Activation Of Complement System Research Articles

Podocyte Pathogenic Bone Morphogenetic Protein-2 Pathway and Immune Cell Behaviors in Primary Membranous Nephropathy.

Primary membranous nephropathy (PMN) is one of the leading causes of end-stage renal disease, and the most frequent cause of massive proteinuria in nondiabetic adults, resulting in fatal complications. However, the underlying pathomechanisms of PMN remain largely unclear. Here, single-cell RNA sequencing is employed to analyze kidney biopsies from eleven PMN patients and seven healthy subjects. Profiling 44060 cells from patients allowed us to characterize the cellular composition and cell-type-specific gene expression in the PMN kidney. The complement-induced BMP2/pSMAD1/COL4 pathway is identified as the pathogenic pathway in podocytes, bridging two key events, i.e., complement system activation and glomerular basement membrane thickening in PMN. Augmented infiltration and activation of myeloid leukocytes and B lymphocytes are found, profiling delicate crosstalk of immune cells in PMN kidneys. Overall, these results provide valuable insights into the roles of podocytes and immune cells in PMN, and comprehensive resources toward the complete understanding of PMN pathophysiology.

#2000 Analysis between site-specific N-glycosylation of monoclonal immunoglobulin and complement system activation

Abstract Background and Aims Monoclonal immunoglobulin produced by clonal plasma cells is the main cause in multiple myeloma (MM) and monoclonal gammopathy of renal significance (MGRS). Hypocomplementemia and deposition of complement components in the kidney is observed in some patients with MM or MGRS. Previous studies have suggested that glycosylation of the immunoglobulin was associated with complement-mediated-effector activities. Whereas, site-specific N-glycosylation characterization for monoclonal immunoglobulin in MM or MGRS and its effects on complement system activation still remains unclear. Method We separated plasma monoclonal IgG1 and IgA immunoglobulin from patients with MM and human plasma immunoglobulin from healthy controls (HC). Purified IgG and IgA molecules were digested by trypsin. Tryptic peptides without enrichment of intact N-glycopeptides were analyzed using a combination of electron-transfer/higher-energy collisional dissociation (EThcD) and stepped collision energy/higher-energy collisional dissociation (sceHCD) mass spectrometry (EThcD-sceHCD-MS/MS). N-glycosylation characterization was compared between monoclonal immunoglobulin from MM patients and healthy controls and its association with complement level was evaluated. Results A total of 46 IgG1 digestion samples (HC, n = 16; MM, n = 30) and 38 IgA1 digestion samples (HC, n = 16; MM, n = 22) were analyzed using the EThcDsceHCD-MS/MS. On average, 34 and 37 unique N-glycopeptides of IgG1, 19 unique N-glycans per IgG were identified from HC and MM. The relative abundance of fucosylated N-glycans of IgG1 in MM was significantly higher than HC (94.7% vs 88.8%, p = 0.002). Other types of N-glycans including sialylated, hybrid and complex were similar between the two groups. The types of N-glycans including fucosylated, sialylated, hybrid and complex were similar between patients with hypocomplementemia and normal complement levels. Regarding IgA1, on average, 63 and 52 unique N-glycopeptides of IgA1, 40 and 35 unique N-glycans per IgA were identified from HC and MM. The relative abundance of fucosylated (41.0% vs 26.4%, p < 0.001), sialylated (61.0% vs 45.6%, p = 0.003), mannose (2.44% vs 0.28%, p < 0.001) N-glycans of IgA1 in MM was significantly higher than HC. In MM, the relative abundance of mannose N-glycans of IgA1 in patients with hypocomplementemia was significantly lower than patients with normal complement levels (1.69% vs 7.52%, p < 0.001). The relative abundance of fucosylated and sialylated N-glycans were similar between patients with hypocomplementemia and normal complement levels. Conclusion Site-specific N-glycosylation characterization of monoclonal IgG1 and IgA1 in MM patients were differentially expressed from healthy controls. Certain specific N-glycan types were associated with complement levels. These findings laid a foundation for future investigations of their biological effects.

#1486 Looking for a new role of known players: the additional value of plasmatic C3 and C4 in predicting IgA Nephropathy prognosis, an observational study

Abstract Background and Aims IgA Nephropathy (IgAN) is the most common glomerular disease worldwide [1]. Complement system activation through the alternative and lectin pathways is crucial in its pathogenesis and leads to worse outcome, eliciting the need for (new) biomarkers to assess risk of disease progression and potential response to new targeted treatments [2, 3]. Only few works have correlated serum C3 and C4 with disease activity and prognosis [4, 5]. Our work explores the potential advantages of incorporating serum C3 and C4 levels into a standardized prognostic model to assess kidney outcome in IgAN. Method This retrospective study, conducted at Sant'Orsola University Hospital in Bologna, investigated the prognostic value of serum complement C3 and C4 in patients with IgAN. The primary outcome was defined as a 40% decline in eGFR or the onset of kidney failure. The study aimed to evaluate whether the addition of serum C3 and C4 to an established predictive model, incorporating variables from the International IgA Prediction Tool (IntIgAPT), enhances the accuracy of outcome prediction. We computed the measures of goodness of fit for each model: Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC), Nagelkerke R2 test (NR2) that depicts the% explained variation of the outcome based on the set of variables included, and Likelihood Ratio Test (LRT); discrimination with the c-index. Furthermore, we aimed to evaluate the characteristics of patients stratified by baseline serum C3 levels (Low <90 mg/dl, Medium 90-140 mg/dl, High >140 mg/dl). Results 101 patients were included in the cohort. 90% were Caucasian and 65.3% were male with a mean age of 42.6 years. As reported in Table 1, mean eGFR and median proteinuria levels at baseline were 70.4 ml/min/1.73 m² and 1.04 g/24 h respectively. Mean serum C3 was 114.9 mg/dL. The Low group had lower values of eGFR at baseline (47.0 vs 75.67 and 68.64 ml/min/1.73 m², p = 0.015), while the Medium group had lower values of uProt (0.75 vs 1.81 and 1.46 g/24 h, p = 0.004). During a median 54.28 months follow-up, the Low group exhibited significantly higher primary outcome incidence (16.3 events vs 2.9 and 1.7 events x 100 pts/year, p = 0.003). We computed a first model (M1) based upon IntIgAPT variables and then a second model (M2) as the same of M1 plus serum C3 and C4 at baseline (Table 2). C3 showed a negative association with outcome (OR 0.88, CI 0.78 to 0.99, p = 0.05) whereas C4 had a positive one (OR 1.21, CI 1.02 to 1.48, p = 0.05). M2 had an improved prediction accuracy than M1, as evidenced by lower AIC (49.1 vs 53.8), higher c-index (0.74 vs 0.65), and NR2 (0.76 vs 0.65). Likelihood ratio test was significant between the two (p = 0.008). Conclusion The inclusion of serum C3 and C4 in a validated prognostic model enhances prediction accuracy and improves the percentage of events explained, highlighting complement's inherent informativeness. In our population lower C3 and higher C4 levels were associated with poorer prognosis in IgAN, characterizing a more ‘Complement-Pathic’ subset of patients. This result expands the current evidence, for the first time to our knowledge, in a Caucasian-prevalent study population.

#2866 The CompAct-HD trial reports a persistent inflammatory profile in patients undergoing haemodialysis, acutely exacerbated with each treatment

Abstract Background and Aims Inflammation induced by haemodialysis (HD) treatment has been recognised for several decades. Despite significant advances in technology, there is evidence that incompatibility between the dialyser, a foreign surface, and the patients’ blood, results in activation of the immune system. With each session, blood-membrane interaction leads to a repetitive activation of the innate complement system and a subsequent inflammatory response. It is now widely acknowledged that the consequences of long-term inflammation include fibrosis and accelerated cardiovascular disease, a common cause of mortality in patients with renal failure. The aim of the CompAct-HD trial is to characterize complement activation and biomarker response to blood-membrane-circuit interaction during HD. Method For a single session, six timed intradialytic blood samples were collected from HD patients during standard treatment with ultrapure water and high flux “biocompatible” membranes. Complement activity potential was determined from timepoint 1 and inflammatory biomarkers from timepoints 2 to 6. Single time point samples were also collected from 7 healthy donors. Highly multiplexed assays enabled to determine 30 biomarkers of inflammation, including cytokines, chemokines, growth factors and complement proteins, from a single blood sample. Data analysis was performed using Microsoft® Excel Version 16.80 and GraphPad Prism 10.1.0. Results 354 patients were recruited from 8 dialysis units across Greater Manchester, UK. An interim analysis was performed on 150 HD patients receiving standard care as well as 7 healthy donors. Dialysis appears to generate an acute inflammatory response, that is, within 15 minutes of commencing treatment which does not appear to resolve by the end of the session. This heightened inflammatory state was observed in HD patients in comparison to healthy donors (Fig. 1) with most pronounced changes seen in cytokines IL-1β, IL-10, IL-12p40 and TNF-α during dialysis. Established markers such as IL-6 also showed a 6-fold increase at the 75th percentile. Similarly, an exaggerated intradialytic response was observed in complement proteins, including the terminal complement complex (TCC) C5b-9 and anaphylatoxin C5a with spikes of up to 7-fold and 10-fold respectively (Fig. 2). A session of HD was shown to cause a relative increase in complement proteins and inflammatory biomarkers. The magnitude of response seen in patients was variable (Fig. 3) with the greatest rise seen in the top quartile (above the Q3 boundary). Conclusion Our findings evidence a sharp inflammatory response to modern day HD treatment across a large cohort of dialysis patients. When compared to healthy donors, we observed heightened levels of inflammation in dialysis patients that is further exacerbated with each treatment session. This study shows that HD has a significant role to play in the chronic inflammatory state of patients with end stage renal failure. Furthermore, here we describe potential targets, in both cytokine and complement proteins, which could be the key to downregulation of inflammation. Using targeted therapeutics, we have an opportunity to deliver a more biocompatible treatment, improving patient outcomes.

#1360 SARS-COV-2 protein in renal tissue enhanced activation of complement system in MN patients with COVID-19 infection

Abstract Background and Aims Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults. Complement plays an important role in the pathogenesis of MN. COVID-19 infection has been reported to be associated with the occurrence and recurrence of MN. Only few kidney biopsies from COVID-19 patients demonstrate the presence of SARS-CoV-2 in the tissue. The clinical and pathological characteristics and complement system activation of patients with SARS-COV2 in renal tissue are unclear, needing to further study. Method From December 2022 to June 2023, patients with renal biopsy-proven MN at Beijing Anzhen hospital who had experienced COVID-19 infection before proteinuria onset and renal biopsy were enrolled. One hundred patients with primary MN diagnosed from December 2018 to June 2019 (with no COVID-19) were enrolled as control. Patient medical records were reviewed for clinical and pathological data. We performed immunofluorescence and in situ hybridization assays for detection of the SARS-COV2. Glomerular staining for factor H, FHR-5 and MAC were detected by immunohistochemical. Serum C5b-9 were detected by enzyme-linked immunosorbent assay. Clinicopathological and immunological features between MN patients with and without SARS-COV2 infection were analyzed. Results A total of 38 MN patients was proteinuria onset after COVID-19 infection, including 11 patients had SARS-COV protein positive staining along capillary loops in glomerular deposits or in cytoplasm of tubular epithelial cells. The immunofluorescence result shows strong colocalization of SARS-COV2 and IgG, which suggests that SARS-COV protein participated in the formation of immune complex. Compared with primary MN patients, the serum albumin level of 38 MN patients with COVID-19 infection were lower (p = 0.011). However, the clinical manifestations of 11 MN patients with SARS-COV2 renal positive staining were obviously serous. Compared with primary MN patients, urinary protein and serum creatine levels significantly increased (p = 0.027 and p = 0.005), while serum albumin levels decreased (p = 0.014) and the proportion of nephrotic syndrome (p = 0.037) was higher. There was no significant difference in pathological manifestations between MN patients with or without COVID-19 infection. In follow-up, the proportion of patients with urinary protein decreased greater than 50% in MN patients with COVID-19 infection was lower than that in primary MN patients. of urinary protein level Serum level of complement C3 (p = 0.007) and MAC (P = 0.001) in MN patients with COVID-19 infection was significantly higher than that of primary MN patients, especially MN patients with renal tissue positive staining of SARS-COV2 protein (p = 0.002 and p = 0.007). In 38 MN patients with COVID-19 infection, compared with patients with renal tissue negative for SARS-COV2 protein, patients with renal tissue positive for SARS-COV2 protein presented with stronger intensity of MAC deposition (p = 0.023) and factor H deposition (p = 0.002). Conclusion The clinical manifestation of MN patients who was onset after COVID-19 infection with renal tissue positive for SARS-COV2 protein were not only significantly worse than those of primary MN patients, but also worse than patients without tissue SARS-COV2 positive MN patients. We speculate that the reason is the enhanced activation of the complement system in renal tissue.

#1643 Long-term cohort study on the prognostic impact of mesangial IgM deposition in IgA nephropathy

Abstract Background and Aims The prognostic importance of mesangial immunoglobulin (Ig) M deposition in IgA nephropathy (IgAN) is not well-understood and is subject to ongoing debate. Moreover, mesangial IgM deposition could also reflect lectin complement system activation. Thus, our study sought to examine the long-term prognostic implications of mesangial IgM deposition in a cohort of IgAN patients. Method We carried out a single-center retrospective study involving 93 consecutive IgAN patients (median age 41 years, 68% male, eGFR 48.7 mL/min, proteinuria 1.1 g/g) from 2010 to 2015. The follow-up period extended until the onset of end-stage kidney disease (ESKD), death, or January 2021, with a median duration of 7 years. An independent pathologist assessed the IgM immunofluorescence pattern, Oxford MEST-C score, and transmission electron microscopy (TEM) lesions using a detailed protocol. Results In our study, 70% (n = 65) of patients exhibited mesangial IgM-positive deposits, while 30% (n = 28) did not show IgM deposition. Both IgM-positive and IgM-negative groups were comparable in terms of age (40 vs 43 years, p 0.6), sex (69 vs 64% male, p 0.6), arterial hypertension prevalence (69 vs 64%, p 0.6), Charlson comorbidity scores (2 vs 1, p 0.3), kidney function (eGFR 46 vs 55 mL/min, p 0.1 and proteinuria 1.2 vs 0.7, p 0.1), pathology findings (including Oxford MEST-C score, IgG and C3 immune deposition), TEM analysis, as well as in their treatment with renin-angiotensin-system inhibitors (63 vs 71%, p 0.4) and immunosuppression (39 vs 39%, p 0.9), and mortality rates (11 vs 7%, p 0.5). However, a notable difference emerged in the progression to ESKD, with 37% of IgM-positive patients advancing to this stage compared to only 11% of those in the IgM-negative group (p 0.01). The multivariate Cox proportional hazards regression analysis identified lower eGFR (HR 0.94, 95% CI: 0.92, 0.97), higher Oxford MEST-C score (HR 1.53, 95% CI: 1.16, 2.02), and mesangial IgM deposits (HR 4.75, 95% CI: 1.25, 17.99) as independent predictors of reduced kidney survival. Conclusion Our study identifies mesangial IgM deposition as a potential risk factor for ESKD in advanced IgAN, suggesting a need for further investigation. Future research should explore whether IgM's activation of the lectin complement pathway and resultant damage, as proven in ischemia-reperfusion injury models, are applicable to IgAN.

#2890 Role of alternative pathway of complement system in membranous nephropathy: a study from STARMEN clinical trials

Abstract Background and Aims Membranous nephropathy (MN) is an antibody-mediated autoimmune disease characterized by glomerular immune complexes containing complement components. A recent animal model of PLA2r antibody-induced MN induced has demonstrated the crucial role of complement pathway, although is still unclear which complement pathway is most involved in its pathogenesis This study aimed to explore the role of alternative pathway of complement cascade in a cohort of patients from STARMEN clinical trial. Method We analyzed longitudinal plasma samples from 51 patients from STARMENT cohort stored in a biobank. Samples were stored at enrollment and longitudinally throughout the follow up at 3, 6, 9, 12, 18 and 24 months. We measured the circulating plasma levels of C3, FB, FH, FHR1, FHR2 and FHR5 in every time. Results Fifty-two patients with a mean age of 56 ± 10 years and 60% male were included. 44% were treated with tacrolimus+Rituximab and 56% with ponticelli regimen. The basal creatinine was 0.9 ± 0.3 mg/dl, median proteinuria/day was 8.8 g/day (IQR 5.7-11.6 gr/day) and serum albumin of 2.6 g/dl (IQR 2.3-2.9 g/dl). All patients were followed-up for two years. Thirty-four patients achieved complete remission (CR), 11 patients partial remission (PR) and 15 did not respond (including relapse). During active disease, the mean concentration of FH, FHR-1 and FHR-2 were significantly increased compared with remission status (complete or partial). We did not find different in other factors: FB or FHR-5. Moreover, a positive correlation was observed between FH and FB with C3. There were no differences according to treatment arm. PLA2r antibodies tested positive in 68%. The median of baseline anti-PLA2R title levels was 80 RU/ml (IQR 43-141). Circulating plasma levels of FHR1 at baseline were significantly higher in PLA2r testing negative vs positive patients (199 ± 108 vs 249 ± 41 µg/ml, p = 0.021). This significant difference was present when remission was achieved (205 ± 97 vs 264 ± 49 µg/ml, p = 0.023). Similar tendency was observed for FB. Conclusion These data provide evidence of complement system activation through the alternative pathway in membranous nephropathy. We know that different subtypes of IgG are behind the different antibodies-induced MN induced, and that every subtype active different complement pathway. The results of this study lead to speculate that not all the antigens that induced MN active complement pathway in the same way.

#2555 C4d—a novel predictor of the disease progression and treatment failure in primary focal segmental glomerulosclerosis?

Abstract Background and Aims Complement system seems to play a role in the pathogenesis of primary focal segmental glomerulosclerosis (pFSGS) where, due to unpredictable clinical course and outcome, novel prognostic factors are sought. The split product of C4 and tissue marker of complement activation, C4d, is a potential candidate whose prognostic significance was determined in this study. Method Patients >18 years with features consistent with pFSGS (full blown nephrotic syndrome, diffuse podocyte foot processes effacement and exclusion of known causes of FSGS), were recruited from our Hospital registry of kidney biopsies, from 2003 to 2021. Patients with end-stage renal disease (ESRD) defined as eGFR <15 ml/min/1.73 m2 were not included. Every renal biopsy specimen was analyzed by light, immunofluorescence and electron microscopy with additional immunochemistry for C4d performed on paraffin-embedded tissue using monoclonal rabbit antibody (detection system Ventana BenchMark Ultra). Samples with at least one non-globally sclerosed glomerulus (GSG) were examined by two renal pathologists who classified every non-GSG into C4d positive and negative. Based on ratio of C4d+ non-GGS/total N of non-GSG and C4d+ nonsclerotic glomeruli (NSG)/total N of NSG, patients were stratified into two groups: <50% and ≥50%. Primary outcome was defined as composite of ESRD and initial eGFR declining >50%. Failure to meet criteria for at least partial remission at the last follow-up visit according to KDIGO 2021 Guidelines was defined as treatment failure. Numeric variables are shown as median with interquartile range (IQR) and P value <0.05 was considered as significant. Results Relevant data of 58 included patients with renal outcomes are shown in Table. Median follow up was 90.7 (IQR 48-167) months. Patients with ≥50% of C4d+ non-GSG had higher proportion of treatment failure (Table) and worse renal survival (log-rank test, p = 0.006). In multivariate Cox regression analysis, after inclusion of age, sex, initial eGFR and 24-h proteinuria, IFTA, serum albumin and C4d category, only C4d ≥50% (HR = 4.077, 95% CI 1.101-15.09, p = 0.035) and IFTA (HR = 1.052, 95% CI 1.019-1.085, p = 0.002) remained independent predictors of progression to defined endpoint. Likewise, patients with ≥50% of C4d+ NSG/total N of NSG had higher proportion of treatment failure (chi-square, p = 0.03) and worse renal survival (log-rank, p = 0.037). Conclusion C4d deposition is an independent predictor of disease progression, treatment failure and renal survival in pFSGS. Significant influence of NSG-C4d deposition on disease progression may indicate pathophysiological role of the complement system activation in pFSGS independently of the presence of glomerular sclerosis.

Lipopolysaccharide with long O-antigen is crucial for Salmonella Enteritidis to evade complement activity and to facilitate bacterial survival in vivo in the Galleria mellonella infection model

Bacterial resistance to serum is a key virulence factor for the development of systemic infections. The amount of lipopolysaccharide (LPS) and the O-antigen chain length distribution on the outer membrane, predispose Salmonella to escape complement-mediated killing. In Salmonella enterica serovar Enteritidis (S. Enteritidis) a modal distribution of the LPS O-antigen length can be observed. It is characterized by the presence of distinct fractions: low molecular weight LPS, long LPS and very long LPS. In the present work, we investigated the effect of the O-antigen modal length composition of LPS molecules on the surface of S. Enteritidis cells on its ability to evade host complement responses. Therefore, we examined systematically, by using specific deletion mutants, roles of different O-antigen fractions in complement evasion. We developed a method to analyze the average LPS lengths and investigated the interaction of the bacteria and isolated LPS molecules with complement components. Additionally, we assessed the aspect of LPS O-antigen chain length distribution in S. Enteritidis virulence in vivo in the Galleria mellonella infection model. The obtained results of the measurements of the average LPS length confirmed that the method is suitable for measuring the average LPS length in bacterial cells as well as isolated LPS molecules and allows the comparison between strains. In contrast to earlier studies we have used much more precise methodology to assess the LPS molecules average length and modal distribution, also conducted more subtle analysis of complement system activation by lipopolysaccharides of various molecular mass. Data obtained in the complement activation assays clearly demonstrated that S. Enteritidis bacteria require LPS with long O-antigen to resist the complement system and to survive in the G. mellonella infection model.

Fracture haematoma proteomics.

The aim of this study was to determine the fracture haematoma (fxH) proteome after multiple trauma using label-free proteomics, comparing two different fracture treatment strategies. A porcine multiple trauma model was used in which two fracture treatment strategies were compared: early total care (ETC) and damage control orthopaedics (DCO). fxH was harvested and analyzed using liquid chromatography-tandem mass spectrometry. Per group, discriminating proteins were identified and protein interaction analyses were performed to further elucidate key biomolecular pathways in the early fracture healing phase. The early fxH proteome was characterized by immunomodulatory and osteogenic proteins, and proteins involved in the coagulation cascade. Treatment-specific proteome alterations were observed. The fxH proteome of the ETC group showed increased expression of pro-inflammatory proteins related to, among others, activation of the complement system, neutrophil functioning, and macrophage activation, while showing decreased expression of proteins related to osteogenesis and tissue remodelling. Conversely, the fxH proteome of the DCO group contained various upregulated or exclusively detected proteins related to tissue regeneration and remodelling, and proteins related to anti-inflammatory and osteogenic processes. The early fxH proteome of the ETC group was characterized by the expression of immunomodulatory, mainly pro-inflammatory, proteins, whereas the early fxH proteome of the DCO group was more regenerative and osteogenic in nature. These findings match clinical observations, in which enhanced surgical trauma after multiple trauma causes dysbalanced inflammation, potentially leading to reduced tissue regeneration, and gained insights into regulatory mechanisms of fracture healing after severe trauma.

Assessment of biomarkers indicating activation of the complement system in pregnant women with fetal growth restriction

Aims: To compare serum levels of sC5b-9, C3, C4, C1-INH, and CH50, which are indicators of complement system activation and regulatory processes, in pregnant women with and without fetal growth restriction (FGR). Methods: This study enrolled eighty-six women with gestational age between 24 and 36 weeks. Maternal blood samples were obtained from 43 patients diagnosed with FGR and 43 from healthy pregnancies. Serum complement levels were measured using commercially available ELISA kits according to the manufacturer’s instructions (SunRed, China). Results: When the levels of complement activation biomarkers of pregnancies with FGR were compared with those of healthy pregnancies, the C1est level was significantly higher, C4 and CH50 levels were slightly lower, and Sc5b9 and C3 levels were similar. Conclusion: While the exact role of complement activation in FGR remains fully elucidated, the elevated levels of C1-INH in women with FGR suggest a compensatory mechanism to mitigate thrombus formation and inflammation. This adaptive response may be a potential therapeutic target for improving placental function and pregnancy outcomes.

Complement propagates visual system pathology following traumatic brain injury

BackgroundTraumatic brain injury (TBI) is associated with the development of visual system disorders. Visual deficits can present with delay and worsen over time, and may be associated with an ongoing neuroinflammatory response that is known to occur after TBI. Complement system activation is strongly associated with the neuroinflammatory response after TBI, but whether it contributes to vision loss after TBI is unexplored.MethodsAcute and chronic neuroinflammatory changes within the dorsal lateral geniculate nucleus (dLGN) and retina were investigated subsequent to a moderate to severe murine unilateral controlled cortical impact. Neuroinflammatory and histopathological outcomes were interpreted in the context of behavioral and visual function data. To investigate the role of complement, cohorts were treated after TBI with the complement inhibitor, CR2-Crry.ResultsAt 3 days after TBI, complement component C3 was deposited on retinogeniculate synapses in the dLGN both ipsilateral and contralateral to the lesion, which was reduced in CR2-Crry treated animals. This was associated with microglia morphological changes in both the ipsilateral and contralateral dLGN, with a less ramified phenotype in vehicle compared to CR2-Crry treated animals. Microglia in vehicle treated animals also had a greater internalized VGlut2 + synaptic volume after TBI compared to CR2-Crry treated animals. Microglia morphological changes seen acutely persisted for at least 49 days after injury. Complement inhibition also reduced microglial synaptic internalization in the contralateral dLGN and increased the association between VGLUT2 and PSD95 puncta, indicating preservation of intact synapses. Unexpectedly, there were no changes in the thickness of the inner retina, retinal nerve fiber layer or retinal ganglion layer. Neuropathological changes in the dLGN were accompanied by reduced visual acuity at subacute and chronic time points after TBI, with improvement seen in CR2-Crry treated animals.ConclusionTBI induces complement activation within the dLGN and promotes microglial activation and synaptic internalization. Complement inhibition after TBI in a clinically relevant paradigm reduces complement activation, maintains a more surveillance-like microglia phenotype, and preserves synaptic density within the dLGN. Together, the data indicate that complement plays a key role in the development of visual deficits after TBI via complement-dependent microglial phagocytosis of synapses within the dLGN.

Ursodeoxycholic and chenodeoxycholic bile acids attenuate systemic and liver inflammation induced by lipopolysaccharide in rats.

Bacterial lipopolysaccharide (LPS) induces general inflammation, by activating pathways involving cytokine production, blood coagulation, complement system activation, and acute phase protein release. The key cellular players are leukocytes and endothelial cells, that lead to tissue injury and organ failure. The aim of this study was to explore the anti-inflammatory, antioxidant, and cytoprotective properties of two bile acids, ursodeoxycholic acid (UDCA) and chenodeoxycholic acid (CDCA) in LPS-induced endotoxemia in rats. The experiment involved six distinct groups of Wistar rats, each subjected to different pretreatment conditions: control and LPS groups were pretreated with propylene glycol, as a bile acid solvent, while the other groups were pretreated with UDCA or CDCA for 10 days followed by an LPS injection on day 10. The results showed that both UDCA and CDCA reduced the production of pro-inflammatory cytokines: TNF-α, GM-CSF, IL-2, IFNγ, IL-6, and IL-1β and expression of nuclear factor-κB (NF-κB) induced by LPS. In addition, pretreatment with these bile acids showed a positive impact on lipid profiles, a decrease in ICAM levels, an increase in antioxidant activity (SOD, |CAT, GSH), and a decrease in prooxidant markers (H2O2 and O2-). Furthermore, both bile acids alleviated LPS-induced liver injury. While UDCA and CDCA pretreatment attenuated homocysteine levels in LPS-treated rats, only UDCA pretreatment showed reductions in other serum biochemical markers, including creatine kinase, lactate dehydrogenase, and high-sensitivity troponin I. It can be concluded that both, UDCA and CDCA, although exerted slightly different effects, can prevent the inflammatory responses induced by LPS, improve oxidative stress status, and attenuate LPS-induced liver injury.

Cutting edge of genetically modified pigs targeting complement activation for xenotransplantation.

In the quest to address the critical shortage of donor organs for transplantation, xenotransplantation stands out as a promising solution, offering a more abundant supply of donor organs. Yet, its widespread clinical adoption remains hindered by significant challenges, chief among them being immunological rejection. Central to this issue is the role of the complement system, an essential component of innate immunity that frequently triggers acute and chronic rejection through hyperacute immune responses. Such responses can rapidly lead to transplant embolism, compromising the function of the transplanted organ and ultimately causing graft failure. This review delves into three key areas of xenotransplantation research. It begins by examining the mechanisms through which xenotransplantation activates both the classical and alternative complement pathways. It then assesses the current landscape of xenotransplantation from donor pigs, with a particular emphasis on the innovative strides made in genetically engineering pigs to evade complement system activation. These modifications are critical in mitigating the discordance between pig endogenous retroviruses and human immune molecules. Additionally, the review discusses pharmacological interventions designed to support transplantation. By exploring the intricate relationship between the complement system and xenotransplantation, this retrospective analysis not only underscores the scientific and clinical importance of this field but also sheds light on the potential pathways to overcoming one of the major barriers to the success of xenografts. As such, the insights offered here hold significant promise for advancing xenotransplantation from a research concept to a viable clinical reality.

Ex vivo C5b-9 Deposition Test to Monitor Complement Activity in Clinical and Subclinical Atypical Hemolytic Uremic Syndrome and in Transplantation-Associated Thrombotic Microangiopathy

IntroductionAtypical Haemolytic Uremic Syndrome (aHUS) is a complement system (CS)-mediated ultrarare disease that manifests as thrombotic microangiopathy (TMA) with preferential small kidney vessels involvement. Transient CS activation is also observed in secondary TMA or in patients at risk to develop aHUS. There is no gold standard test to monitor disease activity but the ex vivo C5b-9 deposition test to be a better approach. MethodsWe assessed the C5b-9 deposition induced by serum samples of patients with aHUS (n=8) and with TMA associated to kidney (n=2), lung (n=1) or hematopoietic stem cell (HSC) transplantation (n=2) during the acute phase of the disease or in remission. As control for transplant associated (TA)-TMA we have analyzed samples of clinically stable kidney and HSC-transplanted patients without signs of TMA. Additionally, we studied one child with genetic risk of aHUS during an acute infection. ResultsIn the acute disease phase or in patients with disease activity despite C5 blockade, a significant increase of C5b-9 deposition was detected. In all patients with clinical response to C5 blockade but one, levels of C5b-9 deposition were within the normal range. Finally, we detected increased C5b-9 deposition levels in an asymptomatic child with genetic risk of aHUS when a concomitant otitis episode was ongoing. ConclusionThe ex vivo C5b-9 deposition test is an auspicious tool to monitor CS activity in aHUS and TA-TMA. In addition, we demonstrate that the test may also be useful to detect subclinical increase of CS activity which expands the spectrum of patients that would benefit from a better CS activity assessment.

Metabolic changes contribute to maladaptive right ventricular hypertrophy in pulmonary hypertension beyond pressure overload: an integrative imaging and omics investigation

Right ventricular (RV) failure remains the strongest determinant of survival in pulmonary hypertension (PH). We aimed to identify relevant mechanisms, beyond pressure overload, associated with maladaptive RV hypertrophy in PH. To separate the effect of pressure overload from other potential mechanisms, we developed in pigs two experimental models of PH (M1, by pulmonary vein banding and M2, by aorto-pulmonary shunting) and compared them with a model of pure pressure overload (M3, pulmonary artery banding) and a sham-operated group. Animals were assessed at 1 and 8 months by right heart catheterization, cardiac magnetic resonance and blood sampling, and myocardial tissue was analyzed. Plasma unbiased proteomic and metabolomic data were compared among groups and integrated by an interaction network analysis. A total of 33 pigs completed follow-up (M1, n = 8; M2, n = 6; M3, n = 10; and M0, n = 9). M1 and M2 animals developed PH and reduced RV systolic function, whereas animals in M3 showed increased RV systolic pressure but maintained normal function. Significant plasma arginine and histidine deficiency and complement system activation were observed in both PH models (M1&M2), with additional alterations to taurine and purine pathways in M2. Changes in lipid metabolism were very remarkable, particularly the elevation of free fatty acids in M2. In the integrative analysis, arginine–histidine–purines deficiency, complement activation, and fatty acid accumulation were significantly associated with maladaptive RV hypertrophy. Our study integrating imaging and omics in large-animal experimental models demonstrates that, beyond pressure overload, metabolic alterations play a relevant role in RV dysfunction in PH.

Escalated complement activation during hospitalization is associated with higher risk of 60-day mortality in SARS-CoV-2-infected patients.

The complement system, an upstream recognition system of innate immunity, is activated upon SARS-CoV-2 infection. To gain a deeper understanding of the extent and duration of this activation, we investigated complement activation profiles during the acute phase of COVID-19, its persistence post-recovery and dynamic changes in relation to disease severity. Serial blood samples were obtained from two cohorts of hospitalized COVID-19 patients (n=457). Systemic complement activation products reflecting classical/lectin (C4d), alternative (C3bBbP), common (C3bc) and terminal pathway (TCC and C5a) were measured during hospitalization (admission, days 3-5 and days 7-10), at 3 months and after 1 year. Levels of activation and temporal profiles during hospitalization were related to disease severity defined as respiratory failure (PO2/FiO2 ratio <26.6kPa) and/or admission to intensive care unit, 60-day total mortality and pulmonary pathology after 3 months. During hospitalization, TCC, C4d, C3bc, C3bBbP and C5a were significantly elevated compared to healthy controls. Severely ill patients had significantly higher levels of TCC and C4d (p<0.001), compared to patients with moderate COVID-19. Escalated levels of TCC and C4d during hospitalization were associated with a higher risk of 60-day mortality (p<0.001), and C4d levels were additionally associated with chest CT changes at 3 months (p<0.001). At 3 months and 1 year, we observed consistently elevated levels of most complement activation products compared to controls. Hospitalized COVID-19 patients display prominent and long-lasting systemic complement activation. Optimal targeting of the system may be achieved through enhanced risk stratification and closer monitoring of in-hospital changes of complement activation products.

Differentiated pattern of complement system activation between MOG-IgG-associated disease and AQP4-IgG-positive neuromyelitis optica spectrum disorder.

Myelin oligodendrocyte glycoprotein antibody (MOG) immunoglobulin G (IgG)-associated disease (MOGAD) has clinical and pathophysiological features that are similar to but distinct from those of aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorders (AQP4-NMOSD). MOG-IgG and AQP4-IgG, mostly of the IgG1 subtype, can both activate the complement system. Therefore, we investigated whether the levels of serum complement components, regulators, and activation products differ between MOGAD and AQP4-NMOSD, and if complement analytes can be utilized to differentiate between these diseases. The sera of patients with MOGAD (from during an attack and remission; N=19 and N=9, respectively) and AQP4-NMOSD (N=35 and N=17), and healthy controls (N=38) were analyzed for C1q-binding circulating immune complex (CIC-C1q), C1 inhibitor (C1-INH), factor H (FH), C3, iC3b, and soluble terminal complement complex (sC5b-9). In attack samples, the levels of C1-INH, FH, and iC3b were higher in the MOGAD group than in the NMOSD group (all, p<0.001), while the level of sC5b-9 was increased only in the NMOSD group. In MOGAD, there were no differences in the concentrations of complement analytes based on disease status. However, within AQP4-NMOSD, remission samples indicated a higher C1-INH level than attack samples (p=0.003). Notably, AQP4-NMOSD patients on medications during attack showed lower levels of iC3b (p<0.001) and higher levels of C3 (p=0.008), C1-INH (p=0.004), and sC5b-9 (p<0.001) compared to those not on medication. Among patients not on medication at the time of attack sampling, serum MOG-IgG cell-based assay (CBA) score had a positive correlation with iC3b and C1-INH levels (rho=0.764 and p=0.010, and rho=0.629 and p=0.049, respectively), and AQP4-IgG CBA score had a positive correlation with C1-INH level (rho=0.836, p=0.003). This study indicates a higher prominence of complement pathway activation and subsequent C3 degradation in MOGAD compared to AQP4-NMOSD. On the other hand, the production of terminal complement complexes (TCC) was found to be more substantial in AQP4-NMOSD than in MOGAD. These findings suggest a strong regulation of the complement system, implying its potential involvement in the pathogenesis of MOGAD through mechanisms that extend beyond TCC formation.

Environmental tobacco smoke exposure exaggerates bleomycin-induced collagen overexpression during pulmonary fibrogenesis.

Environmental tobacco smoke (ETS) is known to cause lung inflammatory and injurious responses. Smoke exposure is associated with the pathobiology related to lung fibrosis, whereas the mechanism that ETS exposure augments pulmonary fibrogenesis is unclear. We hypothesized that ETS exposure could exacerbate fibrotic responses via collagen dynamic dysregulation and complement activation. C57BL/6J and p16-3MR mice were exposed to ETS followed by bleomycin administration. ETS exposure exacerbated bleomycin-induced collagen and lysyl oxidase overexpression in the fibrotic lesion. ETS exposure also led to augmented bleomycin-induced upregulation of C3 and C3AR, which are pro-fibrotic markers. Moreover, overexpressed collagens and C3 levels were highly significant in males than females. The old mice (17 months old) were exposed to ETS and treated with bleomycin to induce fibrogenesiswhich is considered as an aging-associated disease. Fewer gene and protein dysregulations trends were identified between ETS exposure with the bleomycin group and the bleomycin alone group in old mice. Based on our findings, we suggested that ETS exposure increases the risk of developing severe lung fibrotic responses via collagen overexpression and lysyl oxidase-mediated collagen stabilization in the fibrotic lesion,and potentially affected the complement system activation induced by bleomycin. Further, male mice were more susceptible than females during fibrogenesis exacerbation. Thus ETS and bleomycin induced lung fibrotic changes via collagen-lysyl oxidase in anage-dependent mechanism.

Impact of Immunopathy and Coagulopathy on Multi-Organ Failure and Mortality in a Lethal Porcine Model of Controlled and Uncontrolled Hemorrhage.

Uncontrolled hemorrhage is a major preventable cause of death in patients with trauma. However, the majority of large animal models of hemorrhage have utilized controlled hemorrhage rather than uncontrolled hemorrhage to investigate the impact of immunopathy and coagulopathy on multi-organ failure (MOF) and mortality. This study evaluates these alterations in a severe porcine controlled and uncontrolled hemorrhagic shock (HS) model. Anesthetized female swine underwent controlled hemorrhage and uncontrolled hemorrhage by partial splenic resection followed with or without lactated Ringer solution (LR) or Voluven® resuscitation. Swine were surveyed 6 h after completion of splenic hemorrhage or until death. Blood chemistry, physiologic variables, systemic and tissue levels of complement proteins and cytokines, coagulation parameters, organ function, and damage were recorded and assessed. HS resulted in systemic and local complement activation, cytokine release, hypocoagulopathy, metabolic acidosis, MOF, and no animal survival. Resuscitation with LR and Voluven® after HS improved hemodynamic parameters (MAP and SI), metabolic acidosis, hyperkalemia, and survival but resulted in increased complement activation and worse coagulopathy. Compared with the LR group, the animals with hemorrhagic shock treated with Voluven® had worse dilutional anemia, coagulopathy, renal and hepatic dysfunction, increased myocardial complement activation and renal damage, and decreased survival rate. Hemorrhagic shock triggers early immunopathy and coagulopathy and appears associated with MOF and death. This study indicates that immunopathy and coagulopathy are therapeutic targets that may be addressed with a high-impact adjunctive treatment to conventional resuscitation.