RNase 7 Promotes Sensing of Self-DNA by Human Keratinocytes and Activates an Antiviral Immune Response.

RNase 7 is one of the major antimicrobial peptides (AMPs) secreted by keratinocytes. The AMPs human beta defensin 2 and LL-37 promote the toll-like receptor 9-mediated activation of human plasmacytoid dendritic cells (pDCs) by human self-DNA; however, whether keratinocytes respond in a similar way has not yet been addressed. Keratinocytes express several receptors for the detection of cytosolic DNA. Here, we investigated the activation of keratinocytes by RNase 7 in combination with human DNA. The stimulation of keratinocytes with RNase 7 and human DNA induced a strong increase in the production of IP-10. Of note, the stimulation of keratinocytes with human beta defensin 2 and LL-37 in combination with DNA failed to induce the production of IP-10. The production of IP-10 was mediated by the induction of the type I interferon IFN-ß and was significantly downregulated by blocking of the interferon-α/ß receptor and inhibition of stimulator of IFN genes. In addition, the pretreatment of keratinocytes with RNase 7 and DNA significantly reduced the herpes simplex virus-1 infection of human keratinocytes. This study demonstrates that RNase 7 functions as an alarmin by converting self-DNA into a danger signal that directly activates an antiviral immune response in human keratinocytes without the involvement of plasmacytoid dendritic cells.

Magnesium corrosion particles do not interfere with the immune function of primary human and murine macrophages.

Magnesium is currently under investigation as a prospective biodegradable implant material. Biodegradation of magnesium causes a release of magnesium, hydroxide ions and hydrogen gas but it can also lead to the formation of particulate debris. Implant-derived particles may have immunotoxic effects. To investigate the influence of magnesium-derived particles on the immune functions of primary macrophages, up to 500 µg/ml magnesium or magnesium corrosion particles were added to the cell culture medium. No major effects were observed on cell viability and on the release of the proinflammatory cytokine tumor necrosis factor (TNF)α. In addition, the ability of macrophages to stimulate proliferation of allogenic lymphocytes in a mixed leukocyte reaction remained unaffected. When macrophages were incubated with magnesium particles and then infected with the apathogenic Mycobacterium smegmatis, infection-induced TNFα secretion from murine macrophages was inhibited but not from human macrophages. However, the bactericidal activity of either cell type was not influenced. In conclusion, magnesium-related particles did not restrict the immune function of macrophages, suggesting that magnesium implants and corrosion particles derived thereof are highly biocompatible and have a low inflammatory potential.

TLR-2-mediated cytokine and chemokine secretion in human keratinocytes.

The human epidermis provides a first line of defense against exogenous pathogens. Resistance to bacterial skin infections, e.g. with Staphylococcus aureus (S. aureus), is based on the function of intact innate immune mechanisms in the epidermis, mainly provided by keratinocytes. They establish the local cytokine and chemokine milieu which is necessary for attracting other cells participating in an immune response. Toll-like receptor (TLR)-2 recognizes components of S. aureus and is known to be expressed on keratinocytes. The aim of this study was to investigate TLR-2-mediated chemokine and cytokine secretion on human primary keratinocytes (HPKs) both on mRNA and on protein level. As there is no selective TLR-2 ligand known so far, we chose Pam3Cys that acts via TLR-2/TLR-1 heterodimers, lipoteichoic acid (LTA) that acts via TLR-2/TLR-6 and peptidoglycan (PGN) which acts via TLR-2 and Nod. Pam3Cys stimulation yielded in an enhanced secretion of CCL20, CCL2, MMP9 and IL-8 in HPK, whereas stimulation with PGN or LTA showed no or solely slight effects. Our findings show evidence for a functional TLR-2/TLR-1 signalling profile in HPKs upon stimulation with Pam3Cys contributing to the defense against bacterial skin infections.