were expressed as the mean percentage ± SD of body weight relative to the time of challenge. d Viral burden in lymphoid and inflammatory tissues during JE. Viral burden in the spleen and brain of infected mice was assessed by real-time qRT-PCR at the indicated time points post-infection. The viral RNA load was expressed as viral RNA copy number per microgram of total RNA (n = 5–7). *p < 0.05; **p < 0.01; ***p < 0.001 compared with levels in the indicated groups or in BL/6 control mice
Mentions: Because IDO expression in lymphoid and neural tissues was closely associated with JE progression, we were interested in investigating the role of IDO during JE progression. BL/6 mice infected with JEV showed gradually elevated release of the tryptophan catabolite l-kynurenine by cells expressing functional IDO enzyme activity in the sera and brain homogenates relative to basal levels in IDO KO mice (Fig. 2a), which suggests that IDO expression increases during JE progression. Also, we examined and compared the susceptibility of IDO-deficient (KO) mice to JE caused by neurotropic JEV infection with that of wild-type BL/6 mice (Fig. 2b). The ablation of IDO resulted in a markedly increased survival rate of 55 % in IDO KO mice vs. 18 % in BL/6 mice after JEV infection (3.0 × 107 PFU) (left curve in Fig. 2b), thereby signifying significantly enhanced resistance to JE. Likewise, IDO KO mice showed delayed signs of neurological disorder starting 5–6 dpi compared to BL/6 mice, which displayed signs of neurological disorder sooner and in a higher proportion of animals (middle graph in Fig. 2b), and IDO ablation resulted in less change in body weight (right graph in Fig. 2b). These results indicate that IDO ablation ameliorates JE progression. Furthermore, we tested the effect of the IDO-specific inhibitor 1-methyl-[d]-tryptophan (1-MT) on JE progression. As suggested by our other results, oral treatment with 1-MT resulted in reduced mortality, delayed neurological disorder, and less change in body weight compared to untreated BL/6 mice (Fig. 2c). Therefore, this result strengthens our finding that IDO ablation provides enhanced resistance to JE. To better understand JE progression in IDO-ablated mice, we examined viral burden in peripheral lymphoid and CNS tissues after JEV infection. IDO KO mice were observed to contain less amount of virus, with around a tenfold decrease in the spleen and brain compared to levels in BL/6 mice (Fig. 2d). Ultimately, these results suggest that IDO ablation ameliorates JE progression by regulating the viral burden in peripheral lymphoid and CNS tissues.Fig. 2

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