Innate immune responses in keratinocytes during viral skin infections

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DESCRIPTION (provided by applicant): Herpes simplex virus-1 is a common human viral pathogen that causes incurable latent infections. During active disease the virus replicates in epithelial cells in the skin or mucosa leading to cell death and blistering. Keratinocytes are the primary cell type infected by HSV-1 in the skin and understanding how these cells die and contribute to initiating immune responses and wound healing is important for the development of new therapeutic strategies. This project will generate new insight into these processes by examining how interleukin(IL)-36 and IL-1 function and are released from cells. IL-36 represents three novel cytokines, IL-36?, IL-36? and IL-36? of unknown physiological function related to the classical pro-inflammatory IL-1. Our published and unpublished data indicate that IL-36? is the predominant form of IL-36 expressed in skin. Polyinosinic-polycytidylic acid (poly(I:C)) and imiquimod are two immune response modifiers which have shown promise as new alternative treatments for HSV infections. We recently reported that poly(I:C) induces pyroptosis, a form of pro-inflammatory caspase-1 dependent cell death, in keratinocytes. We further showed for the first time that the leaderless IL-36? was released from the cells as they underwent pyroptosis. These observations, and additional new unpublished data, lead us to hypothesize that IL-36? and pyroptosis are involved in one, or more, host-responses during HSV-1 infections and that therapeutic agents such as poly(I:C) and imiquimod act, at least in part, through these mechanisms. Using a mouse model of active HSV-1 skin infections and IL-36 knockout (KO) mice we found that IL-36?, but not IL-36?, deficient mice developed secondary lesions earlier than wild type mice. Furthermore, skin lesions healed poorly in IL-36? KO mice when these mice were challenged with HSV-1 or poly(I:C). In vivo and in vitro administration of recombinant IL-36? stimulated keratinocyte hyperproliferation and promoted wound healing. IL-36? regulated a subset of the genes induced by IL-1? suggesting that while IL-1? has both pro-inflammatory and wound healing properties the function of IL-36? appears to be more limited towards wound healing. To further characterize the biological activity of IL-36?, in comparison to IL-1?, we will establish mechanisms whereby IL-36? promotes wound healing and distinct gene expression (Aim 1). In Aim 2 we will determine how IL-36? and IL-1? are released from HSV-1 infected cells. Aim 3 will investigate the role(s) of IL-36? and IL-1? and their export mechanisms in mediating therapeutic effects of the immune response modifiers imiquimod and poly(I:C). Completion of these aims will improve our understanding of host-responses in keratinocytes towards HSV-1, including the physiological function of IL-36?. The gained knowledge may explain mechanisms of action of therapeutic agents and will inform future drug development, including IL-36? as a novel wound healing agent.