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Aedes aegypti saliva alters leukocyte recruitment and cytokine signaling by antigen-presenting cells during West Nile virus infection.

Schneider BS, Soong L, Coffey LL, Stevenson HL, McGee CE, Higgs S - PLoS ONE (2010)

Bottom Line: Antigen-presenting cell (APC) signals have a profound effect on host antiviral responses and disease severity.Our in vitro results suggest that mosquito saliva significantly decreases the expression of interferon-beta and inducible nitric oxide synthase in macrophages (by as much as 50 and 70%, respectively), whilst transiently enhancing interleukin-10 (IL-10) expression.In vivo results indicate that the predominate effect of mosquito feeding is to significantly reduce the recruitment of T cells, leading the inoculation site of mice exposed to WNV alone to have up to 2.8 fold more t cells as mice infected in the presence of mosquito saliva.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Center for Biodefense & Emerging Infectious Diseases, University of Texas Medical Branch, Galveston, Texas, United States of America.

ABSTRACT
West Nile virus (WNV) is transmitted during mosquito bloodfeeding. Consequently, the first vertebrate cells to contact WNV are cells in the skin, followed by those in the draining lymph node. Macrophages and dendritic cells are critical early responders in host defense against WNV infection, not just because of their role in orchestrating the immune response, but also because of their importance as sites of early peripheral viral replication. Antigen-presenting cell (APC) signals have a profound effect on host antiviral responses and disease severity. During transmission, WNV is intimately associated with mosquito saliva. Due to the ability of mosquito saliva to affect inflammation and immune responses, and the importance of understanding early events in WNV infection, we investigated whether mosquito saliva alters APC signaling during arbovirus infection, and if alterations in cell recruitment occur when WNV infection is initiated with mosquito saliva. Accordingly, experiments were performed with cultured dendritic cells and macrophages, flow cytometry was used to characterize infiltrating cell types in the skin and lymph nodes during early infection, and real-time RT-PCR was employed to evaluate virus and cytokine levels. Our in vitro results suggest that mosquito saliva significantly decreases the expression of interferon-beta and inducible nitric oxide synthase in macrophages (by as much as 50 and 70%, respectively), whilst transiently enhancing interleukin-10 (IL-10) expression. In vivo results indicate that the predominate effect of mosquito feeding is to significantly reduce the recruitment of T cells, leading the inoculation site of mice exposed to WNV alone to have up to 2.8 fold more t cells as mice infected in the presence of mosquito saliva. These shifts in cell population are associated with significantly elevated IL-10 and WNV (up to 4.0 and 10 fold, respectively) in the skin and draining lymph nodes. These results suggest that mosquito saliva dysregulates APC antiviral signaling, and reveal a possible mechanism for the observed enhancement of WNV disease mediated by mosquito saliva via a reduction of T lymphocyte and antiviral activity at the inoculation site, an elevated abundance of susceptible cell types, and a concomitant increase in immunoregulatory activity of IL-10.

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Cytokine mRNA expression in bone marrow-derived DCs following infection with WNV.IFN-β and IL-10 levels were assessed by real-time RT-PCR at 24 and 48 h post-infection (MOI = 5). Their mRNA expression levels were normalized to those of the GAPDH gene. The means ± standard deviation are shown, and an asterisk signifies a statistically significant difference (p<0.05) as compared to the group infected with WNV alone as determined by Mann-Whitney test. IFN-γ, IL-2, IL-4, IL-12, and IL-1β mRNA expression, as well as WNV titers (assessed by titration on cell culture) were found not to vary among groups (data not shown). Control groups were mock infected with PBS alone. This experiment was repeated three times.
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pone-0011704-g003: Cytokine mRNA expression in bone marrow-derived DCs following infection with WNV.IFN-β and IL-10 levels were assessed by real-time RT-PCR at 24 and 48 h post-infection (MOI = 5). Their mRNA expression levels were normalized to those of the GAPDH gene. The means ± standard deviation are shown, and an asterisk signifies a statistically significant difference (p<0.05) as compared to the group infected with WNV alone as determined by Mann-Whitney test. IFN-γ, IL-2, IL-4, IL-12, and IL-1β mRNA expression, as well as WNV titers (assessed by titration on cell culture) were found not to vary among groups (data not shown). Control groups were mock infected with PBS alone. This experiment was repeated three times.

Mentions: To examine the effects of exposure to mosquito saliva on DC function during WNV infection, we measured cytokine expression in bone marrow-derived DCs at 24 h and 48 h p.i. WNV infection of DCs resulted in high type I IFN expression levels, with little to no IFN detectable in uninfected control DCs or DCs treated with SGE alone. At 24 h and 48 h p.i., WNV-infected DCs treated with SGE produced IFN-β mRNA levels that were lower (in 2 of 3 replicates, difference not statistically significant) than those produced in DCs treated with WNV alone (Fig. 3). Expression of IFN-γ was not detected in any group of DCs (data not shown). Expression of the TH2 cytokine IL-4 was statistically no different in WNV-infected and uninfected groups at both time points (data not shown). In contrast to observations in macrophages at 24 h p.i., infection of DCs with WNV alone resulted in a small increase in IL-10 mRNA levels, although this difference was not significant (Fig. 3, p = 0.09). Treatment with SGE or medium alone also resulted in low IL-10 mRNA expression. By 48 h. IL-10 mRNA expression levels were higher than levels at 24 h in infected groups (Fig. 3). Expression of IL-12 in DCs did not vary between WNV-infected groups at either 24 or 48 h p.i. (data not shown).


Aedes aegypti saliva alters leukocyte recruitment and cytokine signaling by antigen-presenting cells during West Nile virus infection.

Schneider BS, Soong L, Coffey LL, Stevenson HL, McGee CE, Higgs S - PLoS ONE (2010)

Cytokine mRNA expression in bone marrow-derived DCs following infection with WNV.IFN-β and IL-10 levels were assessed by real-time RT-PCR at 24 and 48 h post-infection (MOI = 5). Their mRNA expression levels were normalized to those of the GAPDH gene. The means ± standard deviation are shown, and an asterisk signifies a statistically significant difference (p<0.05) as compared to the group infected with WNV alone as determined by Mann-Whitney test. IFN-γ, IL-2, IL-4, IL-12, and IL-1β mRNA expression, as well as WNV titers (assessed by titration on cell culture) were found not to vary among groups (data not shown). Control groups were mock infected with PBS alone. This experiment was repeated three times.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2908538&req=5

pone-0011704-g003: Cytokine mRNA expression in bone marrow-derived DCs following infection with WNV.IFN-β and IL-10 levels were assessed by real-time RT-PCR at 24 and 48 h post-infection (MOI = 5). Their mRNA expression levels were normalized to those of the GAPDH gene. The means ± standard deviation are shown, and an asterisk signifies a statistically significant difference (p<0.05) as compared to the group infected with WNV alone as determined by Mann-Whitney test. IFN-γ, IL-2, IL-4, IL-12, and IL-1β mRNA expression, as well as WNV titers (assessed by titration on cell culture) were found not to vary among groups (data not shown). Control groups were mock infected with PBS alone. This experiment was repeated three times.
Mentions: To examine the effects of exposure to mosquito saliva on DC function during WNV infection, we measured cytokine expression in bone marrow-derived DCs at 24 h and 48 h p.i. WNV infection of DCs resulted in high type I IFN expression levels, with little to no IFN detectable in uninfected control DCs or DCs treated with SGE alone. At 24 h and 48 h p.i., WNV-infected DCs treated with SGE produced IFN-β mRNA levels that were lower (in 2 of 3 replicates, difference not statistically significant) than those produced in DCs treated with WNV alone (Fig. 3). Expression of IFN-γ was not detected in any group of DCs (data not shown). Expression of the TH2 cytokine IL-4 was statistically no different in WNV-infected and uninfected groups at both time points (data not shown). In contrast to observations in macrophages at 24 h p.i., infection of DCs with WNV alone resulted in a small increase in IL-10 mRNA levels, although this difference was not significant (Fig. 3, p = 0.09). Treatment with SGE or medium alone also resulted in low IL-10 mRNA expression. By 48 h. IL-10 mRNA expression levels were higher than levels at 24 h in infected groups (Fig. 3). Expression of IL-12 in DCs did not vary between WNV-infected groups at either 24 or 48 h p.i. (data not shown).

Bottom Line: Antigen-presenting cell (APC) signals have a profound effect on host antiviral responses and disease severity.Our in vitro results suggest that mosquito saliva significantly decreases the expression of interferon-beta and inducible nitric oxide synthase in macrophages (by as much as 50 and 70%, respectively), whilst transiently enhancing interleukin-10 (IL-10) expression.In vivo results indicate that the predominate effect of mosquito feeding is to significantly reduce the recruitment of T cells, leading the inoculation site of mice exposed to WNV alone to have up to 2.8 fold more t cells as mice infected in the presence of mosquito saliva.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Center for Biodefense & Emerging Infectious Diseases, University of Texas Medical Branch, Galveston, Texas, United States of America.

ABSTRACT
West Nile virus (WNV) is transmitted during mosquito bloodfeeding. Consequently, the first vertebrate cells to contact WNV are cells in the skin, followed by those in the draining lymph node. Macrophages and dendritic cells are critical early responders in host defense against WNV infection, not just because of their role in orchestrating the immune response, but also because of their importance as sites of early peripheral viral replication. Antigen-presenting cell (APC) signals have a profound effect on host antiviral responses and disease severity. During transmission, WNV is intimately associated with mosquito saliva. Due to the ability of mosquito saliva to affect inflammation and immune responses, and the importance of understanding early events in WNV infection, we investigated whether mosquito saliva alters APC signaling during arbovirus infection, and if alterations in cell recruitment occur when WNV infection is initiated with mosquito saliva. Accordingly, experiments were performed with cultured dendritic cells and macrophages, flow cytometry was used to characterize infiltrating cell types in the skin and lymph nodes during early infection, and real-time RT-PCR was employed to evaluate virus and cytokine levels. Our in vitro results suggest that mosquito saliva significantly decreases the expression of interferon-beta and inducible nitric oxide synthase in macrophages (by as much as 50 and 70%, respectively), whilst transiently enhancing interleukin-10 (IL-10) expression. In vivo results indicate that the predominate effect of mosquito feeding is to significantly reduce the recruitment of T cells, leading the inoculation site of mice exposed to WNV alone to have up to 2.8 fold more t cells as mice infected in the presence of mosquito saliva. These shifts in cell population are associated with significantly elevated IL-10 and WNV (up to 4.0 and 10 fold, respectively) in the skin and draining lymph nodes. These results suggest that mosquito saliva dysregulates APC antiviral signaling, and reveal a possible mechanism for the observed enhancement of WNV disease mediated by mosquito saliva via a reduction of T lymphocyte and antiviral activity at the inoculation site, an elevated abundance of susceptible cell types, and a concomitant increase in immunoregulatory activity of IL-10.

Show MeSH
Related in: MedlinePlus