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Impact of genotype 1 and 2 of porcine reproductive and respiratory syndrome viruses on interferon-α responses by plasmacytoid dendritic cells.

Baumann A, Mateu E, Murtaugh MP, Summerfield A - Vet. Res. (2013)

Bottom Line: Since inhibition of IFN-α expression might initiate PRRSV pathogenesis, we further characterized PRRSV effects and host modifying factors on IFN-α responses of pDC.The effect did not require live virus and was mediated through the TLR7 pathway.Furthermore, both IFN-γ and IL-4 significantly enhanced the pDC production of IFN-α in response to PRRSV exposure.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Virology and Immunoprophylaxis (IVI), Sensemattstrasse 293, Mittelhäusern, 3147, Switzerland. artur.summerfield@ivi.admin.ch.

ABSTRACT
Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) infections are characterized by prolonged viremia and viral shedding consistent with incomplete immunity. Type I interferons (IFN) are essential for mounting efficient antiviral innate and adaptive immune responses, but in a recent study, North American PRRSV genotype 2 isolates did not induce, or even strongly inhibited, IFN-α in plasmacytoid dendritic cells (pDC), representing "professional IFN-α-producing cells". Since inhibition of IFN-α expression might initiate PRRSV pathogenesis, we further characterized PRRSV effects and host modifying factors on IFN-α responses of pDC. Surprisingly, a variety of type 1 and type 2 PRRSV directly stimulated IFN-α secretion by pDC. The effect did not require live virus and was mediated through the TLR7 pathway. Furthermore, both IFN-γ and IL-4 significantly enhanced the pDC production of IFN-α in response to PRRSV exposure. PRRSV inhibition of IFN-α responses from enriched pDC stimulated by CpG oligodeoxynucleotides was weak or absent. VR-2332, the prototype genotype 2 PRRSV, only suppressed the responses by 34%, and the highest level of suppression (51%) was induced by a Chinese highly pathogenic PRRSV isolate. Taken together, these findings demonstrate that pDC respond to PRRSV and suggest that suppressive activities on pDC, if any, are moderate and strain-dependent. Thus, pDC may be a source of systemic IFN-α responses reported in PRRSV-infected animals, further contributing to the puzzling immunopathogenesis of PRRS.

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PRRSV sensing by pDC does not require live virus and is mediated via TLR7. (A) IFN-α induced by type 1 and 2 PRRSV (MOI of 1 TCID50/cell) in enriched pDC does not require live virus and is potentiated synergistically by IFN-γ. (B) Production of IFN-α by enriched pDC exposed to PRRSV (MOI of 2.5 TCID50/cell) is inhibited by IRS661, a TLR7 antagonist. IFN-α was determined by ELISA in supernatants harvested after 20 h. Bars indicate biological triplicates ± 1 standard deviation in one representative experiment out of two.
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Figure 3: PRRSV sensing by pDC does not require live virus and is mediated via TLR7. (A) IFN-α induced by type 1 and 2 PRRSV (MOI of 1 TCID50/cell) in enriched pDC does not require live virus and is potentiated synergistically by IFN-γ. (B) Production of IFN-α by enriched pDC exposed to PRRSV (MOI of 2.5 TCID50/cell) is inhibited by IRS661, a TLR7 antagonist. IFN-α was determined by ELISA in supernatants harvested after 20 h. Bars indicate biological triplicates ± 1 standard deviation in one representative experiment out of two.

Mentions: UV-inactivated type 1 LVP23 and type 2 VR-2332 PRRSV were used to evaluate if PRRSV-induced IFN-α responses in enriched pDC required live virus. As shown in Figure 3A, the intensity of IFN-α production was not altered by UV-inactivation indicating that the pDC response did not require replicating PRRSV. In the presence of IFN-γ, pDC-derived IFN-α secretion was increased with both UV-untreated and UV-treated PRRSV (see also Figure 4). Considering the central role of TLR7 in sensing RNA viruses by pDC[39], we investigated the effects of the specific TLR7 inhibitor IRS661[40] to inhibit PRRSV-induced IFN-α production. IRS661 is active on porcine cells and inhibits influenza virus-mediated pDC activation compared to a scrambled oligonulceotide[37]. We observed that pDC-derived IFN-α responses were drastically reduced or abrogated by TLR7 inhibition (Figure 3B), indicating that the TLR7 pathway is intimately involved in pDC sensing of PRRSV.


Impact of genotype 1 and 2 of porcine reproductive and respiratory syndrome viruses on interferon-α responses by plasmacytoid dendritic cells.

Baumann A, Mateu E, Murtaugh MP, Summerfield A - Vet. Res. (2013)

PRRSV sensing by pDC does not require live virus and is mediated via TLR7. (A) IFN-α induced by type 1 and 2 PRRSV (MOI of 1 TCID50/cell) in enriched pDC does not require live virus and is potentiated synergistically by IFN-γ. (B) Production of IFN-α by enriched pDC exposed to PRRSV (MOI of 2.5 TCID50/cell) is inhibited by IRS661, a TLR7 antagonist. IFN-α was determined by ELISA in supernatants harvested after 20 h. Bars indicate biological triplicates ± 1 standard deviation in one representative experiment out of two.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3672080&req=5

Figure 3: PRRSV sensing by pDC does not require live virus and is mediated via TLR7. (A) IFN-α induced by type 1 and 2 PRRSV (MOI of 1 TCID50/cell) in enriched pDC does not require live virus and is potentiated synergistically by IFN-γ. (B) Production of IFN-α by enriched pDC exposed to PRRSV (MOI of 2.5 TCID50/cell) is inhibited by IRS661, a TLR7 antagonist. IFN-α was determined by ELISA in supernatants harvested after 20 h. Bars indicate biological triplicates ± 1 standard deviation in one representative experiment out of two.
Mentions: UV-inactivated type 1 LVP23 and type 2 VR-2332 PRRSV were used to evaluate if PRRSV-induced IFN-α responses in enriched pDC required live virus. As shown in Figure 3A, the intensity of IFN-α production was not altered by UV-inactivation indicating that the pDC response did not require replicating PRRSV. In the presence of IFN-γ, pDC-derived IFN-α secretion was increased with both UV-untreated and UV-treated PRRSV (see also Figure 4). Considering the central role of TLR7 in sensing RNA viruses by pDC[39], we investigated the effects of the specific TLR7 inhibitor IRS661[40] to inhibit PRRSV-induced IFN-α production. IRS661 is active on porcine cells and inhibits influenza virus-mediated pDC activation compared to a scrambled oligonulceotide[37]. We observed that pDC-derived IFN-α responses were drastically reduced or abrogated by TLR7 inhibition (Figure 3B), indicating that the TLR7 pathway is intimately involved in pDC sensing of PRRSV.

Bottom Line: Since inhibition of IFN-α expression might initiate PRRSV pathogenesis, we further characterized PRRSV effects and host modifying factors on IFN-α responses of pDC.The effect did not require live virus and was mediated through the TLR7 pathway.Furthermore, both IFN-γ and IL-4 significantly enhanced the pDC production of IFN-α in response to PRRSV exposure.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Virology and Immunoprophylaxis (IVI), Sensemattstrasse 293, Mittelhäusern, 3147, Switzerland. artur.summerfield@ivi.admin.ch.

ABSTRACT
Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) infections are characterized by prolonged viremia and viral shedding consistent with incomplete immunity. Type I interferons (IFN) are essential for mounting efficient antiviral innate and adaptive immune responses, but in a recent study, North American PRRSV genotype 2 isolates did not induce, or even strongly inhibited, IFN-α in plasmacytoid dendritic cells (pDC), representing "professional IFN-α-producing cells". Since inhibition of IFN-α expression might initiate PRRSV pathogenesis, we further characterized PRRSV effects and host modifying factors on IFN-α responses of pDC. Surprisingly, a variety of type 1 and type 2 PRRSV directly stimulated IFN-α secretion by pDC. The effect did not require live virus and was mediated through the TLR7 pathway. Furthermore, both IFN-γ and IL-4 significantly enhanced the pDC production of IFN-α in response to PRRSV exposure. PRRSV inhibition of IFN-α responses from enriched pDC stimulated by CpG oligodeoxynucleotides was weak or absent. VR-2332, the prototype genotype 2 PRRSV, only suppressed the responses by 34%, and the highest level of suppression (51%) was induced by a Chinese highly pathogenic PRRSV isolate. Taken together, these findings demonstrate that pDC respond to PRRSV and suggest that suppressive activities on pDC, if any, are moderate and strain-dependent. Thus, pDC may be a source of systemic IFN-α responses reported in PRRSV-infected animals, further contributing to the puzzling immunopathogenesis of PRRS.

Show MeSH
Related in: MedlinePlus