Human keratinocytes produce the complement inhibitor factor H: synthesis is regulated by interferon-gamma

Complement's involvement in allergic Th2 immunity: a cross-barrier perspective

Type 2 (Th2) allergic diseases are chronic conditions characterized by a Th2-polarized immune response to allergens. These diseases can be categorized by affected barrier sites: skin (atopic dermatitis, allergic contact dermatitis), gut (food allergy), and respiratory tract (e.g., asthma, chronic rhinosinusitis). The global prevalence of Th2 allergic diseases has increased the need for a deeper understanding of their pathophysiology. Several associations have been identified between genetic variants in the genes encoding components of the complement system and allergic disease. Moreover, levels of several complement proteins are elevated in patients with allergy. Experimental evidence demonstrates that the complement system plays a critical role in the development of these diseases across barrier sites. While site-specific differences exist in the complement components involved, key pathways, particularly C3 and C5, are prominent across the skin, gut, and lung.

Therapeutic targeting of alternative pathway and C5 but not C5a protects from disease development in a preclinical model of autoimmune blistering dermatosis

Introduction

Epidermolysis Bullosa Acquisita (EBA) is an autoimmune blistering dermatosis characterized by autoantibodies (AAbs) against type VII collagen (COL7) located at the dermal epidermal junction (DEJ). Local complement activation drives C5a generation associated with neutrophil recruitment and activation resulting in skin lesions and inflammation. Here we tested the impact of C5a/C5adesArg, C5 or combined C5 and alternative pathway (AP) targeting on disease development and skin inflammation in a preclinical mouse model mimicking the effector phase of EBA.

Methods

C57BL/6 mice were treated subcutaneously with purified rabbit anti-mouse-COL7 IgG in the presence of IgG1 mAbs directed against murine C5a/C5adesArg (M031), C5 (mBB5.1), a bifunctional protein comprising mBB5.1 fused to an active fragment of the AP inhibitor factor H (M014) or an IgG1 isotype control mAb. Formation of skin lesions was evaluated 12 days every other day. On day 12, DEJ separation, IgG AAb and C3b deposition and neutrophil infiltration was assessed.

Results

Isotype IgG1-treated mice developed first skin lesions on day 4 peaking on day 12. Prophylactic treatment with either M031 or M014 markedly reduced the development of skin lesions, the dermal/epidermal separation and neutrophil recruitment. Surprisingly, C5 or combined AP/C5 inhibition by M014 but not C5a/C5adesArg-targeting by M031 reduced the development of skin lesions and dermal/epidermal separation in the setting of therapeutic treatment. IgG and C3b deposition was not affected by either treatment. Importantly, direct comparison of isolated C5 targeting by mBB5.1 vs. combined AP/C5 inhibition by M014 revealed that M014 reduced the development of skin lesions earlier and more pronounced than mBB5.1.

Discussion

Our findings identify combined C5/AP targeting as a novel therapeutic option for autoimmune blistering dermatoses.

Association of the Complement System with Subclinical Atherosclerosis in Psoriasis: Findings from an Observational Cohort Study

Psoriasis is a chronic and inflammatory disease that affects the skin and joints and is associated with multiple comorbidities and cardiovascular risk factors. Consequently, patients with psoriasis have an increased risk of cardiovascular diseases such as atherosclerosis, a chronic pathology that shares common inflammatory and immune-response mechanisms with psoriasis, including vascular inflammation and complement activation. To better understand the relationship between atherosclerosis and psoriasis, a proteomics study followed by a bioinformatics analysis was carried out, with a subsequent validation step using ELISA and western blotting. When the plasma from patients with psoriasis alone was compared with that from patients with psoriasis and atherosclerosis, 31 proteins of interest related to the complement system and oxygen transport were identified. After the validation phase, 11 proteins appeared to define the presence of subclinical atherosclerosis in patients with psoriasis, indicating the importance of complement cascades in the development of atherosclerotic plaques in individuals with psoriasis. These results are a step forward in understanding the pathological pathways implicated in the cardiovascular risk associated with this population, which may represent an interesting starting point for developing predictive tools that improve the follow-up of these patients and design more effective therapies.

Potential role of inflammaging mediated by the complement system in enlarged facial pores

BACKGROUND

Enlarged facial pores are a common cosmetic concern of the skin, rather than a disease, and have not received much attention from dermatologists in recent years. Consequently, progress in understanding their pathogenesis has been limited, and current cosmetic solutions have limitations. Given that the complement system has regained interest as a key player in chronic inflammatory skin conditions, various mechanisms involving this system are being investigated.

OBJECTIVE

We aimed to shed light on the mechanism underlying enlarged facial pores by examining the role of the complement system in skin.

METHODS

We conducted a comprehensive literature search utilizing various academic databases including PubMed, Web of Science, and Google Scholar. Employing keywords such as "complement system," "inflammation," "facial pores," "enlarged," and "mechanisms," we compiled a selection of relevant studies. These studies provided a comprehensive understanding of the intricate mechanisms underlying the relationship between the "complement system" and "inflammation" within the context of facial pore enlargement.

RESULTS

Our findings suggest that inflammaging mediated by complement activation may be a critical player in the formation of enlarged facial pores. Specifically, overactivation of the complement system leading to the accumulation of complement fragments could be a major contributor to this process. Notably, the complement system in skin may be involved in a range of skin issues, including aging.

CONCLUSION

Modulating the complement system presents a promising avenue for future research in improving skin health. Further basic and clinical research is necessary to validate these findings, but we hope that this study can serve as a theoretical foundation for the development of targeted cosmetics.

Complement factor I: Regulatory nexus, driver of immunopathology, and therapeutic

Complement factor I (FI) is the nexus for classical, lectin and alternative pathway complement regulation. FI is an 88 kDa plasma protein that circulates in an inactive configuration until it forms a trimolecular complex with its cofactor and substrate whereupon a structural reorganization allows the catalytic triad to cleave its substrates, C3b and C4b. In keeping with its role as the master complement regulatory enzyme, deficiency has been linked to immunopathology. In the setting of complete FI deficiency, a consumptive C3 deficiency results in recurrent infections with encapsulated microorganisms. Aseptic cerebral inflammation and vasculitic presentations are also less commonly observed. Heterozygous mutations in the factor I gene (CFI) have been demonstrated to be enriched in atypical haemolytic uraemic syndrome, albeit with a very low penetrance. Haploinsufficiency of CFI has also been associated with decreased retinal thickness and is a strong risk factor for the development of age-related macular degeneration. Supplementation of FI using plasma purified or recombinant protein has long been postulated, however, technical difficulties prevented progression into clinical trials. It is only using gene therapy that CFI supplementation has reached the clinic with GT005 in phase I/II clinical trials for geographic atrophy.

Preferential production and secretion of the complement regulator factor H-like protein 1 (FHL-1) by human myeloid cells

Factor H is a pivotal complement regulatory protein that is preferentially produced by the liver and circulates in high concentrations in serum. There has been an increasing interest in the extrahepatic production of complement factors, including by cells of the immune system, since this contributes to non-canonical functions of local complement activation and regulation. Here we investigated the production and regulation of factor H and its splice variant factor H-like protein 1 (FHL-1) by human myeloid cells. As validation, we confirmed the predominant presence of intact factor H in serum, despite a strong but comparable mRNA expression of CFH and FHL1 in liver. Comparable levels of CFH and FHL1 were also observed in renal tissue, although a dominant staining for FHL-1 was shown within the proximal tubules. Human in vitro generated pro- and anti-inflammatory macrophages both expressed and produced factor H/FHL-1, but this was strongest in pro-inflammatory macrophages. Production was not affected by LPS activation, but was increased upon stimulation with IFN-γ or CD40L. Importantly, in both macrophage subsets mRNA expression of FHL1 was significantly higher than CFH. Moreover, production of FHL-1 protein could be confirmed using precipitation and immunoblotting of culture supernatants. These data identify macrophages as producers of factor H and FHL-1, thereby potentially contributing to local complement regulation at sites of inflammation.

Innate immunity and microbial dysbiosis in hidradenitis suppurativa - vicious cycle of chronic inflammation

Hidradenitis Suppurativa (HS) is a chronic multifactorial inflammatory skin disease with incompletely understood mechanisms of disease pathology. HS is characterized by aberrant activation of the innate immune system, resulting in activation of pathways that aim to protect against pathogenic microorganisms, and also contribute to failure to resolve inflammation. Imbalance in innate immunity is evident in deregulation of host antimicrobial peptides (AMPs) and the complement system associated with the microbiome dysbiosis. The pathology is further complicated by ability of pathogens associated with HS to overcome host immune response. Potential roles of major AMPs, cathelicidin, defensins, dermcidin, S100 proteins, RNAse 7 and complement proteins are discussed. Dysregulated expression pattern of innate immunity components in conjunction with bacterial component of the disease warrants consideration of novel treatment approaches targeting both host immunity and pathogenic microbiome in HS.

Complement Factor H in cSCC: Evidence of a Link Between Sun Exposure and Immunosuppression in Skin Cancer Progression

Cutaneous squamous cell carcinoma (cSCC) is a common form of skin cancer with an estimated 750,000 cases diagnosed annually in the United States. Most cases are successfully treated with a simple excision procedure, but ~5% of cases metastasize and have a 5-year survival rate of 25-45%. Thus, identification of biomarkers correlated to cSCC progression may be useful in the early identification of high-risk cSCC and in the development of new therapeutic strategies. This work investigates the role of complement factor H (CFH) in the development of cSCC. CFH is a regulatory component of the complement cascade which affects cell mediated immune responses and increases in complement proteins are associated with poor outcomes in multiple cancer types. We provide evidence that sun exposure may increase levels of CFH, suggesting an immunomodulatory role for CFH early in the development of cSCC. We then document increased levels of CFH in cSCC samples, compared to adjacent normal tissue (ANT) routinely excised in a dermatology clinic which, in paired samples, received the same level of sun exposure. We also provide evidence that levels of CFH are even greater in more advanced cases of cSCC. To provide a potential link between CFH and immune modulation, we assessed immune system function by measuring interferon gamma (IFN-γ) and FOXP3 in patient samples. IFN-γ levels were unchanged in cSCC relative to ANT which is consistent with an ineffective cell-mediated immune response. FOXP3 was used to assess prevalence of regulatory T cells within the tissues, indicating either a derailed or inhibitory immune response. Our data suggest that FOXP3 levels are higher in cSCC than in ANT. Our current working model is that increased CFH downstream of sun exposure is an early event in the development of cSCC as it interferes with proper immune surveillance and decreases the effectiveness of the immune response, and creates a more immunosuppressive environment, thus promoting cSCC progression.

Low level of complement factor H increases the risk of cancer-related death in patients with small-cell lung cancer

INTRODUCTION

Pulmonary cancer is a kind of deeply invasive tumour which is difficult to treat, and its mortality rate is high. Previous research has shown that activation of complement could contribute to the progression of non-small-cell lung cancer (SCLC). However, little research has been done on SCLC.

METHODS

Complement factor H (CFH), complements C3 as well as C4 were measured in patients, and the prognostic impact of different parameters was assessed by log-rank function analysis and Cox multifactor models. Besides, we constructed a predictive model based on complement fractions and validated the accuracy of the model.

RESULTS

Among these 242 patients, 200 (82.6%) died. The median survival time was 18.3 months. We found by multifactorial analysis that high levels of CFH decreased the risk of death (HR 0.23, 95% CI 0.10 to 0.57, p<0.001), while elevated complement C4 displayed poor prognosis (HR 2.28, 95% CI 1.66 to 3.13, p<0.001). We screened variables by Cox models and constructed CFH-based prediction models to plot a nomogram by internal validation. The nomogram showed excellent accuracy in assessing the probability of death, yielding an adjusted C-statistics of 0.905.

CONCLUSIONS

CFH can be recognised as a biomarker to predict the risk of death in SCLC. The prediction model established based on CFH, C3 and C4 levels has good accuracy in patients' prognostic assessment.

Thyroid hormone action in epidermal development and homeostasis and its implications in the pathophysiology of the skin

Thyroid hormones (THs) are key endocrine regulators of tissue development and homeostasis. They are constantly released into the bloodstream and help to regulate many cell functions. The principal products released by the follicular epithelial cells are T3 and T4. T4, which is the less active form of TH, is produced in greater amounts than T3, which is the most active form of TH. This mechanism highlights the importance of the peripheral regulation of TH levels that goes beyond the central axis. Skin, muscle, liver, bone and heart are finely regulated by TH. In particular, skin is among the target organs most influenced by TH, which is essential for skin homeostasis. Accordingly, skin diseases are associated with an altered thyroid status. Alopecia, dermatitis and vitiligo are associated with thyroiditis and alopecia and eczema are frequently correlated with the Graves' disease. However, only in recent decades have studies started to clarify the molecular mechanisms underlying the effects of TH in epidermal homeostasis. Herein, we summarize the most frequent clinical epidermal alterations linked to thyroid diseases and review the principal mechanisms involved in TH control of keratinocyte proliferation and functional differentiation. Our aim is to define the open questions in this field that are beginning to be elucidated thanks to the advent of mouse models of altered TH metabolism and to obtain novel insights into the physiopathological consequences of TH metabolism on the skin.

Altered levels of complement components associated with non-immediate drug hypersensitivity reactions

Nonimmediate drug hypersensitivity reactions (niDHRs) range from mild-type maculopapular exanthema (MPE) to severe type Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) with unentirely clarified pathogenesis. This study sought to explore whether complement components participated in niDHRs. The participants comprised of three groups as follows: MPE (n = 65), SJS/TEN (n = 13, contains 7 SJS, 2 SJS-TEN overlap and 4 TEN), and equal healthy controls (n = 78). Skin pathological changes were confirmed by hematoxylin and eosin staining. The mRNA and protein levels of complement components were assessed. In the MPE group, there were no alterations in complement components at the protein and mRNA levels found except for a decrease in factor H mRNA. In the SJS/TEN group, up-regulated levels of C3aR and C5aR mRNA and down-regulated factor H mRNA levels in blood were noted. A lower plasma protein level of C3, Factor H and a higher level of C3a, C5, C5a, C5b-9, Factor B (p < 0.05) were found in the SJS/TEN group compared with in the control (p < 0.05). In SJS/TEN skin lesions, indirect immunofluorescence assays showed positive specific staining for C5b-9, but not C3. Both C3aR and C5aR were positive staining in the SJS/TEN samples, while staining for C1q, mannose-binding lectin (MBL), Factor B, and Factor H were only weak or negative. The findings reported here are the first to define the expression profiles/extent of the presence of various complement components at the mRNA and protein levels in niDHRs, especially in SJS/TEN. These altered complement components might, at least in part, be integral to the mechanisms underlying the pathogeneses of SJS and TEN.

Regulation of regulators: Role of the complement factor H-related proteins

The complement system, while being an essential and very efficient effector component of innate immunity, may cause damage to the host and result in various inflammatory, autoimmune and infectious diseases or cancer, when it is improperly activated or regulated. Factor H is a serum glycoprotein and the main regulator of the activity of the alternative complement pathway. Factor H, together with its splice variant factor H-like protein 1 (FHL-1), inhibits complement activation at the level of the central complement component C3 and beyond. In humans, there are also five factor H-related (FHR) proteins, whose function is poorly characterized. While data indicate complement inhibiting activity for some of the FHRs, there is increasing evidence that FHRs have an opposite role compared with factor H and FHL-1, namely, they enhance complement activation directly and also by competing with the regulators FH and FHL-1. This review summarizes the current stand and recent data on the roles of factor H family proteins in health and disease, with focus on the function of FHR proteins.

Complement System in Cutaneous Squamous Cell Carcinoma

Epidermal keratinocyte-derived cutaneous squamous cell carcinoma (cSCC) is the most common metastatic skin cancer with high mortality rates in the advanced stage. Chronic inflammation is a recognized risk factor for cSCC progression and the complement system, as a part of innate immunity, belongs to the microenvironment of tumors. The complement system is a double-edged sword in cancer, since complement activation is involved in anti-tumor cytotoxicity and immune responses, but it also promotes cancer progression directly and indirectly. Recently, the role of several complement components and inhibitors in the regulation of progression of cSCC has been shown. In this review, we will discuss the role of complement system components and inhibitors as biomarkers and potential new targets for therapeutic intervention in cSCC.

Upregulation of Complement Factor H by SOCS-1/3⁻STAT4 in Lung Cancer

Complement factor H (CFH) is a fluid phase regulator of complement proteins and functions to prevent complement attack and immune surveillance. CFH is known to inactivate therapeutic antibody-dependent complement-mediated cellular cytotoxicity. We found that CFH was highly expressed in human lung cancer cells and tissues. To investigate mechanisms of CFH upregulation, we searched for a CFH transcription factor and its regulatory factors. First, signal transducer and activator of transcription 4 (STAT4) expression patterns coincided with CFH expression patterns in lung cancer tissues. Knockdown of STAT4 led to decreased CFH secretion from lung cancer cells. STAT4 bound directly to the CFH promoter, as demonstrated by luciferase reporter assay, electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation (ChIP) assay, suggesting that STAT4 is a transcription factor for CFH. In addition, a low level of suppressors of cytokine signaling (SOCS)-1/3, a Janus kinase (JAK) inhibitor, was observed in lung cancer cells and its transfection decreased CFH protein levels and promoter activity. Unexpectedly, the low level of SOCS-1/3 was not due to epigenetic silencing. Instead, differential methylation was found on the regulatory region of STAT4 between normal and lung cancer cells. In conclusion, our results demonstrated that CFH is upregulated by constitutive activation of STAT4, which is accounted for by SOCS silencing in lung cancer cells.

Self-Damage Caused by Dysregulation of the Complement Alternative Pathway: Relevance of the Factor H Protein Family

The alternative pathway is a continuously active surveillance arm of the complement system, and it can also enhance complement activation initiated by the classical and the lectin pathways. Various membrane-bound and plasma regulatory proteins control the activation of the potentially deleterious complement system. Among the regulators, the plasma glycoprotein factor H (FH) is the main inhibitor of the alternative pathway and its powerful amplification loop. FH belongs to a protein family that also includes FH-like protein 1 and five factor H-related (FHR-1 to FHR-5) proteins. Genetic variants and abnormal rearrangements involving the FH protein family have been linked to numerous systemic and organ-specific diseases, including age-related macular degeneration, and the renal pathologies atypical hemolytic uremic syndrome, C3 glomerulopathies, and IgA nephropathy. This review covers the known and recently emerged ligands and interactions of the human FH family proteins associated with disease and discuss the very recent experimental data that suggest FH-antagonistic and complement-activating functions for the FHR proteins.

Complement Activation in Inflammatory Skin Diseases

The complement system is a fundamental part of the innate immune system, playing a crucial role in host defense against various pathogens, such as bacteria, viruses, and fungi. Activation of complement results in production of several molecules mediating chemotaxis, opsonization, and mast cell degranulation, which can contribute to the elimination of pathogenic organisms and inflammation. Furthermore, the complement system also has regulating properties in inflammatory and immune responses. Complement activity in diseases is rather complex and may involve both aberrant expression of complement and genetic deficiencies of complement components or regulators. The skin represents an active immune organ with complex interactions between cellular components and various mediators. Complement involvement has been associated with several skin diseases, such as psoriasis, lupus erythematosus, cutaneous vasculitis, urticaria, and bullous dermatoses. Several triggers including auto-antibodies and micro-organisms can activate complement, while on the other hand complement deficiencies can contribute to impaired immune complex clearance, leading to disease. This review provides an overview of the role of complement in inflammatory skin diseases and discusses complement factors as potential new targets for therapeutic intervention.

Intracellular complement activation-An alarm raising mechanism?

It has become increasingly apparent that the complement system, being an ancient defense mechanism, is not operative only in the extracellular milieu but also intracellularly. In addition to the known synthetic machinery in the liver and by macrophages, many other cell types, including lymphocytes, adipocytes and epithelial cells produce selected complement components. Activation of e.g. C3 and C5 inside cells may have multiple effects ranging from direct antimicrobial defense to cell differentiation and possible influence on metabolism. Intracellular activation of C3 and C5 in T cells is involved in the maintenance of immunological tolerance and promotes differentiation of T helper cells into Th1-type cells that activate cell-mediated immune responses. Adipocytes are unique in producing many complement sensor proteins (like C1q) and Factor D (adipsin), the key enzyme in promoting alternative pathway amplification. The effects of complement activation products are mediated by intracellular and cell membrane receptors, like C3aR, C5aR1, C5aR2 and the complement regulator MCP/CD46, often jointly with other receptors like the T cell receptor, Toll-like receptors and those of the inflammasomes. These recent observations link complement activation to cellular metabolic processes, intracellular defense reactions and to diverse adaptive immune responses. The complement components may thus be viewed as intracellular alarm molecules involved in the cellular danger response.

Acute phase proteins as promising biomarkers: Perspectives and limitations for human and veterinary medicine

Acute phase proteins (APPs) are highly conserved plasma proteins that are increasingly secreted by the liver in response to a variety of injuries, independently of their location and cause. APPs favor the systemic regulation of defense, coagulation, proteolysis, and tissue repair. Various APPs have been applied as general diagnostic parameters for a long time. Through proteomic techniques, more and more APPs have been discovered to be differentially altered. Since they are not consistently explainable by a stereotypic hepatic expression of sets of APPs, most of these results have unfortunately been neglected or attributed to the nonspecificity of the acute phase reaction. Moreover, it appears that various extrahepatic tissues are also able to express APPs. These extrahepatic APPs show focally specific roles in tissue homeostasis and repair and are released primarily into interstitial and distal fluids. Since these focal proteins might leak into the circulatory system, mixtures of hepatic and extrahepatic APP species can be expected in blood. Hence, a selective alteration of parts of APPs might be expected. There are several hints on multiple molecular forms and fragments of tissue-derived APPs. These differences offer the chance for multiple selective determinations. Thus, specific proteoforms might indeed serve as tissue-specific disease indicators.

The complement system in cancer: Ambivalence between tumour destruction and promotion

Constituting a part of the innate immune system, the complement system consists of over 50 proteins either acting as part of a 3-branch activation cascade, a well-differentiated regulatory system in fluid phase or on each tissue, or as receptors translating the activation signal to multiple cellular effector functions. Complement serves as first line of defence against infections from bacteria, viruses and parasites by orchestrating the immune response through opsonisation, recruitment of immune cells to the site of infection and direct cell lysis. Complement is generally recognised as a protective mechanism against the formation of tumours in humans, but is often limited by various resistance mechanisms interfering with its cytotoxic action, now considered as a great barrier of successful antibody-based immunotherapy. However, recent studies also indicate a pro-tumourigenic potential of complement in certain cancers and under certain conditions. In this review, we present recent findings on the possible dual role of complement in destroying cancer, especially if resistance mechanisms are blocked, but also under certain inflammatory conditions-promoting tumour development.

Complement system in dermatological diseases - fire under the skin

The complement system plays a key role in several dermatological diseases. Overactivation, deficiency, or abnormality of the control proteins are often related to a skin disease. Autoimmune mechanisms with autoantibodies and a cytotoxic effect of the complement membrane attack complex on epidermal or vascular cells can cause direct tissue damage and inflammation, e.g., in systemic lupus erythematosus (SLE), phospholipid antibody syndrome, and bullous skin diseases like pemphigoid. By evading complement attack, some microbes like Borrelia spirochetes and staphylococci can persist in the skin and cause prolonged symptoms. In this review, we present the most important skin diseases connected to abnormalities in the function of the complement system. Drugs having an effect on the complement system are also briefly described. On one hand, drugs with free hydroxyl on amino groups (e.g., hydralazine, procainamide) could interact with C4A, C4B, or C3 and cause an SLE-like disease. On the other hand, progress in studies on complement has led to novel anti-complement drugs (recombinant C1-inhibitor and anti-C5 antibody, eculizumab) that could alleviate symptoms in diseases associated with excessive complement activation. The main theme of the manuscript is to show how relevant the complement system is as an immune effector system in contributing to tissue injury and inflammation in a broad range of skin disorders.

The epidermal growth factor receptor is a regulator of epidermal complement component expression and complement activation

The complement system is activated in response to tissue injury. During wound healing, complement activation seems beneficial in acute wounds but may be detrimental in chronic wounds. We found that the epidermal expression of many complement components was only increased to a minor extent in skin wounds in vivo and in cultured keratinocytes after exposure to supernatant from stimulated mononuclear cells. In contrast, the epidermal expression of complement components was downregulated in ex vivo injured skin lacking the stimulation from infiltrating inflammatory cells but with intact injury-induced epidermal growth factor receptor (EGFR)-mediated growth factor response. In cultured primary keratinocytes, stimulation with the potent EGFR ligand, TGF-α, yielded a significant downregulation of complement component expression. Indeed, EGFR inhibition significantly enhanced the induction of complement components in keratinocytes and epidermis following stimulation with proinflammatory cytokines. Importantly, EGFR inhibition of cultured keratinocytes either alone or in combination with proinflammatory stimulus promoted activation of the complement system after incubation with serum. In keratinocytes treated solely with the EGFR inhibitor, complement activation was dependent on serum-derived C1q, whereas in keratinocytes stimulated with a combination of proinflammatory cytokines and EGFR inhibition, complement activation was found even with C1q-depleted serum. In contrast to human keratinocytes, EGFR inhibition did not enhance complement component expression or cause complement activation in murine keratinocytes. These data demonstrate an important role for EGFR in regulating the expression of complement components and complement activation in human epidermis and keratinocytes and, to our knowledge, identify for the first time a pathway important for the epidermal regulation of complement activation.

Complement factor H gene (CFH) polymorphisms C-257T, G257A and haplotypes are associated with protection against severe dengue phenotype, possible related with high CFH expression

Four genetic polymorphisms located at the promoter (C-257T) and coding regions of CFH gene (exon 2 G257A, exon 14 A2089G and exon 19 G2881T) were investigated in 121 dengue patients (DENV-3) in order to assess the relationship between allele/haplotypes variants and clinical outcomes. A statistical value was found between the CFH-257T allele (TT/TC genotypes) and reduced susceptibility to severe dengue (SD). Statistical associations indicate that individuals bearing a T allele presented significantly higher protein levels in plasma. The -257T variant is located within a NF-κB binding site, suggesting that this variant might have effect on the ability of the CFH gene to respond to signals via the NF-κB pathway. The G257A allelic variant showed significant protection against severe dengue. When CFH haplotypes effect was considered, the ancestral CG/CG promoter-exon 2 SNP genotype showed significant risk to SD either in a general comparison (ancestral × all variant genotypes), as well as in individual genotypes comparison (ancestral × each variant genotype), where the most prevalent effect was observed in the CG/CG × CA/TG comparison. These findings support the involvement of -257T, 257A allele variants and haplotypes on severe dengue phenotype protection, related with high basal CFH expression.

Complement factor H: a biomarker for progression of cutaneous squamous cell carcinoma

The incidence of cutaneous squamous cell carcinoma (cSCC) is increasing globally. We have studied the expression of complement system components in cSCC. Expression profiling of cSCC cell lines (n=8) and normal human epidermal keratinocytes (n=5) with Affymetrix and quantitative real-time PCR (qPCR) revealed upregulation of complement factor H (CFH) and factor H-like protein-1 (FHL-1) in cSCC cell lines. The expression of CFH and FHL-1 mRNAs was also significantly higher in cSCC tumors (n=6) than in normal skin (n=11). Analysis of CFH and FHL-1 expression in vivo in invasive cSCCs (n=65), in situ cSCCs (n=38), and premalignant lesions (actinic keratoses, n=37) by immunohistochemistry showed that they were specifically expressed by tumor cells in cSCCs and the staining intensity was stronger in cSCCs than in in situ cSCCs and actinic keratoses. The expression of CFH by cSCC cells was upregulated by IFN-γ and the basal CFH and FHL-1 expression was dependent on extracellular signal-regulated kinase (ERK)1/2 and p38 signaling. Knockdown of CFH and FHL-1 expression inhibited proliferation and migration of cSCC cells and inhibited basal ERK1/2 activation. These results provide evidence for a role of CFH and FHL-1 in cSCC progression and identify them as progression markers and potential therapeutic targets in SCCs of skin.

Properdin and factor h: opposing players on the alternative complement pathway "see-saw"

Properdin and factor H are two key regulatory proteins having opposite functions in the alternative complement pathway. Properdin up-regulates the alternative pathway by stabilizing the C3bBb complex, whereas factor H downregulates the pathway by promoting proteolytic degradation of C3b. While factor H is mainly produced in the liver, there are several extrahepatic sources. In addition to the liver, factor H is also synthesized in fetal tubuli, keratinocytes, skin fibroblasts, ocular tissue, adipose tissue, brain, lungs, heart, spleen, pancreas, kidney, muscle, and placenta. Neutrophils are the major source of properdin, and it is also produced by monocytes, T cells and bone marrow progenitor cell line. Properdin is released by neutrophils from intracellular stores following stimulation by N-formyl-methionine-leucine-phenylalanine (fMLP) and tumor necrosis factor alpha (TNF-α). The HEP G2 cells derived from human liver has been found to produce functional properdin. Endothelial cells also produce properdin when induced by shear stress, thus is a physiological source for plasma properdin. The diverse range of extrahepatic sites for synthesis of these two complement regulators suggests the importance and need for local availability of the proteins. Here, we discuss the significance of the local synthesis of properdin and factor H. This assumes greater importance in view of recently identified unexpected and novel roles of properdin and factor H that are potentially independent of their involvement in complement regulation.

Essential role of surface-bound complement factor H in controlling immune complex-induced arthritis

Factor H (fH) is an endogenous negative regulator of the alternative pathway (AP) that binds polyanions as well as complement activation fragments C3b and C3d. The AP is both necessary and sufficient to develop collagen Ab-induced arthritis (CAIA) in mice; the mechanisms whereby normal control of the AP is overcome and injury develops are unknown. Although primarily a soluble circulating protein, fH can also bind to tissues in a manner dependent on the carboxyl-terminal domain containing short consensus repeats 19 and 20. We examined the role of fH in CAIA by blocking its binding to tissues through administration of a recombinant negative inhibitor containing short consensus repeats 19 and 20 (rfH19-20), which impairs fH function and amplifies surface AP activation in vitro. Administration of rfH19-20, but not control rfH3-5, significantly worsened clinical disease activity, histopathologic injury, and C3 deposition in the synovium and cartilage in wild-type and fH(+/-) mice. In vitro studies demonstrated that rfH19-20 increased complement activation on cartilage extracts and injured fibroblast-like synoviocytes, two major targets of complement deposition in the joint. We conclude that endogenous fH makes a significant contribution to inhibition of the AP in CAIA through binding to sites of immune complex formation and complement activation.

The immune system--a hidden treasure for biomarker discovery in cutaneous melanoma

This chapter describes how skin immune system (SIS) is specifically involved in the development of cutaneous melanoma. Local immune surveillance is presented as a complex process that comprises markers to be monitored in disease's evolution and in therapy. The ranking of tissue or soluble immune markers in a future panel of diagnostic/prognostic panel are evaluated. Taking into account the difficulties of cutaneous melanoma patients' management, this chapter shows the immune surveillance at the skin level, the conditions that favor the tumor escape from the immunological arm, the immune pattern of skin melanoma with diagnostic/prognostic relevance, the circulatory immune markers, and, last but not least, how immune markers are used in immune-therapy monitoring. The chapter cannot be exhaustive but will give the reader a glimpse of the complex immune network that lies within tumor escape and where to search for immune-therapeutical targets in skin melanoma.

Factor h: a complement regulator in health and disease, and a mediator of cellular interactions

Complement is an essential part of innate immunity as it participates in host defense against infections, disposal of cellular debris and apoptotic cells, inflammatory processes and modulation of adaptive immune responses. Several soluble and membrane-bound regulators protect the host from the potentially deleterious effects of uncontrolled and misdirected complement activation. Factor H is a major soluble regulator of the alternative complement pathway, but it can also bind to host cells and tissues, protecting them from complement attack. Interactions of factor H with various endogenous ligands, such as pentraxins, extracellular matrix proteins and DNA are important in limiting local complement-mediated inflammation. Impaired regulatory as well as ligand and cell recognition functions of factor H, caused by mutations or autoantibodies, are associated with the kidney diseases: atypical hemolytic uremic syndrome and dense deposit disease and the eye disorder: age-related macular degeneration. In addition, factor H binds to receptors on host cells and is involved in adhesion, phagocytosis and modulation of cell activation. In this review we discuss current concepts on the physiological and pathophysiological roles of factor H in light of new data and recent developments in our understanding of the versatile roles of factor H as an inhibitor of complement activation and inflammation, as well as a mediator of cellular interactions. A detailed knowledge of the functions of factor H in health and disease is expected to unravel novel therapeutic intervention possibilities and to facilitate the development or improvement of therapies.

Regulated secretion of complement factor H by RPE and its role in RPE migration

BACKGROUND

Variants in the gene for complement factor H (CFH) have been implicated as a major risk factor for the development of age-related macular degeneration (AMD). Little is known, however, about the factors regulating local expression and secretion of CFH by retinal pigment epithelial cells (RPE).

METHODS

Cultured human early passage RPE cells, highly differentiated, polarized human RPE cultures, and bovine RPE explants were incubated in the presence or absence of recombinant human or bovine interferon-gamma (IFN-gamma; 25 ng/ml). CFH expression in cell lysates, and secretion into culture supernatants were examined by Western blot. CHF expression and localization was analyzed by confocal microscopy. Migration assay was performed in a modified Boyden chamber with early passage human RPE cells after stimulation with recombinant CFH protein (1-100 ng/ml).

RESULTS

CFH was expressed in the cell lysates of RPE cells, and this expression was significantly upregulated by IFN-gamma. Immunoreactivity for CFH was detected in RPE cells of bovine explants and highly differentiated human RPE monolayers, and the level of immunoreactivity increased after IFN-gamma stimulation. Confocal microscopy revealed that CFH was predominantly localized in the apical cytoplasm of polarized human RPE. Western blot confirmed that IFN-gamma increased CFH secretion into RPE supernatants. Dose-dependent RPE cell chemotactic migration was induced by CFH.

CONCLUSION

IFN-gamma promotes CFH expression in the apical compartment of RPE cells and increases secretion of CFH into RPE culture supernatants. Furthermore, CFH promotes chemotactic migration of RPE. This study suggests that interactions between CFH and IFN-gamma have the potential to play a role in the pathogenesis of AMD.

Polymorphisms within the C3 gene are associated with specific IgE levels to common allergens and super-antigens among atopic dermatitis patients

Atopic dermatitis (AD) is a chronic inflammatory skin disease. Twin and family studies suggest a strong genetic component of the disease. The keratinocytes secrete high amounts of C3 after stimulation with pro-inflammatory cytokines, which may play a functional role in skin inflammation. In this study, we genotyped four different single nucleotide polymorphisms (SNPs) by melting curve analysis using sequence specific hybridization probes in a well-characterized cohort of AD patients. Among four SNPs within C3 gene, higher frequencies of rs10410674 (23.5% vs 12.2%) and rs366510 (13.8% vs 6.5%) were observed in AD patients as compared with control group. None of the tested polymorphisms showed significant association with the risk of the disease phenotype. Analysis of rs10402876 SNP revealed its association with less severe AD disease expression (low SCORAD). Total serum IgE levels were not different among AD patients having any of the four SNPs. However, we observed significantly less serum-specific IgE levels to common allergens (Dermatophagoides pteronyssinus and birch pollens) and Staphylococcal enterotoxin B in AD patients having rs366510 SNP. Thus, associations of polymorphism within C3 gene with less severe AD disease expression and a weaker sensitization to common allergens suggest the role of these SNPs in the development of AD.

The relative importance of local and systemic complement production in ischaemia, transplantation and other pathologies

Besides a critical role in innate host defence, complement activation contributes to inflammatory and immunological responses in a number of pathological conditions. Many tissues outside the liver (the primary source of complement) synthesise a variety of complement proteins, either constitutively or response to noxious stimuli. The significance of this local synthesis of complement has become clearer as a result of functional studies. It revealed that local production not only contributes to the systemic pool of complement but also influences local tissue injury and provides a link with the antigen-specific immune response. Extravascular production of complement seems particularly important at locations with poor access to circulating components and at sites of tissue stress responses, notably portals of entry of invasive microbes, such as interstitial spaces and renal tubular epithelial surfaces. Understanding the relative importance of local and systemic complement production at such locations could help to explain the differential involvement of complement in organ-specific pathology and inform the design of complement-based therapy. Here, we will describe the lessons we have learned over the last decade about the local synthesis of complement and its association with inflammatory and immunological diseases, placing emphasis on the role of local synthesis of complement in organ transplantation.

Expression of terminal complement components by human keratinocytes

Human keratinocytes are important constituents of the skin immune system. They produce several cytokines, chemokines as well as some complement proteins. As regards soluble complement proteins, so far keratinocytes have been shown to synthesize only C3, factor B, factor H and factor I. Synthesis and regulation of synthesis of other complement proteins has not yet been studied. Here we studied the synthesis of terminal complement components, C5-C9 by human keratinocytes. We also studied the regulation of terminal complement synthesis in keratinocytes by several cytokines, namely, IL-1alpha, IL-2, IL-6, TGF-beta1, TNF-alpha, and IFN-gamma. Human keratinocytes constitutively expressed C5, C7, C8gamma and C9 mRNA but not C6, C8alpha and C8beta mRNA. They released C7 and C9, but not C5, C6 and C8. None of the cytokines tested had any influence on the synthesis of terminal components except TNF-alpha, which strongly upregulated C9 production. In conclusion, we demonstrate that keratinocytes are capable of synthesizing some of the terminal complement components and that the synthesis of C9 is regulated by TNF-alpha.

Induction of C3 and CCL2 by C3a in keratinocytes: a novel autocrine amplification loop of inflammatory skin reactions

The complement fragment-3a (C3a) acts via a G protein-coupled C3aR and is of importance in allergic and inflammatory diseases. Recent studies suggest the presence of complement proteins in the epidermal compartment and synthesis of some of these proteins (C3, factor B, and factor H) by human primary keratinocytes (KCs) during inflammation. However, expression of C3aR and its role in human KCs is not elucidated thus far. In this study, we demonstrate the expression of C3aR on KCs as detected by quantitative real-time RT-PCR and flow cytometry. IFN-gamma and IFN-alpha strongly up-regulated the surface expression of C3aR on KCs among all other cytokines tested. After up-regulation of C3aR by IFN-gamma and IFN-alpha, we observed the induction of five genes (CCL2, CCL5, CXCL8, CXCL10, and C3) after stimulation of KCs with C3a in microarray analysis. We confirmed the induction of C3 and CCL2 at RNA and protein levels. Furthermore, incubation of C3 with skin mast cells tryptase resulted in the generation of C3 fragments with C3a activity. In conclusion, our data illustrate that epidermal KCs express functional C3aR. The increases of C3 and CCL2 synthesis by C3a and C3 activation by skin mast cell tryptase delineates a novel amplification loop of complement activation and inflammatory responses that may influence the pathogenesis of allergic/inflammatory skin diseases.

Synthesis of complement proteins in the human chorion is differentially regulated by cytokines

The aim of the current paper was to determine the chorion's contribution to complement synthesis in the placenta and its regulation by cytokines. Biosynthetic labeling followed by immunoprecipitation with polyclonal antibodies was performed in chorionic tissue and chorion-derived cells. Eight complement proteins, factor B, C3, C1r, C1s, C1 inhibitor, factor H, C4 and C2 were detected in chorionic tissue and were secreted extracellularly. In chorion-derived cells, IL-1beta stimulated factor B synthesis but had no effect on C1r, C1 inhibitor, C1s, factor H and C4. TNFalpha had no stimulative effect on any of the complement proteins tested. In contrast, both IL-1beta and TNFalpha highly induced IL-6 secretion in chorion-derived cells, demonstrating the overall responsiveness of these cells to these stimuli. Interestingly, IFN-gamma increased the synthesis of C1s, C1r, C1 inhibitor, C4 and factor H in chorion-derived cells. The fact that the latter two complement proteins have opposing effects on immune activation of the complement cascade demonstrates the complex balance required to both maintain an ability to ward off infections but simultaneously suppress the immune response to enable tolerance of the allograft fetus.