Increased Autoreactivity of the Complement-Activating Molecule Mannan-Binding Lectin in a Type 1 Diabetes Model

Mannan-Binding Lectin Is Associated with Inflammation and Kidney Damage in a Mouse Model of Type 2 Diabetes

Autoreactivity of the complement system may escalate the development of diabetic nephropathy. We used the BTBR OB mouse model of type 2 diabetes to investigate the role of the complement factor mannan-binding lectin (MBL) in diabetic nephropathy. Female BTBR OB mice (n = 30) and BTBR non-diabetic WT mice (n = 30) were included. Plasma samples (weeks 12 and 21) and urine samples (week 19) were analyzed for MBL, C3, C3-fragments, SAA3, and markers for renal function. Renal tissue sections were analyzed for fibrosis, inflammation, and complement deposition. The renal cortex was analyzed for gene expression (complement, inflammation, and fibrosis), and isolated glomerular cells were investigated for MBL protein. Human vascular endothelial cells cultured under normo- and hyperglycemic conditions were analyzed by flow cytometry. We found that the OB mice had elevated plasma and urine concentrations of MBL-C (p < 0.0001 and p < 0.001, respectively) and higher plasma C3 levels (p < 0.001) compared to WT mice. Renal cryosections from OB mice showed increased MBL-C and C4 deposition in the glomeruli and increased macrophage infiltration (p = 0.002). Isolated glomeruli revealed significantly higher MBL protein levels (p < 0.001) compared to the OB and WT mice, and no renal MBL expression was detected. We report that chronic inflammation plays an important role in the development of DN through the binding of MBL to hyperglycemia-exposed renal cells.

The role of innate immunity in diabetic nephropathy and their therapeutic consequences

Diabetic nephropathy (DN) is an enduring condition that leads to inflammation and affects a substantial number of individuals with diabetes worldwide. A gradual reduction in glomerular filtration and emergence of proteins in the urine are typical aspects of DN, ultimately resulting in renal failure. Mounting evidence suggests that immunological and inflammatory factors are crucial for the development of DN. Therefore, the activation of innate immunity by resident renal and immune cells is critical for initiating and perpetuating inflammation. Toll-like receptors (TLRs) are an important group of receptors that identify patterns and activate immune responses and inflammation. Meanwhile, inflammatory responses in the liver, pancreatic islets, and kidneys involve inflammasomes and chemokines that generate pro-inflammatory cytokines. Moreover, the activation of the complement cascade can be triggered by glycated proteins. This review highlights recent findings elucidating how the innate immune system contributes to tissue fibrosis and organ dysfunction, ultimately leading to renal failure. This review also discusses innovative approaches that can be utilized to modulate the innate immune responses in DN for therapeutic purposes.

The Complement Pathway: New Insights into Immunometabolic Signaling in Diabetic Kidney Disease

Significance: The metabolic disorder, diabetes mellitus, results in microvascular complications, including diabetic kidney disease (DKD), which is partly believe to involve disrupted energy generation in the kidney, leading to injury that is characterized by inflammation and fibrosis. An increasing body of evidence indicates that the innate immune complement system is involved in the pathogenesis of DKD; however, the precise mechanisms remain unclear. Recent Advances: Complement, traditionally thought of as the prime line of defense against microbial intrusion, has recently been recognized to regulate immunometabolism. Studies have shown that the complement activation products, Complement C5a and C3a, which are potent pro-inflammatory mediators, can mediate an array of metabolic responses in the kidney in the diabetic setting, including altered fuel utilization, disrupted mitochondrial respiratory function, and reactive oxygen species generation. In diabetes, the lectin pathway is activated via autoreactivity toward altered self-surfaces known as danger-associated molecular patterns, or via sensing altered carbohydrate and acetylation signatures. In addition, endogenous complement inhibitors can be glycated, whereas diet-derived glycated proteins can themselves promote complement activation, worsening DKD, and lending support for environmental influences as an additional avenue for propagating complement-induced inflammation and kidney injury. Critical Issues: Recent evidence indicates that conventional renoprotective agents used in DKD do not target the complement, leaving this web of inflammatory stimuli intact. Future Directions: Future studies should focus on the development of novel pharmacological agents that target the complement pathway to alleviate inflammation, oxidative stress, and kidney fibrosis, thereby reducing the burden of microvascular diseases in diabetes. Antioxid. Redox Signal. 37, 781-801.

The Complement System in Metabolic-Associated Kidney Diseases

Metabolic syndrome (MS) is a group of clinical abnormalities characterized by central or abdominal obesity, hypertension, hyperuricemia, and metabolic disorders of glucose or lipid. Currently, the prevalence of MS is estimated about 25% in general population and is progressively increasing, which has become a challenging public health burden. Long-term metabolic disorders can activate the immune system and trigger a low-grade chronic inflammation named “metaflammation.” As an important organ involved in metabolism, the kidney is inevitably attacked by immunity disequilibrium and “metaflammation.” Recently, accumulating studies have suggested that the complement system, the most important and fundamental component of innate immune responses, is actively involved in the development of metabolic kidney diseases. In this review, we updated and summarized the different pathways through which the complement system is activated in a series of metabolic disturbances and the mechanisms on how complement mediate immune cell activation and infiltration, renal parenchymal cell damage, and the deterioration of renal function provide potential new biomarkers and therapeutic options for metabolic kidney diseases.

Mannose-binding lectin activates the nuclear factor-κB and renal inflammation in the progression of diabetic nephropathy

Increased serum mannose-binding lectin (MBL) level has been proven to correlate with the development of diabetic nephropathy (DN). Here, we aim to find the role and mechanism of MBL involved in the progression of DN. Patients with DN were recruited and divided into two groups according to different rs1800450 genotypes of the MBL2 gene, and inflammatory profiles in monocytes/macrophages were compared between the two groups. MBL was given to treat macrophages, HK2, and HMC, and a co-culture transwell system was then employed. Renal inflammation and fibrosis parameters were measured after knocking down or overexpressing MBL genes in mice. Proinflammatory profile, manifesting as enhanced IL-1β production and M1 polarization, was found in monocytes/macrophages from DN with a rs1800450 GG genotype of MBL2 gene who had higher MBL level, compared with those with a rs1800450 GA genotype. In mechanism, MBL directly induced inflammatory responses in macrophages, which promoted inflammatory and fibrotic markers in HK2 and HMCs during co-culture. Further experiments showed that MBL can promote macrophages transforming to the M1 subset mainly by activating the nuclear factor-κB pathway. After downregulation of MBL, the blood glucose, triglyceride, urine protein, injuries of glomerulus and tubules, and the degree of renal inflammation and fibrosis were ameliorated in db/db mice treated with AAV-MBL1/2-shRNA. Overexpression of MBL promoted macrophage infiltration in the kidney. In conclusion, MBL is a crucial mediator in the progression of DN via activating the nuclear factor-κB pathway in macrophages. This will serve as a genetic base for some patients with DN who have poor outcomes and provide a direction for the screening.

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.

The pattern-recognition molecule H-ficolin in relation to diabetic kidney disease, mortality, and cardiovascular events in type 1 diabetes

H-ficolin recognizes patterns on microorganisms and stressed cells and can activate the lectin pathway of the complement system. We aimed to assess H-ficolin in relation to the progression of diabetic kidney disease (DKD), all-cause mortality, diabetes-related mortality, and cardiovascular events. Event rates per 10-unit H-ficolin-increase were compared in an observational follow-up of 2,410 individuals with type 1 diabetes from the FinnDiane Study. DKD progression occurred in 400 individuals. The unadjusted hazard ratio (HR) for progression was 1.29 (1.18–1.40) and 1.16 (1.05–1.29) after adjustment for diabetes duration, sex, HbA_1c, systolic blood pressure, and smoking status. After adding triglycerides to the model, the HR decreased to 1.07 (0.97–1.18). In all, 486 individuals died, including 268 deaths of cardiovascular causes and 192 deaths of complications to diabetes. HRs for all-cause mortality and cardiovascular mortality were 1.13 (1.04–1.22) and 1.05 (0.93–1.17), respectively, in unadjusted analyses. These estimates lost statistical significance in adjusted models. However, the unadjusted HR for diabetes-related mortality was 1.19 (1.05–1.35) and 1.18 (1.02–1.37) with the most stringent adjustment level. Our results, therefore, indicate that H-ficolin predicts diabetes-related mortality, but neither all-cause mortality nor fatal/non-fatal cardiovascular events. Furthermore, H-ficolin is associated with DKD progression, however, not independently of the fully adjusted model.

MALDI-TOF Protein Profiling Reflects Changes in Type 1 Diabetes Patients Depending on the Increased Amount of Adipose Tissue, Poor Control of Diabetes and the Presence of Chronic Complications

Introduction: Protein profiling allows the determination of the presence of proteins marking various stages of the disease, and differentiates between people at risk of various diseases. In type 1 diabetes, protein profiling had been previously used to find blood markers other than islet autoantibodies to indicate the pancreatic beta cell destruction process and to reflect the progression of type 1 diabetes mellitus (T1DM). However, T1DM is an auto-immune disease and its clinical presentation changes in time of its duration. The aim of the study: To find differences in protein profiles in patients with type 1 diabetes according to diabetes control (HbA1c > 7%) and with presence of diabetic complications or obesity. It may help to identify subgroups of patients who may need a better clinical supervision and individualized treatment. Material and methods: A group of 103 patients with auto-immunologically confirmed T1DM, and meeting the following inclusion criteria: Caucasian race, duration of diabetes >5 years, were used in the study. Criteria of exclusion: past or present cancer (treated with chemo-/radiotherapy), diseases of the liver (ALT > 3 × ULN) except for people with simple hepatic steatosis, chronic renal disease (eGFR < 30 mL/1.73 m²/min), and acute inflammation (CRP > 5 mg/dL). The study group was divided in terms of the presence of chronic complications, obesity, or poor metabolic control (HbA1c > 7%). Protein profiling was completed by using the MALDI-TOF MS (matrix-assisted laser desorption/ionization-time of flight mass spectrometry) analyzer. Results: Differentiating proteins were identified in all of the groups. The groups burdened with complications, obesity, and poor metabolic control were characterized by increased levels of fibrinogen, complement C4 and C3. Conclusion: The groups of type 1 diabetes patients burdened with complications, obesity, and poor metabolic control were characterized by increased levels of fibrinogen, complement C4 and C3. Further detailed studies are necessary to determine more subtle changes in the proteomic profile of patients with type 1 diabetes.

Complement, a Therapeutic Target in Diabetic Kidney Disease

Currently available treatments of diabetic kidney disease (DKD) remain limited despite improved understanding of DKD pathophysiology. The complement system is a central part of innate immunity, but its dysregulated activation is detrimental and results in systemic diseases with overt inflammation. Growing evidence suggests complement activation in DKD. With existent drugs and clinical success of treating other kidney diseases, complement inhibition has emerged as a potential novel therapy to halt the progression of DKD. This article will review DKD, the complement system's role in diabetic and non-diabetic disease, and the potential benefits of complement targeting therapies especially for DKD patients.

Role of complement in diabetes

Accumulating evidence suggests a role for the complement system in the pathogenesis of diabetes and the vascular complications that characterise this condition. Complement proteins contribute to the development of type 1 diabetes (T1D) by enhancing the underlying organ-specific autoimmune processes. Complement upregulation and activation is also an important feature of insulin resistance and the development of type 2 diabetes (T2D). Moreover, animal and human studies indicate that complement proteins are involved in the pathogenic mechanisms leading to diabetic microvascular and macrovascular complications. The adverse vascular effects of complement appear to be related to enhancement of the inflammatory process and the predisposition to a thrombotic environment, eventually leading to vascular occlusion. Complement proteins have been considered as therapeutic targets to prevent or treat vascular disease but studies have been mainly conducted in animal models, while human work has been both limited and inconclusive so far. Further studies are needed to understand the potential role of complement proteins as therapeutic targets for reversal of the pathological processes leading to T1D and T2D and for the prevention/treatment of diabetic vascular complications.

High Expression of Complement Components in the Kidneys of Type 2 Diabetic Rats With Diabetic Nephropathy

Background: Diabetic nephropathy (DN) is the leading cause of end-stage failure of the kidneys; however, its pathogenesis remains unknown. This study assessed the expression of complement components in the kidneys of rats with type 2 DN to investigate their role in DN. Methods: A rat model of type 2 DN was induced by a high-fat diet combined with low-dose streptozotocin. Blood glucose, fasting insulin levels, insulin resistance index, and 24-h urinary albumin excretion (UAE) were measured. Renal tissue morphological features were observed. The mesangial index and arteriosclerosis index were calculated. Immunohistochemistry and western blot were used to measure the expression of complement components in the kidneys. Results: The kidney weight: body weight (mg/g) ratio in the DN group was significantly greater than those in the control and diabetes mellitus (DM) groups. The arteriosclerosis index, mesangial index, and tube area percentage in the DN group were significantly higher than those in the control and DM groups, but these parameters did not significantly differ between the control and DM groups. The expression of the complement components C1q, mannose-binding lectin (MBL), mannan-binding lectin-associated serine protease (MASP)-2, B factor, C3, and C5b-9 in the DN group was significantly higher than that in the control and DM groups but did not significantly differ between the control and DM groups. Most of the complement components were mainly expressed at the renal tubular site. Correlation analysis showed that 24-h UAE were positively correlated with C1q, MBL, MASP-2, B factor, and C5b-9 expression. MI was positively correlated with MBL, B factor, C3, and C5b-9 expression. AI was positively correlated with C1q, MBL, MASP-2, and B factor expression. Conclusion: Complement components including C1q, MBL, MASP-2, B factor, C3, and C5b-9, were highly expressed in the kidneys of type 2 diabetic rats with DN. Most of the complement components were mainly expressed in the renal tubules. High expression of complement components was found to be associated with the progress of DN. Our study suggests that complement system activation is a progressive factor in type 2 diabetic nephropathy. Inhibition of pathological complement activation may be a promising therapeutic strategy for DN.

Endothelial heparan sulfate deficiency reduces inflammation and fibrosis in murine diabetic nephropathy

Inflammation plays a vital role in the development of diabetic nephropathy, but the underlying regulatory mechanisms are only partially understood. Our previous studies demonstrated that, during acute inflammation, endothelial heparan sulfate (HS) contributes to the adhesion and transendothelial migration of leukocytes into perivascular tissues by direct interaction with L-selectin and the presentation of bound chemokines. In the current study, we aimed to assess the role of endothelial HS on chronic renal inflammation and fibrosis in a diabetic nephropathy mouse model. To reduce sulfation of HS specifically in the endothelium, we generated Ndst1 ^f/f Tie2Cre ⁺ mice in which N-deacetylase/N-sulfotransferase-1 (Ndst1), the gene that initiates HS sulfation modifications in HS biosynthesis, was expressly ablated in endothelium. To induce diabetes, age-matched male Ndst1 ^f/f Tie2Cre ^- (wild type) and Ndst1 ^f/f Tie2Cre ⁺ mice on a C57Bl/6J background were injected intraperitoneally with streptozotocin (STZ) (50 mg/kg) on five consecutive days (N = 10-11/group). Urine and plasma were collected. Four weeks after diabetes induction the animals were sacrificed and kidneys were analyzed by immunohistochemistry and qRT-PCR. Compared to healthy controls, diabetic Ndst1 ^f/f Tie2Cre ^- mice showed increased glomerular macrophage infiltration, mannose binding lectin complement deposition and glomerulosclerosis, whereas these pathological reactions were prevented significantly in the diabetic Ndst1 ^f/f Tie2Cre ⁺ animals (all three p < 0.01). In addition, the expression of the podocyte damage marker desmin was significantly higher in the Ndst1 ^f/f Tie2Cre ^- group compared to the Ndst1 ^f/f Tie2Cre ⁺ animals (p < 0.001), although both groups had comparable numbers of podocytes. In the cortical tubulo-interstitium, similar analyses show decreased interstitial macrophage accumulation in the diabetic Ndst1 ^f/f Tie2Cre ⁺ animals compared to the diabetic Ndst1 ^f/f Tie2Cre ^- mice (p < 0.05). Diabetic Ndst1 ^f/f Tie2Cre ⁺ animals also showed reduced interstitial fibrosis as evidenced by reduced density of αSMA-positive myofibroblasts (p < 0.01), diminished collagen III deposition (p < 0.001) and reduced mRNA expression of collagen I (p < 0.001) and fibronectin (p < 0.001). Our studies indicate a pivotal role of endothelial HS in the development of renal inflammation and fibrosis in diabetic nephropathy in mice. These results suggest that HS is a possible target for therapy in diabetic nephropathy.

Non-genetic mechanisms of diabetic nephropathy

Diabetic nephropathy (DN) is one of the most common microvascular complications in diabetes mellitus patients and is characterized by thickened glomerular basement membrane, increased extracellular matrix formation, and podocyte loss. These phenomena lead to proteinuria and altered glomerular filtration rate, that is, the rate initially increases but progressively decreases. DN has become the leading cause of end-stage renal disease. Its prevalence shows a rapid growth trend and causes heavy social and economic burden in many countries. However, this disease is multifactorial, and its mechanism is poorly understood due to the complex pathogenesis of DN. In this review, we highlight the new molecular insights about the pathogenesis of DN from the aspects of immune inflammation response, epithelial-mesenchymal transition, apoptosis and mitochondrial damage, epigenetics, and podocyte-endothelial communication. This work offers groundwork for understanding the initiation and progression of DN, as well as provides ideas for developing new prevention and treatment measures.

Diabetic nephropathy - is this an immune disorder?

Chronic diabetes is associated with metabolic and haemodynamic stresses which can facilitate modifications to DNA, proteins and lipids, induce cellular dysfunction and damage, and stimulate inflammatory and fibrotic responses which lead to various types of renal injury. Approximately 30-40% of patients with diabetes develop nephropathy and this renal injury normally progresses in about a third of patients. Due to the growing incidence of diabetes, diabetic nephropathy is now the main cause of end-stage renal disease (ESRD) worldwide. Accumulating evidence from experimental and clinical studies has demonstrated that renal inflammation plays a critical role in determining whether renal injury progresses during diabetes. However, the immune response associated with diabetic nephropathy is considerably different to that seen in autoimmune kidney diseases or in acute kidney injury arising from episodes of ischaemia or infection. This review evaluates the role of the immune system in the development of diabetic nephropathy, including the specific contributions of leucocyte subsets (macrophages, neutrophils, mast cells, T and B lymphocytes), danger-associated molecular patterns (DAMPs), inflammasomes, immunoglobulin and complement. It also examines factors which may influence the development of the immune response, including genetic factors and exposure to other kidney insults. In addition, this review discusses therapies which are currently under development for targeting the immune system in diabetic nephropathy and indicates those which have proceeded into clinical trials.

Incident microalbuminuria and complement factor mannan-binding lectin-associated protein 19 in people with newly diagnosed type 1 diabetes

BACKGROUND

Evidence links the lectin pathway of complement activation to diabetic kidney disease. Upon carbohydrate-recognition by pattern-recognition molecules, eg, mannan-binding lectin (MBL), the MBL-associated serine protease (MASP-2) is activated and initiates the complement cascade. The MASP2 gene encodes MASP-2 and the alternative splice product MBL-associated protein 19 (MAp19). Both MAp19 and MASP-2 circulate in complex with MBL. We tested the hypothesis that MAp19 and MASP-2 concentrations predict the risk of incident microalbuminuria.

METHODS

Baseline MAp19 and MASP-2 were measured in 270 persons with newly diagnosed type 1 diabetes tracked for incidence of persistent microalbuminuria in a prospective observational 18-year-follow-up study.

RESULTS

Seventy-five participants (28%) developed microalbuminuria during follow-up. MBL-associated protein 19 concentrations were higher in participants that later progressed to microalbuminuria as compared with those with persistent normoalbuminuria (268 ng/mL [95% CI, 243-293] vs 236 ng/mL [95% CI, 223-250], P = .02). Participants with MAp19 concentration within the highest quartile of the cohort had an increased risk of microalbuminuria as compared with participants with MAp19 concentration within the combined lower 3 quartiles in unadjusted Cox analysis, hazard ratio 1.86 ([95% CI, 1.17-2.96], P = .009). This remained significant in adjusted models, eg, adjusting for age, sex, HbA_1c , systolic blood pressure, urinary albumin excretion, smoking, serum creatinine, and serum cholesterol. MBL-associated serine protease concentration was not associated with incidence of microalbuminuria.

CONCLUSIONS

In conclusion, the results show an association between baseline MAp19 concentration and the incidence of microalbuminuria in an 18-year-follow-up study on persons with newly diagnosed type 1 diabetes.

Global Autorecognition and Activation of Complement by Mannan-Binding Lectin in a Mouse Model of Type 1 Diabetes

Increasing evidence links mannan-binding lectin (MBL) to late vascular complications of diabetes. MBL is a complement-activating pattern recognition molecule of the innate immune system that can mediate an inflammation response through activation of the lectin pathway. In two recent animal studies, we have shown that autoreactivity of MBL is increased in the kidney in diabetic nephropathy. We hypothesize that long-term exposure to uncontrolled high blood glucose in diabetes may mediate formation of neoepitopes in several tissues and that MBL is able to recognize these structures and thus activate the lectin pathway. To test this hypothesis, we induced diabetes by injection of low-dose streptozotocin in MBL double-knockout (MBL/DKO) mice. Development of diabetes was followed by measurements of blood glucose and urine albumin-to-creatinine ratio. Fluorophore-labelled recombinant MBL was injected intravenously in diabetic and nondiabetic mice followed by ex vivo imaging of several organs. We observed that MBL accumulated in the heart, liver, brain, lung, pancreas, and intestines of diabetic mice. We furthermore detected increased systemic complement activation after administration of MBL, thus indicating MBL-mediated systemic complement activation in these animals. These new findings indicate a global role of MBL during late diabetes-mediated vascular complications in various tissues.

The role of the complement system in diabetic nephropathy

The development of type 1 and type 2 diabetes mellitus has a substantial negative impact on morbidity and mortality and is responsible for substantial individual and socioeconomic costs worldwide. One of the most serious consequences of diabetes mellitus is the development of diabetic angiopathy, which manifests clinically as microvascular and macrovascular complications. One microvascular complication, diabetic nephropathy, is the most common cause of end-stage renal disease in developed countries. Although several available therapeutic interventions can delay the onset and progression of diabetic nephropathy, morbidity associated with this disease remains high and new therapeutic approaches are needed. In addition, not all patients with diabetes mellitus will develop diabetic nephropathy and thus new biomarkers are needed to identify individuals who will develop this life-threatening disease. An increasing body of evidence points toward a role of the complement system in the pathogenesis of diabetic nephropathy. For example, circulating levels of mannose-binding lectin (MBL), a pattern recognition molecule of the innate immune system, have emerged as a robust biomarker for the development and progression of this disease, and evidence suggests that MBL, H-ficolin, complement component C3 and the membrane attack complex might contribute to renal injury in the hyperglycaemic mileu. New approaches to modulate the complement system might lead to the development of new agents to prevent or slow the progression of diabetic nephropathy.

Diabetes Is Associated with Increased Autoreactivity of Mannan-Binding Lectin

Mannan-binding lectin (MBL) has been reported to be involved in the pathophysiology of diabetic nephropathy. MBL is a pattern-recognition molecule of the innate immune system that initiates the lectin pathway of the complement system upon recognition of evolutionary conserved pathogen-associated molecular patterns or to altered self-tissue. Our group have previously shown direct effects of MBL on diabetes-induced kidney damage, and we hypothesized that MBL may cause autoactivation of the complement system via binding to neoepitopes induced by hyperglycemia. In the present study, we induced diabetes in MBL knockout mice and in wild type C57BL/6J mice by low-dose streptozotocin injection and measured blood glucose and urine albumin-to-creatinine ratio to monitor development of diabetes. After 24 weeks, fluorescently labelled recombinant MBL was injected intravenously in diabetic MBL knockout mice after which the distribution was investigated using in vivo fluorescence imaging. Mice were subjected to in vivo and ex vivo imaging 24 hours after injection. MBL was found to accumulate in the kidneys of diabetic mice as compared to healthy control mice (p < 0.0001). These findings support the hypothesis of a significant role of MBL and the complement system in the pathophysiology of diabetic nephropathy.