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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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IFN-α is induced by CD172lowCD4high pDC. Intracelluar staining of IFN-α was performed in CD172a enriched cells exposed to mock, PRRSV (MOI of 1 TCID50/cell) or CpG. Pseudo-color plot of pDC defined as CD172lowCD4high and CD172+CD4- populations are gated (left panel) and density plot show that only gated pDC are positive for intracellular IFN-α (right panel) after PRRSV or CpG stimulation. Gate frequency is indicated as mean ± 1 standard deviation of one experiment performed in triplicate.
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Figure 2: IFN-α is induced by CD172lowCD4high pDC. Intracelluar staining of IFN-α was performed in CD172a enriched cells exposed to mock, PRRSV (MOI of 1 TCID50/cell) or CpG. Pseudo-color plot of pDC defined as CD172lowCD4high and CD172+CD4- populations are gated (left panel) and density plot show that only gated pDC are positive for intracellular IFN-α (right panel) after PRRSV or CpG stimulation. Gate frequency is indicated as mean ± 1 standard deviation of one experiment performed in triplicate.

Mentions: Since both type 1 and type 2 PRRSV isolates were not strongly suppressive, we analyzed their ability to directly activate pDC secretion of IFN-α. Incubation of CD172a+ cells with LV or its MARC-145 cell-adapted form, LVP23, at an MOI of 0.1 did not elicit reproducible IFN-α expression (data not shown), but showed robust IFN-α production at an MOI of 1 (Figure 1B). To further investigate if pDC production of IFN-α was a universal response to PRRSV, type 2 strains VR-2332, JA-1262, a virulent recent USA field isolate, SY0608, a highly pathogenic field isolate from China, and the avirulent type 1 Olot/91 strain were incubated with enriched pDC. All isolates directly elicited IFN-α secretion by pDC, with type 2 PRRSV prototype VR-2332 displaying the lowest activity, whereas type 1 strain Olot/91 showing the highest average effect (Figure 1C). Overall, all isolates induced IFN-α secretion and the range of IFN-α production was independent of genotype or isolate virulence. To assess whether monocytes could be involved in the PRRSV-induced IFN-α secretion, we incubated unsorted PBMCs, CD14+, CD14+CD4- and CD14-CD4+ sorted cells with LV, LVP23, and CpG-ODN as a positive control. Whereas no or only low levels of IFN-α were found in PBMCs after PRRSV exposure (Figure 1D), high amounts were detected in the CD14-CD4+ cell fraction (Figure 1E). No IFN-α was detected in CD14+ cells (data not shown) excluding the possibility that monocytes induce IFN-α in response to PRRSV. To confirm that pDC were indeed the source of IFN-α in enriched CD172a cells, CD4, CD172a and intracellular IFN-α staining was performed. It revealed that only a proportion of CD4+ cells among the CD172a+ fraction were IFN-α positive after PRRSV or CpG-ODN stimulation whereas no IFN-α expressing cells were observed in the CD172+CD4- cells (Figure 2). Together with the data shown in Figure 1E, these results demonstrate that CD172a+CD14-CD4+ pDC[23] are the source of PRRSV-derived IFN-α responses. We also observed a higher percentage of pDC when they were stimulated by PRRSV (4%) compared to mock (1.5%) after 16 h of culture suggesting that PRRSV promotes survival of the pDC. It confirms that PRRSV interacted with pDC and promoted IFN-α secretion since the frequency of mock-treated pDC decreased in absence of stimulus.


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)

IFN-α is induced by CD172lowCD4high pDC. Intracelluar staining of IFN-α was performed in CD172a enriched cells exposed to mock, PRRSV (MOI of 1 TCID50/cell) or CpG. Pseudo-color plot of pDC defined as CD172lowCD4high and CD172+CD4- populations are gated (left panel) and density plot show that only gated pDC are positive for intracellular IFN-α (right panel) after PRRSV or CpG stimulation. Gate frequency is indicated as mean ± 1 standard deviation of one experiment performed in triplicate.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: IFN-α is induced by CD172lowCD4high pDC. Intracelluar staining of IFN-α was performed in CD172a enriched cells exposed to mock, PRRSV (MOI of 1 TCID50/cell) or CpG. Pseudo-color plot of pDC defined as CD172lowCD4high and CD172+CD4- populations are gated (left panel) and density plot show that only gated pDC are positive for intracellular IFN-α (right panel) after PRRSV or CpG stimulation. Gate frequency is indicated as mean ± 1 standard deviation of one experiment performed in triplicate.
Mentions: Since both type 1 and type 2 PRRSV isolates were not strongly suppressive, we analyzed their ability to directly activate pDC secretion of IFN-α. Incubation of CD172a+ cells with LV or its MARC-145 cell-adapted form, LVP23, at an MOI of 0.1 did not elicit reproducible IFN-α expression (data not shown), but showed robust IFN-α production at an MOI of 1 (Figure 1B). To further investigate if pDC production of IFN-α was a universal response to PRRSV, type 2 strains VR-2332, JA-1262, a virulent recent USA field isolate, SY0608, a highly pathogenic field isolate from China, and the avirulent type 1 Olot/91 strain were incubated with enriched pDC. All isolates directly elicited IFN-α secretion by pDC, with type 2 PRRSV prototype VR-2332 displaying the lowest activity, whereas type 1 strain Olot/91 showing the highest average effect (Figure 1C). Overall, all isolates induced IFN-α secretion and the range of IFN-α production was independent of genotype or isolate virulence. To assess whether monocytes could be involved in the PRRSV-induced IFN-α secretion, we incubated unsorted PBMCs, CD14+, CD14+CD4- and CD14-CD4+ sorted cells with LV, LVP23, and CpG-ODN as a positive control. Whereas no or only low levels of IFN-α were found in PBMCs after PRRSV exposure (Figure 1D), high amounts were detected in the CD14-CD4+ cell fraction (Figure 1E). No IFN-α was detected in CD14+ cells (data not shown) excluding the possibility that monocytes induce IFN-α in response to PRRSV. To confirm that pDC were indeed the source of IFN-α in enriched CD172a cells, CD4, CD172a and intracellular IFN-α staining was performed. It revealed that only a proportion of CD4+ cells among the CD172a+ fraction were IFN-α positive after PRRSV or CpG-ODN stimulation whereas no IFN-α expressing cells were observed in the CD172+CD4- cells (Figure 2). Together with the data shown in Figure 1E, these results demonstrate that CD172a+CD14-CD4+ pDC[23] are the source of PRRSV-derived IFN-α responses. We also observed a higher percentage of pDC when they were stimulated by PRRSV (4%) compared to mock (1.5%) after 16 h of culture suggesting that PRRSV promotes survival of the pDC. It confirms that PRRSV interacted with pDC and promoted IFN-α secretion since the frequency of mock-treated pDC decreased in absence of stimulus.

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