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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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Cytokine-enhancement of pDC IFN-α production induced by type 1 and 2 PRRSV. LVP23 (A) or VR-2332 (B) at an MOI of 1 TCID50/cell were incubated with pDC alone or in the presence of IFN-β (100 U/mL), IFN-γ (10 ng/mL), Flt3-L (100 U/mL), GM-CSF (100 U/mL) and IL-4 (100 U/mL). IFN-α was determined by ELISA in supernatants harvested after 20 h. Boxplots are marked by the median (middle line), 25th and 75th percentiles (boxes), maximum and minimum values (whiskers) and the mean (dotted line) representing three independent experiments each performed in triplicate cultures. Significant difference in the median value is indicated by an asterisk mark compared to untreated cells (“none”) using the Mann–Whitney Rank Sum test (P < 0.02).
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Figure 4: Cytokine-enhancement of pDC IFN-α production induced by type 1 and 2 PRRSV. LVP23 (A) or VR-2332 (B) at an MOI of 1 TCID50/cell were incubated with pDC alone or in the presence of IFN-β (100 U/mL), IFN-γ (10 ng/mL), Flt3-L (100 U/mL), GM-CSF (100 U/mL) and IL-4 (100 U/mL). IFN-α was determined by ELISA in supernatants harvested after 20 h. Boxplots are marked by the median (middle line), 25th and 75th percentiles (boxes), maximum and minimum values (whiskers) and the mean (dotted line) representing three independent experiments each performed in triplicate cultures. Significant difference in the median value is indicated by an asterisk mark compared to untreated cells (“none”) using the Mann–Whitney Rank Sum test (P < 0.02).

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)

Cytokine-enhancement of pDC IFN-α production induced by type 1 and 2 PRRSV. LVP23 (A) or VR-2332 (B) at an MOI of 1 TCID50/cell were incubated with pDC alone or in the presence of IFN-β (100 U/mL), IFN-γ (10 ng/mL), Flt3-L (100 U/mL), GM-CSF (100 U/mL) and IL-4 (100 U/mL). IFN-α was determined by ELISA in supernatants harvested after 20 h. Boxplots are marked by the median (middle line), 25th and 75th percentiles (boxes), maximum and minimum values (whiskers) and the mean (dotted line) representing three independent experiments each performed in triplicate cultures. Significant difference in the median value is indicated by an asterisk mark compared to untreated cells (“none”) using the Mann–Whitney Rank Sum test (P < 0.02).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 4: Cytokine-enhancement of pDC IFN-α production induced by type 1 and 2 PRRSV. LVP23 (A) or VR-2332 (B) at an MOI of 1 TCID50/cell were incubated with pDC alone or in the presence of IFN-β (100 U/mL), IFN-γ (10 ng/mL), Flt3-L (100 U/mL), GM-CSF (100 U/mL) and IL-4 (100 U/mL). IFN-α was determined by ELISA in supernatants harvested after 20 h. Boxplots are marked by the median (middle line), 25th and 75th percentiles (boxes), maximum and minimum values (whiskers) and the mean (dotted line) representing three independent experiments each performed in triplicate cultures. Significant difference in the median value is indicated by an asterisk mark compared to untreated cells (“none”) using the Mann–Whitney Rank Sum test (P < 0.02).
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