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Interleukin-6 is crucial for recall of influenza-specific memory CD4 T cells.

Longhi MP, Wright K, Lauder SN, Nowell MA, Jones GW, Godkin AJ, Jones SA, Gallimore AM - PLoS Pathog. (2008)

Bottom Line: Specifically, we find that CD4+ but not CD8+ T cell memory is critically dependent upon IL-6.This effect of IL-6 includes its ability to suppress CD4+CD25+ regulatory T cells (Treg).We demonstrate that influenza-induced IL-6 limits the activity of virus-specific Tregs, thereby facilitating the activity of virus-specific memory CD4+ T cells.

View Article: PubMed Central - PubMed

Affiliation: Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Heath Park, Cardiff, United Kingdom.

ABSTRACT
Currently, our understanding of mechanisms underlying cell-mediated immunity and particularly of mechanisms that promote robust T cell memory to respiratory viruses is incomplete. Interleukin (IL)-6 has recently re-emerged as an important regulator of T cell proliferation and survival. Since IL-6 is abundant following infection with influenza virus, we analyzed virus-specific T cell activity in both wild type and IL-6 deficient mice. Studies outlined herein highlight a novel role for IL-6 in the development of T cell memory to influenza virus. Specifically, we find that CD4+ but not CD8+ T cell memory is critically dependent upon IL-6. This effect of IL-6 includes its ability to suppress CD4+CD25+ regulatory T cells (Treg). We demonstrate that influenza-induced IL-6 limits the activity of virus-specific Tregs, thereby facilitating the activity of virus-specific memory CD4+ T cells. These experiments reveal a critical role for IL-6 in ensuring, within the timeframe of an acute infection with a cytopathic virus, that antigen-specific Tregs have no opportunity to down-modulate the immune response, thereby favoring pathogen clearance and survival of the host.

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Related in: MedlinePlus

Challenge of H17 influenza virus immune mice with the heterologous virus, PR8.WT and IL-6−/− mice infected 6 weeks previously with H17 influenza virus were rechallenged i.n. with 20 HAU of the PR8 virus. Four days post secondary infection the lungs were harvested and the number of CD4+ T cells analyzed by flow cytometry (A). Proliferation and cytokine production was measured in splenocytes of H17-immune mice re-challenged 4 days previously with PR8 virus (B). The cells were labelled with CFSE and incubated for 6 days with H17 influenza-infected APCs as described in materials and methods. Specific proliferation was measured CFSE dilution and IFNγ production on gated CD4+ cells. The dot plots show a representative of 5 mice per group.
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ppat-1000006-g006: Challenge of H17 influenza virus immune mice with the heterologous virus, PR8.WT and IL-6−/− mice infected 6 weeks previously with H17 influenza virus were rechallenged i.n. with 20 HAU of the PR8 virus. Four days post secondary infection the lungs were harvested and the number of CD4+ T cells analyzed by flow cytometry (A). Proliferation and cytokine production was measured in splenocytes of H17-immune mice re-challenged 4 days previously with PR8 virus (B). The cells were labelled with CFSE and incubated for 6 days with H17 influenza-infected APCs as described in materials and methods. Specific proliferation was measured CFSE dilution and IFNγ production on gated CD4+ cells. The dot plots show a representative of 5 mice per group.

Mentions: Re-challenge with homologous virus as described above poses the problem that neutralizing antibodies, induced following the primary infection may differ between WT and IL-6−/− mice altering their ability to control the second infection thereby impacting on the extent of the T cell response induced following the second infection. Comparable neutralizing antibody activity was observed in WT and IL-6−/− serum analyzed 8 weeks post infection thus the impairment in the CD4+ T cell memory response observed in the IL-6−/− mice did not impinge on their ability to generate adequate neutralizing antibodies (Figure 5A). Since the presence of neutralizing antibodies would confer resistance to re-infection with a homologous virus resulting in very little restimulation of memory T cells, a more stringent test of T cell memory was performed. Mice infected 8 weeks previously with the H17 strain of influenza were rechallenged with the heterologous virus, PR8. This virus was considered appropriate since serum from H17 infected mice failed to neutralize PR8 (data not shown), but CD4+ T cells purified from the spleens of WT H17-infected memory mice proliferated in vitro when co-cultured with PR8-infected APCs indicating that the viruses share T cell epitopes (Figure 5B). Four days post-infection with the PR8 virus, CD4+ T cells in the lungs of both H17-memory and naïve WT and IL-6−/− mice were enumerated by flow cytometry. A pronounced difference was observed in the number of CD4+ T cells in the lungs of WT and IL6−/− H17 memory mice following rechallenge with PR8 (Figure 6A). A significant increase in the number of CD4+ T cells was detected in the lungs of WT H17-memory mice 4 days after PR8 infection compared to naïve mice infected 4 days previously with the PR8 virus. No such difference was observed in the lungs of similarly infected IL-6−/− mice indicating an impaired recall response in these animals. A comparison of virus burden in both groups of animals revealed higher levels of virus in the lungs of IL6−/− mice compared to the WT mice (Table 1). This is likely to be due to the impaired CD4+ T cell responses since no difference was observed in the CD8+ T cell response (measured by enumerating tetramer-positive cells in lungs and spleen (data not shown)) induced following rechallenge of both groups of mice with PR8. To confirm that influenza-specific CD4+ T cells were functionally impaired in H17-memory mice lacking IL-6, the ability of the cells to proliferate in response to the H17 influenza virus was compared by CFSE dilution (Figure 6B). Spleen cells from both groups of mice were labeled with CFSE and stimulated with APCs infected either with the H17 influenza virus or a control recombinant vaccinia virus for 6 days. The percentage of cells that had proliferated was assessed by CFSE dilution and their capacity to produce IFNγ was assessed by intracellular cytokine staining. As indicated in Figure 6B, more influenza-specific proliferation was observed in the cultures from WT mice than IL-6−/− mice and a higher percentage of these cells produced IFNγ. Collectively, these data confirm that IL-6 plays an essential role in the CD4+ T cell memory response to influenza virus. The impact of IL-6 on the influenza-specific T cell response appears to be selective for CD4+ T-cells implying that IL-6 has a different effect on the behavior of CD4+ and CD8+ T cells. CD4+ and CD8+ T-cells purified from naïve WT mice express the membrane-bound IL-6 receptor (IL-6R), whilst its expression is downregulated on both populations upon activation ([8] and data not shown). It is not possible therefore to attribute the effect of IL-6 on CD4+ and CD8+ memory T cells to an obvious difference in classical IL-6 signaling capacity.


Interleukin-6 is crucial for recall of influenza-specific memory CD4 T cells.

Longhi MP, Wright K, Lauder SN, Nowell MA, Jones GW, Godkin AJ, Jones SA, Gallimore AM - PLoS Pathog. (2008)

Challenge of H17 influenza virus immune mice with the heterologous virus, PR8.WT and IL-6−/− mice infected 6 weeks previously with H17 influenza virus were rechallenged i.n. with 20 HAU of the PR8 virus. Four days post secondary infection the lungs were harvested and the number of CD4+ T cells analyzed by flow cytometry (A). Proliferation and cytokine production was measured in splenocytes of H17-immune mice re-challenged 4 days previously with PR8 virus (B). The cells were labelled with CFSE and incubated for 6 days with H17 influenza-infected APCs as described in materials and methods. Specific proliferation was measured CFSE dilution and IFNγ production on gated CD4+ cells. The dot plots show a representative of 5 mice per group.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2279258&req=5

ppat-1000006-g006: Challenge of H17 influenza virus immune mice with the heterologous virus, PR8.WT and IL-6−/− mice infected 6 weeks previously with H17 influenza virus were rechallenged i.n. with 20 HAU of the PR8 virus. Four days post secondary infection the lungs were harvested and the number of CD4+ T cells analyzed by flow cytometry (A). Proliferation and cytokine production was measured in splenocytes of H17-immune mice re-challenged 4 days previously with PR8 virus (B). The cells were labelled with CFSE and incubated for 6 days with H17 influenza-infected APCs as described in materials and methods. Specific proliferation was measured CFSE dilution and IFNγ production on gated CD4+ cells. The dot plots show a representative of 5 mice per group.
Mentions: Re-challenge with homologous virus as described above poses the problem that neutralizing antibodies, induced following the primary infection may differ between WT and IL-6−/− mice altering their ability to control the second infection thereby impacting on the extent of the T cell response induced following the second infection. Comparable neutralizing antibody activity was observed in WT and IL-6−/− serum analyzed 8 weeks post infection thus the impairment in the CD4+ T cell memory response observed in the IL-6−/− mice did not impinge on their ability to generate adequate neutralizing antibodies (Figure 5A). Since the presence of neutralizing antibodies would confer resistance to re-infection with a homologous virus resulting in very little restimulation of memory T cells, a more stringent test of T cell memory was performed. Mice infected 8 weeks previously with the H17 strain of influenza were rechallenged with the heterologous virus, PR8. This virus was considered appropriate since serum from H17 infected mice failed to neutralize PR8 (data not shown), but CD4+ T cells purified from the spleens of WT H17-infected memory mice proliferated in vitro when co-cultured with PR8-infected APCs indicating that the viruses share T cell epitopes (Figure 5B). Four days post-infection with the PR8 virus, CD4+ T cells in the lungs of both H17-memory and naïve WT and IL-6−/− mice were enumerated by flow cytometry. A pronounced difference was observed in the number of CD4+ T cells in the lungs of WT and IL6−/− H17 memory mice following rechallenge with PR8 (Figure 6A). A significant increase in the number of CD4+ T cells was detected in the lungs of WT H17-memory mice 4 days after PR8 infection compared to naïve mice infected 4 days previously with the PR8 virus. No such difference was observed in the lungs of similarly infected IL-6−/− mice indicating an impaired recall response in these animals. A comparison of virus burden in both groups of animals revealed higher levels of virus in the lungs of IL6−/− mice compared to the WT mice (Table 1). This is likely to be due to the impaired CD4+ T cell responses since no difference was observed in the CD8+ T cell response (measured by enumerating tetramer-positive cells in lungs and spleen (data not shown)) induced following rechallenge of both groups of mice with PR8. To confirm that influenza-specific CD4+ T cells were functionally impaired in H17-memory mice lacking IL-6, the ability of the cells to proliferate in response to the H17 influenza virus was compared by CFSE dilution (Figure 6B). Spleen cells from both groups of mice were labeled with CFSE and stimulated with APCs infected either with the H17 influenza virus or a control recombinant vaccinia virus for 6 days. The percentage of cells that had proliferated was assessed by CFSE dilution and their capacity to produce IFNγ was assessed by intracellular cytokine staining. As indicated in Figure 6B, more influenza-specific proliferation was observed in the cultures from WT mice than IL-6−/− mice and a higher percentage of these cells produced IFNγ. Collectively, these data confirm that IL-6 plays an essential role in the CD4+ T cell memory response to influenza virus. The impact of IL-6 on the influenza-specific T cell response appears to be selective for CD4+ T-cells implying that IL-6 has a different effect on the behavior of CD4+ and CD8+ T cells. CD4+ and CD8+ T-cells purified from naïve WT mice express the membrane-bound IL-6 receptor (IL-6R), whilst its expression is downregulated on both populations upon activation ([8] and data not shown). It is not possible therefore to attribute the effect of IL-6 on CD4+ and CD8+ memory T cells to an obvious difference in classical IL-6 signaling capacity.

Bottom Line: Specifically, we find that CD4+ but not CD8+ T cell memory is critically dependent upon IL-6.This effect of IL-6 includes its ability to suppress CD4+CD25+ regulatory T cells (Treg).We demonstrate that influenza-induced IL-6 limits the activity of virus-specific Tregs, thereby facilitating the activity of virus-specific memory CD4+ T cells.

View Article: PubMed Central - PubMed

Affiliation: Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Heath Park, Cardiff, United Kingdom.

ABSTRACT
Currently, our understanding of mechanisms underlying cell-mediated immunity and particularly of mechanisms that promote robust T cell memory to respiratory viruses is incomplete. Interleukin (IL)-6 has recently re-emerged as an important regulator of T cell proliferation and survival. Since IL-6 is abundant following infection with influenza virus, we analyzed virus-specific T cell activity in both wild type and IL-6 deficient mice. Studies outlined herein highlight a novel role for IL-6 in the development of T cell memory to influenza virus. Specifically, we find that CD4+ but not CD8+ T cell memory is critically dependent upon IL-6. This effect of IL-6 includes its ability to suppress CD4+CD25+ regulatory T cells (Treg). We demonstrate that influenza-induced IL-6 limits the activity of virus-specific Tregs, thereby facilitating the activity of virus-specific memory CD4+ T cells. These experiments reveal a critical role for IL-6 in ensuring, within the timeframe of an acute infection with a cytopathic virus, that antigen-specific Tregs have no opportunity to down-modulate the immune response, thereby favoring pathogen clearance and survival of the host.

Show MeSH
Related in: MedlinePlus