HSV-1 triggers paracrine fibroblast growth factor response from cortical brain cells via immediate-early protein ICP0.

BACKGROUND: Herpes simplex virus-1 (HSV-1) infections of the central nervous system (CNS) can result in HSV-1 encephalitis (HSE) which is characterized by severe brain damage and long-term disabilities. Different cell types including neurons and astrocytes become infected in the course of an HSE which leads to an activation of glial cells. Activated glial cells change their neurotrophic factor profile and modulate inflammation and repair. The superfamily of fibroblast growth factors (FGFs) is one of the largest family of neurotrophic factors comprising 22 ligands. FGFs induce pro-survival signaling in neurons and an anti-inflammatory answer in glial cells thereby providing a coordinated tissue response which favors repair over inflammation. Here, we hypothesize that FGF expression is altered in HSV-1-infected CNS cells. METHOD: We employed primary murine cortical cultures comprising a mixed cell population of astrocytes, neurons, microglia, and oligodendrocytes. Astrocyte reactivity was morphometrically monitored by an automated image analysis algorithm as well as by analyses of A1/A2 marker expression. Altered FGF expression was detected by quantitative real-time PCR and its paracrine FGF activity. In addition, HSV-1 mutants were employed to characterize viral factors important for FGF responses of infected host cells. RESULTS: Astrocytes in HSV-1-infected cortical cultures were transiently activated and became hypertrophic and expressed both A1- and A2-markers. Consistently, a number of FGFs were transiently upregulated inducing paracrine neurotrophic signaling in neighboring cells. Most prominently, FGF-4, FGF-8, FGF-9, and FGF-15 became upregulated in a switch-on like mechanism. This effect was specific for CNS cells and for a fully functional HSV-1. Moreover, the viral protein ICP0 critically mediated the FGF switch-on mechanism. CONCLUSIONS: HSV-1 uses the viral protein ICP0 for the induction of FGF-expression in CNS cells. Thus, we propose that HSV-1 triggers FGF activity in the CNS for a modulation of tissue response upon infection.

RNase 7 Strongly Promotes TLR9-Mediated DNA Sensing by Human Plasmacytoid Dendritic Cells.

Plasmacytoid dendritic cells (pDCs) were described to accumulate in the skin of patients with psoriasis and to be recruited into the dermis upon allergen challenge in atopic dermatitis. Activation of pDCs in the skin has been identified as an important initiator of psoriasis development. Ribonuclease (RNase) 7 is one of the major antimicrobial peptides secreted by keratinocytes and is expressed in significantly higher amounts in lesional skin of patients with atopic dermatitis or psoriasis than in healthy individuals. The skin-derived antimicrobial peptides human ß-defensin 2 and LL-37 indirectly stimulate the activity of skin pDCs, but to our knowledge, an immunomodulatory potential of RNase 7 has not yet been reported. We show here that RNase 7 enables human pDCs to recognize self-DNA and promotes their rapid sensing of bacterial DNA. This very fast innate immune response was sufficient to up-regulate the expression of several antiviral IFN-stimulated genes in human peripheral blood mononuclear cells and to inhibit an infection of primary human keratinocytes with herpes simplex virus 1. RNase 7 was a markedly stronger trigger for IFN-α expression in human pDCs than the other antimicrobial peptides. Our data indicate that RNase 7 exhibits potent immunomodulatory functions and supports the efficient recognition of microbial infections by human skin-infiltrating pDCs.