Activated macrophages are essential in a murine model for T cell-mediated chronic psoriasiform skin inflammation

Heparanase is preferentially expressed in human psoriatic lesions and induces development of psoriasiform skin inflammation in mice

Heparanase is the sole mammalian endoglycosidase that selectively degrades heparan sulfate, the key polysaccharide associated with the cell surface and extracellular matrix of a wide range of tissues. Extensively studied for its capacity to promote cancer progression, heparanase enzyme was recently implicated as an important determinant in several inflammatory disorders as well. Applying immunohistochemical staining, we detected preferential expression of heparanase by epidermal keratinocytes in human psoriatic lesions. To investigate the role of the enzyme in the pathogenesis of psoriasis, we utilized heparanase transgenic mice in a model of 12-O-tetradecanoyl phorbol 12-myristate 13-acetate-induced cutaneous inflammation. We report that over-expression of the enzyme promotes development of mouse skin lesions that strongly recapitulate the human disease in terms of histomorphological appearance and molecular/cellular characteristics. Importantly, heparanase of epidermal origin appears to facilitate abnormal activation of skin-infiltrating macrophages, thus generating psoriasis-like inflammation conditions, characterized by induction of STAT3, enhanced NF-κB signaling, elevated expression of TNF-α and increased vascularization. Taken together, our results reveal, for the first time, involvement of heparanase in the pathogenesis of psoriasis and highlight a role for the enzyme in facilitating abnormal interactions between immune and epithelial cell subsets of the affected skin. Heparanase inhibitors (currently under clinical testing in malignant diseases) could hence turn highly beneficial in psoriatic patients as well.

CD8 T cells regulate allergic contact dermatitis by modulating CCR2-dependent TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells

Monocytes and their derived cells have critical roles in inflammation and immune defense. However, their function in skin diseases such as allergic contact dermatitis remains poorly defined. Using a model of contact hypersensitivity (CHS) toward 2,4-dinitrochlorobenzene, we show that Ly6C+ CD11b+ monocytic cells participate in the pathophysiology of CHS and their accumulation is regulated by effector CD8 T cells. These Ly6C+ CD11b+ monocytic cells are the primary contributors of tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) and derive from Ly6C(hi)CCR2+ monocytes, as they were absent in non-inflamed skin and accumulate as a consequence of inflammation in a C-C chemokine receptor type 2 (CCR2)-dependent manner. Importantly, CCR2(-/-) mice, or wild-type mice depleted of monocytes via clodronate liposomes, display a marked decrease in TNF-α and iNOS expression accompanied by attenuated skin inflammation. Using transgenic mice and antibody depletion, we show that effector CD8 T cells regulate the accumulation of Ly6C+ CD11b+ monocytic cells through IL-17 and activate them for TNF-α and iNOS through IFN-γ. CD8 T cell-derived IFN-γ was also critical for the accumulation of the major histocompatibility complex II-expressing Ly6C+ CD11b+ subset, which expressed intermediate levels of CD11c and costimulatory molecules. Taken together, our findings provide further insight into the pathophysiology of allergic contact dermatitis by showing that CD8 T cells regulate the inflammatory cascade through TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells.

A cutting edge overview: psoriatic disease

Psoriasis is a lifelong skin disease, affecting about 2% of the global population. Generalized involvement of the body (erythroderma), extensive pustular lesions, and an associated arthritis known as psoriatic arthritis (PsA) are severe complications of psoriasis. Genetic, immunologic, and environmental factors contribute to its pathogenesis. A complete understanding of the pathogenesis of psoriasis and psoriatic arthritis is lacking. Cytokines, chemokines, adhesion molecules, growth factors like NGF, neuropeptides, and T cell receptors all act in an integrated way to evolve into unique inflammatory and proliferative processes typical of psoriasis and PsA. Management of psoriasis requires exemplary skin care along with careful monitoring of arrays of comorbidities which includes arthritis and coronary artery disease. In many ways, psoriasis can be considered a model autoimmune disease. This statement itself is ironic considering that it was not recognized as immune mediated until relatively recently. Fortunately, the immunobiology has made enormous strides and there are now excellent therapeutic options for patients. In this thematic review, we have attempted to provide summaries of not only basic science and clinical research, but also an overview of future research directions.

Complement modulates the cutaneous microbiome and inflammatory milieu

The skin is colonized by a plethora of microbes that include commensals and potential pathogens, but it is currently unknown how cutaneous host immune mechanisms influence the composition, diversity, and quantity of the skin microbiota. Here we reveal an interactive role for complement in cutaneous host-microbiome interactions. Inhibiting signaling of the complement component C5a receptor (C5aR) altered the composition and diversity of the skin microbiota as revealed by deep sequencing of the bacterial 16S rRNA gene. In parallel, we demonstrate that C5aR inhibition results in down-regulation of genes encoding cutaneous antimicrobial peptides, pattern recognition receptors, and proinflammatory mediators. Immunohistochemistry of inflammatory cell infiltrates in the skin showed reduced numbers of macrophages and lymphocytes with C5aR inhibition. Further, comparing cutaneous gene expression in germ-free mice vs. conventionally raised mice suggests that the commensal microbiota regulates expression of complement genes in the skin. These findings demonstrate a component of host immunity that impacts colonization of the skin by the commensal microbiota and vice versa, a critical step toward understanding host-microbe immune mutualism of the skin and its implications for health and disease. Additionally, we reveal a role for complement in homeostatic host-microbiome interactions of the skin.

TSG-6 released from intradermally injected mesenchymal stem cells accelerates wound healing and reduces tissue fibrosis in murine full-thickness skin wounds

Proper activation of macrophages (Mφ) in the inflammatory phase of acute wound healing is essential for physiological tissue repair. However, there is a strong indication that robust Mφ inflammatory responses may be causal for the fibrotic response always accompanying adult wound healing. Using a complementary approach of in vitro and in vivo studies, we here addressed the question of whether mesenchymal stem cells (MSCs)-due to their anti-inflammatory properties-would control Mφ activation and tissue fibrosis in a murine model of full-thickness skin wounds. We have shown that the tumor necrosis factor-α (TNF-α)-stimulated protein 6 (TSG-6) released from MSCs in co-culture with activated Mφ or following injection into wound margins suppressed the release of TNF-α from activated Mφ and concomitantly induced a switch from a high to an anti-fibrotic low transforming growth factor-β1 (TGF-β1)/TGF-β3 ratio. This study provides insight into what we believe to be a previously undescribed multifaceted role of MSC-released TSG-6 in wound healing. MSC-released TSG-6 was identified to improve wound healing by limiting Mφ activation, inflammation, and fibrosis. TSG-6 and MSC-based therapies may thus qualify as promising strategies to enhance tissue repair and to prevent excessive tissue fibrosis.

TSG-6 released from intradermally injected mesenchymal stem cells accelerates wound healing and reduces tissue fibrosis in murine full-thickness skin wounds

Proper activation of macrophages (Mφ) in the inflammatory phase of acute wound healing is essential for physiological tissue repair. However, there is a strong indication that robust Mφ inflammatory responses may be causal for the fibrotic response always accompanying adult wound healing. Using a complementary approach of in vitro and in vivo studies, we here addressed the question of whether mesenchymal stem cells (MSCs)-due to their anti-inflammatory properties-would control Mφ activation and tissue fibrosis in a murine model of full-thickness skin wounds. We have shown that the tumor necrosis factor-α (TNF-α)-stimulated protein 6 (TSG-6) released from MSCs in co-culture with activated Mφ or following injection into wound margins suppressed the release of TNF-α from activated Mφ and concomitantly induced a switch from a high to an anti-fibrotic low transforming growth factor-β1 (TGF-β1)/TGF-β3 ratio. This study provides insight into what we believe to be a previously undescribed multifaceted role of MSC-released TSG-6 in wound healing. MSC-released TSG-6 was identified to improve wound healing by limiting Mφ activation, inflammation, and fibrosis. TSG-6 and MSC-based therapies may thus qualify as promising strategies to enhance tissue repair and to prevent excessive tissue fibrosis.

Mononuclear phagocyte system in kidney disease and repair

The mononuclear phagocyte system is comprised of circulating monocytes, tissue macrophages and dendritic cells (DCs) that play key roles in tissue homeostasis, immune surveillance, and immune and non-immune-mediated tissue injury and repair. This review summarizes the various subsets within this system that exhibit significant functional and phenotypic diversity that can adapt to their surrounding microenvironments during inflammation and in response to colony-stimulating factor (CSF)-1. The current understanding of the co-ordination of monocyte infiltration into the homeostatic and diseased kidney through adhesion molecules, chemokines and chemokine receptors, and cytokines are described. Furthermore, the significant confusion and controversy associated with monocyte differentiation into renal macrophages and DCs following infiltration into the kidney, the considerable functional and phenotypic overlap between both tissue populations and their respective roles in immune and non-immune-mediated renal is also discussed. Understanding the factors that control the activation and recruitment of cells from the mononuclear phagocyte system during renal injury may offer an avenue for the development of new cellular and growth factor-based therapies in combination with existing therapies as an alternative treatment option for patients with renal disease.

Cytokines are systemic effectors of lymphatic function in acute inflammation

The response of the lymphatic system to inflammatory insult and infection is not completely understood. Using a near-infrared fluorescence (NIRF) imaging system to noninvasively document propulsive function, we noted the short-term cessation of murine lymphatic propulsion as early as 4h following LPS injection. Notably, the effects were systemic, displaying bilateral lymphatic pumping cessation after a unilateral insult. Furthermore, IL-1β, TNF-α, and IL-6, cytokines that were found to be elevated in serum during lymphatic pumping cessation, were shown separately to acutely and systemically decrease lymphatic pulsing frequency and velocity following intradermal administration. Surprisingly, marked lymphatic vessel dilation and leakiness were noted in limbs contralateral to IL-1β intradermal administration, but not in ipsilateral limbs. The effects of IL-1β on lymphatic pumping were abated by pre-treatment with an inhibitor of inducible nitric oxide synthase, L-NIL (N-iminoethyl-L-lysine). The results suggest that lymphatic propulsion is systemically impaired within 4h of acute inflammatory insult, and that some cytokines are major effectors of lymphatic pumping cessation through nitric oxide-mediated mechanisms. These findings may help in understanding the actions of cytokines as mediators of lymphatic function in inflammatory and infectious states.

Serum prolidase activity in psoriasis patients

This study aimed to evaluate serum prolidase activity and the effects of gender, body mass index (BMI), disease severity and duration, and therapy type on prolidase activity in patients with psoriatic as well as the relationship between serum NO· and prolidase levels in these patients. The study included 29 clinically documented plaque patients with psoriasis and 24 healthy volunteers. Data such as age, sex, BMI, duration and severity of disease, and type of therapy were assessed. NO· levels were determined by the Griess reaction. Serum prolidase assay is based on a colorimetric determination of proline by Chinard's reagent. We did not determine any difference in serum NO· levels of psoriatic patients when compared to controls. Serum prolidase levels in psoriasis patients were significantly higher than those in controls. There was no significant difference in prolidase activity between male and female. No statistically significant correlations were found between serum prolidase levels and BMI, PASI and disease duration. When compared between topical treatment group and systemic treatment group, there was no significant difference in serum prolidase activity. In conclusion, patients with psoriasis exhibit higher serum prolidase activity independent of gender, BMI, disease severity or duration, type of treatments or NO· level. However, further studies are needed to verify these findings as well as altered collagen synthesis in patients with psoriasis.

α1β1 integrin-mediated adhesion inhibits macrophage exit from a peripheral inflammatory lesion

Integrins are adhesion molecules critical for the recruitment of leukocytes from blood into peripheral tissues. However, whether integrins are also involved in leukocyte exit from peripheral tissues via afferent lymphatics to the draining lymph node remains poorly understood. In this article, we show that adhesion by the collagen IV-binding integrin α1β1 unexpectedly inhibited macrophage exit from inflamed skin. We monitored macrophages exiting mouse footpads using a newly developed in situ pulse labeling technique. Blockade of α1β1 integrin or genetic deletion (Itga1(-/-)) increased macrophage exit efficiency. Chemotaxis assays through collagen IV showed more efficient migration of Itga1(-/-) macrophages relative to wild type. Given that macrophages are key orchestrators of inflammation, α1β1 integrin adhesion may represent a mechanism for regulating inflammatory responses by controlling macrophage exit or persistence in inflamed tissues.

Reduced CD18 levels drive regulatory T cell conversion into Th17 cells in the CD18hypo PL/J mouse model of psoriasis

Defective development and function of CD4(+)CD25(high+)Foxp3(+) regulatory T cells (Tregs) contribute to the pathogenesis of psoriasis and other autoimmune diseases. Little is known about the influence of adhesions molecules on the differentiation of Foxp3(+) Tregs into proinflammatory Th17 cells occurring in lesional skin and blood of psoriasis patients. In the CD18(hypo) PL/J mouse model of psoriasis, reduced expression of CD18/β2 integrin to 2-16% of wild-type levels is associated with progressive loss of Tregs, impaired cell-cell contact between Tregs and dendritic cells (DCs), as well as Treg dysfunction as reported earlier. In the present investigation, Tregs derived from CD18(hypo) PL/J mice were analyzed for their propensity to differentiate into IL-17-producing Th17 cells in vivo and in in vitro Treg-DC cocultures. Adoptively transferred CD18(hypo) PL/J Tregs were more inclined toward conversion into IL-17-producing Th17 cells in vivo in an inflammatory as well as noninflammatory environment compared with CD18(wt) PL/J Tregs. Addition of neutralizing Ab against CD18 to Treg-DC cocultures in vitro promoted conversion of CD18(wt) PL/J Tregs to Th17 cells in a dose-dependent manner similar to conversion rates of CD18(hypo) PL/J Tregs. Reduced thymic output of naturally occurring Tregs and peripheral conversion of Tregs into Th17 cells therefore both contribute to the loss of Tregs and the psoriasiform dermatitis observed in CD18(hypo) PL/J mice. Our data overall indicate that CD18 expression levels impact Treg development as well as Treg plasticity and that differentiation of Tregs into IL-17-producing Th17 cells is distinctly facilitated by a subtotal deficiency of CD18.

β(2) integrins inhibit TLR responses by regulating NF-κB pathway and p38 MAPK activation

Outside-in signals from β(2) integrins require immunoreceptor tyrosine-based activation motif adapters in myeloid cells that are known to dampen TLR responses. However, the relationship between β(2) integrins and TLR regulation is unclear. Here we show that deficiency in β(2) integrins (Itgb2(-/-) ) causes hyperresponsiveness to TLR stimulation, demonstrating that β(2) integrins inhibit signals downstream of TLR ligation. Itgb2(-/-) macrophages and dendritic cells produced more IL-12 and IL-6 than WT cells when stimulated with TLR agonists and Itgb2(-/-) mice produced more inflammatory cytokines than WT mice when injected with LPS. TLR hypersensitivity was not the result of insufficient ABIN-3, A20, Hes-1, or IRAK-M expression, nor to changes in IL-10 production or sensitivity, though Itgb2(-/-) macrophages had reduced p38 MAPK phosphorylation after LPS treatment. Furthermore, a Cbl-b-MyD88 regulatory axis is not required for TLR inhibition in macrophages. Instead, Itgb2(-/-) macrophages presented with enhanced IκBα degradation, leading to changes in NF-κB recruitment to target promoters and elevated cytokine, chemokine, and anti-apoptotic gene transcription. Thus, β(2) integrins limit TLR signaling by inhibiting NF-κB pathway activation and promoting p38 MAPK activation, thereby fine-tuning TLR-induced inflammatory responses.

Plasmin induces intercellular adhesion molecule 1 expression in human endothelial cells via nuclear factor-κB/mitogen-activated protein kinases-dependent pathways

Activation of endothelial cells (ECs) by proinflammatory stimuli triggers expression of cellular adhesion molecules including intercellular adhesion molecule 1 (ICAM-1) on the cell surface. Such molecules mediate the transendothelial migration of inflammatory cells, which is an early key step of atherogenesis. We have previously demonstrated that plasmin activates human inflammatory cells via the annexin A2 heterotetramer (A2t). Here we show that human umbilical vein endothelial cells (HUVECs) and human microvascular endothelial cells express high amounts of A2t, as shown by Western blotting, fluorescence microscopy and flow cytometry. Activation of HUVEC by plasmin led to cleavage of the annexin A2 subunit of the receptor complex, followed by the activation of Akt/nuclear factor (NF)-kB signaling, and phosphorylation of MAP kinases p38 and ERK1/2. Further, plasmin stimulates the NF-kB/p38-dependent expression of ICAM-1 by HUVEC. The plasmin-induced activation of cells was abolished when annexin A2 was down-regulated by small-interfering RNA. In vivo, we show co-localization of the ECs marker CD31 with the plasmin receptor A2t and ICAM-1 in human atherosclerotic plaques of human femoral arteries, which also exhibit activated NF-κB signaling as revealed by immunofluorescence staining for phosphorylated Iκbα. In addition, plasma of patients with advanced atherosclerosis exhibited enhanced plasmin activity and up-regulated levels of plasmin-α2-antiplasmin. These data point to a previously unrecognized functional role of plasmin in EC biology, which could be of particular relevance in the development of atherosclerosis.

The effect of adipose tissue derived MSCs delivered by a chemically defined carrier on full-thickness cutaneous wound healing

Mesenchymal stem cells (MSCs) have properties which make them promising for the treatment of chronic non-healing wounds. A major so far unmet challenge is the efficient, safe and painless delivery of MSCs to skin wounds. Recently, a surface carrier of medical-grade silicone coated by plasma polymerisation with a thin layer of acrylic acid (ppAAc) was developed, and shown to successfully deliver MSCs to deepithelialised human dermis in vitro. Here we studied the potential of the ppAAc carrier to deliver human adipose tissue derived MSCs (AT-MSCs) to murine full-thickness excisional skin wounds in vivo. Further we investigate the mechanism of action of MSCs in accelerating wound healing in these wounds. AT-MSCs cultured on ppAAc carriers for 4 days or longer fully retained their cell surface marker expression profile, colony-forming-, differentiation- and immunosuppressive potential. Importantly, AT-MSCs delivered to murine wounds by ppAAc carriers significantly accelerated wound healing, similar to AT-MSCs delivered by intradermal injection. More than 80% of AT-MSCs were transferred from carriers to wounds in 3 days. AT-MSCs were detectable in wounds for at least 5 days after wounding. Carrier delivered AT-MSCs were demonstrated to have the capacity to down-modulate TNF-α-dependent inflammation, increase anti-inflammatory M2 macrophage numbers, and induce TGF-β(1)-dependent angiogenesis, myofibroblast differentiation and granulation tissue formation, thereby enhancing overall tissue repair.

Neutrophil-derived IL-1β is sufficient for abscess formation in immunity against Staphylococcus aureus in mice

Neutrophil abscess formation is critical in innate immunity against many pathogens. Here, the mechanism of neutrophil abscess formation was investigated using a mouse model of Staphylococcus aureus cutaneous infection. Gene expression analysis and in vivo multispectral noninvasive imaging during the S. aureus infection revealed a strong functional and temporal association between neutrophil recruitment and IL-1β/IL-1R activation. Unexpectedly, neutrophils but not monocytes/macrophages or other MHCII-expressing antigen presenting cells were the predominant source of IL-1β at the site of infection. Furthermore, neutrophil-derived IL-1β was essential for host defense since adoptive transfer of IL-1β-expressing neutrophils was sufficient to restore the impaired neutrophil abscess formation in S. aureus-infected IL-1β-deficient mice. S. aureus-induced IL-1β production by neutrophils required TLR2, NOD2, FPR1 and the ASC/NLRP3 inflammasome in an α-toxin-dependent mechanism. Taken together, IL-1β and neutrophil abscess formation during an infection are functionally, temporally and spatially linked as a consequence of direct IL-1β production by neutrophils.

Invasive infections caused by the human pathogen Staphylococcus aureus result in more deaths annually than infections caused by any other single infectious agent in the United States. Although neutrophil recruitment and abscess formation is crucial for effective host defense against this pathogen, how neutrophils sense and mount an inflammatory response are not completely clear. Using gene expression analysis and in vivo bioluminescence and fluorescence imaging, we found that neutrophil recruitment during a S. aureus cutaneous infection is functionally and temporally linked to IL-1β/IL-1R activation. Surprisingly, neutrophils themselves were determined to be the most abundant cell type that produced IL-1β during infection. Further, neutrophil-derived IL-1β, in the absence of other cellular sources of IL-1β, was sufficient for neutrophil recruitment, abscess formation, and bacterial clearance. Finally, mouse neutrophils produced IL-1β in direct response to live S. aureus in vitro. These findings expand our understanding of the acute neutrophil response to infection in which early recruited neutrophils serve as a source of IL-1β that is essential for amplifying and sustaining the neutrophilic response to promote abscess formation and bacterial clearance. Therapies aimed at promoting IL-1β production by neutrophils may be an effective immunotherapeutic strategy to control S. aureus infections.

NF-κB: an essential transcription factor in psoriasis

Nuclear factor kappa B (NF-κB) is a protein transcription factor that orchestrates inflammation and other complex biological processes. It is a key regulatory element in a variety of immune and inflammatory pathways, in cellular proliferation and differentiation and in apoptosis. Therefore NF-κB is a crucial mediator involved in the pathogenesis of psoriasis. Psoriasis, an inflammatory dermatosis, is marked by elevated levels of active, phosphorylated NF-κB. Genomic studies have also linked psoriasis with mediators in the NF-κB pathway. NF-κB has been hypothesized to connect the altered keratinocyte and immune cell behavior that characterizes the psoriatic milieu. Several anti-psoriatic therapies, including tumor necrosis factor-α blockers and glucocorticoids, reduce active NF-κB levels and related down-stream elements, and other biologics currently in development, including interleukin-17 blockers, may also target this pathway. Compounds that specifically target NF-κB signaling may be developed as novel therapeutics for chronic inflammatory disorders including psoriasis. However, chronic NF-κB inhibition could also result in immunodeficiencies. Therefore, a delicate balance must be found that maximizes therapeutic potential while limiting harmful effects, and may be achieved through several possible approaches, including localized therapy, selective inhibition of NF-κB signaling in pathologic cells, incomplete pathway inhibition or short treatment durations.

Critical involvement of macrophage infiltration in the development of Sjögren's syndrome-associated dry eye

Lymphocytic infiltration of the lacrimal gland and ocular surface in autoimmune diseases such as Sjögren's syndrome (SS) causes an aqueous-deficient dry eye that is associated with significant morbidity. Previous studies from our laboratory and others have established autoimmune regulator (Aire)-deficient mice as a useful model to examine exocrinopathy and ocular surface disease associated with SS. Consistent with human SS, autoreactive CD4(+) T cells play an indispensible role in the development of exocrine and ocular surface disease in Aire knockout mice. We report that in addition to CD4(+) T cells, a large number of macrophages infiltrate the corneal stroma, limbus, and lacrimal glands of diseased mice. Adoptive transfer of autoreactive CD4(+) T cells from Aire knockout mice led to local infiltration of macrophages and ocular surface damage in immunodeficient recipients. Depletion of local macrophages, through subconjunctival injection of clodronate liposome, attenuated lissamine green staining and improved ocular phenotype. Alternatively, systemic depletion of macrophages had no effect on ocular phenotype but led to significant improvements in lacrimal gland exocrinopathy and tear secretion. Our results suggested that autoreactive CD4(+) T cells provoked macrophage infiltration to the eye and lacrimal gland, where they played a functional role in directing the development of autoimmune dry eye.

S100A8 and S100A9 are messengers in the crosstalk between epidermis and dermis modulating a psoriatic milieu in human skin

S100A8 and S100A9 are members of the S100A8 protein family that exist as homodimers and heterodimers in neutrophils, monocytes, and macrophages. Recent studies have shown the pivotal roles of S100A8 and S100A9 in the propagation of inflammation and keratinocyte proliferation in psoriasis. We found significant up-regulation of S100A8 and S100A9 secretion from keratinocytes in psoriatic lesions. To mimic the in vivo secretory conditions of S100A8 and S100A9 from psoriatic epidermal keratinocytes, we used the culture medium (CM) of S100A8 and S100A8/A9 adenovirus-transduced keratinocytes to investigate the functions of S100A8 and S100A9. We detected increased levels of various pro-inflammatory cytokines in the CM, including IL-8 and TNF-α, which are involved in aggravating psoriatic skin lesions, and IL-6 and members of the CXCL family of pro-angiogenic cytokines. The CM increased immune cell migration and increased angiogenesis in human umbilical vein endothelial cells. In conclusion, we found that the upregulated production of S100A8 and S100A9 by psoriatic epidermal keratinocytes activated adjacent keratinocytes to produce several cytokines. Moreover, S100A8 and S100A9 themselves function as pro-angiogenic and chemotactic factors, generating a psoriatic milieu in skin.

Apilimod inhibits the production of IL-12 and IL-23 and reduces dendritic cell infiltration in psoriasis

Psoriasis is characterized by hyperplasia of the epidermis and infiltration of leukocytes into both the dermis and epidermis. IL-23, a key cytokine that induces T_H17 cells, has been found to play a critical role in the pathogenesis of psoriasis. Apilimod is a small-molecule compound that selectively suppresses synthesis of IL-12 and IL-23. An open-label clinical study of oral administration of apilimod was conducted in patients with psoriasis. Substantial improvements in histology and clinical measurements were observed in patients receiving 70mg QD. The expression of IL-23p19 and IL-12/IL-23p40 in skin lesions was significantly reduced in this dose group, with a simultaneous increase in IL-10 observed. A decrease in the levels of T_H1 and T_H17 cytokines/chemokines in skin lesions followed these p19 and p40 changes. In parallel, a reduction in skin-infiltrating CD11c⁺ dendritic cells and CD3⁺ T cells was seen, with a greater decrease in the CD11c⁺ population. This was accompanied by increases in T and B cells, and decreases in neutrophils and eosinophils in the periphery. This study demonstrates the immunomodulatory activity of apilimod and provides clinical evidence supporting the inhibition of IL-12/IL-23 synthesis for the treatment of T_H1- and T_H17-mediated inflammatory diseases.

Role of TNF-α in virus-induced airway hyperresponsiveness and neuronal M₂ muscarinic receptor dysfunction

BACKGROUND AND PURPOSE

Infections with respiratory viruses induce exacerbations of asthma, increase acetylcholine release and potentiate vagally mediated bronchoconstriction by blocking inhibitory M₂ muscarinic receptors on parasympathetic neurons. Here we test whether virus-induced M₂ receptor dysfunction and airway hyperresponsiveness are tumour necrosis factor-alpha (TNF-α) dependent.

EXPERIMENTAL APPROACH

Guinea pigs were pretreated with etanercept or phosphate-buffered saline 24 h before intranasal infection with parainfluenza. Four days later, pulmonary inflation pressure, heart rate and blood pressure were measured. M₂ receptor function was assessed by the potentiation by gallamine (an M₂ receptor antagonist) of bronchoconstriction caused by electrical stimulation of the vagus nerves and measured as increased pulmonary inflation pressure. Human airway epithelial cells were infected with influenza and TNF-α concentration in supernatant was measured before supernatant was applied to human neuroblastoma cells. M₂ receptor expression in these neuroblastoma cells was measured by qRT-PCR.

KEY RESULTS

Influenza-infected animals were hyperresponsive to vagal stimulation but not to intravenous ACh. Gallamine did not potentiate vagally induced bronchoconstriction in virus-infected animals, indicating M₂ receptor dysfunction. Etanercept prevented virus-induced airway hyperresponsiveness and M₂ receptor dysfunction, without changing lung viral titres. Etanercept caused a non-significant decrease in total cells, macrophages and neutrophils in bronchoalveolar lavage. Influenza infection significantly increased TNF-α release from isolated epithelial cells, sufficient to decrease M₂ receptors in neuroblastoma cells. This ability of supernatants from infected epithelial cells to inhibit M₂ receptor expression was blocked by etanercept.

CONCLUSIONS AND IMPLICATIONS

TNF-α is a key mediator of virus-induced M₂ muscarinic receptor dysfunction and airway hyperresponsiveness.

Role of cellular oxidative stress and cytochrome c in the pathogenesis of psoriasis

Oxidative-free radicals and apoptosis have linked to chronic skin diseases. Higher levels of oxidative radicals and the release of mitochondrial cytochrome c may have a role in the pathogenesis of psoriasis. We investigated the possible role of cellular oxidative stress and release of cytochrome c of mitochondria in the pathogenesis of psoriasis. Disease severity was assessed by psoriasis area severity index score (PASI) of 55 psoriasis patients, they grouped as mild (11), moderate (20) and severe (24), also 20 healthy individuals used as controls. All groups were subjected for serum malondialdehyde (MDA), nitric oxide (NO·), superoxide dismutase (SOD), catalase (CAT), total antioxidant status (TAS) and serum cytochrome c concentrations. We found that, (1) Severity wise increase in MDA and NO·, and decrease in SOD, CAT and TAS levels in all patients with different degrees of psoriasis; (2) PASI showed positive correlation with the increase in MDA and NO·, and negatively with decreased SOD, CAT and TAS levels; (3) significant increase in cytochrome c level was observed among psoriasis patients which showed negative correlation to MDA and NO· levels in mild and positively with moderate and severe groups. The release of mitochondrial cytochrome c indicates the induction of apoptosis mediated via oxidative stress which ultimately plays role in the pathogenesis of psoriasis.

Sun exposure rapidly reduces plasmacytoid dendritic cells and inflammatory dermal dendritic cells in psoriatic skin

BACKGROUND

Interferon (IFN)-α-producing plasmacytoid dendritic cells (pDCs), inflammatory CD11c+CD1c- myeloid dendritic cells (mDCs) and macrophages have been found to contribute to the pathogenesis of psoriasis. Heliotherapy is a well-established treatment modality of this disease, although the details of how the effects are mediated are unknown.

OBJECTIVES

To test the hypothesis that exposure to natural sun affects pathogenic DC subsets in lesional skin.

METHODS

Skin biopsies were obtained from lesional and nonlesional skin in 10 patients with moderate to severe psoriasis subjected to controlled sun exposure on Gran Canaria. Biopsies were obtained at baseline, day 2 and day 16 and examined by immunohistochemistry.

RESULTS

Sixteen days of heliotherapy had excellent clinical effect on patients with psoriasis, with significant reductions in Psoriasis Area and Severity Index (PASI) scores. In lesional skin pDC numbers and expression of MxA, a surrogate marker for IFN-α, were rapidly reduced. Inflammatory CD11c+CD1c- mDCs were significantly reduced whereas resident dermal CD11c+CD1c+ mDCs were unaffected. Expression levels of the maturation marker DC-LAMP (CD208) on mDCs were significantly reduced after sun exposure, as were the numbers of lesional dermal macrophages. A decrease of dermal DC subsets and macrophages was already observed after 1 day of sun exposure. An additional finding was that DC-SIGN (CD209) is primarily expressed on CD163+ macrophages and not DCs.

CONCLUSIONS

The clinical improvement in psoriasis following sun exposure is associated with rapid changes in dermal DC populations and macrophages in lesional skin, preceding the clinical effect. These findings support the concept that these DC subsets are involved in the pathogenesis of psoriasis and suggest that sun-induced clinical benefit may partly be explained by its effect on dermal DCs.

Gsdma3 mutation causes bulge stem cell depletion and alopecia mediated by skin inflammation

Primary cicatricial alopecias (PCAs) are a group of permanent hair loss disorders, of which the pathogenesis is still poorly understood. The alopecia and excoriation (AE) mouse strain is a dominant mutant generated from ethyl nitrosourea mutagenesis. AE mice exhibit a progressive alopecia phenotype similar to that seen in PCAs, resulting from a point mutation in the gasdermin A3 gene. Mutant mice begin to show alopecia on the head from postnatal day 22 and experience complete hair loss by the age of 6 months, along with hyperkeratosis and catagen delay. The results of a histological examination showed that bulge stem cells in AE skin are gradually depleted, as indicated by decreased keratin 15 and CD34 expression, and reduced bromodeoxyuridine label-retaining cells in the AE bulge. In addition, AE mice display an inflammatory condition in the skin from postnatal day 7, including elevated tumor necrosis factor-α and monocyte chemotactic protein-1 mRNA levels and significantly increased macrophages and dendritic cell number. Immune privilege in the bulge was also compromised in AE skin. Consistently, after treatment with the immunosuppressive agent, cyclosporine A, immune privilege collapse, stem cell destruction, and alopecia phenotype of AE mice were all rescued. Collectively, our data demonstrate that immune-mediated destruction of bulge stem cells plays a crucial role in the pathogenesis of alopecia in AE mice, and this strain might be an interesting model for PCAs, especially for lichen planopilaris.

Studying the mononuclear phagocyte system in the molecular age

The mononuclear phagocyte system (MPS) comprises monocytes, macrophages and dendritic cells. Tissue phagocytes share several cell surface markers, phagocytic capability and myeloid classification; however, the factors that regulate the differentiation, homeostasis and function of macrophages and dendritic cells remain largely unknown. The purpose of this manuscript is to review the tools that are currently available and those that are under development to study the origin and function of mononuclear phagocytes.

Colony-stimulating factor-1 promotes kidney growth and repair via alteration of macrophage responses

Colony-stimulating factor (CSF)-1 controls the survival, proliferation, and differentiation of macrophages, which are recognized as scavengers and agents of the innate and the acquired immune systems. Because of their plasticity, macrophages are endowed with many other essential roles during development and tissue homeostasis. We present evidence that CSF-1 plays an important trophic role in postnatal organ growth and kidney repair. Notably, the injection of CSF-1 postnatally enhanced kidney weight and volume and was associated with increased numbers of tissue macrophages. Moreover, CSF-1 promotes postnatal renal repair in mice after ischemia-reperfusion injury by recruiting and influencing macrophages toward a reparative state. CSF-1 treatment rapidly accelerated renal repair with tubular epithelial cell replacement, attenuation of interstitial fibrosis, and functional recovery. Analysis of macrophages from CSF-1-treated kidneys showed increased expression of insulin-like growth factor-1 and anti-inflammatory genes that are known CSF-1 targets. Taken together, these data suggest that CSF-1 is important in kidney growth and the promotion of endogenous repair and resolution of inflammatory injury.

Depletion of antigen-presenting cells by clodronate liposomes reverses the psoriatic skin phenotype in KC-Tie2 mice

BACKGROUND

There is ongoing debate regarding the initiation of psoriatic plaque as primarily arising from an anomaly in epidermal keratinocytes (KCs) or from abnormalities in immunocytes that secondarily activate otherwise normal KCs. In mice engineered to overexpress the angiopoietin receptor Tie2 in KCs, skin spontaneously develops the characteristic clinical, histological and immune cell phenotypes of psoriasis which can be reversed with either transgene repression or ciclosporin administration, suggesting key roles for both KCs and T cells in mediating the skin disease in this murine model.

OBJECTIVES

To determine if antigen-presenting cells (APCs) and macrophages alone are sufficient to sustain psoriasiform inflammation in the KC-Tie2 murine model of psoriasis.

METHODS

Clodronate liposomes were intradermally injected into involved dorsal skin of KC-Tie2 or control animals once a week for 6weeks and acanthosis, angiogenesis, immune cell infiltration and cytokine production were quantitated using immunohistochemistry and interactive image analyses, enzyme-linked immunosorbent assay (ELISAs) and quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Clodronate liposome injection eliminated CD11c+, F4/80+ and CD11b+ cells in the skin and returned CD8+ T-cell numbers to control mouse levels. APC depletion in KC-Tie2 mouse skin resulted in resolution of the acanthotic skin phenotype, decreased dermal angiogenesis, and a return to control mouse levels for interleukin (IL)-1α, IL-6, IL-23 and tumour necrosis factor (TNF)-α expression and modest reductions in interferon-γ and IL-17.

CONCLUSIONS

These findings suggest a critical role for APCs and myeloid cell-derived IL-23 and TNF-α and underscore the importance of Th1 and Th17 T cells in maintaining the psoriasiform skin phenotype in the KC-Tie2 mouse model.

Multiple helminth infection of the skin causes lymphocyte hypo-responsiveness mediated by Th2 conditioning of dermal myeloid cells

Infection of the mammalian host by schistosome larvae occurs via the skin, although nothing is known about the development of immune responses to multiple exposures of schistosome larvae, and/or their excretory/secretory (E/S) products. Here, we show that multiple (4x) exposures, prior to the onset of egg laying by adult worms, modulate the skin immune response and induce CD4⁺ cell hypo-responsiveness in the draining lymph node, and even modulate the formation of hepatic egg-induced granulomas. Compared to mice exposed to a single infection (1x), dermal cells from multiply infected mice (4x), were less able to support lymph node cell proliferation. Analysis of dermal cells showed that the most abundant in 4x mice were eosinophils (F4/80⁺MHC-II⁻), but they did not impact the ability of antigen presenting cells (APC) to support lymphocyte proliferation to parasite antigen in vitro. However, two other cell populations from the dermal site of infection appear to have a critical role. The first comprises arginase-1⁺, Ym-1⁺ alternatively activated macrophage-like cells, and the second are functionally compromised MHC-II^hi cells. Through the administration of exogenous IL-12 to multiply infected mice, we show that these suppressive myeloid cell phenotypes form as a consequence of events in the skin, most notably an enrichment of IL-4 and IL-13, likely resulting from an influx of RELMα-expressing eosinophils. We further illustrate that the development of these suppressive dermal cells is dependent upon IL-4Rα signalling. The development of immune hypo-responsiveness to schistosome larvae and their effect on the subsequent response to the immunopathogenic egg is important in appreciating how immune responses to helminth infections are modulated by repeated exposure to the infective early stages of development.

Schistosomiasis is a major helminth disease that infects more than 200 million people in the tropics. Free-swimming aquatic cercariae infect through the skin after contact with contaminated water, and in endemic areas this can occur frequently. However, nothing is known about how multiple exposures affects innate immunity in the skin, and/or whether it impacts the acquired immune response. Consequently, we have developed an infection model in the mouse to examine the immune response to multiple infections prior to the production of eggs. We show that multiple exposures to schistosome larvae cause lymphocyte hypo-responsiveness, partly mediated by macrophages and dendritic cells from the skin which have a ‘down-regulated’ phenotype and are not able to act as efficient antigen presenting cells (APCs). These regulated APCs are conditioned amongst high levels of the cytokines IL-4 and IL-13 which follow an influx of abundant eosinophils. In the absence of the regulatory APCs, and in the absence of the common receptor chain for IL-4 and IL-13 (i.e. IL-4Rα), lymphocyte proliferation is restored. These findings are important in understanding how dermal immune responses are modulated so that we can devise new strategies for vaccine delivery, or the treatment of chronic inflammatory conditions of the skin.

An unrestrained proinflammatory M1 macrophage population induced by iron impairs wound healing in humans and mice

Uncontrolled macrophage activation is now considered to be a critical event in the pathogenesis of chronic inflammatory diseases such as atherosclerosis, multiple sclerosis, and chronic venous leg ulcers. However, it is still unclear which environmental cues induce persistent activation of macrophages in vivo and how macrophage-derived effector molecules maintain chronic inflammation and affect resident fibroblasts essential for tissue homeostasis and repair. We used a complementary approach studying human subjects with chronic venous leg ulcers, a model disease for macrophage-driven chronic inflammation, while establishing a mouse model closely reflecting its pathogenesis. Here, we have shown that iron overloading of macrophages--as was found to occur in human chronic venous leg ulcers and the mouse model--induced a macrophage population in situ with an unrestrained proinflammatory M1 activation state. Via enhanced TNF-α and hydroxyl radical release, this macrophage population perpetuated inflammation and induced a p16(INK4a)-dependent senescence program in resident fibroblasts, eventually leading to impaired wound healing. This study provides insight into the role of what we believe to be a previously undescribed iron-induced macrophage population in vivo. Targeting this population may hold promise for the development of novel therapies for chronic inflammatory diseases such as chronic venous leg ulcers.

Plasmin plays an essential role in amplification of psoriasiform skin inflammation in mice

Background

Although increased levels of plasminogen activators have been found in psoriatic lesions, the role of plasmin converted from plasminogen by plasminogen activators in pathogenesis of psoriasis has not been investigated.

Methodology/Principal Findings

Here we examined the contribution of plasmin to amplification of inflammation in patients with psoriasis. We found that plasminogen was diminished, but that the amount and activity of its converted product plasmin were markedly increased in psoriasis. Moreover, annexin II, a receptor for plasmin was dramatically increased in both dermis and epidermis in psoriasis. Plasmin at sites of inflammation was pro-inflammatory, eliciting production of inflammatory factors, including CC chemokine ligand 20 (CCL20) and interleukin-23 (IL-23), that was mediated by the nuclear factor-kappaB (NF-κB) signaling pathway and that had an essential role in the recruitment and activation of pathogenic C-C chemokine receptor type 6 (CCR6)⁺ T cells. Moreover, intradermal injection of plasmin or plasmin together with recombinant monocyte/macrophage chemotactic protein-1 (MCP-1) resulted in induction of psoriasiform skin inflammation around the injection sites with several aspects of human psoriasis in mice.

Conclusions/Significance

Plasmin converted from plasminogen by plasminogen activators plays an essential role in amplification of psoriasiform skin inflammation in mice, and targeting plasmin receptor - annexin II - may harbor therapeutic potential for the treatment of human psoriasis.

Psoriasis: from pathogenesis to novel therapeutic approaches

Psoriasis is one of the commonest chronic inflammatory disorders. Its cause is unknown, but a wealth of studies indicate that the disease results from a complex and dynamic interplay between genetic and environmental factors that trigger an excessive inflammatory response in the skin. Dendritic cells and effector T-cells are central in the development of the psoriastic lesion, and cytokines produced by these cells stimulate keratinocytes to proliferate and increase the migration of inflammatory cells into the skin, promoting epidermal hyperplasia and inflammation. Understanding the immunology of the psoriatic plaque has led to new therapeutic options and novel candidates for immunomodulation, and has changed the ways psoriatic patients are managed.

IL-20: biological functions mediated through two types of receptor complexes

IL-20 was discovered 10 years ago as a new member of the IL-10 family of cytokines. IL-20 shares the highest amino-acid sequence identity with IL-10, IL-24 and IL-19. IL-20 is secreted by immune cells and activated epithelial cells like keratinocytes. A high expression of the corresponding IL-20 receptor chains is detected on epithelial cells. In terms of function, IL-20 might therefore mediate a crosstalk between epithelial cells and tissue-infiltrating immune cells under inflammatory conditions. Transgenic and knockout mouse models for some cytokines and receptors of the IL-10-type cytokines have provided new insights into the biology of this family. This review will focus on the biological functions of IL-20 and its receptors within the IL-10 cytokine network.

Role of wound macrophages in skin flap loss or survival in an experimental diabetes model

BACKGROUND

Tightly controlled wound inflammation is a central determinant of skin flap survival in healthy mice. This study investigated inflammatory response patterns in caudally pedicled skin flaps in diabetic mice during severely impaired conditions of necrotic skin flap tissue loss.

METHODS

Skin flap biopsies were analysed by RNase protection assay, quantitative real-time polymerase chain reaction, immunohistochemistry, enzyme-linked immunosorbent assay and immunoblotting.

RESULTS

Skin flaps were characterized by the necrotic loss of tissue starting from distal areas of the flaps in diabetic mice. Decay of epidermal and dermal structures within skin flap tissue was paralleled by an immune cell-mediated expression of chemokines (macrophage inflammatory protein 2, macrophage chemoattractant protein 1), cyclo-oxygenase (COX) 2 and inducible nitric oxide synthase (iNOS). Distal regions of necrotic skin flap tissue were infiltrated by excess numbers of neutrophils and macrophages, and the latter were polarized towards a proinflammatory state as they expressed COX-2 and iNOS. Experimental depletion of inflammatory macrophages inhibited necrotic destruction of the distal skin flap tissue in diabetic mice despite the persistence of neutrophil infiltration and inflammation.

CONCLUSION

Wound macrophages play a pivotal role in determining the survival or loss of skin flap tissue under disturbed wound healing conditions in obese diabetic mice.

Differentiation and function of mouse monocyte-derived dendritic cells in steady state and inflammation

Although monocytes were originally described as precursors to all the different subpopulations of macrophages found in the steady state and formed under inflammatory and infectious conditions, recent data have demonstrated conclusively that monocytes can also differentiate into dendritic cells (DCs). Monocytes are the precursors to different subsets of DCs, such as Langerhans cells and DCs found in the lamina propria of the gastrointestinal, respiratory, and urogenital tracts. In addition, monocyte-derived DCs (moDCs), newly formed during inflammatory reactions, appear to fulfill an essential role in defense mechanisms against pathogens by participating in the induction of both adaptive and innate immune responses. In this regard, moDCs have the capacity to activate antigen-specific CD4(+) T-cell responses and to cross-prime CD8(+) T cells, during viral, bacterial, and parasitic infections. In addition, monocytes have been recently described as the precursors to a subset of DCs specialized in innate immunity against pathogens, named TipDCs [for TNF-alpha (tumor necrosis factor-alpha)-iNOS (inducible nitric oxide synthase)-producing DCs] that display a remarkable microbicidal activity and also provide iNOS-dependent help for antibody production by B cells. Importantly, in contrast to DCs developing in the steady state, moDCs formed during inflammatory and infectious processes are subjected to diverse soluble mediators that determine the multiple functional specificities displayed by moDCs, as a result of the remarkable developmental plasticity of monocytes. In this review, we discuss recent findings dealing with the differentiation and functional relevance of moDCs that have widened the frontiers of DC immunobiology in relation to innate and adaptive immunity and the etiology of chronic inflammatory diseases.

GABA and GABA(A) receptor expression on immune cells in psoriasis: a pathophysiological role

Psoriasis is a chronic inflammatory disease in which pruritus is a common symptom. Pruritus may be associated with the gamma-aminobutyric acid (GABA) system. The distribution of GABA and its GABA(A) receptor (R) was studied in involved and non-involved psoriatic skin, as well as normal healthy control skin, using an immunohistochemistry technique. Pruritus was determined using a visual analog scale. Inflammatory cells immunoreactive for the GABA ligand and the GABA(A) R were increased (P < 0.01, respectively) in the involved skin. Cells stained for GABA ligand were mostly macrophages with some lymphocytes, while cells stained for GABA(A) R were macrophages, neutrophils or lymphocytes. There was a positive correlation when comparing GABA ligand (P = 0.05) and GABA(A) R (P < 0.05) expressing inflammatory cells, with pruritus. The GABA ligand and its GABA(A) R may play a role for the pathogenesis of psoriasis as well as for pruritus in this disease.

Recombinant, ETA'-based CD64 immunotoxins: improved efficacy by increased valency, both in vitro and in vivo in a chronic cutaneous inflammation model in human CD64 transgenic mice

BACKGROUND

Dysregulated, activated macrophages play a pivotal role in chronic inflammatory diseases such as arthritis and atopic dermatitis. These cells display increased expression of the high-affinity Fcgamma receptor (CD64), making them ideal targets for CD64-specific immunotoxins. We previously showed that a chemically linked immunotoxin, the monoclonal H22-RicinA, specifically eliminated infiltrating activated macrophages and resolved chronic cutaneous inflammation. However, several disadvantages are associated with classic immunotoxins, and we therefore followed a fusion protein strategy to express the antigen-binding site alone (scFv H22) fused to a derivative of Pseudomonas exotoxin A (ETA').

OBJECTIVES

To assess the potential effect of increased valency on efficacy, we produced monovalent [H22(scFv)-ETA'] and bivalent [H22(scFv)(2)-ETA'] versions and evaluated their potential for eliminating activated macrophages both in vitro and in vivo.

METHODS

Both immunotoxins were produced by bacterial fermentation. Binding was assessed by flow cytometry on the monocytic CD64+ cell line U937. Toxicity was analysed by XTT and apoptosis induction by annexin V bioassay. The in vivo effect was tested in a human CD64 transgenic mouse model for cutaneous inflammation.

RESULTS

The cytotoxic effects of both immunotoxins were clearly due to apoptosis with an IC(50) of 140 pmol L(-1) for monovalent and only 14 pmol L(-1) for the divalent version. In vivo treatment with H22(scFv)-ETA' reduced CD64+ activated macrophages to 21% of their initial numbers whereas H22(scFv)(2)-ETA' treatment reduced these cells to 4.8% (P < 0.001).

CONCLUSIONS

These data clearly show increased efficacy due to increased valency of the anti-CD64 immunotoxin. Both recombinant immunotoxins have a low IC(50), making them suitable for the treatment of diseases involving dysregulated, activated macrophages.

Beta(2) integrin deficiency yields unconventional double-negative T cells distinct from mature classical natural killer T cells in mice

Expressed on leucocytes, beta(2) integrins (CD11/CD18) are specifically involved in leucocyte function. Using a CD18-deficient (CD18(-/-)) mouse model, we here report on their physiological role in lymphocyte differentiation and trafficking. CD18(-/-) mice present with a defect in the distribution of lymphocytes with highly reduced numbers of naïve B and T lymphocytes in inguinal and axillary lymph nodes. In contrast, cervical lymph nodes were fourfold enlarged harbouring unconventional T-cell receptor-alphabeta (TCR-alphabeta) and TCR-gammadelta CD3(+) CD4(-) CD8(-) (double-negative; DN) T cells that expanded in situ. Using adoptive transfer experiments, we found that these cells did not home to peripheral lymph nodes of CD18(wt) recipients but, like antigen-experienced T or natural killer (NK) T cells, recirculated through non-lymphoid organs. Lacking regulatory functions in vitro, CD18(-/-) TCR-alphabeta DN T cells did not suppress the proliferation of polyclonally activated CD4(+) or CD8(+) (single-positive; SP) T cells. Most interestingly, CD18(-/-) TCR-alphabeta DN T cells showed intermediate TCR expression levels, an absent activation through allogeneic major histocompatibility complex and a strong proliferative dependence on interleukin-2, hence, closely resembling NKT cells. However, our data oppose former reports, clearly showing that, because of an absent reactivity with CD1d-alphaGalCer dimers, these cells are not mature classical NKT cells. Our data indicate that CD18(-/-) TCR-alphabeta DN T cells, like NKT and TCR-gammadelta T cells, share characteristics of both adaptive and innate immune cells, and may accumulate as a compensatory mechanism to the functional defect of adaptive immunity in CD18(-/-) mice.

Molecular pathophysiology of psoriasis and molecular targets of antipsoriatic therapy

Psoriasis is a chronic inflammatory skin disease characterised by elevated red scaly plaques on specific body sites. Histologically, the plaques are defined by epidermal hyperplasia, epidermal and dermal infiltration by leukocytes, and changes in the dermal microvasculature. Differentiation and activation are disturbed in lesional psoriatic keratinocytes, and the pool of proliferating keratinocytes is increased, which is accompanied by enhanced production of proinflammatory cytokines, adhesion molecules and antimicrobial peptides. These changes in psoriatic keratinocytes are caused by altered expression of genes associated with epidermal differentiation, and by activation of signalling pathways involving signal transducer and activator of transcription 3 (STAT3), type I interferon (IFN) and mitogen-activated protein kinase (MAPK). The number of T cells, and myeloid and plasmacytoid dendritic cells (DCs) is markedly increased in psoriatic lesions. Myeloid DCs produce interleukin (IL)-23, tumour necrosis factor (TNF)-alpha and inducible nitric oxide synthase (iNOS), which are crucial cytokines in the pathogenesis of psoriasis. IL-23 stimulates the secretion of IL-22 by T helper 17 cells, and IL-22 induces epidermal hyperplasia. The crosstalk between keratinocytes and leukocytes via their proinflammatory cytokines creates the vicious circle of chronic skin inflammation seen in psoriasis. This suggests that optimal treatment of psoriasis needs to target pathogenic pathways in both leukocytes and keratinocytes.

Molecular dissection of psoriasis: integrating genetics and biology

Psoriasis is a common and debilitating disease of the skin, nails, and joints, with an acknowledged but complex genetic basis. Early genome-wide linkage studies of psoriasis focused on segregation of microsatellite markers in families; however, the only locus consistently identified resided in the major histocompatibility complex. Subsequently, several groups mapped this locus to the vicinity of HLA-C, and two groups have reported HLA-Cw6 itself to be the major susceptibility allele. More recently, the development of millions of single-nucleotide polymorphisms, coupled with the development of high-throughput genotyping platforms and a comprehensive map of human haplotypes, has made possible a genome-wide association approach using cases and controls rather than families. Taking advantage of these developments, we participated in a collaborative genome-wide association study of psoriasis involving thousands of cases and controls. Initial analysis of these data revealed and/or confirmed association between psoriasis and seven genetic loci-HLA-C, IL12B, IL23R, IL23A, IL4/IL13, TNFAIP3, and TNIP1-and ongoing studies are revealing additional loci. Here, we review the epidemiology, immunopathology, and genetics of psoriasis, and present a disease model integrating its genetics and immunology.

Extracellular adherence protein of Staphylococcus aureus suppresses disease by inhibiting T-cell recruitment in a mouse model of psoriasis

Psoriasis is a T-cell-mediated inflammatory disease. Previous studies focused on lymphocyte function-associated antigen 1 (LFA-1)-expressing T cells as a molecular target for therapeutic intervention. By contrast, information on therapeutic effects and the underlying mechanism of blocking the LFA-1 counter receptor, ICAM-1 is scarce. Here, we used the CD18 (beta2-integrin) hypomorphic (CD18hypo) mouse model of psoriasis to investigate the therapeutic role of extracellular adherence protein (Eap) of Staphylococcus aureus, which exerts antiinflammatory activities by interacting with the ICAM-1 function. We show that ICAM-1 is predominantly upregulated on endothelial cells in lesional skin of CD18hypo mice. In vitro Eap was found to disrupt cell-cell contacts between T cells and dendritic cells, and inhibit T-cell proliferation. By contrast, in vivo Eap rather blocked transmigration of T cells from vessels to inflamed skin of CD18hypo mice, but did not inhibit their proliferation and activation. Most importantly, Eap successfully suppressed the disease by blocking T-cell extravasation into the inflamed skin. Together, these data indicate that interaction between LFA-1 and ICAM-1 is causally involved in the pathogenesis of psoriasiform skin inflammation, and targeting ICAM-1 to selectively block T-cell extravasation by Eap without immune suppression may represent a potential therapeutic strategy for psoriasis.

Depletion of macrophages in mice results in higher dengue virus titers and highlights the role of macrophages for virus control

Monocytes and macrophages are target cells for dengue infection. Besides their potential role for virus replication, activated monocytes/macrophages produce cytokines that may be critical for dengue pathology. To study the in vivo role of monocytes and macrophages for virus replication, we depleted monocytes and macrophages in IFN-alphabetagammaR knockout mice with clodronate liposomes before dengue infection. Although less virus was first recovered in the draining LN in the absence of macrophages, monocyte/macrophage depletion eventually resulted in a ten-fold higher systemic viral titer. A massive infiltration of CD11b(+)CD11c(low)Ly6C(low) monocytes into infected organs was observed in parallel with increasing virus titers before viremia was controlled. Depletion of monocytes in the blood before or after local infection had no impact on virus titers, suggesting that monocytes are not required as "virus-shuttles". Our data provide evidence that systemic viremia is established independently of tissue macrophages present at the site of infection and blood monocytes. Instead, we demonstrate the importance of monocytes/macrophages for the control of dengue virus.

Targeting NF-kappa B with a natural triterpenoid alleviates skin inflammation in a mouse model of psoriasis

Psoriasis vulgaris is a common chronic inflammatory skin disease involving cytokines and an activated cellular immune system. At variance to skin from patients with atopic dermatitis or from healthy subjects, human psoriatic skin lesions exhibit strong activation of transcription factor NF-kappaB that is mainly confined to dermal macrophages, whereas only a few dendritic cells but no CD3+ lymphocytes show activated NF-kappaB. Since NF-kappaB signaling is required for the induction and/or function of many cytokines and aberrant cytokine expression has been proposed as an underlying cause of psoriasis, we investigated whether NF-kappaB targeting would affect the course of the disease in the CD18 hypomorphic (CD18(hypo)) mouse model of psoriasis. When mice with severe psoriasiform lesions were treated systemically or locally with the IkappaB kinase inhibitor acetyl-11-keto-beta-boswellic acid (AKbetaBA), NF-kappaB signaling and the subsequent NF-kappaB-dependent cytokine production as shown by the TNF-alpha production of macrophages were profoundly suppressed. Additionally, application of the compound counteracted the intradermal MCP-1, IL-12, and IL-23 expression in previously lesional skin areas, led to resolution of the abundant immune cell infiltrates, and significantly reduced the increased proliferation of the keratinocytes. Overall, the AKbetaBA treatment was accompanied by a profound improvement of the psoriasis disease activity score in the CD18(hypo) mice with reconstitution of a nearly normal phenotype within the chosen observation period. Our data demonstrate that NF-kappaB signaling is pivotal for the pathogenesis in the CD18(hypo) mouse model of psoriasis. Therefore, targeting NF-kappaB might provide an effective strategy for the treatment of psoriasis.

Reactive oxygen intermediate-induced pathomechanisms contribute to immunosenescence, chronic inflammation and autoimmunity

Deregulation of reactive oxygen intermediates (ROI) resulting in either too high or too low concentrations are commonly recognized to be at least in part responsible for many changes associated with aging. This article reviews ROI-dependent mechanisms critically contributing to the decline of immune function during physiologic - or premature - aging. While ROI serve important effector functions in cellular metabolism, signalling and host defence, their fine-tuned generation declines over time, and ROI-mediated damage to several cellular components and/or signalling deviations become increasingly prevalent. Although distinct ROI-associated pathomechanisms contribute to immunosenescence of the innate and adaptive immune system, mutual amplification of dysfunctions may often result in hyporesponsiveness and immunodeficiency, or in chronic inflammation with hyperresponsiveness/deregulation, or both. In this context, we point out how imbalanced ROI contribute ambiguously to driving immunosenescence, chronic inflammation and autoimmunity. Although ROI may offer a distinct potential for therapeutic targeting along with the charming opportunity to rescue from deleterious processes of aging and chronic inflammatory diseases, such modifications, owing to the complexity of metabolic interactions, may carry a marked risk of unforeseen side effects.