Interferon-gamma induces biosynthesis of complement components C2, C4 and factor H by human proximal tubular epithelial cells

Inhibition of interferon gamma impairs induction of experimental epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a muco-cutaneous autoimmune disease characterized and caused by autoantibodies targeting type VII collagen (COL7). The treatment of EBA is notoriously difficult, with a median time to remission of 9 months. In preclinical EBA models, we previously discovered that depletion of regulatory T cells (Treg) enhances autoantibody-induced, neutrophil-mediated inflammation and blistering. Increased EBA severity in Treg-depleted mice was accompanied by an increased cutaneous expression of interferon gamma (IFN-γ). The functional relevance of IFN-γ in EBA pathogenesis had been unknown. Given that emapalumab, an anti-IFN-γ antibody, is approved for primary hemophagocytic lymphohistiocytosis patients, we sought to assess the therapeutic potential of IFN-γ inhibition in EBA. Specifically, we evaluated if IFN-γ inhibition has modulatory effects on skin inflammation in a pre-clinical EBA model, based on the transfer of COL7 antibodies into mice. Compared to isotype control antibody, anti-IFN-γ treatment significantly reduced clinical disease manifestation in experimental EBA. Clinical improvement was associated with a reduced dermal infiltrate, especially Ly6G+ neutrophils. On the molecular level, we noted few changes. Apart from reduced CXCL1 serum concentrations, which has been demonstrated to promote skin inflammation in EBA, the expression of cytokines was unaltered in the serum and skin following IFN-γ blockade. This validates IFN-γ as a potential therapeutic target in EBA, and possibly other diseases with a similar pathogenesis, such as bullous pemphigoid and mucous membrane pemphigoid.

HK-2 cell response to TGF-β highly depends on cell culture medium formulations

The immortalized human renal proximal tubular epithelial cell line HK-2 is most commonly used to study renal cell physiology and human kidney diseases with tubulointerstitial fibrosis such as diabetic nephropathy, obstructive uropathy or allograft fibrosis. Epithelial-to-mesenchymal transition (EMT) is the main pathological process of tubulointerstitial fibrosis in vitro. Transforming growth factor-beta (TGF-β) is a key inducer of EMT. Several pro-fibrotic gene expression differences have been observed in a TGF-β-induced EMT model of HK-2 cells. However, growth conditions and medium formulations might greatly impact these differences. We investigated gene and protein expression of HK-2 cells cultured in six medium formulations. TGF-β1 increased the expression of ACTA2, TGFB1, COL4A1, EGR2, VIM and CTGF genes while reducing PPARG in all medium formulations. Interestingly, TGF-β1 treatment either increased or decreased EGR1, FN, IL6 and C3 gene expression, depending on medium formulations. The cell morphology was slightly affected, but immunoblots revealed TGFB1 and vimentin protein overexpression in all media. However, fibronectin expression as well as the nuclear translocation of EGR1 was medium dependent. In conclusion, our study demonstrates that, using the HK-2 in vitro model of EMT, the meticulous selection of appropriate cell culture medium formulation is essential to achieve reliable scientific results.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Shiga Toxin 2a Binds to Complement Components C3b and C5 and Upregulates Their Gene Expression in Human Cell Lines

Enterohemorrhagic Escherichia coli (EHEC) infections can cause EHEC-associated hemolytic uremic syndrome (eHUS) via its main virulent factor, Shiga toxins (Stxs). Complement has been reported to be involved in the progression of eHUS. The aim of this study was to investigate the interactions of the most effective subtype of the toxin, Stx2a, with pivotal complement proteins C3b and C5. The study further examined the effect of Stx2a stimulation on the transcription and synthesis of these complement proteins in human target cell lines. Binding of Stx2a to C3b and C5 was evaluated by ELISA. Kidney and gut cell lines (HK-2 and HCT-8) were stimulated with varied concentrations of Stx2a. Subsequent evaluation of complement gene transcription was studied by real-time PCR (qPCR), and ELISAs and Western blots were performed to examine protein synthesis of C3 and C5 in supernatants and lysates of stimulated HK-2 cells. Stx2a showed a specific binding to C3b and C5. Gene transcription of C3 and C5 was upregulated with increasing concentrations of Stx2a in both cell lines, but protein synthesis was not. This study demonstrates the binding of Stx2a to complement proteins C3b and C5, which could potentially be involved in regulating complement during eHUS infection, supporting further investigations into elucidating the role of complement in eHUS pathogenesis.

Suppression of complement component 2 expression by hepatitis B virus contributes to the viral persistence in chronic hepatitis B patients

Previously, we identified rare missense mutations of complement component 2 (C2) to be associated with chronic hepatitis B (CHB) by exome sequencing. However, up to now, little is known about the role of C2 in CHB. In the present study, we aimed to perform preliminary exploration about the underlying role of C2 in CHB. Serum samples from 113 CHB patients and 30 healthy controls, and liver biopsy samples from 5 CHB patients and 3 healthy controls were obtained from the Third Affiliated Hospital of Sun Yat-sen University between January 2018 and January 2020. HepG2.2.15 and HepG2-NTCP cells infected with HBV were used to examine the influence of HBV infection on C2 expression. IFN-treated HepG2.2.15 cells were used to assess the effect of IFN on C2 expression. C2-overexpressing or C2-silencing HepG2.2.15 cells were constructed to evaluate the effect of C2 on HBV infection. Western blot and RT-qPCR were used to measure C2 expression in biopsy samples. HBeAg and HBsAg in culture medium and C2 of serum samples were measured by ELISA. HBV-DNA was measured by RT-qPCR. GSE84044, GSE54747 and GSE27555 were downloaded from GEO. C2 expression in liver tissue and serum was significantly lower in CHB patients compared to healthy controls, and significantly higher C2 expression was found in CHB patients with lower ALT, AST, Scheuer grade and stages compared to CHB patients with higher ALT, AST, Scheuer grades and Scheuer stage. Besides, HBV infection could decrease C2 expression by increasing expression of Sp1 and reducing expression of HDAC4. Moreover, C2 could enhance the anti-virus effect of IFN on HepG2.2.15 cells and also inhibit HBV replication in HepG2.2.15 cells by inhibition of p38-MAPK signalling pathway. In conclusion, HBV may promote viral persistence in CHB patients by inhibiting C2 expression.

Podocytes Produce and Secrete Functional Complement C3 and Complement Factor H

Podocytes are an important part of the glomerular filtration barrier and the key player in the development of proteinuria, which is an early feature of complement mediated renal diseases. Complement factors are mainly liver-born and present in circulation. Nevertheless, there is a growing body of evidence for additional sites of complement protein synthesis, including various cell types in the kidney. We hypothesized that podocytes are able to produce complement components and contribute to the local balance of complement activation and regulation. To investigate the relevant balance between inhibiting and activating sides, our studies focused on complement factor H (CFH), an important complement regulator, and on C3, the early key component for complement activation. We characterized human cultured podocytes for the expression and secretion of activating and regulating complement factors, and analyzed the secretion pathway and functional activity. We studied glomerular CFH and C3 expression in puromycin aminonucleoside (PAN) -treated rats, a model for proteinuria, and the physiological mRNA-expression of both factors in murine kidneys. We found, that C3 and CFH were expressed in cultured podocytes and expression levels differed from those in cultivated glomerular endothelial cells. The process of secretion in podocytes was stimulated with interferon gamma and located in the Golgi apparatus. Cultured podocytes could initiate the complement cascade by the splitting of C3, which can be shown by the generation of C3a, a functional C3 split product. C3 contributed to external complement activation. Podocyte-secreted CFH, in conjunction with factor I, was able to split C3b. Podocytes derived from a patient with a CFH mutation displayed impaired cell surface complement regulation. CFH and C3 were synthesized in podocytes of healthy C57Bl/6-mice and were upregulated in podocytes of PAN treated rats. These data show that podocytes produce functionally active complement components, and could therefore influence the local glomerular complement activation and regulation. This modulating effect should therefore be considered in all diseases where glomerular complement activation occurs. Furthermore, our data indicate a potential novel role of podocytes in the innate immune system.

Methyl cellosolve-induced renal oxidative stress and time-dependent up-regulation of pro-inflammatory cytokines, apoptotic, and oncogenic markers in rats

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MC significantly increased and decrease the kidney levels of MDA and NO respectively after 14 and 21 days.

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MC administration resulted in the disorganization of the renal redox system.

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MC significantly increased the kidney levels of TNF-α and IL-6 after 7, 14 and 21 days, and IL-1β after 14 and 21 days.

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MC significantly increased kidney p53, Bax, and caspase-3 after 14 and 21 days, and decreased Bcl-2 after 14 and 21 days.

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MC significantly increased the kidney levels of c-Myc and K-Ras after 7, 14 and 21 days.

Methyl cellosolve (MC) is used in production of textile, paints, stains, inks, surface coatings, and anti-icing additive in hydraulic fluids and jet fuel. Consequently, the present study investigated its effect on renal cells, in a time-course study in male Wistar rats. Animals were orally administered 50 mg/kg body weight of MC for a period of 7, 14, and 21 days. Following 7 days of administration of MC, there was a significant increase in the levels of K-Ras, c-Myc, TNF-α, IL-6 and NO, while GSH level and SOD activity were significantly reduced compared with control. At the end of 14 days exposure, RKW, GSH, NO, and Bcl-2 levels were significantly decreased, while levels of K-Ras, c-Myc, p53, Bax, caspase-3, TNF-α, IL-1β, IL-6, MDA and GPx activity were significantly increased compared with control. After 21 days of MC administration, RKW, GSH, NO, IL-10 and Bcl-2 levels were significantly decreased, while levels of K-Ras, c-Myc, p53, Bax, caspase-3, TNF-α, IL-1β, IL-6, MDA and GST activity were significantly increased compared with control. Exposures to MC in any way should be strictly avoided as it could trigger renal damage through the disorganization of the antioxidant system, up-regulation of inflammatory, apoptotic, and oncogenic markers in rats.

High levels of urinary complement proteins are associated with chronic renal damage and proximal tubule dysfunction in immunoglobulin A nephropathy

AIM

Complement activation is involved in the pathogenesis and progression of immunoglobulin A nephropathy (IgAN); however, the clinical implication of abnormal complement protein levels in serum and urine is not clear. To address this we analyzed the correlation between disease activity and complement proteins in serum and urine from IgAN patients, and compared to patients with other types of chronic kidney disease (CKD) as well as healthy controls.

METHODS

We included 85 Chinese patients with IgAN, 23 patients with non-proliferative CKD, and 20 healthy individuals. Patients were divided according to the Oxford classification of M0E0S0T0 (group 1, n = 20), M1E1S0-1 T0-1 (group 2, n = 25), M1E1S0-1 T2 or M0E0S1T1-2 (group 3, n = 40). Complement factor H (CFH), mannose-binding lectin and membrane attack complex in serum and urine were measured by enzyme-linked immunosorbent assay.

RESULTS

Urinary CFH, membrane attack complex and serum CFH were increased in both IgAN and CKD patients compared with healthy controls. The urinary excretion of CFH was the highest in IgAN patients with most tubulointerstitial damage (IgAN group 3). Urinary CFH and mannose-binding lectin levels were significantly higher in IgAN patients with crescents formation (C1-2) than in patients without (C0). Urinary complement protein excretion correlated negatively with estimated glomerular filtration rate, and positively with urinary retinol-binding protein and α1-microglobulin excretion indicating proximal tubule dysfunction.

CONCLUSION

Increased urinary excretion of complement proteins in IgAN is related to chronic injury and tubular dysfunction. This warrants caution using urinary complement proteins as markers of disease activity.

Calcineurin inhibitor-induced complement system activation via ERK1/2 signalling is inhibited by SOCS-3 in human renal tubule cells

One factor that significantly contributes to renal allograft loss is chronic calcineurin inhibitor (CNI) nephrotoxicity (CIN). Among other factors, the complement (C-) system has been proposed to be involved CIN development. Hence, we investigated the impact of CNIs on intracellular signalling and the effects on the C-system in human renal tubule cells. In a qPCR array, CNI treatment upregulated C-factors and downregulated SOCS-3 and the complement inhibitors CD46 and CD55. Additionally, ERK1/-2 was required for these regulations. Following knock-down and overexpression of SOCS-3, we found that SOCS-3 inhibits ERK1/-2 signalling. Finally, we assessed terminal complement complex formation, cell viability and apoptosis. Terminal complement complex formation was induced by CNIs. Cell viability was significantly decreased, whereas apoptosis was increased. Both effects were reversed under complement component-depleted conditions. In vivo, increased ERK1/-2 phosphorylation and SOCS-3 downregulation were observed at the time of transplantation in renal allograft patients who developed a progressive decline of renal function in the follow-up compared to stable patients. The progressive cohort also had lower total C3 levels, suggesting higher complement activity at baseline. In conclusion, our data suggest that SOCS-3 inhibits CNI-induced ERK1/-2 signalling, thereby blunting the negative control of C-system activation.

Interaction of uromodulin and complement factor H enhances C3b inactivation

Recent studies suggest that uromodulin plays an important role in chronic kidney diseases. It can interact with several complement components, various cytokines and immune system cells. Complement factor H (CFH), as a regulator of the complement alternative pathway, is also associated with various renal diseases. Thus, we have been suggested that uromodulin regulates complement activation by interacting with CFH during tubulointerstitial injury. We detected co‐localization of uromodulin and CFH in the renal tubules by using immunofluorescence. Next, we confirmed the binding of uromodulin with CFH in vitro and found that the affinity constant (K_D) of uromodulin binding to CFH was 4.07 × 10⁻⁶M based on surface plasmon resonance results. The binding sites on CFH were defined as the short consensus repeat (SCR) units SCR1–4, SCR7 and SCR19–20. The uromodulin‐CFH interaction enhanced the cofactor activity of CFH for factor I‐mediated cleavage of C3b to iC3b. These results indicate that uromodulin plays a role via binding and enhancing the function of CFH.

Proinflammatory Cytokines and Potassium Channels in the Kidney

Proinflammatory cytokines affect several cell functions via receptor-mediated processes. In the kidney, functions of transporters and ion channels along the nephron are also affected by some cytokines. Among these, alteration of activity of potassium ion (K(+)) channels induces changes in transepithelial transport of solutes and water in the kidney, since K(+) channels in tubule cells are indispensable for formation of membrane potential which serves as a driving force for the transepithelial transport. Altered K(+) channel activity may be involved in renal cell dysfunction during inflammation. Although little information was available regarding the effects of proinflammatory cytokines on renal K(+) channels, reports have emerged during the last decade. In human proximal tubule cells, interferon-γ showed a time-dependent biphasic effect on a 40 pS K(+) channel, that is, delayed suppression and acute stimulation, and interleukin-1β acutely suppressed the channel activity. Transforming growth factor-β1 activated KCa3.1 K(+) channel in immortalized human proximal tubule cells, which would be involved in the pathogenesis of renal fibrosis. This review discusses the effects of proinflammatory cytokines on renal K(+) channels and the causal relationship between the cytokine-induced changes in K(+) channel activity and renal dysfunction.

Activation of complement system in kidney after ketoprofen-induced kidney injury in sheep

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used to treat inflammatory pain in humans and animals. An overdose of an NSAID is nephrotoxic and can lead to acute kidney injury (AKI). Complement activation occurs in several types of renal disorders with proteinuria. The aim of this study was to investigate whether complement system becomes activated in kidneys after a high dose of NSAID. Kidney tissue and urine samples were collected from six sheep with ketoprofen-induced AKI and from six healthy control sheep. The localization of complement proteins in kidney tissue was carried out using immunohistochemical stainings, and excretion of C3 was tested by immunoblotting.

RESULTS

The complement system was found to become activated in the kidney tissue as demonstrated by positive immunostaining for C1q, C3c, C4c, C5, C9 and factor H and by Western blotting analysis of C3 activation products in urine samples in sheep with AKI.

CONCLUSIONS

Our results thus suggest that the alternative complement pathway is activated, and it may contribute to the acute tubular injury seen in the kidneys of NSAID-induced AKI sheep. Inhibition of complement activation may serve as potential therapeutic target for intervention in drug-induced AKI.

Overview of complement activation and regulation

Complement is an important component of the innate immune system that is crucial for defense from microbial infections and for clearance of immune complexes and injured cells. In normal conditions complement is tightly controlled by a number of fluid-phase and cell surface proteins to avoid injury to autologous tissues. When complement is hyperactivated, as occurs in autoimmune diseases or in subjects with dysfunctional regulatory proteins, it drives a severe inflammatory response in numerous organs. The kidney appears to be particularly vulnerable to complement-mediated inflammatory injury. Injury may derive from deposition of circulating active complement fragments in glomeruli, but complement locally produced and activated in the kidney also may have a role. Many kidney disorders have been linked to abnormal complement activation, including immune-complex–mediated glomerulonephritis and rare genetic kidney diseases, but also tubulointerstitial injury associated with progressive proteinuric diseases or ischemia-reperfusion.

CAWS administration increases the expression of interferon γ and complement factors that lead to severe vasculitis in DBA/2 mice

Background

Candida albicans water-soluble fraction (CAWS), a mannoprotein-β-glucan complex obtained from the culture supernatant of C. albicans NBRC1385, causes CAWS-mediated vasculitis (CAWS-vasculitis) in B6 and DBA/2 mice with mild and lethal symptoms, respectively. Why CAWS is lethal only in DBA/2 mice remains unknown.

Results

We performed DNA microarray analyses using mRNA obtained from peripheral blood mononuclear cells (PBMCs) of B6 and DBA/2 mice and compared their respective transcriptomes. We found that the mRNA levels of interferon-γ (Ifng) and several genes that regulate the complement system, such as C3, C4, Cfb, Cfh, and Fcna, were increased dramatically only in DBA/2 mice at 4 and 8 weeks after CAWS administration. The dramatic increase was confirmed by quantitative real-time polymerase chain reactions (qRT-PCR). Moreover, mRNA levels of immune-related genes, such as Irf1, Irf7, Irf9, Cebpb, Ccl4, Itgam, Icam1, and IL-12rb1, whose expression levels are known to be increased by Ifng, were also increased, but only in DBA/2 mice. By contrast, the mRNA level of Dectin-2, the critical receptor for the α-mannans of CAWS, was increased slightly and similarly in both B6 and DBA/2 mice after CAWS administration.

Conclusions

Taken together, our results suggest that CAWS administration induces Dectin-2 mediated CAWS-vasculitis in both B6 and DBA/2 mice and the expression of Ifng, but only in DBA/2 mice, which led to increased expression of C3, C4, Cfb, Cfh, and Fcna and an associated increase in lethality in these mice. This model may contribute to our understanding of the pathogenesis of severe human vasculitis.

The role of complement in the early immune response to transplantation

The complement system is a key element of the innate immune system, and the production of complement components can be divided into central (hepatic) and peripheral compartments. Essential complement components such as C3 are produced in both of these compartments, but until recently the functional relevance of the peripheral synthesis of complement was unclear. Here, we review recent findings showing that local peripheral synthesis of complement in a transplanted organ is required for the immediate response of the donor organ to tissue stress and for priming alloreactive T cells that can mediate transplant rejection. We also discuss recent insights into the role of complement in antibody-mediated rejection, and we examine how new treatment strategies that take into account the separation of central and peripheral production of complement are expected to make a difference to transplant outcome.

Excretion of complement proteins and its activation marker C5b-9 in IgA nephropathy in relation to renal function

Background

Glomerular damage in IgA nephropathy (IgAN) is mediated by complement activation via the alternative and lectin pathways. Therefore, we focused on molecules stabilizing and regulating the alternative pathway C3 convertase in urine which might be associated with IgAN pathogenesis.

Methods

Membrane attack complex (MAC), properdin (P), factor H (fH) and Complement receptor type 1 (CR1) were quantified in urine samples from 71 patients with IgAN and 72 healthy controls. Glomerular deposition of C5, fH and P was assessed using an immunofluorescence technique and correlated with histological severity of IgAN and clinical parameters. Fibrotic changes and glomerular sclerosis were evaluated in renal biopsy specimens.

Results

Immunofluorescence studies revealed glomerular depositions of C5, fH and P in patients with IgAN. Urinary MAC, fH and P levels in IgAN patients were significantly higher than those in healthy controls (p < 0.001), but CR1 was significantly lower than that in healthy controls (p < 0.001). Urinary MAC and fH levels were positively correlated with serum creatinine (sCr), urinary N-acetyl-β-D-glucosaminidase (u-NAG), urinary β2 microglobulin (u-Bm), urinary protein (p < 0.001), interstitial fibrosis (MAC: p < 0.01, fH: p < 0.05) and the percentage of global glomerular sclerosis (p < 0.01). Urinary P was positively correlated with u-NAG, u-Bm, and urinary protein (p < 0.01).

Conclusions

Complement activation occurs in the urinary space in IgAN and the measurement of levels of MAC and fH in the urine could be a useful indicator of renal injury in patients with IgAN.

Expression of complement components, receptors and regulators by human dendritic cells

Integration of innate and adaptive arms of the immune response at a cellular and molecular level appears to be fundamental to the development of powerful effector functions in host defence and aberrant immune responses. Here we provide evidence that the functions of human complement activation and antigen presentation converge on dendritic cells (DCs). We show that several subsets of human DCs [i.e., monocyte derived (CD1a(+)CD14(-)), dermal (CD1a(+)DC-SIGN(+)), Langerhans (CD1a(+)Langerin(+)), myeloid (CD1c(+)CD19(-)), plamacytoid (CD45RA(+)CD123(+))] express many of the components of the classical and alternative and terminal pathways of complement. Moreover human DCs have receptors known to detect the biologically active peptides C3a and C5a (C3aR, C5aR) and the covalently bound fragments C3b and metabolites iC3b and C3d which serve in immune adhesion (i.e., CR3, CR4, CRIg). We also show that the human DC surface is characterised by membrane bound regulators of complement activation, which are also known to participate in intracellular signalling (i.e., CD46, CD55, CD59). This work provides an extensive description of complement components relevant to the integrated actions of complement and DC, illuminated by animal studies. It acts as a resource that allows further understanding and exploitation of role of complement in human health and immune mediated diseases.

Genotypic diversity of complement component C4 does not predict kidney transplant outcome

Gene copy number of complement component C4, which varies among individuals, may determine the intrinsic strength of the classical complement pathway. Presuming a major role of complement as an effector in transplant rejection, we hypothesized that C4 genetic diversity may partially explain the variation in allograft outcomes. This retrospective study included 1969 deceased-donor kidney transplants randomly selected from the Collaborative Transplant Study DNA bank. We determined recipient and donor gene copy number of total C4, C4 isotypes (C4A and C4B), and C4 gene length variants (C4L and C4S) by quantitative real-time PCR analysis. Groups defined according to recipient C4 gene copy number (low, intermediate, and high) had similar 10-year allograft survival. Genotypic groups showed comparable rates of graft dysfunction, treatment for rejection, immunological graft loss, hospitalization for infection, malignant disease, and death. Similarly, separate analyses of C4A, C4B, C4L, and C4S; combined evaluation of donor and recipient C4 genotype; or analysis of recipients with higher risk for rejection did not reveal considerable outcome effects. In conclusion, we did not demonstrate that C4 gene copy number associates with transplant outcome, and we found no evidence that the resulting variation in the strength of classical complement activation influences susceptibility to rejection.

Mannose-binding lectin is produced by vaginal epithelial cells and its level in the vaginal fluid is influenced by progesterone

Mannose-binding lectin (MBL) is a recognition molecule of the complement (C) system and binds to carbohydrate ligands present on a wide range of pathogenic bacteria, viruses, fungi, and parasites. MBL has been detected in the cervico-vaginal cavity where it can provide a first-line defence against infectious agents colonizing the lower tract of the reproductive system. Analysis of the cervico-vaginal lavage (CVL) obtained from 11 normal cycling women at different phases of the menstrual cycle revealed increased levels of MBL in the secretive phase. Part of this MBL derives from the circulation as indicated by the presence of transferrin in CVL tested as a marker of vascular and tissue permeability. The local synthesis of MBL is suggested by the finding that its level is substantially higher than that of transferrin in the secretive phase. The contribution of endometrium is negligible since the MBL level did not change before and after hysterectomy. RT-PCR and in situ RT-PCR analysis showed that the vaginal tissue, and in particular the basal layer of the epithelium, is a source of MBL which binds to the basal membrane and to cells of the outer layers of the epithelium. In conclusion, we have shown that MBL detected in CVL derives both from plasma as result of transudation and from local synthesis and its level is progesterone dependent increasing in the secretive phase of the menstrual cycle.

Mesenchymal stem cells inhibit complement activation by secreting factor H

Mesenchymal stem cells (MSCs) possess potent and broad immunosuppressive capabilities, and have shown promise in clinical trials treating many inflammatory diseases. Previous studies have found that MSCs inhibit dendritic cell, T-cell, and B-cell activities in the adaptive immunity; however, whether MSCs inhibit complement in the innate immunity, and if so, by which mechanism, have not been established. In this report, we found that MSCs constitutively secrete factor H, which potently inhibits complement activation. Depletion of factor H in the MSC-conditioned serum-free media abolishes their complement inhibitory activities. In addition, production of factor H by MSCs is augmented by inflammatory cytokines TNF-α and interferon-γ (IFN-γ) in dose- and time-dependent manners, while IL-6 does not have a significant effect. Furthermore, the factor H production from MSCs is significantly suppressed by the prostaglandin E2 (PGE2) synthesis inhibitor indomethacin and the indoleamine 2,3-dioxygenase (IDO) inhibitor 1-methyl-d-tryptophan (1-MT), both of which inhibitors are known to efficiently dampen MSCs immunosuppressive activity. These results indicate that MSCs inhibit complement activation by producing factor H, which could be another mechanism underlying MSCs broad immunosuppressive capabilities.

Effect of pro-inflammatory mediators on membrane-associated mucins expressed by human ocular surface epithelial cells

Membrane-associated mucins are altered on the ocular surface in non-Sjögren's dry eye. This study sought to determine if inflammatory mediators, present in tears of dry eye patients, regulate membrane-associated mucins MUC1 and -16 at the level of gene expression, protein biosynthesis and/or ectodomain release. A human corneal limbal epithelial cell line (HCLE), which produces membrane-associated mucins, was used. Cells were treated with interleukin (IL)-6, -8, or -17, tumor necrosis factor-alpha (TNF-alpha), and Interferon-gamma (IFN-gamma), or a combination of TNF-alpha and IFN-gamma, or IFN-gamma and IL-17, for 1, 6, 24, or 48 h. Presence of receptors for these mediators was verified by RT-PCR. Effects of the cytokines on expression levels of MUC1 and -16 were determined by real-time PCR, and on mucin protein biosynthesis and ectodomain release in cell lysates and culture media, respectively, by immunoblot analysis. TNF-alpha and IFN-gamma each significantly induced MUC1 expression, cellular protein content and ectodomain release over time. Combined treatment with the two cytokines was not additive. By comparison, one of the inflammatory mediators, IFN-gamma, affected all three parameters-gene expression, cellular protein, and ectodomain release-for MUC16. Combined treatment with TNF-alpha and IFN-gamma showed effects similar to IFN-gamma alone, except that ectodomain release followed that of TNF-alpha, which induced MUC16 ectodomain release. In conclusion, inflammatory mediators present in tears of dry eye patients can affect MUC1 and -16 on corneal epithelial cells and may be responsible for alterations of surface mucins in dry eye.

Protein load impairs factor H binding promoting complement-dependent dysfunction of proximal tubular cells

Intrarenal complement activation plays an important role in the progression of chronic kidney disease. A key target of the activated complement cascade is the proximal tubule, a site where abnormally filtered plasma proteins and complement factors combine to promote injury. This study determined whether protein overloading of human proximal tubular cells (HK-2) in culture enhances complement activation by impairing complement regulation. Addition of albumin or transferrin to the cells incubated with diluted human serum as a source of complement caused increased apical C3 deposition. Soluble complement receptor-1 (an inhibitor of all 3 activation pathways) blocked complement deposition while the classical and lectin pathway inhibitor, magnesium chloride-EGTA, was, ineffective. Media containing albumin as well as complement had additive proinflammatory effects as shown by increased fractalkine and transforming growth factor-beta mRNA expression. This paralleled active C3 and C5b-9 generations, effects not shared by transferrin. Factor H, one of the main natural inhibitors of the alternative pathway, binds to heparan sulfate proteoglycans. Both the density of heparan sulfate and factor H binding were reduced with protein loading, thereby enhancing the albumin- and serum-dependent complement activation potential. Thus, protein overload reduces the ability of the tubule cell to bind factor H and counteract complement activation, effects instrumental to renal disease progression.

Expression of gamma interferon-dependent genes is blocked independently by virion host shutoff RNase and by US3 protein kinase

Gamma interferon receptor alpha (IFN-gammaR alpha) is stable but posttranslationally modified in herpes simplex virus 1(F) [HSV-1(F)]-infected cells. Studies with antibody directed to the phosphorylation site indicate that IFN-gammaR alpha is phosphorylated by the U(S)3 kinase. The modification is abolished in cells infected with DeltaU(S)3, DeltaU(L)13, or Delta(U(S)3/U(L)13) mutant virus. Transcripts of the IFN-gamma-dependent genes do not accumulate in cells transduced with the U(S)3 protein kinase and treated with IFN-gamma. In contrast, the accumulation of IFN-gamma-dependent gene transcripts is suppressed in cells infected with the wild-type virus, in cells infected with the DeltaU(S)3 mutant virus, and to a lesser extent in the DeltaU(L)41 virus-infected cells. The accumulation of IFN-gamma-dependent gene transcripts in DeltaU(L)41-infected cells could be due at least in part to a significant delay and reduction in the accumulation of the U(S)3 protein. The results suggest that the expression of IFN-gamma-dependent genes is blocked independently by the degradation of IFN-gamma-dependent gene transcripts--a function of the virion host shutoff RNase--and by posttranslational modification of the IFN-gammaR alpha protein.

New boundaries for complement in renal disease

Complement is an important component of the innate immune system whose function is integrated with the adaptive immune response. Since complement proteins are produced in virtually any cell in the body, it is important to question which pools of complement are responsible for what actions. This is particularly so in the case of complement-mediated renal disease, where distinct sites may require individualized approaches for therapy. From experimental and clinical evidence to date, it seems that the circulating pool of complement underlies much of the pathology traditionally associated with glomerular disease, including capillary wall injury. In contrast, the renal tubulointerstitium is the domain of local synthesis of complement, notably the axial component C3, principally expressed by the tubular epithelium. This means that therapeutic targeting will have to ensure penetration of the interstitial space in certain disorders. Likewise, monitoring of disease activity may benefit from evaluating this extravascular pool. Therapeutic and diagnostic applications in human disease are already taking this into account, with transplantation leading the way.

Levels of urinary complement factor H in patients with IgA nephropathy are closely associated with disease activity

Factor H plays a key inhibitory role in control of the activation of alternative pathway of complement system. The aim of the study was to investigate the predictive value of factor H as a biomarker of renal injury in IgA nephropathy (IgAN). Urine factor H concentration from 202 patients was measured and compared with that of 60 healthy volunteers. Forty-eight patients fulfilled Haas-I or II (group 1), 60 fulfilled Haas-III (group 2) and 94 fulfilled Haas-IV or V (group 3). Co-deposition of factor H and C3b in kidneys were investigated using confocal microscope. The levels of urinary factor H, when expressed as a ratio of urinary creatinine, were significantly higher in groups 3 than group 1 and 2, also significantly higher in group 2 than group 1. In addition, the levels of urinary factor H were significantly higher in those with factor H deposition in the kidney than those without deposition. The levels of urinary factor H may be a useful biomarker to evaluate kidney injury in IgAN.

Kidney transplantation in patients suffering from hereditary complete complement C4 deficiency

Hereditary complete C4 deficiency (C4def) is a very rare condition that predisposes to immune complex disease and end-stage renal failure. Whether such patients should undergo renal transplantation is debated. The clinical outcome of five transplantations in three C4def patients is described. The first patient lost one allograft after 6 years because of chronic allograft rejection. Back on dialysis, he suffered from meningitis caused by Neisseria menigitidis and Aspergillus. One year after a second transplantation under alemtuzumab induction, he developed fulminant Kaposi's sarcoma and died. His sister is now 6 years post-transplantation without complications. The third patient lost his first graft after 3 years because of chronic allograft nephropathy and recurrence of glomerulonephritis. He has now been living with a second graft for over 9 years. He suffered from pneumonia, a generalized varicella infection and Hemophilis parainfluenzae bronchitis. Patients with complete C4def are at increased risk for infection after kidney transplantation. Under certain precautions and with judicious use of immunosuppression, good long-term results are achievable.

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.

Oxidative stress modulates complement factor H expression in retinal pigmented epithelial cells by acetylation of FOXO3

Age-related macular degeneration (AMD), the leading cause of severe vision loss in the elderly, is a complex disease that results from genetic modifications that increase susceptibility to environmental exposures. Smoking, a major source of oxidative stress, increases the incidence and severity of AMD, and antioxidants slow progression, suggesting that oxidative stress plays a major role. Polymorphisms in the complement factor H (CFH) gene that reduce activity of CFH increase the risk of AMD. In this study we demonstrate an interaction between these two risk factors, because oxidative stress reduces the ability of an inflammatory cytokine, interferon-gamma, to increase CFH expression in retinal pigmented epithelial cells. The interferon-gamma-induced increase in CFH is mediated by transcriptional activation by STAT1, and its suppression by oxidative stress is mediated by acetylation of FOXO3, which enhances FOXO3 binding to the CFH promoter, reduces its binding to STAT1, inhibits STAT1 interaction with the CFH promoter, and reduces expression of CFH. Expression of SIRT1, a mammalian homolog of NAD-dependent protein deacetylase sir2, attenuated FOXO3 recruitment to the CFH regulatory region and reversed the H(2)O(2)-induced repression of CFH gene expression. These data suggest an important interaction between environmental exposure and genetic susceptibility in the pathogenesis of AMD and, by elucidating molecular signaling involved in the interaction, provide potential targets for therapeutic intervention.

The Many Effects of Complement C3- and C5-Binding Proteins in Renal Injury

The complement system is an important component of the innate immune system and a modulator of adaptive immunity. The entire complement system is focused on C3 and C5. Thus, there are proteins that activate C3 and C5, those that regulate this activation, and those that transduce the effects of C3 and C5 activation products; each can affect the kidney in renal injury. The normal kidney has the inherent capacity to protect itself from complement activation through cellular expression of decay-accelerating factor, membrane cofactor protein (in human beings), and Crry (in rodents). In addition, plasma factor H protects vascular spaces in the kidney. Although the main function of these proteins is to limit complement activation, there is now considerable evidence that they can transduce signals on engagement in immune cells. The G-protein-coupled 7-span transmembrane receptors for C3a and C5a, and the integral membrane complement receptors (CR) for C3b, iC3b, and C3dg, are expressed outside the kidney, particularly in cells of hematopoietic and immune lineage. These are important in renal injury through their infiltration of the kidney and/or by affecting kidney-directed immune responses. There is mounting evidence that intrinsic glomerular and tubular cell C3aR and C5aR expression and activation also can affect renal injury. CR1 on podocytes and the beta2 integrins CR3 and CR4 in kidney dendritic cells have functions that remain poorly defined. Cells of the kidney also have the capacity to produce and activate their own complement proteins. Thus, intrinsic renal cells express decay-accelerating factor, membrane cofactor protein, Crry, C3aR, C5aR, CR1, CR3, and CR4. These can be engaged by C3 and C5 activation products derived from systemic and local pools in renal injury. Given their capacity to provide signals that influence kidney cellular behavior, their activation can have substantial effects in renal injury. Defining these in a cell- and disease-specific fashion is an exciting challenge for future research.

Ischemic epigenetics and the transplanted kidney

The primary purpose of this investigation was to study oxidative demethylation of DNA following ischemia/reperfusion injury (I/RI) that putatively influences posttransplant gene expression in transplanted kidneys. Our hypothesis was that as a result of I/RI, oxidative damage, which is inherent in solid organ transplantation, may lead to aberrant demethylation of cytosine-guanine (CpG) sites within gene promoter regions of DNA. The methylated CpG sites normally contribute to the binding of proteins that render DNA inaccessible to transcription factors. Therefore, conversion of methylated cytosines to nonmethylated cytosines by oxidative damage in postischemic organs might facilitate enhanced gene expression in donor organs by exposing the demethylated CpG site in a gene promoter to DNA-binding proteins that enhance gene transcription. In this study, we investigated the demethylation of a specific CpG within the IFNgamma response element resident in the promoter region of the C3 gene in the rat kidney. In response to 24 hours of cold ischemia and a subsequent 2 hours of reperfusion in an isolated ex-vivo circuit, we observed a significant change in the ratio of methylated to unmethylated cytosines at this site. Epigenetic modifications to donor DNA have not been previously investigated, but our own data suggests that they have the potential to modify gene expression posttransplantation. Since epigenetic modification may become stable and heritable upon mitosis, such changes to the donor organ DNA may persist with enormous implications for transplant outcomes.

Deficiency of C4 from donor or recipient mouse fails to prevent renal allograft rejection

Complement effector products generated in the transplanted kidney are known to mediate transplant rejection, but which of the three main activation pathways of complement trigger this response is unclear. Here we assessed the role of the classical and lectin pathways by studying the common component C4 in mouse kidney transplant rejection. We transplanted wild-type or C4-null H-2(b) donor kidneys into H-2(k) or H-2(d) recipients, or vice-versa, to assess the roles of donor kidney and recipient expression of complement. Intragraft C4 gene expression rose substantially during rejection. However, we found no significant association between graft acceptance and the presence of C4 in either the donor kidney or recipient mouse. At the time of rejection, we found no significant differences in alloantibody response in the different groups. Tubular deposition of C3 to C9 occurred regardless of the absence or presence of C4 in either the donor or recipient mouse, indicating that C4 was dispensable for complement activation at this site. These data suggest that complement activation and renal allograft rejection are independent of the classical and lectin pathways in these models, implying that in the absence of these pathways the alternative pathway is the main trigger for complement-mediated rejection.

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

Locally synthesized complement is believed to play an important role in host defense and inflammation at organ level. In the epidermis, keratinocytes have so far been shown to synthesize two complement components, C3 and factor B. Here, we studied the synthesis of factor H by human keratinocytes. We also studied the regulation of factor H synthesis in keratinocytes by several cytokines, namely IL-1alpha, IL-2, IL-6, TGF-beta1, TNF-alpha and IFN-gamma. Human keratinocytes expressed factor H mRNA and constitutively released small amounts of factor H protein into the culture medium. This release was strongly upregulated by IFN-gamma but not by other cytokines tested. Western blot analysis revealed that IFN-gamma augments the synthesis of both molecular species, factor H (FH; 155kDa) and factor H-like protein-1 (FHL-1; 45kDa), of factor H. Factor H released in response to IFN-gamma was functionally active. In conclusion, we demonstrate that keratinocytes are capable of synthesizing factor H and that this synthesis is regulated by IFN-gamma.

Minireview: functions of the renal tract epithelium in coordinating the innate immune response to infection

Infection of the urinary tract remains one of the most common infections affecting mankind. Renal epithelial cells, being one of the first cells to come into contact with invading organisms, are in a key position to coordinate host defense. The epithelium not only provides a physical barrier to infection, but can also augment the immune response via the production of a number of inflammatory mediators and antimicrobial proteins. Recent work has demonstrated that cells of the innate immune system, including epithelial cells, express toll-like receptors (TLRs), with the capacity to recognize bacterial components. Although the exact mechanisms remain unclear, engagement of TLRs can lead to epithelial cell activation and the production of inflammatory mediators. These include complement proteins, other bactericidal peptides, and chemotactic cytokines. The resulting inflammatory infiltrate serves to aid bacterial clearance, but can also lead to renal damage. In this review, we describe how renal epithelial cells contribute to the innate immune response to ascending urinary tract infection. We specifically relate previous work to more recent developments in this field. An improved understanding of the mechanisms involved may highlight potential therapeutic avenues to aid bacterial clearance and prevent the renal scarring associated with infection.

Preconditioning Strategies to Limit Graft Immunogenicity and Cold Ischemic Organ Injury

During the transplant process, the graft is exposed to numerous events, which may enhance its immunogenicity. In particular, factors related to brain death, such as hemodynamic instability and systemic release of cytokines, cold preservation on harvesting, and reperfusion injury, are known to accumulate in harm, conveying a proinflammatory state to the graft before transplant. Alloimmune reactivity is initiated when the host immune system detects non–self-antigens in the context of “danger signals.” Eliminating these danger signals by modifying the graft before transplant has the potential to attenuate the alloimmune response. The molecules, which mediate danger signals, have not yet been fully identified. Free oxygen radicals and interferon-γ are important candidates. One of the most important protective mechanisms against oxidative stress is the heme oxygenase 1 system. Up-regulation of heme oxygenase 1 in grafts has been shown to prevent ischemia-reperfusion damage and improve long-term graft survival in various transplant models. The benefit of blocking the action of interferon-γ in kidney transplants is less clear because the compound plays such a complex and pivotal role in the immune response, and experimental data with interferon-γ receptor knockout mice are conflicting. It has recently become clear that catecholamines are important graft-modifying agents. Dopamine is capable of stimulating the induction of protective enzymes like heme oxygenase-1 (HO-1) rendering the organ more resistant to the insult of ischemia/reperfusion and inflammation. Retrospective clinical data suggest that treatment of brain-dead organ donors with catecholamines is associated with less rejection and a better long-term graft survival of kidneys transplanted from these donors. Catecholamines can also modulate cytokine production and prevent cold-induced damage. Other substances, such as proteoglycans and phosphatidylethanolamine-bound hyaluronic acid, may interfere with the actions of interferon-γ. Further studies of these compounds in experimental animal models and in prospective randomized clinical trials will help establish their efficacy in donor pretreatment. It is important to underscore that donor pretreatment will have great advantages for the recipient because an improved long-term graft survival could thus be achieved cost-efficiently and without great effort or side effects.

Role for complement in development of Helicobacter-induced gastritis in interleukin-10-deficient mice

The mechanisms by which the immune response can eradicate gastric Helicobacter infection are unknown. We hypothesized that Helicobacter-induced activation of the complement system could promote both inflammation and eradication of Helicobacter from the stomach. In vitro studies demonstrated that Helicobacter felis activates complement in normal mouse serum but not in serum from Rag2(-/-) mice, indicating that H. felis activates complement through the classical pathway. Next, we infected complement-depleted wild-type control and interleukin-10-deficient (IL-10(-/-)) mice with H. felis. Helicobacter infection of wild-type mice elicited a mild, focal gastritis and did not alter serum complement levels. Infection of IL-10(-/-) mice with H. felis elicited severe gastritis. After the initial colonization, the IL-10(-/-) mice completely cleared Helicobacter from the stomach by day 8. In contrast to wild-type mice, H. felis-infected IL-10(-/-) mice had a marked increase in serum complement levels. Complement depletion of wild-type mice did not affect the intensity of gastric inflammation or the extent of Helicobacter colonization compared to that for the wild-type control mice. In contrast, complement depletion of Helicobacter-infected IL-10(-/-) mice decreased the severity of gastritis, decreased the Helicobacter-induced infiltration of neutrophils into the stomach, and delayed the clearance of bacteria. In vitro studies of stimulated splenocytes and neutrophils from IL-10(-/-) mice produced a twofold increase in complement production compared to that for wild-type mice. Pretreatment with IL-10 inhibited this increase. These studies identify a role for complement in the local immune response to gastric Helicobacter in IL-10(-/-) mice and suggest a role for IL-10 in the regulation of complement production.

Rat glomerular epithelial cells produce and bear factor H on their surface that is up-regulated under complement attack

BACKGROUND

Factor H is a potent complement inhibitory molecule that is primarily produced by the liver and appears in plasma as a soluble protein. Yet there is evidence that other cells, including those in the kidney, can produce factor H, and that it can be cell-associated as well as present as a plasma protein. Here we studied factor H in rat glomerular epithelial cells (GEC).

METHODS

A polyclonal antibody to factor H was used to identify factor H protein. A polymerase chain reaction (PCR)-based strategy was utilized to clone the full-length cDNA of GEC factor H. The relative quantity of factor H mRNA was measured by quantitative reverse transcription (RT)-PCR in cultured GEC exposed to complement activation and in the passive Heymann nephritis (PHN) model of membranous nephropathy.

RESULTS

By immunofluorescence microscopy, factor H protein was present on the plasma membranes of cultured GEC. Based upon Western blot studies, this appeared to be the full-length 150 kD factor H protein. Factor H cDNA cloned from GEC was identical to the newly deposited sequence for rat liver factor H cDNA. In cultured GEC in which complement was activated, factor H mRNA increased over time. Similarly, in the PHN model in which complement was activated on GEC in vivo, factor H mRNA and protein also increased over time.

CONCLUSION

Cultured GEC and glomeruli express factor H mRNA and protein. As modeled both in vitro and in vivo in the rat, factor H is up-regulated in membranous nephropathy. This is likely to be a direct response of GEC to complement attack and may represent a protective response of this cell.

Locally produced complement and its role in renal allograft rejection

The role of innate immunity in allograft injury is just beginning to become clear, and complement is probably one of a number of factors that are activated very early in the course of transplantation. Kidney transplantation into complement-inhibited rats reduces subsequent inflammation of the graft, probably as a result of reduction of ischemia reperfusion damage as well as diminution of immune mediated damage. Closer analysis of the role of locally synthesised components in mice has suggested that regional synthesis of complement proteins, in particular by the renal tubule, may play a more important role than circulating components. A marked effect on the antidonor T cell response may be explained by the triggering of complement receptors present on antigen presenting cells or T cells infiltrating the graft, or by a more direct effect of complement on the liaison between proximal tubule cells and T cells. Therapeutic control is likely to require a shift to a more targeted approach, directed at complement components produced in the extravascular tissue compartment.

C5a is important in the tubulointerstitial component of experimental immune complex glomerulonephritis

Interstitial injury is the hallmark of glomerulonephritis which is progressing to end-stage renal disease (ESRD). In humans and experimental animals, we have shown that interstitial disease is accompanied by up-regulation of complement components in tubular epithelial cells. Glomerulonephritis was induced in mice by the intraperitoneal injection of horse spleen apoferritin (HSA) and lipopolysaccharide (LPS). In addition to wild-type C57/B6 mice, animals in which the C5a receptor had been deleted (C5aR KO) were used. Animals were killed after 3 or 6 weeks, and kidneys harvested. At three weeks, both groups had evidence of mild mesangial matrix expansion and increased cellularity; there were no crescents, sclerotic lesions, or interstitial disease. At six weeks, glomerular lesions were advanced, but identical in the two groups. Both groups had evidence of an identical pattern of C3 gene expression in the tubular epithelium by in situ hybridization. There was a marked difference, however, in the extent of interstitial injury. Wild-type animals had significantly greater numbers of infiltrating interstitial cells, greater expansion of the peritubular space, more tubular atrophy, and more apoptotic tubular cells than did C5aR KOs. The anaphylotoxic fragment of C5, C5a, is not likely to be important in the glomerular component of this model of progressive glomerulonephritis. On the other hand, the interstitial component is markedly attenuated in knockout animals. These data support a role for complement in the interstitial component of this glomerulonephritis model. They are consistent with our hypotheses of a role for complement in the progression of some forms of glomerulonephritis to ESRD.

Intrarenal synthesis of complement

During the past decade, research has shown that the kidney has the capacity to synthesize most of the activation pathway components of the complement cascade. As well as implying physiological roles in local clearance of immune complexes and defense against invasive organisms, an increasing amount of evidence indicates that the intrarenal synthesis of complement makes an important contribution in the pathogenesis of renal injury. Here we review this evidence and present a case for more definitive investigation of these functions.

Free radicals upregulate complement expression in rabbit isolated heart

Both free radicals and complement activation can injure tissue. Our study determined whether free radicals alter complement production by the myocardium. Isolated hearts from New Zealand White rabbits were perfused on a Langendorff apparatus and exposed to xanthine (X; 100 microM) plus xanthine oxidase (XO; 8 mU/ml) (X/XO). The free radical-generating system significantly (P < 0.05) increased C1q and also increased C1r, C3, C8, and C9 transcription compared with controls. Immunohistological examination revealed augmented membrane attack complex deposition on X/XO-treated tissue. X/XO-treated hearts also exhibited significant (P < 0.05) increases in coronary perfusion pressure and left ventricular end-diastolic pressure and a decrease in left-ventricular developed pressure. N-(2-mercaptopropionyl)-glycine (3 mM), in conjunction with the superoxide dismutase mimetic SC-52608 (100 microM), significantly (P < 0.05) reduced the upregulation of C1q, C1r, C3, C8, and C9 mRNA expression elicited by X/XO. The antioxidants also ameliorated the deterioration in function caused by X/XO. Local complement activation may represent a mechanism by which free radicals mediate tissue injury.

Age-associated changes in the immune system of German shepherd dogs

In order to look into the ageing of the canine immune system we investigated age-related changes and associated gender-related differences in parameters of innate and acquired immunity in German Shepherd dogs. We obtained the following findings: white blood cell counts, peripheral blood lymphocytes, lymphocyte proliferative activity and interleukin-2 (IL-2) serum concentrations were significantly lower in the group of old animals, whereas the concentrations of gamma-globulins and the functional activity of the complement system were significantly higher in the elderly. Phagocytic and bactericidal activity of polymorphonuclear cells, as well as their 'killing function,' the serum cytokine-like activities of tumour necrosis factor-alpha and the plasma concentrations of immunoglobulin G, as well as of alpha- and beta-globulins, were not significantly affected by age, whereas natural killer-cell activity and the serum cytokine-like activities of IL-1 were significantly higher only in the group of female old animals. With regard to gender-related differences, lymphocyte proliferative activities as well as plasma concentrations of alpha-globulin were significantly higher in the group of female animals, whereas the absolute numbers of segmented neutrophils were significantly lower. Species analogies with regard to ageing as presumed to exist between man and laboratory rodents also seem to be applicable to the dog. The observed age-related changes in the canine immune system are probably among the main causes for the multimorbidity of old age, affecting life expectancy and mortality in the dog and should be recognized and considered by the attending veterinarian.

Preconditioning reduces tissue complement gene expression in the rabbit isolated heart

Both preconditioning and inhibition of complement activation have been shown to ameliorate myocardial ischemia-reperfusion injury. The recent demonstration that myocardial tissue expresses complement components led us to investigate whether preconditioning affects complement expression in the isolated heart. Hearts from New Zealand White rabbits were exposed to either two rounds of 5 min global ischemia followed by 10 min reperfusion (ischemic preconditioning) or 10 microM of the ATP-dependent K+ (KATP) channel opener pinacidil for 30 min (chemical preconditioning) before induction of 30 min global ischemia followed by 60 min of reperfusion. Both ischemic and chemical preconditioning significantly (P < 0.05) reduced myocardial C1q, C1r, C3, C8, and C9 mRNA levels. Western blot and immunohistochemistry demonstrated a similar reduction in C3 and membrane attack complex protein expression. The K(ATP) channel blocker glyburide (10 microM) reversed the depression of C1q, C1r, C3, C8, and C9 mRNA expression observed in the pinacidil-treated hearts. The results suggest that reduction of local tissue complement production may be one means by which preconditioning protects the ischemic myocardium.

C3a is made by proximal tubular HK-2 cells and activates them via the C3a receptor

BACKGROUND

Some individual components of complement are synthesized by the kidney. However, it is not known whether these form functional pathways that are able to mediate more fundamental cellular events. We examined the ability of HK-2 tubular cells to produce an intact alternative pathway of complement and to respond to the C3a fragment thus produced through the C3a receptor.

METHODS

The production of mRNA for alternative pathway components was detected by reverse transcription-polymerase chain reaction, whereas protein synthesis was investigated by probing Western blots of concentrated culture supernatants with polyclonal antisera. Levels of C3a and inositol phosphate produced by HK-2 cells were determined by radioimmunoassay, whereas those of transforming growth factor-beta1 (TGF-beta1) were measured by ELISA. Intracellular tyrosine phosphorylation in response to C3a was evaluated by Western blotting and chemiluminescence.

RESULTS

HK-2 cells produce the complement polypeptides C3a, C3, and factors B and H. They also contain mRNA for all components of the alternative pathway and the C3a receptor. mRNA levels were up-regulated by interleukin-1alpha, interleukin-1beta, and tumor necrosis factor-alpha. Incubation of HK-2 cells with C3a led to an increase in intracellular inositol phosphate and to tyrosine phosphorylation of at least two proteins in a pertussis-toxin-sensitive fashion. C3a and C3a desarg also up-regulated the secretion of TGF-beta1 by these cells.

CONCLUSION

HK-2 cells produce an intact alternative pathway of complement. In addition, both locally produced and urinary C3a have the potential to activate these cells, resulting in inflammatory events such as TGF-beta1 production.

Role of tubule epithelial cells in the pathogenesis of tubulointerstitial fibrosis induced by glomerular disease

Tubulointerstitial fibrosis is a final common pathway for progressive renal injury in most 'inflammatory' and 'non-inflammatory' glomerulopathies. Indeed, the level of tubulointerstitial fibrosis correlates closely with the degree of chronic renal dysfunction in these settings. An emerging body of evidence suggests that tubule epithelial cells are dynamic players in the pathogenesis of tubulointerstitial fibrosis. Here we briefly review the potential mechanisms of tubule cell activation in patients with glomerular disease. These mechanisms include: (a) direct involvement of glomerular and tubulointerstitial compartments by the primary disease; (b) secondary activation of tubule epithelial cells by glomerulus-derived cytokines; (c) perturbation of tubule epithelial cell function by plasma proteins and associated moieties filtered in excess through injured glomeruli; (d) tubulointerstitial ischaemia downstream to glomerular injury; and (e) hyperfunction of remnant tubules. Activated tubule epithelial cells are, in turn, a rich source of cytokines, chemokines and other mediators that promote leukocyte recruitment, cytotoxicity and fibrogenesis, thereby establishing a 'vicious cycle' of tubulointerstitial injury. The further delineation of the role played by the tubule epithelial cell in the pathogenesis of tubulointerstitial fibrosis may suggest novel approaches for the treatment of progressive renal diseases.

Expression of decay accelerating factor mRNA and complement C3 mRNA in human diseased kidney

BACKGROUND

Decay accelerating factor (DAF), a product of mesangial cells in vitro, is expressed on the surface of cells and is a candidate for the focal suppression of complement activation. It is not clear at present whether the levels of expression of DAF and intrarenal C3 synthesis correlate with the level of tissue injury.

METHODS

Immunohistochemistry for DAF and C3 and nonradioactive in situ hybridization with digoxigenin-labeled oligonucleotide probe for DAF and C3 mRNA were performed in 22 tissue samples of kidneys from patients with IgA nephropathy (IgAN), 6 with membranous nephropathy (MN), 6 with lupus nephritis (LN), and five normal kidneys.

RESULTS

In the normal kidney, DAF was confined to the juxtaglomerular apparatus and little or no C3 was detected; however, a few glomerular cells were positive for DAF mRNA but no C3 mRNA positive cells were detected. In diseased kidneys, DAF and C3 as well as their mRNAs were detected in mesangial cells, tubular cells and infiltrating cells. Glomerular epithelial cells and Bowman's capsule cells contained little or no DAF and C3 but were positive for their mRNAs. The mean percentages of mesangial cells positive for DAF and C3 mRNAs were 49.3 +/- 11.5% and 50.7 +/- 10.3% in IgAN, and 17.0 +/- 6.3% and 19.4 +/- 9.0% in MN, respectively. The percentage of mesangial cells positive for DAF and C3 mRNAs among intraglomerular cells correlated positively with the degree of mesangial proliferation and glomerular sclerosis in IgAN. In contrast, in LN the percentage of glomerular cells positive for DAF mRNA correlated negatively with the degree of glomerular injury, while the percentage of cells positive for C3 mRNA did not change with the progression of the disease. The ratio of C3 mRNA/DAF mRNA of glomerular cells correlated with the degree of glomerular injury in both IgAN and LN. In the tubulointerstitium, the percentage of cells expressing mRNA, and C3 mRNA/DAF mRNA radio correlated with the degree of tubular atrophy and interstitial broadening in both IgAN and LN.

CONCLUSIONS

We conclude that DAF and C3 mRNAs are synthesized in human diseased kidneys, and that a balance between locally synthesized DAF and C3 may be important in the progression of glomerulonephritis.

Anti-CD40 Ligand Antibody Treatment of SNF1 Mice with Established Nephritis: Preservation of Kidney Function

Prior studies have demonstrated that treatment of young, prenephritic lupus-prone mice with Ab directed against CD40 ligand (CD40L) prolongs survival and decreases the incidence of severe nephritis. In this report, we show that for (SWR × NZB)F1 (SNF1) animals with established lupus nephritis, long-term treatment with anti-CD40L beginning at either 5.5 or 7 mo of age prolonged survival and decreased the incidence of severe nephritis. “Older” mice were chosen for these studies to more closely resemble the clinical presentation of patients with established renal disease. We show that age at the start of treatment, which typically correlates with severity of disease, is an important factor when determining an efficacious therapeutic protocol since animals that began treatment at 7 mo of age required a more aggressive treatment protocol than animals at 5.5 mo of age. Remarkably, several anti-CD40L-treated animals beginning treatment at age 5.5 mo demonstrated a decline in proteinuria, as opposed to increasing proteinuria levels seen in hamster IgG (HIg)-treated controls, and histologic examination of kidneys from anti-CD40L-treated mice revealed dramatically diminished inflammation, sclerosis/fibrosis, and vasculitis, in marked contrast to the massive inflammation and kidney destruction observed in control animals that received hamster IgG. Spleens from anti-CD40L-treated mice also exhibited markedly reduced inflammation and fibrosis compared with controls. Together, these results show that treatment of older, nephritic SNF1 animals with long-term anti-CD40L immunotherapy significantly prolongs survival, reduces the severity of nephritis, and diminishes associated inflammation, vasculitis, and fibrosis.