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Interleukin-1α released from HSV-1-infected keratinocytes acts as a functional alarmin in the skin.

Milora KA, Miller SL, Sanmiguel JC, Jensen LE - Nat Commun (2014)

Bottom Line: The extracellular release of IL-1α is independent of inflammatory caspases.We conclude that IL-1α acts as an alarmin essential for leukocyte recruitment and protective immunity against HSV-1.This function may have evolved to counteract an immune evasion mechanism deployed by HSV-1.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Temple Autoimmunity Center, Temple University School of Medicine, 1158 MERB, 3500 N Broad Street, Philadelphia, Pennsylvania 19140, USA.

ABSTRACT
Herpes simplex virus-1 (HSV-1) is a human pathogen that utilizes several strategies to circumvent the host immune response. An immune evasion mechanism employed by HSV-1 is retention of interleukin-1β (IL-1β) in the intracellular space, which blocks the pro-inflammatory activity of IL-1β. Here we report that HSV-1-infected keratinocytes actively release the also pro-inflammatory IL-1α, preserving the ability of infected cells to signal danger to the surrounding tissue. The extracellular release of IL-1α is independent of inflammatory caspases. In vivo recruitment of leukocytes to early HSV-1 microinfection sites within the epidermis is dependent upon IL-1 signalling. Following cutaneous HSV-1 infection, mice unable to signal via extracellular IL-1α exhibit an increased mortality rate associated with viral dissemination. We conclude that IL-1α acts as an alarmin essential for leukocyte recruitment and protective immunity against HSV-1. This function may have evolved to counteract an immune evasion mechanism deployed by HSV-1.

No MeSH data available.


Related in: MedlinePlus

HSV-1 infected keratinocytes release IL-1αPrimary human keratinocytes were treated with medium only, 25 μg ml-1 poly(I:C), or HSV-1 as indicated. After one hour cells were rinsed with PBS and fresh medium without agents was added. Cultures were allowed to incubate further for 1 (white bars), 2 (grey), 6 (striped) or 24 (black) hours before conditioned medium (a-b) and cells (c) were collected. (a-b) Extracellular levels of IL-1α (a) and IL-1β (b) protein (in the culture medium) were determined by ELISA. (c) IL-1α mRNA levels were determined using the ΔΔCt method with GAPDH as the internal reference gene and medium only treated cells as the external reference point. Data points (n = 2) are means ± s.d. from one representative experiment of at least 3 independent experiments with similar outcomes. *, P < 0.05 (compared to medium only, t-test); **, P < 0.01.
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Figure 1: HSV-1 infected keratinocytes release IL-1αPrimary human keratinocytes were treated with medium only, 25 μg ml-1 poly(I:C), or HSV-1 as indicated. After one hour cells were rinsed with PBS and fresh medium without agents was added. Cultures were allowed to incubate further for 1 (white bars), 2 (grey), 6 (striped) or 24 (black) hours before conditioned medium (a-b) and cells (c) were collected. (a-b) Extracellular levels of IL-1α (a) and IL-1β (b) protein (in the culture medium) were determined by ELISA. (c) IL-1α mRNA levels were determined using the ΔΔCt method with GAPDH as the internal reference gene and medium only treated cells as the external reference point. Data points (n = 2) are means ± s.d. from one representative experiment of at least 3 independent experiments with similar outcomes. *, P < 0.05 (compared to medium only, t-test); **, P < 0.01.

Mentions: HSV-1 evades the inflammatory functions of IL-1β by preventing secretion of the mature cytokine 11,12. If a similar immunosuppressive strategy is in place to neutralize the related function of IL-1α is unknown. Since keratinocytes express approximately 10-fold more IL-1α than IL-1β 15, 16, 17 and are one of the major cell types in which HSV-1 replicates, we were interested in the role of these cells in signalling danger to the host. Using direct and indirect approaches, it has previously been demonstrated that keratinocytes release IL-1α following infection with the HSV-1 isolates KOS and F 18,19. TLR3 plays an important role in protecting the central nervous system from HSV-1 infections, presumably thorough detection of double stranded RNA that may be produced during the viral life-cycle 20,21. We previously reported that poly(I:C), a synthetic double stranded RNA analogue, induced chemokine expression in keratinocytes and that this induction is partially dependent upon IL-1α release from the cells 22. As predicted, based on these observations, we found elevated levels of IL-1α in medium from cells treated with poly(I:C) (Fig. 1a). Similar levels of IL-1α were present in medium from HSV-1 NS isolate infected human (Fig. 1a) and mouse (Supplementary Fig. 1) primary keratinocytes 6 and 24-hours post-infection (human Fig. 1a; 24-hours mouse Supplementary Fig. 1). While increased IL-1β levels were detected after poly(I:C) treatment, analogous changes in IL-1β levels were not detected after HSV-1 infection (Fig. 1b). The IL-1β released by keratinocytes in response to poly(I:C) has previously been shown to be the inactive pro-IL-1β form 23. Hence, our data demonstrates that IL-1α, but not IL-1β, is successfully released from keratinocytes infected with the HSV-1 NS isolate.


Interleukin-1α released from HSV-1-infected keratinocytes acts as a functional alarmin in the skin.

Milora KA, Miller SL, Sanmiguel JC, Jensen LE - Nat Commun (2014)

HSV-1 infected keratinocytes release IL-1αPrimary human keratinocytes were treated with medium only, 25 μg ml-1 poly(I:C), or HSV-1 as indicated. After one hour cells were rinsed with PBS and fresh medium without agents was added. Cultures were allowed to incubate further for 1 (white bars), 2 (grey), 6 (striped) or 24 (black) hours before conditioned medium (a-b) and cells (c) were collected. (a-b) Extracellular levels of IL-1α (a) and IL-1β (b) protein (in the culture medium) were determined by ELISA. (c) IL-1α mRNA levels were determined using the ΔΔCt method with GAPDH as the internal reference gene and medium only treated cells as the external reference point. Data points (n = 2) are means ± s.d. from one representative experiment of at least 3 independent experiments with similar outcomes. *, P < 0.05 (compared to medium only, t-test); **, P < 0.01.
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Related In: Results  -  Collection

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Figure 1: HSV-1 infected keratinocytes release IL-1αPrimary human keratinocytes were treated with medium only, 25 μg ml-1 poly(I:C), or HSV-1 as indicated. After one hour cells were rinsed with PBS and fresh medium without agents was added. Cultures were allowed to incubate further for 1 (white bars), 2 (grey), 6 (striped) or 24 (black) hours before conditioned medium (a-b) and cells (c) were collected. (a-b) Extracellular levels of IL-1α (a) and IL-1β (b) protein (in the culture medium) were determined by ELISA. (c) IL-1α mRNA levels were determined using the ΔΔCt method with GAPDH as the internal reference gene and medium only treated cells as the external reference point. Data points (n = 2) are means ± s.d. from one representative experiment of at least 3 independent experiments with similar outcomes. *, P < 0.05 (compared to medium only, t-test); **, P < 0.01.
Mentions: HSV-1 evades the inflammatory functions of IL-1β by preventing secretion of the mature cytokine 11,12. If a similar immunosuppressive strategy is in place to neutralize the related function of IL-1α is unknown. Since keratinocytes express approximately 10-fold more IL-1α than IL-1β 15, 16, 17 and are one of the major cell types in which HSV-1 replicates, we were interested in the role of these cells in signalling danger to the host. Using direct and indirect approaches, it has previously been demonstrated that keratinocytes release IL-1α following infection with the HSV-1 isolates KOS and F 18,19. TLR3 plays an important role in protecting the central nervous system from HSV-1 infections, presumably thorough detection of double stranded RNA that may be produced during the viral life-cycle 20,21. We previously reported that poly(I:C), a synthetic double stranded RNA analogue, induced chemokine expression in keratinocytes and that this induction is partially dependent upon IL-1α release from the cells 22. As predicted, based on these observations, we found elevated levels of IL-1α in medium from cells treated with poly(I:C) (Fig. 1a). Similar levels of IL-1α were present in medium from HSV-1 NS isolate infected human (Fig. 1a) and mouse (Supplementary Fig. 1) primary keratinocytes 6 and 24-hours post-infection (human Fig. 1a; 24-hours mouse Supplementary Fig. 1). While increased IL-1β levels were detected after poly(I:C) treatment, analogous changes in IL-1β levels were not detected after HSV-1 infection (Fig. 1b). The IL-1β released by keratinocytes in response to poly(I:C) has previously been shown to be the inactive pro-IL-1β form 23. Hence, our data demonstrates that IL-1α, but not IL-1β, is successfully released from keratinocytes infected with the HSV-1 NS isolate.

Bottom Line: The extracellular release of IL-1α is independent of inflammatory caspases.We conclude that IL-1α acts as an alarmin essential for leukocyte recruitment and protective immunity against HSV-1.This function may have evolved to counteract an immune evasion mechanism deployed by HSV-1.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology and Immunology, Temple Autoimmunity Center, Temple University School of Medicine, 1158 MERB, 3500 N Broad Street, Philadelphia, Pennsylvania 19140, USA.

ABSTRACT
Herpes simplex virus-1 (HSV-1) is a human pathogen that utilizes several strategies to circumvent the host immune response. An immune evasion mechanism employed by HSV-1 is retention of interleukin-1β (IL-1β) in the intracellular space, which blocks the pro-inflammatory activity of IL-1β. Here we report that HSV-1-infected keratinocytes actively release the also pro-inflammatory IL-1α, preserving the ability of infected cells to signal danger to the surrounding tissue. The extracellular release of IL-1α is independent of inflammatory caspases. In vivo recruitment of leukocytes to early HSV-1 microinfection sites within the epidermis is dependent upon IL-1 signalling. Following cutaneous HSV-1 infection, mice unable to signal via extracellular IL-1α exhibit an increased mortality rate associated with viral dissemination. We conclude that IL-1α acts as an alarmin essential for leukocyte recruitment and protective immunity against HSV-1. This function may have evolved to counteract an immune evasion mechanism deployed by HSV-1.

No MeSH data available.


Related in: MedlinePlus