Significance We identified a previously undescribed disease mechanism for psoriasis (Ps) and psoriasis arthritis (PsA)-like disease by developing a new mouse model having characteristic features similar to those of Ps and PsA in human patients. Mannan-induced activation of tissue macrophages triggers IL-17A secretion from γδ T cells, causing Ps-like inflammation. Such inflammation was significantly increased under a reduced oxidative environment. Increased frequency of monocytes/macrophages, depletion experiments, and the disease suppressor function of macrophage-derived reactive oxygen species clearly argue in favor of a role for monocytes/macrophages in this disease model, which is in accordance with the findings in patients with the psoriatic form of skin lesions and arthritis. This novel PsA model could be immensely useful to test new therapeutics for patients with Ps and PsA.

Fungi, such as Candida spp., are commonly found on the skin and at mucosal surfaces. Yet, they rarely cause invasive infections in immunocompetent individuals, an observation reflecting the ability of our innate immune system to control potentially invasive microbes found at biological boundaries. Antimicrobial proteins and peptides are becoming increasingly recognized as important effectors of innate immunity. This is illustrated further by the present investigation, demonstrating a novel antifungal role of histidine-rich glycoprotein (HRG), an abundant and multimodular plasma protein. HRG bound to Candida cells, and induced breaks in the cell walls of the organisms. Correspondingly, HRG preferentially lysed ergosterol-containing liposomes but not cholesterol-containing ones, indicating a specificity for fungal versus other types of eukaryotic membranes. Both antifungal and membrane-rupturing activities of HRG were enhanced at low pH, and mapped to the histidine-rich region of the protein. Ex vivo, HRG-containing plasma as well as fibrin clots exerted antifungal effects. In vivo, Hrg−/− mice were susceptible to infection by C. albicans, in contrast to wild-type mice, which were highly resistant to infection. The results demonstrate a key and previously unknown antifungal role of HRG in innate immunity.

During bleeding the skin is subjected to oxidative insults from free heme and radicals, generated from extracellular hemoglobin. The lipocalin α1-microglobulin (A1M) was recently shown to have reductase properties, reducing heme-proteins and other substrates, and to scavenge heme and radicals. We investigated the expression and localization of A1M in skin and the possible role of A1M in the protection of skin tissue from damage induced by heme and reactive oxygen species. Skin explants, keratinocyte cultures and purified collagen I were exposed to heme, reactive oxygen species, and/or A1M and investigated by biochemical methods and electron microscopy. The results demonstrate that A1M is localized ubiquitously in the dermal and epidermal layers, and that the A1M-gene is expressed in keratinocytes and up-regulated after exposure to heme and reactive oxygen species. A1M inhibited the heme- and reactive oxygen species-induced ultrastructural damage, up-regulation of antioxidation and cell cycle regulatory genes, and protein carbonyl formation in skin and keratinocytes. Finally, A1M bound to purified collagen I (Kd = 0.96×10−6 M) and could inhibit and repair the destruction of collagen fibrils by heme and reactive oxygen species. The results suggest that A1M may have a physiological role in protection of skin cells and matrix against oxidative damage following bleeding.

Tissue factor pathway inhibitor (TFPI) inhibits tissue factorinduced coagulation, but may, via its C terminus, also modulate cell surface, heparin, and lipopolysaccharide interactions as well as participate in growth inhibition. Here we show that C-terminal TFPI peptide sequences are antimicrobial against the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa, Gram-positive Bacillus subtilis and Staphylococcus aureus, as well as the fungi Candida albicans and Candida parapsilosis. Fluorescence studies of peptide-treated bacteria, paired with analysis of peptide effects on liposomes, showed that the peptides exerted membrane-breaking effects similar to those seen for the "classic" human antimicrobial peptide LL-37. The killing of E. coli, but not P. aeruginosa, by the C-terminal peptide GGLIKTKRKRKKQRVKIAYEEIFVKNM (GGL27), was enhanced in human plasma and largely abolished in heatinactivated plasma, a phenomenon linked to generation of antimicrobial C3a and activation of the classic pathway of complement activation. Furthermore, GGL27 displayed antiendotoxic effects in vitro and in vivo in a mouse model of LPS shock. Importantly, TFPI was found to be expressed in the basal layers of normal epidermis, and was markedly up-regulated in acute skin wounds as well as wound edges of chronic leg ulcers. Furthermore, C-terminal fragments of TFPI were associated with bacteria present in human chronic leg ulcers. These findings suggest a new role for TFPI in cutaneous defense against infections.

Cutibacterium acnes is an abundant skin commensal with several proposed mutualistic functions. A protein with strong antioxidant activity was recently identified from the C . acnes secretome. This protein, termed RoxP, facilitated aerobic bacterial growth in vitro and ex vivo . As reducing events naturally occurred outside of the bacterial cell, it was further hypothesized that RoxP could also serve to modulate redox status of human skin. The biological function of RoxP was here assessed in vitro and in vivo , through oxidatively stressed cell cultures and through protein quantification from skin affected by oxidative disease (actinic keratosis and basal cell carcinoma), respectively. 16S rDNA amplicon deep sequencing and single locus sequence typing was used to correlate bacterial prevalence to cutaneous RoxP abundances. We show that RoxP positively influence the viability of monocytes and keratinocytes exposed to oxidative stress, and that a congruent concentration decline of RoxP can be observed in skin affected by oxidative disease. Basal cell carcinoma was moreover associated with microbial dysbiosis, characterized by reduced C . acnes prevalence. C . acnes ’s secretion of RoxP, an exogenous but naturally occurring antioxidant on human skin, is likely to positively influence the human host. Results furthermore attest to its prospective usability as a biopharmaceutical.

The altered expression patterns of glypican and syndecan-1 and -4 in chronic ulcers reflect their possible roles during inflammation and cell proliferation. Hence, analysis of PG expression should be of interest in future studies on normal as well as defective wound healing.

Recently it was demonstrated by Gautam, et al. that release of neutrophil-borne heparin-binding protein (HBP), also known as CAP37/azurocidin, induced endothelial hyperpermeability and neutrophil efflux. Here, we show that chronic leg ulcer fluid, in contrast to wound fluid from acute wounds, contains highly increased levels of HBP. Immunohistochemistry demonstrated the presence of HBP in chronic ulcer tissues. Furthermore, secreted products of Pseudomonas aeruginosa were found to induce release of HBP from human neutrophils. Our data suggest a possible link between bacterial presence and HBP-release in chronic ulcers. Thus, targeting HBP offers an interesting option for reduction of endothelial barrier dysfunction in chronic ulcers.

Chronic venous ulcers are characterized by chronic inflammation. Heme and iron, originating from blood cell hemolysis as well as extravascular necrosis, have been implicated as important pathogenic factors due to their promotion of oxidative stress. It was recently reported that the plasma and tissue protein alpha1-microglobulin is involved in heme metabolism. The protein binds heme, and a carboxy-terminally processed form, truncated alpha1-microglobulin, also degrades heme. Here, we show the presence of micromolar levels of heme and free iron in chronic leg ulcer fluids. Micromolar amounts of alpha1-microglobulin was also present in the ulcer fluids and bound to added radiolabeled heme. Truncated alpha1-microglobulin was found in the ulcer fluids and exogenously added alpha1-microglobulin was processed into the truncated alpha1-microglobulin form. Histochemical analysis of chronic wound tissue showed the presence of iron deposits, heme/porphyrins in infiltrating cells basement membranes and fibrin cuffs around vessels, and alpha1-microglobulin ubiquitously distributed but especially abundant in basement membranes around vessels and at fibrin cuffs. Our results suggest that alpha1-microglobulin constitutes a previously unknown defense mechanism against high heme and iron levels during skin wound healing. Excessive heme and iron, which are not buffered by alpha1-microglobulin, may underlie the chronic inflammation in chronic ulcers.