AIM2 Suppresses Inflammation and Epithelial Cell Proliferation during Glomerulonephritis.

Absent in melanoma-2 (AIM2) is an inflammasome-forming innate immune sensor for dsDNA but also exhibits inflammasome-independent functions such as restricting cellular proliferation. AIM2 is expressed in the kidney, but its localization and function are not fully characterized. In normal human glomeruli, AIM2 localized to podocytes. In patients with glomerulonephritis, AIM2 expression increased in CD44+-activated parietal epithelial cells within glomerular crescents. To explore AIM2 effects in glomerular disease, studies in Aim2 -/- mice were performed. Aim2-/- glomeruli showed reduced expression of Wilm tumor gene-1 (WT1), WT1-driven podocyte genes, and increased proliferation in outgrowth assays. In a nephrotoxic serum (NTS)-induced glomerulonephritis model, Aim2-/- (B6) mice exhibited more severe glomerular crescent formation, tubular injury, inflammation, and proteinuria compared with wild-type controls. Inflammasome activation markers were absent in both Aim2 -/- and wild-type kidneys, despite an increased inflammatory transcriptomic signature in Aim2 -/- mice. Aim2 -/- mice also demonstrated dysregulated cellular proliferation and an increase in CD44+ parietal epithelial cells during glomerulonephritis. The augmented inflammation and epithelial cell proliferation in Aim2 -/- (B6) mice was not due to genetic background, as Aim2 -/- (B6.129) mice demonstrated a similar phenotype during NTS glomerulonephritis. The AIM2-like receptor (ALR) locus was necessary for the inflammatory glomerulonephritis phenotype observed in Aim2 -/- mice, as NTS-treated ALR -/- mice displayed equal levels of injury as wild-type controls. Podocyte outgrowth from ALR -/- glomeruli was still increased, however, confirming that the ALR locus is dispensable for AIM2 effects on epithelial cell proliferation. These results identify a noncanonical role for AIM2 in suppressing inflammation and epithelial cell proliferation during glomerulonephritis.

Dysregulation of proinflammatory versus anti-inflammatory human TH17 cell functionalities in the autoinflammatory Schnitzler syndrome.

BACKGROUND: TH17 cells have so far been considered to be crucial mediators of autoimmune inflammation. Two distinct types of TH17 cells have been described recently, which differed in their polarization requirement for IL-1ß and in their cytokine repertoire. Whether these distinct TH17 phenotypes translate into distinct TH17 cell functions with implications for human health or disease has not been addressed yet. OBJECTIVE: We hypothesized the existence of proinflammatory and anti-inflammatory human TH17 cell functions based on the differential expression of IL-10, which is regulated by IL-1ß. Considering the crucial role of IL-1ß in the pathogenesis of autoinflammatory syndromes, we hypothesized that IL-1ß mediates the loss of anti-inflammatory TH17 cell functionalities in patients with Schnitzler syndrome, an autoinflammatory disease. METHODS: To assess proinflammatory versus anti-inflammatory TH17 cell functions, we performed suppression assays and tested the effects of IL-1ß dependent and independent TH17 subsets on modulating proinflammatory cytokine secretion by monocytes. Patients with Schnitzler syndrome were analyzed for changes in TH17 cell functions before and during therapy with IL-1ß-blocking drugs. RESULTS: Both TH17 cell subsets differ in their ability to suppress T-cell proliferation and their ability to modulate proinflammatory cytokine production by antigen-presenting cells because of their differential IL-10 expression properties. In patients with Schnitzler syndrome, systemic overproduction of IL-1ß translates into a profound loss of anti-inflammatory TH17 cell functionalities, which can be reversed by anti-IL-1ß treatment. CONCLUSION: IL-1ß signaling determines the differential expression pattern of IL-10, which is necessary and sufficient to induce proinflammatory versus anti-inflammatory TH17 cell functions. Our data introduce TH17 cell subsets as novel players in autoinflammation and thus novel therapeutic targets in autoinflammatory syndromes including other IL-1ß mediated diseases. This demonstrates for the first time alterations in the adaptive immune system in patients with autoinflammatory syndromes.

The role of interleukin-1 beta in the pathophysiology of Schnitzler's syndrome.

INTRODUCTION: Schnitzler's syndrome (SchS) is a disabling autoinflammatory disorder, characterized by a chronic urticarial rash, an M-protein, arthralgia, and other signs of systemic inflammation. Anti-interleukin-1 (IL-1) beta antibodies are highly effective, but the pathophysiology is still largely unknown. Here we studied the effect of in-vivo IL-1 inhibition on serum markers of inflammation and cellular immune responses. METHODS: Eight patients with SchS received monthly subcutaneous (s.c.) injections with 150 mg canakinumab for six months. Blood was drawn for measurement of serum markers of inflammation (12 times per patient) and for functional and phenotypic analysis of both freshly isolated and toll-like receptor (TLR)-ligand-stimulated peripheral blood mononuclear cells (PBMCs) (five times per patient). All data were compared to results of healthy controls. RESULTS: IL-6 levels in serum and in lysates of freshly isolated PBMCs and serum myeloid-related protein (MRP8)/14 and S100A12 levels correlated with disease activity. In vitro, LPS stimulation resulted in higher IL-6 and IL-1 beta production in PBMCs from symptomatic SchS patients compared to healthy controls, whereas patient cells were relatively hyporesponsive to poly:IC and Pam3Cys. The mRNA microarray of PBMCs showed distinct transcriptomes for controls, symptomatic patients and anti-IL-1-treated patients. Numbers of T- and B-cell subsets as well as M-protein concentrations were not affected by IL-1 inhibition. Free light chain levels were elevated in 4 out of 8 patients. CONCLUSIONS: In conclusion, patient PBMCs are hyperresponsive to LPS, and clinical efficacy of IL-1 beta inhibition in patients with SchS is associated with in-vivo and ex-vivo suppression of inflammation. Interestingly, patient PBMCs showed divergent responses to TLR2/6, TLR3 and TLR4 ligands. Our data underscore that IL-1 beta plays a pivotal role in SchS.

Schnitzler's syndrome: lessons from 281 cases.

Schnitzler's syndrome is an autoinflammatory disorder characterized by the association of a monoclonal IgM (or IgG) gammopathy, a chronic urticarial rash, and signs and symptoms of systemic inflammation, including fever, arthralgias and bone pain. It was first described in 1972. This review summarizes the clinical features, efficacy of therapies, and follow-up data of the 281 cases that have been reported to date. Also, the results of skin histology, bone imaging, laboratory investigations, and studies of the pathogenesis will be discussed, including the pivotal role of interleukin-1 beta in this disorder.

Sustained efficacy of the monoclonal anti-interleukin-1 beta antibody canakinumab in a 9-month trial in Schnitzler's syndrome.

OBJECTIVES: Schnitzler's syndrome is a chronic disabling autoinflammatory disorder, characterised by chronic urticaria, paraproteinemia and systemic inflammation. The interleukin (IL) 1 receptor antagonist anakinra is a very effective treatment, but requires daily injection and blocks both IL-1α and IL-1ß. Canakinumab is a selective human monoclonal anti-IL-1ß antibody with a long half-life. We investigated the long-term efficacy and safety of canakinumab in Schnitzler's syndrome. METHODS: In an open-label, single-treatment arm trial, eight patients with Schnitzler's syndrome received monthly injections with 150 mg canakinumab subcutaneously for 6 months, followed by a 3-month observation period. Primary outcome was complete or clinical remission at day 14. Secondary outcome measures included inflammatory markers, quality of life, time to relapse, safety and tolerability. RESULTS: After stopping anakinra, patients developed moderate to severe clinical symptoms. Canakinumab induced complete or clinical remission at day 14 in all eight patients. Median C-reactive protein concentrations decreased from 169 mg/l at baseline to less than 10 mg/l on day 14 and remained low or undetectable. One patient discontinued participation on day 39 because of return of symptoms while all others remained in complete or clinical remission during the 6-month treatment period. Relapse after last canakinumab dose occurred within 3 months in four patients. For two patients, remission continued several months post-study. Five patients reported at least one adverse event, predominantly mild upper respiratory tract infections. One patient died in a traffic accident. CONCLUSIONS: In this 9-month study, monthly 150 mg canakinumab injection was an effective and well-tolerated treatment for Schnitzler's syndrome. Our data demonstrate that IL-1ß plays a pivotal role in this disease. CLINICALTRIALS.GOV: NCT01276522.

Microbiome dynamics of human epidermis following skin barrier disruption.

BACKGROUND: Recent advances in sequencing technologies have enabled metagenomic analyses of many human body sites. Several studies have catalogued the composition of bacterial communities of the surface of human skin, mostly under static conditions in healthy volunteers. Skin injury will disturb the cutaneous homeostasis of the host tissue and its commensal microbiota, but the dynamics of this process have not been studied before. Here we analyzed the microbiota of the surface layer and the deeper layers of the stratum corneum of normal skin, and we investigated the dynamics of recolonization of skin microbiota following skin barrier disruption by tape stripping as a model of superficial injury. RESULTS: We observed gender differences in microbiota composition and showed that bacteria are not uniformly distributed in the stratum corneum. Phylogenetic distance analysis was employed to follow microbiota development during recolonization of injured skin. Surprisingly, the developing neo-microbiome at day 14 was more similar to that of the deeper stratum corneum layers than to the initial surface microbiome. In addition, we also observed variation in the host response towards superficial injury as assessed by the induction of antimicrobial protein expression in epidermal keratinocytes. CONCLUSIONS: We suggest that the microbiome of the deeper layers, rather than that of the superficial skin layer, may be regarded as the host indigenous microbiome. Characterization of the skin microbiome under dynamic conditions, and the ensuing response of the microbial community and host tissue, will shed further light on the complex interaction between resident bacteria and epidermis.

Strong induction of AIM2 expression in human epidermis in acute and chronic inflammatory skin conditions.

Absent in melanoma 2 (AIM2) is a double-stranded DNA receptor, and its activation initiates an interleukin-1 beta processing inflammasome. AIM2 is implicated in host defense against several pathogens, but could hypothetically also contribute to autoinflammatory or autoimmune diseases, such as is the case for NLRP3. Using thoroughly characterised antibodies, we analysed AIM2 expression in human tissues and primary cells. A strong epidermal upregulation of AIM2 protein expression was observed in several acute and chronic inflammatory skin disorders, such as psoriasis, atopic dermatitis, venous ulcera, contact dermatitis, and experimental wounds. We also found AIM2 induction by interferon-gamma in submerged and three-dimensional in vitro models of human epidermis. Our data highlight the dynamics of epidermal AIM2 expression, showing Langerhans cell and melanocyte-restricted expression in normal epidermis but a pronounced induction in subpopulations of epidermal keratinocytes under inflammatory conditions.

Pattern recognition receptors in infectious skin diseases.

During the last decade, multiple pattern recognition receptors (PRRs) have been identified. These are involved in the innate immune response against a plethora of pathogens. However, PRR functioning can also be detrimental, even during infections. This review discusses the current knowledge on PRRs that recognize dermatotropic pathogens, and potential therapeutical implications.

Pattern recognition receptors in immune disorders affecting the skin.

Pattern recognition receptors (PRRs) evolved to protect organisms against pathogens, but excessive signaling can induce immune responses that are harmful to the host. Putative PRR dysfunction is associated with numerous immune disorders that affect the skin, such as systemic lupus erythematosus, cryopyrin-associated periodic syndrome, and primary inflammatory skin diseases including psoriasis and atopic dermatitis. As yet, the evidence is often confined to genetic association studies without additional proof of a causal relationship. However, insight into the role of PRRs in the pathophysiology of some disorders has already resulted in new therapeutic approaches based on immunomodulation of PRRs.

Hornerin is a component of the epidermal cornified cell envelopes.

A single-nucleotide polymorphism within the gene encoding hornerin (HRNR) has recently been linked with atopic dermatitis (AD) susceptibility. HRNR shares features with filaggrin, a key protein for keratinocyte differentiation, but conflicting reports have been published concerning its expression in the epidermis, and its role is still unknown. To analyze HRNR expression and function in the epidermis, anti-HRNR antibodies were produced and used in Western blot analysis and immunohistochemical, confocal, and immunoelectron microscopy analyses of human skin and of cornified cell envelopes purified from plantar stratum corneum. We also tested whether HRNR was a substrate of transglutaminases. In the epidermis, HRNR was detected at the periphery of keratohyalin granules in the upper granular layer and at the corneocyte periphery in the whole cornified layer. Detected in Western blot analysis as numerous bands, HRNR was relatively insoluble and only extracted from epidermis with urea and/or reducing agents. The presence of HRNR in the purified envelopes was confirmed by immunoelectron microscopy and by Western blot analysis after V8-protease digestion. HRNR was shown to be a substrate of transglutaminase 3. These data demonstrate that HRNR is a component of cornified cell envelopes of human epidermis. Its reduced expression in AD may contribute to the epidermal barrier defect observed in the disease.

A comprehensive analysis of pattern recognition receptors in normal and inflamed human epidermis: upregulation of dectin-1 in psoriasis.

Human epidermis plays an important role in host defense by acting as a physical barrier and signaling interface between the environment and the immune system. Pattern recognition receptors (PRRs) are crucial to maintain homeostasis and provide protection during infection, but are also causally involved in monogenic auto-inflammatory diseases. This study aimed to investigate the epidermal expression of PRRs and several associated host defense molecules in healthy human skin, psoriasis, and atopic dermatitis (AD). Using microarray analysis and real-time quantitative PCR, we found that many of these genes are transcribed in normal human epidermis. Only a few genes were differentially induced in psoriasis (CLEC7A (dectin-1), Toll-like receptor (TLR) 4, and mannose receptor C type 1 (MRC1)) or AD (MRC1, IL1RN, and IL1ß) compared with normal epidermis. A remarkably high expression of dectin-1 mRNA was observed in psoriatic epidermis and this was corroborated by immunohistochemistry. In cultured primary human keratinocytes, dectin-1 expression was induced by IFN-γ, IFN-α, and Th17 cytokines. Keratinocytes were unresponsive, however, to dectin-1 ligands such as ß-glucan or heat-killed Candida albicans, nor did we observe synergy with TLR2/TLR5 ligands. In conclusion, upregulation of dectin-1 in psoriatic lesions seems to be under control of psoriasis-associated cytokines. Its role in the biology of skin inflammation and infection remains to be explored.

Two adjacent nodules on the leg.

Poroma is a rare benign neoplasm (derived from the intraepidermal part of the eccrine or apocrine duct), which may clinically mimic malignant tumors such as (amelanotic) malignant melanoma and porocarcinoma. Histopathological examination is the key to the correct diagnosis, which is illustrated in the present case, in which a pigmented basal cell carcinoma and a poroma are in close proximity to each other. Despite a clinical differential diagnosis of melanoma, histopathology showed the typical characteristics of a poroma, a rare but much more favorable tumor. Histopathological features of poroma are discussed.

Concerted action of wild-type and mutant TNF receptors enhances inflammation in TNF receptor 1-associated periodic fever syndrome.

TNF, acting through p55 tumor necrosis factor receptor 1 (TNFR1), contributes to the pathogenesis of many inflammatory diseases. TNFR-associated periodic syndrome (TRAPS, OMIM 142680) is an autosomal dominant autoinflammatory disorder characterized by prolonged attacks of fevers, peritonitis, and soft tissue inflammation. TRAPS is caused by missense mutations in the extracellular domain of TNFR1 that affect receptor folding and trafficking. These mutations lead to loss of normal function rather than gain of function, and thus the pathogenesis of TRAPS is an enigma. Here we show that mutant TNFR1 accumulates intracellularly in peripheral blood mononuclear cells of TRAPS patients and in multiple cell types from two independent lines of knockin mice harboring TRAPS-associated TNFR1 mutations. Mutant TNFR1 did not function as a surface receptor for TNF but rather enhanced activation of MAPKs and secretion of proinflammatory cytokines upon stimulation with LPS. Enhanced inflammation depended on autocrine TNF secretion and WT TNFR1 in mouse and human myeloid cells but not in fibroblasts. Heterozygous TNFR1-mutant mice were hypersensitive to LPS-induced septic shock, whereas homozygous TNFR1-mutant mice resembled TNFR1-deficient mice and were resistant to septic shock. Thus WT and mutant TNFR1 act in concert from distinct cellular locations to potentiate inflammation in TRAPS. These findings establish a mechanism of pathogenesis in autosomal dominant diseases where full expression of the disease phenotype depends on functional cooperation between WT and mutant proteins and also may explain partial responses of TRAPS patients to TNF blockade.

Endovascular abdominal aortic aneurysm repair complicated by spondylodiscitis and iliaco-enteral fistula.

Infections of abdominal aortic endografts are rare. There are no reports on the association with spondylodiscitis. We report a case of a 74-year-old man who underwent endovascular aneurysm repair (EVAR) and subsequently femorofemoral bypass placement due to occlusion of the right limb of the endograft. Six months later, he presented with rectal bleeding, weight loss, back pain, and low abdominal pain. Computed tomography revealed extensive abscess formation with air in and around the endograft and psoas muscles, in continuity with destructive spondylodiscitis L3-4. There was a small bowel loop in close proximity to the occluded right leg of the endograft, which was filled with air bubbles. An axillofemoral bypass was created followed by a laparotomy. Intra-operatively, an iliaco-enteral fistula was found. The small bowel defect was sutured, the endograft completely removed, and the infrarenal aorta and both common iliac arteries were closed. Necrotic fragments of the former L3-4 disk were removed. The postoperative course was uneventful. Seven months postoperatively, the patient had recovered well. Iliaco-enteric fistula and spondylodiscitis are rare complications of aortic aneurysm repair. This is the first report of spondylodiscitis after EVAR.

Hybrid treatment of a symptomatic popliteal pseudoaneurysm due to type-I endoleak after previous endovascular exclusion.

PURPOSE: The development of endovascular repair of popliteal aneurysms has provided an alternative, minimally invasive way of treatment. We present a case of a late type-I endoleak, after previous exclusion of a popliteal pseudoaneurysm, leading to rupture and massive hematoma, which was excluded in a hybrid procedure. CASE REPORT: A 95-year-old woman presented with progressive swelling with skin ulceration and necrosis cranial to the medial side of her left knee. Four years earlier, a left popliteal pseudoaneurysm was excluded with a stent-graft. Rupture of the popliteal artery with massive hematoma was demonstrated by ultrasound examination and a spiral computed tomography scan, with high suspicion of a type-I endoleak. Endovascular repair of the endoleak with a polytetrafluoroethylene-covered stent-graft was followed by surgical resection of the damaged skin and evacuation of the hematoma. CONCLUSION: Type-I endoleaks after endovascular exclusion of popliteal pseudoaneurysms do occur and may lead to rupture. A symptomatic pseudoaneurysm may be successfully treated by a hybrid procedure.