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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

Viral replication and innate immune responses of IDO-ablated microglia in response to JEV infection. Primary microglia recovered from BL/6 and IDO KO mice were infected with JEV at MOIs of 1.0 and 10 for viral replication and 10 for cytokine expression. JEV replication and the expression of cytokines, IFN-α/β, RLRs, ISGs, and IRF transcription factors were evaluated by real-time qRT-PCR using extracted total RNA at the indicated time point or 24 h pi. a JEV replication. b, c The expression of IFN-α/β and the ISG gene. d, e RLR and IRF expression. f TNF-α and IL-6 expression. The bar charts show the average ± SD of values derived from primary microglia assayed in quadruplicates
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Fig9: Viral replication and innate immune responses of IDO-ablated microglia in response to JEV infection. Primary microglia recovered from BL/6 and IDO KO mice were infected with JEV at MOIs of 1.0 and 10 for viral replication and 10 for cytokine expression. JEV replication and the expression of cytokines, IFN-α/β, RLRs, ISGs, and IRF transcription factors were evaluated by real-time qRT-PCR using extracted total RNA at the indicated time point or 24 h pi. a JEV replication. b, c The expression of IFN-α/β and the ISG gene. d, e RLR and IRF expression. f TNF-α and IL-6 expression. The bar charts show the average ± SD of values derived from primary microglia assayed in quadruplicates

Mentions: Microglia cells are CNS-resident macrophages that play an important role in regulating the neuroinflammation caused by sterile and non-sterile insults [53]. Bystander damage caused by pro-inflammatory mediators released from microglia likely contributes to the exacerbation of JE progression. Furthermore, because IDO-ablated microglia are considered to show stronger inflammatory responses after the virus gains access to the CNS, we examined the innate immune responses of primary microglia cells derived from the brain of fetal BL/6 and IDO KO mice in response to JEV infection. Our results revealed that primary microglia recovered from the brain of IDO-ablated mice showed similar innate immune responses to JEV infection as shown in macrophages derived from BM cells of IDO KO mice. IDO-ablated microglia were observed to allow JEV replication with moderately but not significantly lower levels compared to those of BL/6 mice (Fig. 9a). Consistent with this, IDO-ablated microglia displayed no apparent enhancement of IFN-I innate responses when the expression of IFN-α/β and ISG genes (ISG49, ISG54, ISG56) was examined (Fig. 9b, c). Also, no significant differences in the expression of RLRs and transcription factors IRF3 and IRF7 were observed between microglia derived from IDO KO and BL/6 mice (Fig. 9d, e), and both IDO-ablated and wild-type microglia showed comparable expression of pro-inflammatory cytokines TNF-α and IL-6 in response to JEV infection (Fig. 9f). Therefore, these results indicate that microglia could not provide dominant contribution to the regulation of JEV dissemination and JE progression in the CNS under an IDO-ablated environment.Fig. 9


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)

Viral replication and innate immune responses of IDO-ablated microglia in response to JEV infection. Primary microglia recovered from BL/6 and IDO KO mice were infected with JEV at MOIs of 1.0 and 10 for viral replication and 10 for cytokine expression. JEV replication and the expression of cytokines, IFN-α/β, RLRs, ISGs, and IRF transcription factors were evaluated by real-time qRT-PCR using extracted total RNA at the indicated time point or 24 h pi. a JEV replication. b, c The expression of IFN-α/β and the ISG gene. d, e RLR and IRF expression. f TNF-α and IL-6 expression. The bar charts show the average ± SD of values derived from primary microglia assayed in quadruplicates
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4835894&req=5

Fig9: Viral replication and innate immune responses of IDO-ablated microglia in response to JEV infection. Primary microglia recovered from BL/6 and IDO KO mice were infected with JEV at MOIs of 1.0 and 10 for viral replication and 10 for cytokine expression. JEV replication and the expression of cytokines, IFN-α/β, RLRs, ISGs, and IRF transcription factors were evaluated by real-time qRT-PCR using extracted total RNA at the indicated time point or 24 h pi. a JEV replication. b, c The expression of IFN-α/β and the ISG gene. d, e RLR and IRF expression. f TNF-α and IL-6 expression. The bar charts show the average ± SD of values derived from primary microglia assayed in quadruplicates
Mentions: Microglia cells are CNS-resident macrophages that play an important role in regulating the neuroinflammation caused by sterile and non-sterile insults [53]. Bystander damage caused by pro-inflammatory mediators released from microglia likely contributes to the exacerbation of JE progression. Furthermore, because IDO-ablated microglia are considered to show stronger inflammatory responses after the virus gains access to the CNS, we examined the innate immune responses of primary microglia cells derived from the brain of fetal BL/6 and IDO KO mice in response to JEV infection. Our results revealed that primary microglia recovered from the brain of IDO-ablated mice showed similar innate immune responses to JEV infection as shown in macrophages derived from BM cells of IDO KO mice. IDO-ablated microglia were observed to allow JEV replication with moderately but not significantly lower levels compared to those of BL/6 mice (Fig. 9a). Consistent with this, IDO-ablated microglia displayed no apparent enhancement of IFN-I innate responses when the expression of IFN-α/β and ISG genes (ISG49, ISG54, ISG56) was examined (Fig. 9b, c). Also, no significant differences in the expression of RLRs and transcription factors IRF3 and IRF7 were observed between microglia derived from IDO KO and BL/6 mice (Fig. 9d, e), and both IDO-ablated and wild-type microglia showed comparable expression of pro-inflammatory cytokines TNF-α and IL-6 in response to JEV infection (Fig. 9f). Therefore, these results indicate that microglia could not provide dominant contribution to the regulation of JEV dissemination and JE progression in the CNS under an IDO-ablated environment.Fig. 9

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