Collectin 11 has a pivotal role in host defense against kidney and bladder infection in mice

The urinary tract is constantly exposed to microorganisms. Host defense mechanisms in protection from microbial colonization and development of urinary tract infections require better understanding to control kidney infection. Here we report that the lectin collectin 11 (CL-11), particularly kidney produced, has a pivotal role in host defense against uropathogen infection. CL-11 was found in mouse urine under normal and pathological conditions. Mice with global gene ablation of Colec11 had increased susceptibility to and severity of kidney and to an extent, bladder infection. Mice with kidney-specific Colec11 ablation exhibited a similar disease phenotype to that observed in global Colec11 deficient mice, indicating the importance of kidney produced CL-11 for protection against kidney and bladder infection. Conversely, intravesical or systemic administration of recombinant CL-11 reduced susceptibility to and severity of kidney and bladder infection. Mechanism analysis revealed that CL-11 can mediate several key innate defense mechanisms (agglutination, anti- adhesion, opsonophagocytosis), and limit local inflammatory responses to pathogens. Furthermore, CL-11-mediated innate defense mechanisms can act on clinically relevant microorganisms including multiple antibiotic resistant strains. CL-11 was detectable in eight of 24 urine samples from patients with urinary tract infections but not detectable in urine samples from ten healthy individuals. Thus, our findings demonstrate that CL-11 is a key factor of host defense mechanisms in kidney and bladder infection with therapeutic potential for human application.

Soluble Collectin 11 (CL-11) Acts as an Immunosuppressive Molecule Potentially Used by Stem Cell-Derived Retinal Epithelial Cells to Modulate T Cell Response

Retinal pigment epithelium (RPE) cell allotransplantation is seen as a possible solution to retinal diseases. However, the RPE-complement system triggered by the binding of collectin-11 (CL-11) is a potential barrier for RPE transplantation as the complement-mediated inflammatory response may promote T cell recognition. To address this, we investigated the role of CL-11 on T cell immuno-response. We confirmed that RPE cells up-regulated MHC class I and expressed MHC class II molecules in an inflammatory setting. Co-cultures of RPE cells with T cells led to the inhibition of T cell proliferation. We found that CL-11 was partially responsible for this effect as T cell binding of CL-11 inhibited T cell proliferation in association with the downregulation of CD28. We also found that the suppressive action of CL-11 was abrogated in the presence of the RGD peptide given to block the T cell binding of CL-11 by its collagen-like domain. Because RPE cells can bind and secrete CL-11 under stress conditions, we postulate that soluble CL-11 contributes to the immunosuppressive properties of RPE cells. The investigation of this dual biological activity of CL-11, namely as a trigger of the complement cascade and a modulator of T cell responses, may provide additional clues about the mechanisms that orchestrate the immunogenic properties of RPE cells.

Local complement synthesis-A process with near and far consequences for ischemia reperfusion injury and transplantation

The model of the solid organ as a target for circulating complement deposited at the site of injury, for many years concealed the broader influence of complement in organ transplantation. The study of locally synthesized complement especially in transplantation cast new light on complement's wider participation in ischaemia-reperfusion injury, the presentation of donor antigen and finally rejection. The lack of clarity, however, has persisted as to which complement activation pathways are involved and how they are triggered, and above all whether the distinction is relevant. In transplantation, the need for clarity is heightened by the quest for precision therapies in patients who are already receiving potent immunosuppressives, and because of the opportunity for well-timed intervention. This review will present new evidence for the emerging role of the lectin pathway, weighed alongside the longer established role of the alternative pathway as an amplifier of the complement system, and against contributions from the classical pathway. It is hoped this understanding will contribute to the debate on precisely targeted versus broadly acting therapeutic innovation within the aim to achieve safe long term graft acceptance.

FC 130: Kinetics of Renal Injury After Rhabdomyolysis: Implication of Innate Immune Cells and Complement Activation

BACKGROUND AND AIMS

In rhabdomyolysis—characterized by massive striated muscle damage—main complication is Acute Kidney Injury (AKI) occurring in up to 50% cases. Physiopathology of rhabdomyolysis induced AKI (RIAKI) was historically described as the association of intrarenal vasoconstriction, tubular obstruction by myoglobin casts and direct tubular toxicity (by oxidative stress, lipid peroxidation). Recently, it became evident that the innate immunity also plays a role. Macrophages infiltrate contributes to direct tubular toxicity and we found activation of the complement system in patients and mice with RIAKI, in part mediated by myoglobin released heme [1]. Still, the mechanisms by which the innate immunity contribute to the RIAKI kidney injury and to which extend there are comparable to ischemia reperfusion injury (IRI) are not fully understood.

METHOD

We performed a kinetic model of glycerol (GLY) induced RIAKI in C57BL/6 mice at 1, 3, 12, 24 hours and 7 days and analysed kidney function (biochemical parameters, histology), injury markers (Quantigene: analyse simultaneously expression of 80 genes, chosen from RIAKI transcriptomic signature (1)), complement deposits (immunofluorescence). We evaluated the abundance of tissue-infiltrating immune and stromal cell populations using gene expression (MCP counter), validated by flow cytometry. Kinetic of expression of RIAKI genes was compared to scRNAseq of IRI model [2]. We compared WT mice to ones deficient of the classical (C1q–/–, C4–/–), alternative (C3–/– and FB–/–) and lectin (Collectin-11-/-) pathways. Finally, we analysed complement activation fragments in the urine of 15 RIAKI patients as compared to controls (n = 5) and IRI patients (n = 5).

RESULTS

Upon rhabdomyolysis, AKI in mice starts as early as 3 h post-GLY injection. Despite early upregulation of cytoprotective transcription factors (Maff, Myc, Sox9 within 3 h) and genes implicated in heme detoxification (HO1 and ferritin), both proximal and distal tubules are affected between 6 and 12 h post injury and endothelial injury is evident from 3 h. Granulocytes, monocytes and eosinophils increased in blood and infiltrated the kidney at 12 h due to preceding overexpression of chemoattractants (Cxcl1, Lgals3, Ccl2, Ccl7, Ccl12), likely by injured tubules. At 24 h, the phenotype of RIAKI kidney infiltrating inflammatory monocytes, eosinophils and resident macrophages revealed strong upregulation of C5aR1 (5x, 7x and 2x), while its levels in neutrophils tend to decrease, suggesting C5a-mediated activation. This was paralleled by intrarenal complement deposits on injured tubules and complement biomarkers in urine. To underscore the pathological relevance of complement, we found that alternative and to some extend lectin pathway deficient mice were partially protected, as opposed to mice deficient for classical pathway (Figure 1). Complement activation byproducts, notably Ba, C3a and C5a were increased in RIAKI patient urine as compared to control (including when normalized by proteinuria) (Figure 2).

CONCLUSION

The kinetic of RIAKI follows the pattern of IRI acute kidney injury with specificities regarding early response to heme overload. Despite numerous protective mechanisms initiated, kidney tubules and blood vessels are rapidly affected. This results in early kidney inflammation, complement deposition and chemoattraction of immune cell with complement responsive phenotype. Complement biomarkers are increased in urine of RIAKI mice and patients alike. Our study underlines the importance to study the first hours post injury to understand the mechanisms involved in order to propose specific treatment. Complement targeting has to be explored as a therapeutic strategy in this disease.

Complement in ischaemia-reperfusion injury and transplantation

Until recently, the only known condition in which complement could mediate transplant injury was the rare occurrence of antibody-mediated rejection, in which the original concept of antibody immunity against the transplant was supported by complementary proteins present in the serum. This has changed within the last two decades because of evidence that the processes of ischaemia–reperfusion injury followed by T cell–mediated rejection are also critically dependent on components generated by the complement system. We now have a clearer understanding of the complement triggers and effectors that mediate injury, and a detailed map of their local sites of production and activation in the kidney. This is providing helpful guidelines as to how these harmful processes that restrict transplant outcomes can be targeted for therapeutic benefit. Here we review some of the recent advances highlighting relevant therapeutic targets.

Fucose as a new therapeutic target in renal transplantation

Ischaemia/reperfusion injury (IRI) is an inevitable and damaging consequence of the process of kidney transplantation, ultimately leading to delayed graft function and increased risk of graft loss. A key driver of this adverse reaction in kidneys is activation of the complement system, an important part of the innate immune system. This activation causes deposition of complement C3 on renal tubules as well as infiltration of immune cells and ultimately damage to the tubules resulting in reduced kidney function. Collectin-11 (CL-11) is a pattern recognition molecule of the lectin pathway of complement. CL-11 binds to a ligand that is exposed on the renal tubules by the stress caused by IRI, and through attached proteases, CL-11 activates complement and this contributes to the consequences outlined above. Recent work in our lab has shown that this damage-associated ligand contains a fucose residue that aids CL-11 binding and promotes complement activation. In this review, we will discuss the clinical context of renal transplantation, the relevance of the complement system in IRI, and outline the evidence for the role of CL-11 binding to a fucosylated ligand in IRI as well as its downstream effects. Finally, we will detail the simple but elegant theory that increasing the level of free fucose in the kidney acts as a decoy molecule, greatly reducing the clinical consequences of IRI mediated by CL-11.

Ex vivo delivery of Mirococept: A dose-finding study in pig kidney after showing a low dose is insufficient to reduce delayed graft function in human kidney

The complement system plays a pivotal role in the pathogenesis of ischemia-reperfusion injury in solid organ transplantation. Mirococept is a potent membrane-localizing complement inhibitor that can be administered ex vivo to the donor kidney prior to transplantation. To evaluate the efficacy of Mirococept in reducing delayed graft function (DGF) in deceased donor renal transplantation, we undertook the efficacy of mirococept (APT070) for preventing ischaemia-reperfusion injury in the kidney allograft (EMPIRIKAL) trial (ISRCTN49958194). A dose range of 5-25 mg would be tested, starting with 10 mg in cohort 1. No significant difference between Mirococept at 10 mg and control was detected; hence the study was stopped to enable a further dose saturation study in a porcine kidney model. The optimal dose of Mirococept in pig kidney was 80 mg. This dose did not induce any additional histological damage compared to controls or after a subsequent 3 hours of normothermic machine perfusion. The amount of unbound Mirococept postperfusion was found to be within the systemic dose range considered safe in the Phase I trial. The ex vivo administration of Mirococept is a safe and feasible approach to treat DGF in deceased donor kidney transplantation. The porcine kidney study identified an optimal dose of 80 mg (equivalent to 120 mg in human kidney) that provides a basis for further clinical development.

Successful simultaneous liver-kidney transplantation for renal failure associated with hereditary complement C3 deficiency

Hereditary complement C3 deficiency is associated with recurrent bacterial infections and proliferative glomerulonephritis. We describe a case of an adult with complete deficiency of complement C3 due to homozygous mutations in C3 gene: c.1811delT (Val604Glyfs*2), recurrent bacterial infections, crescentic glomerulonephritis, and end-stage renal failure. Following isolated kidney transplantation he would remain C3 deficient with a similar, or increased, risk of infections and glomerulonephritis. As C3 is predominantly synthesized in the liver, with a small proportion of C3 monocyte derived and kidney derived, he proceeded to simultaneous liver-kidney transplantation. The procedure has been successful with restoration of his circulating C3 levels, normal liver and kidney function at 26 months of follow-up. Simultaneous liver-kidney transplant is a viable option to be considered in this rare setting.

l-Fucose prevention of renal ischaemia/reperfusion injury in Mice

In a recent study, we identified a fucosylated damage‐associated ligand exposed by ischemia on renal tubule epithelial cells, which after recognition by collectin‐11 (CL‐11 or collectin kidney 1 (CL‐K1)), initiates complement activation and acute kidney injury. We exploited the ability to increase the local tissue concentration of free l‐fucose following systemic administration, in order to block ligand binding by local CL‐11 and prevent complement activation. We achieved a thirty‐five‐fold increase in the intrarenal concentration of l‐fucose following an IP bolus given before the ischemia induction procedure ‐ a concentration found to significantly block in vitro binding of CL‐11 on hypoxia‐stressed renal tubule cells. At this l‐fucose dose, complement activation and acute post‐ischemic kidney injury are prevented, with additional protection achieved by a second bolus after the induction procedure. CL‐11^−/− mice gained no additional protection from l‐fucose administration, indicating that the mechanism of l‐fucose therapy was largely CL‐11‐dependent. The hypothesis is that a high dose of l‐fucose delivered to the kidney obstructs the carbohydrate recognition site on CL‐11 thereby reducing complement‐mediated damage following ischemic insult. Further work will examine the utility in preventing post‐ischemic injury during renal transplantation, where acute kidney injury is known to correlate with poor graft survival.

Complement C5a inhibition moderates lipid metabolism and reduces tubulointerstitial fibrosis in diabetic nephropathy

Background

Complement C5 mediates pro-inflammatory responses in many immune-related renal diseases. Given that the C5a level is elevated in diabetes, we investigated whether activation of C5a/C5aR signalling plays a pathogenic role in diabetic nephropathy (DN) and the therapeutic potential of C5a inhibition for renal fibrosis.

Methods

Human renal biopsies from patients with DN and control subjects were used for immunohistochemical staining of complement C5 components. Renal function and tubulointerstitial injury were compared between db/m mice, vehicle-treated mice and C5a inhibitor-treated db/db mice. A cell culture model of tubule epithelial cells (HK-2) was used to demonstrate the effect of C5a on the renal fibrotic pathway.

Results

Increased levels of C5a, but not of its receptor C5aR, were detected in renal tubules from patients with DN. The intensity of C5a staining was positively correlated with the progression of the disease. In db/db mice, administration of a novel C5a inhibitor, NOX-D21, reduced the serum triglyceride level and attenuated the upregulation of diacylglycerolacyltransferase-1 and sterol-regulatory element binding protein-1 expression and lipid accumulation in diabetic kidney. NOX-D21-treated diabetic mice also had reduced serum blood urea nitrogen and creatinine levels with less glomerular and tubulointerstitial damage. Renal transforming growth factor beta 1 (TGF-β1), fibronectin and collagen type I expressions were reduced by NOX-D21. In HK-2 cells, C5a stimulated TGF-β production through the activation of the PI3K/Akt signalling pathway.

Conclusions

Blockade of C5a signalling by NOX-D21 moderates altered lipid metabolism in diabetes and improved tubulointerstitial fibrosis by reduction of lipid accumulation and TGF-β-driven fibrosis in diabetic kidney.

Long- and short-term outcomes in renal allografts with deceased donors: A large recipient and donor genome-wide association study

Improvements in immunosuppression have modified short-term survival of deceased-donor allografts, but not their rate of long-term failure. Mismatches between donor and recipient HLA play an important role in the acute and chronic allogeneic immune response against the graft. Perfect matching at clinically relevant HLA loci does not obviate the need for immunosuppression, suggesting that additional genetic variation plays a critical role in both short- and long-term graft outcomes. By combining patient data and samples from supranational cohorts across the United Kingdom and European Union, we performed the first large-scale genome-wide association study analyzing both donor and recipient DNA in 2094 complete renal transplant-pairs with replication in 5866 complete pairs. We studied deceased-donor grafts allocated on the basis of preferential HLA matching, which provided some control for HLA genetic effects. No strong donor or recipient genetic effects contributing to long- or short-term allograft survival were found outside the HLA region. We discuss the implications for future research and clinical application.

Structural and functional diversity of collectins and ficolins and their relationship to disease

Pattern recognition molecules are sensors for the innate immune system and trigger a number of pathophysiological functions after interaction with the corresponding ligands on microorganisms or altered mammalian cells. Of those pattern recognition molecules used by the complement system, collagen-like lectins (collectins) are an important subcomponent. Whereas the best known of these collectins, mannose-binding lectin, largely occurs as a circulating protein following production by hepatocytes, the most recently described collectins exhibit strong local biosynthesis. This local production and release of soluble collectin molecules appear to serve local tissue functions at extravascular sites, including a developmental function. In this article, we focus on the characteristics of collectin-11 (CL-11 or CL-K1), whose ubiquitous expression and multiple activities likely reflect a wide biological relevance. Collectin-11 appears to behave as an acute phase protein whose production associated with metabolic and physical stress results in locally targeted inflammation and tissue cell death. Early results indicate the importance of fucosylated ligand marking the injured cells targeted by collectin-11, and we suggest that further characterisation of this and related ligands will lead to better understanding of pathophysiological significance and exploitation for clinical benefit.

C5aR1 promotes acute pyelonephritis induced by uropathogenic E. coli

C5a receptor 1 (C5aR1) is a G protein-coupled receptor for C5a and also an N-linked glycosylated protein. In addition to myeloid cells, C5aR1 is expressed on epithelial cells. In this study, we examined the role of C5aR1 in bacterial adhesion/colonization of renal tubular epithelium and addressed the underlying mechanisms of this role. We show that acute kidney infection was significantly reduced in mice with genetic deletion or through pharmacologic inhibition of C5aR1 following bladder inoculation with uropathogenic E. coli (UPEC). This was associated with reduced expression of terminal α-mannosyl residues (Man; a ligand for type 1 fimbriae of E. coli) on the luminal surface of renal tubular epithelium and reduction of early UPEC colonization in these mice. Confocal microscopy demonstrated that UPEC bind to Man on the luminal surface of renal tubular epithelium. In vitro analyses showed that C5a stimulation enhances Man expression in renal tubular epithelial cells and subsequent bacterial adhesion, which, at least in part, is dependent on TNF-α driven by C5aR1-mediated intracellular signaling. Our findings demonstrate a previously unknown pathogenic role for C5aR1 in acute pyelonephritis, proposing a potentially novel mechanism by which C5a/C5aR1 signaling mediates upregulation of carbohydrate ligands on renal tubules to facilitate UPEC adhesion.

Collectin-11 Promotes the Development of Renal Tubulointerstitial Fibrosis

Collectin-11 is a recently described soluble C-type lectin, a pattern recognition molecule of the innate immune system that has distinct roles in host defense, embryonic development, and acute inflammation. However, little is known regarding the role of collectin-11 in tissue fibrosis. Here, we investigated collectin-11 in the context of renal ischemia-reperfusion injury. Compared with wild-type littermate controls, Collec11 deficient (CL-11^-/- ) mice had significantly reduced renal functional impairment, tubular injury, renal leukocyte infiltration, renal tissue inflammation/fibrogenesis, and collagen deposition in the kidneys after renal ischemia-reperfusion injury. In vitro, recombinant collectin-11 potently promoted leukocyte migration and renal fibroblast proliferation in a carbohydrate-dependent manner. Additionally, compared with wild-type kidney grafts, CL-11^-/-mice kidney grafts displayed significantly reduced tubular injury and collagen deposition after syngeneic kidney transplant. Our findings demonstrate a pathogenic role for collectin-11 in the development of tubulointerstitial fibrosis and suggest that local collectin-11 promotes this fibrosis through effects on leukocyte chemotaxis and renal fibroblast proliferation. This insight into the pathogenesis of tubulointerstitial fibrosis may have implications for CKD mediated by other causes as well.

Deconstructing the Lectin Pathway in the Pathogenesis of Experimental Inflammatory Arthritis: Essential Role of the Lectin Ficolin B and Mannose-Binding Protein-Associated Serine Protease 2

Complement plays an important role in the pathogenesis of rheumatoid arthritis. Although the alternative pathway (AP) is known to play a key pathogenic role in models of rheumatoid arthritis, the importance of the lectin pathway (LP) pattern recognition molecules such as ficolin (FCN) A, FCN B, and collectin (CL)-11, as well as the activating enzyme mannose-binding lectin-associated serine protease-2 (MASP-2), are less well understood. We show in this article that FCN A-/- and CL-11-/- mice are fully susceptible to collagen Ab-induced arthritis (CAIA). In contrast, FCN B-/- and MASP-2-/-/sMAp-/- mice are substantially protected, with clinical disease activity decreased significantly (p < 0.05) by 47 and 70%, respectively. Histopathology scores, C3, factor D, FCN B deposition, and infiltration of synovial macrophages and neutrophils were similarly decreased in FCN B-/- and MASP-2-/-/sMAp-/- mice. Our data support that FCN B plays an important role in the development of CAIA, likely through ligand recognition in the joint and MASP activation, and that MASP-2 also contributes to the development of CAIA, likely in a C4-independent manner. Decreased AP activity in the sera from FCN B-/- and MASP-2-/-/sMAp-/- mice with arthritis on adherent anti-collagen Abs also support the hypothesis that pathogenic Abs, as well as additional inflammation-related ligands, are recognized by the LP and operate in vivo to activate complement. Finally, we also speculate that the residual disease seen in our studies is driven by the AP and/or the C2/C4 bypass pathway via the direct cleavage of C3 through an LP-dependent mechanism.

Complement Recognition Pathways in Renal Transplantation

The complement system, consisting of soluble and cell membrane-bound components of the innate immune system, has defined roles in the pathophysiology of renal allograft rejection. Notably, the unavoidable ischemia-reperfusion injury inherent to transplantation is mediated through the terminal complement activation products C5a and C5b-9. Furthermore, biologically active fragments C3a and C5a, produced during complement activation, can modulate both antigen presentation and T cell priming, ultimately leading to allograft rejection. Earlier work identified renal tubule cell synthesis of C3, rather than hepatic synthesis of C3, as the primary source of C3 driving these effects. Recent efforts have focused on identifying the local triggers of complement activation. Collectin-11, a soluble C-type lectin expressed in renal tissue, has been implicated as an important trigger of complement activation in renal tissue. In particular, collectin-11 has been shown to engage L-fucose at sites of ischemic stress, activating the lectin complement pathway and directing the innate immune response to the distressed renal tubule. The interface between collectin-11 and L-fucose, in both the recipient and the allograft, is an attractive target for therapies intended to curtail renal inflammation in the acute phase.

A double-blind randomised controlled investigation into the efficacy of Mirococept (APT070) for preventing ischaemia reperfusion injury in the kidney allograft (EMPIRIKAL): study protocol for a randomised controlled trial

Background

Delayed graft function (DGF) is traditionally defined as the requirement for dialysis during the first week after transplantation. DGF is a common complication of renal transplantation, and it negatively affects short- and long-term graft outcomes. Ischaemia reperfusion injury (IRI) is a prime contributor to the development of DGF. It is well established that complement system activation plays a pivotal role in the pathogenesis of IRI. Mirococept is a highly effective complement inhibitor that can be administered ex vivo to the donor kidney just before transplantation. Preclinical and clinical evidence suggests that Mirococept inhibits inflammatory responses that follow IRI. The EMPIRIKAL trial (REC 12/LO/1334) aims to evaluate the efficacy of Mirococept in reducing the incidence of DGF in cadaveric renal transplantation.

Methods/design

EMPIRIKAL is a multicentre double-blind randomised case-control trial designed to test the superiority of Mirococept in the prevention of DGF in cadaveric renal allografts, as compared to standard cold perfusion fluid (Soltran®). Patients will be randomised to Mirococept or placebo (Pbo) and will be enrolled in cohorts of N = 80 with a maximum number of 7 cohorts. The first cohort will be randomised to 10 mg of Mirococept or Pbo. After the completion of each cohort, an interim analysis will be carried out in order to evaluate the dose allocation for the next cohort (possible doses: 5–25 mg). Immunosuppression therapy, antibiotic and antiviral prophylaxis will be administered as per local centre protocols. The enrolment will take approximately 24 months, and patients will be followed for 12 months. The primary endpoint is DGF, defined as the requirement for dialysis during the first week after transplantation. Secondary endpoints include duration of DGF, functional DGF, renal function at 12 months, acute rejection episodes at 6 and 12 months, primary non-function and time of hospital stay on first admission and in the first year following transplant. Safety evaluation will include the monitoring of laboratory data and the recording of all adverse events.

Discussion

The EMPIRIKAL trial is the first study to evaluate the efficacy of an ex vivo administered complement inhibitor (Mirococept) in preventing DGF in cadaveric human renal transplantation. Mirococept has a unique ‘cytotopic’ property that permits its retention in the organ microvasculature.

Trial registration

ISRCTN registry, ISRCTN49958194. Registered on 3 August 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-1972-x) contains supplementary material, which is available to authorized users.

Thrombalexins: Cell-Localized Inhibition of Thrombin and Its Effects in a Model of High-Risk Renal Transplantation

Allograft transplantation into sensitized recipients with antidonor antibodies results in accelerated antibody-mediated rejection (AMR), complement activation, and graft thrombosis. We have developed a membrane-localizing technology of wide applicability that enables therapeutic agents, including anticoagulants, to bind to cell surfaces and protect the donor endothelium. We describe here how this technology has been applied to thrombin inhibitors to generate a novel class of drugs termed thrombalexins (TLNs). Using a rat model of hyperacute rejection, we investigated the potential of one such inhibitor (thrombalexin-1 [TLN-1]) to prevent acute antibody-mediated thrombosis in the donor organ. TLN-1 alone was able to reduce intragraft thrombosis and significantly delay rejection. The results confirm a pivotal role for thrombin in AMR in vivo. This approach targets donor organs rather than the recipient and is intended to be directly translatable to clinical use.

Role of the lectin complement pathway in kidney transplantation

In the last 15 years two major advances in the role of complement in the kidney transplant have come about. The first is that ischaemia reperfusion injury and its profound effect on transplant outcome is dependent on the terminal product of complement activation, C5b-9. The second key observation relates to the function of the small biologically active fragments C3a and C5a released by complement activation in increasing antigen presentation and priming the T cell response that results in transplant rejection. In both cases local synthesis of C3 principally by the renal tubule cells plays an essential role that overshadows the role of the circulating pool of C3 generated largely by hepatocyte synthesis. More recent efforts have investigated the molecules expressed by renal tissue that can trigger complement activation. These have revealed a prominent effect of collectin-11 (CL-11), a soluble C-type lectin that is expressed in renal tissue and aligns with its major ligand L-fucose at sites of complement activation following ischaemic stress. Biochemical studies have shown that interaction between CL-11 and L-fucose results in complement activation by the lectin complement pathway, precisely targeting the innate immune response to the ischaemic tubule surface. Therapeutic approaches to reduce inflammatory and immune stimulation in ischaemic kidney have so far targeted C3 or its activation products and several are in clinical trials. The finding that lectin-fucose interaction is an important trigger of lectin pathway complement activation within the donor organ opens up further therapeutic targets where intervention could protect the donor kidney against complement.

The complement factor 5a receptor 1 has a pathogenic role in chronic inflammation and renal fibrosis in a murine model of chronic pyelonephritis

Complement factor 5a (C5a) interaction with its receptor (C5aR1) contributes to the pathogenesis of inflammatory diseases, including acute kidney injury. However, its role in chronic inflammation, particularly in pathogen-associated disorders, is largely unknown. Here we tested whether the development of chronic inflammation and renal fibrosis is dependent on C5aR1 in a murine model of chronic pyelonephritis. C5aR1-deficient (C5aR1-/-) mice showed a significant reduction in bacterial load, tubule injury and tubulointerstitial fibrosis in the kidneys following infection, compared with C5aR1-sufficient mice. This was associated with reduced renal leukocyte infiltration specifically for the population of Ly6Chi proinflammatory monocytes/macrophages and reduced intrarenal gene expression of key proinflammatory and profibrogenic factors in C5aR1-/- mice following infection. Antagonizing C5aR1 decreased renal bacterial load, tissue inflammation and tubulointerstitial fibrosis. Ex vivo and in vitro studies showed that under infection conditions, C5a/C5aR1 interaction upregulated the production of proinflammatory and profibrogenic factors by renal tubular epithelial cells and monocytes/macrophages, whereas the phagocytic function of monocytes/macrophages was down-regulated. Thus, C5aR1-dependent bacterial colonization of the tubular epithelium, C5a/C5aR1-mediated upregulation of local inflammatory responses to uropathogenic E. coli and impairment of phagocytic function of phagocytes contribute to persistent bacterial colonization of the kidney, chronic renal inflammation and subsequent tubulointerstitial fibrosis.

Complement-here, there and everywhere, but what about the transplanted organ?

The part of the innate immune system that communicates and effectively primes the adaptive immune system was termed "complement" by Ehrlich to reflect its complementarity to antibodies having previously been described as "alexine" (i.e protective component of serum) by Buchner and Bordet. It has been established that complement is not solely produced systemically but may have origin in different tissues where it can influence organ specific functions that may affect the outcome of transplanted organs. This review looks at the role of complement in particular to kidney transplantation. We look at current literature to determine whether blockade of the peripheral or central compartments of complement production may prevent ischaemic reperfusion injury or rejection in the transplanted organ. We also review new therapeutics that have been developed to inhibit components of the complement cascade with varying degrees of success leading to an increase in our understanding of the multiple triggers of this complex system. In addition, we consider whether biomarkers in this field are effective markers of disease or treatment.

Collectin-11 detects stress-induced L-fucose pattern to trigger renal epithelial injury

Physiochemical stress induces tissue injury as a result of the detection of abnormal molecular patterns by sensory molecules of the innate immune system. Here, we have described how the recently discovered C-type lectin collectin-11 (CL-11, also known as CL-K1 and encoded by COLEC11) recognizes an abnormal pattern of L-fucose on postischemic renal tubule cells and activates a destructive inflammatory response. We found that intrarenal expression of CL-11 rapidly increases in the postischemic period and colocalizes with complement deposited along the basolateral surface of the proximal renal tubule in association with L-fucose, the potential binding ligand for CL-11. Mice with either generalized or kidney-specific deficiency of CL-11 were strongly protected against loss of renal function and tubule injury due to reduced complement deposition. Ex vivo renal tubule cells showed a marked capacity for CL-11 binding that was induced by cell stress under hypoxic or hypothermic conditions and prevented by specific removal of L-fucose. Further analysis revealed that cell-bound CL-11 required the lectin complement pathway-associated protease MASP-2 to trigger complement deposition. Given these results, we conclude that lectin complement pathway activation triggered by ligand-CL-11 interaction in postischemic tissue is a potent source of acute kidney injury and is amenable to sugar-specific blockade.

Systematic assessment of the influence of complement gene polymorphisms on kidney transplant outcome

The importance of the innate immune system, including complement, in causing transplant injury and augmenting adaptive immune responses is increasingly recognized. Therefore variability in graft outcome may in part be due to genetic polymorphism in genes encoding proteins of the immune system. This study assessed the relationship between single nucleotide polymorphisms (SNPs) in complement genes and outcome after transplantation. Analysis was performed on two patient cohorts of 650 and 520 transplant recipients. 505 tagged SNPs in 47 genes were typed in both donor and recipient. The relationships between SNPs and graft survival, serum creatinine, delayed graft function and acute rejection were analyzed. One recipient SNP in the gene encoding mannose binding lectin was associated with graft outcome after correction for analysis of multiple SNPs (p=6.41 × 10(-5)). When further correction was applied to account for analysis of the effect of SNPs in both donor and recipient this lost significance. Despite association p values of <0.001 no SNP was significantly associated with clinical phenotypes after Bonferroni correction. In conclusion, the variability seen in transplant outcome in this patient cohort cannot be explained by variation in complement genes. If causal genetic effects exist in these genes, they are too small to be detected by this study.

Kinetics of mast cell migration during transplantation tolerance

BACKGROUND

After inflammatory stimulus, mast cells (MC) migrate to secondary lymphoid organs contributing to adaptive immune response. There is growing evidence that MC also contribute to transplant tolerance, but little is known about MC kinetics in the setting of transplant tolerance and rejection. Likewise it has been demonstrated that complement split products, which are known to act as chemoattractants for MC, are necessary for transplant tolerance.

METHODS

Naive skin and lymph nodes, skin grafts and draining lymph nodes from wild type and complement deficient mice treated with a tolerogenic protocol were analyzed.

RESULTS

Early after tolerance induction MC leave the graft and migrate to the draining lymph nodes. After this initial efflux, MC reappear in tolerant skin grafts in numbers exceeding that of naive skin. MC density in draining lymph nodes obtained from tolerant mice also increased post transplant. There was no difference in MC density, migration and degranulation status between wild type and complement deficient mice implicating that chemotaxis is not disturbed in complement deficient mice.

CONCLUSION

This study gives detailed insight in kinetics of MC migration during transplant tolerance induction and rejection providing further evidence for a role of MC in transplant tolerance.

Mannan-binding lectin-associated serine protease 2 is critical for the development of renal ischemia reperfusion injury and mediates tissue injury in the absence of complement C4

Mannan-binding lectin-associated serine protease 2 (MASP-2) has been described as the essential enzyme for the lectin pathway (LP) of complement activation. Since there is strong published evidence indicating that complement activation via the LP critically contributes to ischemia reperfusion (IR) injury, we assessed the effect of MASP-2 deficiency in an isogenic mouse model of renal transplantation. The experimental transplantation model used included nephrectomy of the remaining native kidney at d 5 post-transplantation. While wild-type (WT) kidneys grafted into WT recipients (n=7) developed acute renal failure (control group), WT grafts transplanted into MASP-2-deficient recipients (n=7) showed significantly better kidney function, less C3 deposition, and less IR injury. In the absence of donor or recipient complement C4 (n=7), the WT to WT phenotype was preserved, indicating that the MASP-2-mediated damage was independent of C4 activation. This C4-bypass MASP-2 activity was confirmed in mice deficient for both MASP-2 and C4 (n=7), where the protection from postoperative acute renal failure was no greater than in mice with MASP-2 deficiency alone. Our study highlights the role of LP activation in renal IR injury and indicates that injury occurs through MASP-2-dependent activation events independent of C4.

The innate immune system and transplantation

The sensitive and broadly reactive character of the innate immune system makes it liable to activation by stress factors other than infection. Thermal and metabolic stresses experienced during the transplantation procedure are sufficient to trigger the innate immune response and also augment adaptive immunity in the presence of foreign antigen on the donor organ. The resulting inflammatory and immune reactions combine to form a potent effector response that can lead to graft rejection. Here we examine the evidence that the complement and toll-like receptor systems are central to these pathways of injury and present a formidable barrier to transplantation. We review extensive information about the effector mechanisms that are mediated by these pathways, and bring together what is known about the damage-associated molecular patterns that initiate this sequence of events. Finally, we refer to two ongoing therapeutic trials that are evaluating the validity of these concepts in man.

Which pathways trigger the role of complement in ischaemia/reperfusion injury?

Investigations into the role of complement in ischemia/reperfusion (I/R) injury have identified common effector mechanisms that depend on the production of C5a and C5b-9 through the cleavage of C3. These studies have also defined an important role for C3 synthesized within ischemic kidney. Less clear however is the mechanism of complement activation that leads to the cleavage of C3 in ischemic tissues and to what extent the potential trigger mechanisms are organ dependent - an important question which informs the development of therapies that are more selective in their ability to limit the injury, yet preserve the other functions of complement where possible. Here we consider recent evidence for each of the three major pathways of complement activation (classical, lectin, and alternative) as mediators of I/R injury, and in particular highlight the role of lectin molecules that increasingly seem to underpin the injury in different organ models and in addition reveal unusual routes of complement activation that contribute to organ damage.

C3a and C5a promote renal ischemia-reperfusion injury

Renal ischemia reperfusion injury triggers complement activation, but whether and how the small proinflammatory fragments C3a and C5a contribute to the pathogenesis of this injury remains to be elucidated. Using C3aR-, C5aR-, or C3aR/C5aR-deficient mice and models of renal ischemia-reperfusion injury, we found that deficiency of either or both of these receptors protected mice from injury, but the C3aR/C5aR- and C5aR-deficient mice were most protected. Protection from injury was associated with less cellular infiltration and lower mRNA levels of kidney injury molecule-1, proinflammatory mediators, and adhesion molecules in postischemic kidneys. Furthermore, chimera studies showed that the absence of C3aR and C5aR on renal tubular epithelial cells or circulating leukocytes attenuated renal ischemia-reperfusion injury. In vitro, C3a and C5a stimulation induced inflammatory mediators from both renal tubular epithelial cells and macrophages after hypoxia/reoxygenation. In conclusion, although both C3a and C5a contribute to renal ischemia-reperfusion injury, the pathogenic role of C5a in this injury predominates. These data also suggest that expression of C3aR and C5aR on both renal and circulating leukocytes contributes to the pathogenesis of renal ischemia-reperfusion injury.

Common genetic variants in complement genes other than CFH, CD46 and the CFHRs are not associated with aHUS

It is well established that common genetic variants in CFH, CD46 and the CFHRs are additional risk factors for the development of aHUS. To examine the hypothesis that common variants in other complement genes have a similar effect we genotyped 501 SNPs in 47 complement genes in 94 aHUS patients from Newcastle, 126 aHUS patients from Paris, 374 UK controls and 165 French controls. We replicated the associations in CFH, CD46 and the CFHRs but found no association with any other complement gene. The strongest associations replicated in both cohorts were found for four SNPs within CD46 (p-value<10(-3)) and five SNPs within CFH (p-value<5×10(-3)). Significant replicable associations with single SNPs in CFHR2, CFHR4 and an intergenic SNP (CR1-CD46) were also found. Analysis of the Paris cohort showed that the association with CD46 SNPs was only present in those patients with complement mutations. Haplotype analysis showed at-risk and protective haplotypes in both CD46 and CFH. The CD46 haplotype was only disease-associated in those patients with mutations.

Inhibition of TLR2 promotes graft function in a murine model of renal transplant ischemia-reperfusion injury

Toll-like receptors (TLRs) are important molecules involved in the activation of innate and subsequent development of adaptive immunity. TLRs are ligated by exogenous ligands from pathogens and by endogenous ligands released in inflammatory diseases. Activation of TLR leads to activation of NF-κB and release of proinflammatory cytokines, such as IL-6 and TNF-α. TLRs play an important role in the pathogenesis of renal diseases. Increased expression of TLRs have been associated with ischemic kidney damage, acute kidney injury, end-stage renal failure, acute renal transplant rejection, and delayed allograft function. OPN301 is a mouse anti-human TLR2 antibody that cross-reacts with mouse TLR2. We show that inhibition of TLR2 promotes graft function in an isograft model of renal transplantation. Recipient mice were treated intravenously with OPN301 before reperfusion of the transplanted kidney that had been subjected to 30 min of cold ischemia. After 5 d, the residual native kidney was removed, and renal transplant function was assessed 24 h later by measurement of blood urea nitrogen. Renal function in both saline- and isotype-treated mice was similar, with significant improvement in OPN301-treated mice (isotype-treated vs. OPN301-treated: 33.9±3.2 vs. 19.8±1.9 μM; P<0.01). The histopathological appearance corresponded with renal functional results. In OPN301-treated recipients, renal structure was well preserved, whereas in the saline-treated group, tubular injury was severe, with marked tubular thinning, epithelial shedding, cast formation and necrosis. Inhibition of TLR2 also leads to a decrease in C3d deposition, although it is unclear whether this is due directly to TLR2 inhibition or a decrease in renal inflammation. This study shows that inhibition of TLR2 with a therapeutic agent (OPN301) provides significant protection from ischemia/reperfusion injury in a model of kidney transplantation.

Functional modulation of human monocytes derived DCs by anaphylatoxins C3a and C5a

Anaphylatoxins C3a and C5a are important modulators for dendritic cell activation and function in mice. In order to verify the significance of these observations in man, we have investigated the functional modulation of human monocytes derived DCs by C3a and C5a. Here we report that engagement of C3aR or C5aR on human monocytes derived DCs (moDCs) enhances the cell activation and their capacity for allostimulation. In addition, we show that intracellular production of cAMP is reduced and PI3K/AKT, ERK and NF-κB signalling is increased following stimulation with C3a or C5a, identifying intracellular signalling pathways that could convert cell surface C3aR and C5aR engagement into changes in moDC functions. Our data provide evidence that human DCs are equipped to react to C3a/C5a and undergo phenotypic change as well as functional modulation. Complement offers a potential route to modulate human DC function and regulate T cell mediated immunity.

Coexpression of donor peptide/recipient MHC complex and intact donor MHC: evidence for a link between the direct and indirect pathways

T lymphocytes recognize foreign antigens presented by donor or recipient cells through the direct and indirect pathways respectively. This raises the question of how directly and indirectly activated T cells interact. A 4-cell model involving the interaction of CD4(+) and CD8(+) T cells recognizing major histocompatibility complex (MHC) class II on recipient antigen presenting cell (APC), and MHC class I on donor APC, has been proposed. However, this would require complex co-ordination between all the participating cell types. The semidirect pathway of alloantigen presentation suggests a simpler mechanism. Although exchange of MHC class II molecules between donor and recipient cells has been described, coexpression of recipient MHC molecules presenting donor derived allopeptides (indirect presentation) and donor MHC (direct presentation) on the same cell, a key requirement for the semidirect alloantigen presentation pathway, has not been demonstrated. We have used a mouse transplantation model to demonstrate the presence of cells expressing both donor MHC class I/II molecules, and a donor MHC class II peptide in the context of a recipient MHC class II molecule. This would allow indirectly activated CD4(+) T cells to regulate directly activated CD4(+) T cells, or to help directly activated CD8(+) T cells, thus providing physical evidence for the semidirect pathway.

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.

Deficiency of C5aR prolongs renal allograft survival

Interaction between C5a, a product of complement activation, and its receptor (C5aR) upregulates antigen-specific T cell responses by modulating the activation of antigen-presenting cells and T cells. Whether this C5a-C5aR interaction contributes to the immune responses that promote renal allograft rejection is unknown. Here, we found that deficiency of C5aR in both graft and recipient reduced allospecific T cell responses and prolonged renal allograft survival. In addition, lack of C5aR impaired the function of donor and recipient antigen-presenting cells and inhibited the response of recipient T cells to allostimulation. Furthermore, deficiency of C5aR in both graft and recipient reduced early inflammation in the grafts, with less cellular infiltration around the vessels and fewer F4/80 positive cells in the peritubular interstitium. These data demonstrate that C5aR is critical for a full adaptive immune response and mediates renal allograft rejection. Engagement of C5aR on dendritic cells and T cells modulates their function, enhancing allospecific T cell responses that lead to allograft rejection. Targeting C5a signaling may have therapeutic potential for T cell-mediated graft rejection.

Toll-like receptor 4 stimulation triggers crescentic glomerulonephritis by multiple mechanisms including a direct effect on renal cells

A role for toll-like receptor 4 (TLR4) has been suggested in previous studies of glomerulonephritis, but the complex integration of these effects has not been explored. To separate effects on the innate and adaptive immune responses, we use the autologous nephrotoxic nephritis model with two disease induction protocols. First, we give a TLR4 ligand at the time of immunization and show the effects are mediated via TLR4 by comparing wild-type and TLR4-deficient mice. In wild-type mice histological measures of disease and serum creatinine are all at least twice as high as TLR4-deficient mice, due to an enhanced immune response to the nephritogenic sheep IgG. Second, we stimulate TLR4 later in the course of disease development and construct four groups of bone marrow chimeric or sham chimeric mice to study the role of TLR4 on bone marrow or renal cells. The most striking finding is that renal cell TLR4 stimulation increases glomerular crescent formation, with a mean of 21% and 25% in the two groups of mice with renal cell TLR4 compared with 0.1% and 0.6% in the two groups without, with differences mirrored by changes in serum creatinine. These findings, in a single disease model, illustrate that TLR4 stimulation triggers crescentic glomerulonephritis by effects on both the adaptive and innate immune response, with a crucial direct effect on renal cells.

Pivotal role of CD4+ T cells in renal fibrosis following ureteric obstruction

Tubulointerstitial fibrosis is a common consequence of a diverse range of kidney diseases that lead to end-stage renal failure. The degree of fibrosis is related to leukocyte infiltration. Here, we determined the role of different T cell populations on renal fibrosis in the well-characterized mouse model of unilateral ureteric obstruction. Depletion of CD4(+) T cells in wild-type mice with a monoclonal antibody significantly reduced the amount of interstitial expansion and collagen deposition after 2 weeks of obstruction. Reconstitution of lymphopenic RAG knockout mice with purified CD4(+) but not CD8(+) T cells, prior to ureteric obstruction, resulted in a significant increase in interstitial expansion and collagen deposition. Wild-type mice had significantly greater interstitial expansion and collagen deposition compared with lymphopenic RAG(-/-) mice, following ureteric obstruction; however, macrophage infiltration was equivalent in all groups. Thus, our results suggest that renal injury with subsequent fibrosis is likely to be a multifactorial process, with different arms of the immune system involved at different stages. In this ureteric obstruction model, we found a critical role for CD4(+) T cells in kidney fibrosis. These cells could be a potential target of therapeutic intervention to prevent excessive fibrosis and loss of function due to renal injury.

Complement fragments C3a and C5a: the salt and pepper of the immune response

The influence of complement on B-cell responses has been known for many years, but the notion that T-cell recognition, expansion and differentiation are complement dependent has only recently gained impetus. DC, and to a lesser extent T cells, produce a range of complement components necessary for complement activation, and these cells also express receptors that detect complement-activation products such as C3a and C5a (anaphylatoxins). In the absence of C3a-receptor (C3aR) signalling, DC lose their capacity to induce potent Th1 responses against alloantigen and also favour the emergence of Treg. A study in this issue of the European Journal of Immunology not only spotlights the importance of C5aR signalling in DC interaction with T cells, but also shows how cooperation with other signalling pathways determines the outcome of T-cell activation. Remove C5aR from the equation, TLR2-stimulated DC induce naive CD4(+) Th cells to undergo differentiation not only mainly to Th17 cells but also to Treg, via a TGF-beta-dependent pathway. Thus, anaphylatoxins in conjunction with other danger signalling pathways modify the function of DC in antigen presentation and help to shape the primary immune response. Future work will need to address the impact of anaphylatoxins on protective immunity in vivo and determine the wider implications of anaphylatoxins for allo- and autoimmunity.

Dendritic cell function in allostimulation is modulated by C5aR signaling

Regulation of T cell immunity by C5a has been suggested from recent studies. However, the underlying mechanisms, particularly the involved cells and biochemical basis, are not well defined. In this study, the direct modulation of dendritic cell (DC) activation and its function in T cell stimulation by C5a-C5aR interaction and the involved signaling pathways were investigated. We show that DCs from C5aR(-/-) mice and normal DCs treated with C5aR antagonist have less-activated phenotype characterized with increased IL-10 and decreased IL-12p70 production in response to LPS stimulation, lowered surface expression of MHC class II, B7.2, and consequently have reduced capacity to stimulate allospecific T cells. Conversely, C5a stimulation up-regulates DC activation and its function in allostimulation. Furthermore, stimulation of C5aR mediates the inhibition of cAMP production and protein kinase A activity and is involved in activation of PI3K/AKT and NF-kappaB signaling in DCs. These results demonstrate that C5a acts directly on C5aR expressed on DCs resulting in the cell activation and subsequently enhances its capacity for allospecific T cell stimulation. It also suggests that NF-kappaB signaling induced by down-regulation of cAMP/ protein kinase A pathway and up-regulation of PI3K/AKT pathway following C5a stimulation may contribute to up-regulation of DC function.

The role of anaphylatoxins C3a and C5a in regulating innate and adaptive immune responses

C3a and C5a, the small (approximately 10KDa) cleavage fragments released by complement activation, are potent mediators of inflammation. They are anaphylatoxins and act as cell activators with nanomolar affinity, exerting their functions through binding to specific receptors (C3aR and C5aR or C5L2 respectively). Recent studies suggest that locally generated complement effector molecules including C3a and C5a contribute to pathological processes in inflammatory and immunological diseases as well as adaptive immune response besides its host defence mechanism. Targeting the receptors and/or their ligands can reduce undesired inflammatory responses and tissue damage in certain pathological conditions. In this article we describe the recent developments in this important area and focus on the role of C3a/C5a in inflammatory and autoimmune diseases and in adaptive immune responses.

Synergy between type 1 fimbriae expression and C3 opsonisation increases internalisation of E. coli by human tubular epithelial cells

BACKGROUND

Bacterial infection of the urinary tract is a common clinical problem with E. coli being the most common urinary pathogen. Bacterial uptake into epithelial cells is increasingly recognised as an important feature of infection. Bacterial virulence factors, especially fimbrial adhesins, have been conclusively shown to promote host cell invasion. Our recent study reported that C3 opsonisation markedly increases the ability of E. coli strain J96 to internalise into human proximal tubular epithelial cells via CD46, a complement regulatory protein expressed on host cell membrane. In this study, we further assessed whether C3-dependent internalisation by human tubular epithelial cells is a general feature of uropathogenic E. coli and investigated features of the bacterial phenotype that may account for any heterogeneity.

RESULTS

In 31 clinical isolates of E. coli tested, C3-dependent internalisation was evident in 10 isolates. Type 1 fimbriae mediated-binding is essential for C3-dependent internalisation as shown by phenotypic association, type 1 fimbrial blockade with soluble ligand (mannose) and by assessment of a type 1 fimbrial mutant.

CONCLUSION

we propose that efficient internalisation of uropathogenic E. coli by the human urinary tract depends on co-operation between type 1 fimbriae-mediated adhesion and C3 receptor -ligand interaction.

Fc gamma RIII and Fc gamma RIV are indispensable for acute glomerular inflammation induced by switch variant monoclonal antibodies

The relative ability of IgG subclasses to cause acute inflammation and the roles of specific effector mechanisms in this process are not clear. We explored this in an in vivo model of glomerular inflammation in the mouse. Trinitrophenol was planted on the glomerular basement membrane after conjugation to nephrotoxic Ab. The relative nephritogenicity of anti-trinitrophenol switch variant mAbs was then explored and shown to be IgG2a > IgG2b, with no disease caused by IgG1. Using knockout mice, we showed that FcgammaRIII was necessary for both neutrophil influx and glomerular damage induced by IgG2a and IgG2b. Surprisingly, IgG1 did not cause disease although it binds to FcgammaRIII. Using blocking Abs, we showed that this was explained by an additional requirement for FcgammaRIV, which does not bind to IgG1. IgG2a- or IgG2b-induced neutrophil influx was not affected by deficiency of either FcgammaRI or C3. Bone marrow chimeras were constructed to test the effect of combined deficiency of FcgammaRI and C3, and there was no effect on IgG2a- or IgG2b-mediated neutrophil influx. However, IgG2b-induced albuminuria and thrombosis were reduced in C3-deficient mice, showing an additional role for complement in IgG2b-mediated glomerular damage. The results show that IgG2a and IgG2b are the pathogenic subclasses in acute neutrophil-mediated glomerular inflammation, with an indispensable role for both FcgammaRIII and FcgammaRIV. Additionally, complement contributes to IgG2b-induced glomerular injury.