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Membranoproliferative glomerulonephritis (MPGN) type II (dense deposit disease) is an inflammatory renal disease characterized by electron-dense deposits and complement C3 on the glomerular basement membrane. There is no effective therapy. We investigated the role of C5 activation in a model of MPGN that develops spontaneously in complement factor H-deficient mice ($Cfh^{-/-}$). At 12 months there was a significant reduction in mortality, glomerular cellularity, neutrophil numbers, and serum creatinine levels in$Cfh^{-/-}$mice deficient in C5. Excessive glomerular neutrophil numbers, frequently seen in patients with MPGN during disease flares, were also observed in$Cfh^{-/-}$mice after the administration of an antiglomerular basement membrane antibody. This exaggerated injurious phenotype was absent in$Cfh^{-/-}$mice deficient in C5 but not in$Cfh-'-$mice deficient in C6, indicating a key role for C5 activation in the induction of renal lesions. Importantly, the renal injury was completely reversed in$Cfh-'-$mice pretreated with an anti-murine C5 antibody. These results demonstrate an important role for C5 in both spontaneous MPGN and experimentally induced nephritis in factor H-deficient mice and provide preliminary evidence that C5 inhibition therapy might be useful in human MPGN type II.

Historically, the membrane attack complex, composed of complement components C5b-9, has been connected to lytic cell death and implicated in secondary injury after a CNS insult. However, studies to date have utilized either non-littermate control rat models, or mouse models that lack significant C5b-9 activity. To investigate what role C5b-9 plays in spinal cord injury and recovery, we generated littermate PVG C6 wildtype and deficient rats and tested functional and histological recovery after moderate contusion injury using the Infinite Horizon Impactor. We compare the effect of C6 deficiency on recovery of locomotor function and histological injury parameters in PVG rats under two conditions: (1) animals maintained as separate C6 WT and C6-D homozygous colonies; and (2) establishment of a heterozygous colony to generate C6 WT and C6-D littermate controls. The results suggest that maintenance of separate homozygous colonies is inadequate for testing the effect of C6 deficiency on locomotor and histological recovery after SCI, and highlight the importance of using littermate controls in studies involving genetic manipulation of the complement cascade.

C5b-9 regulates peritubular myofibroblast accumulation in experimental focal segmental glomerulosclerosis. In human focal segmental glomerulosclerosis (FSGS), the tubulointerstitial deposition of the complement (C5b-9) membrane attack complex is correlated with interstitial myofibroblast accumulation and proteinuria. Here, we hypothesized that C5b-9 formation regulates renal myofibroblast accumulation in Adriamycin nephropathy. Adriamycin nephropathy was induced in complement C6-sufficient (C6+) and C6-deficient (C6-) piebold viral glaxo (PVG) rats. Groups of animals (N = 7 to 8 each) were examined on days 21 and 42. A group of C6+ animals, injected with vehicle, served as the control group. C6+ and C6- rats with Adriamycin nephropathy had equivalent proteinuria. C5b-9 deposition was increased and present on the apical surface of proximal tubular epithelial cells (day 21 and 42) and peritubular region (day 42 only) in C6+ rats with Adriamycin nephropathy, and absent in C6- rats. Peritubular myofibroblast accumulation increased in a time-dependent manner in C6+ proteinuric rats (control 1.2 ± 0.4; Adriamycin nephropathy day 21 11.0 ± 0.7; Adriamycin nephropathy day 42 19.8 ± 1.7 cells per high power field). In C6- rats this increase was blunted by 87% and 56% on days 21 and 42, respectively (P < 0.01), and was associated with reduced interstitial extracellular matrix (ECM) deposition. Tubulointerstitial injury, tubular vimentin and interstitial monocyte accumulation were also reduced in C6- rats with Adriamycin nephropathy on day 21, but not at day 42. In contrast, the increase in periglomerular myofibroblast accumulation and glomerulosclerosis in Adriamycin nephropathy were not altered by C6 deficiency. These data suggest that glomerular ultrafiltration of complement components and the intratubular formation of C5b-9 is a specific promotor of peritubular myofibroblast accumulation in FSGS.

Complement component C6 is a part of the lytic membrane attack complex formed during complement activation. Animal modeling to define the role of C5a vs. C5b-9 in human disease has used rodents deficient in C6, yet the molecular basis for the deficiencies has not been ascertained. Oligonucleotides derived from a 493 bp EST sequence of the rat C6 gene were used to isolate full-length transcripts of rat C6 mRNA. Sequence analysis confirmed that the derived amino acid sequence for rat C6 is highly homologous to human and mouse. We identified a 31 bp deletion in exon 10 of the C6 gene that leads to C6 deficiency in a strain of PVG rats (PVG/c-) and developed a PCR-based genotyping test. In addition, we identified four point mutations in the mouse C6 gene that may result in C6 deficiency observed in the Peru-Coppock mouse strain. A serendipitous finding from this study was a coagulation defect in the C6 deficient mice and rats. C6 deficient mice or rats demonstrated prolonged tail bleeding times that was reversed by treatment with purified rat C6 protein. Further, adenosine diphosphate induced platelet aggregation were markedly reduced in C6 deficient rats. The molecular basis for these coagulations defects is unknown at present.

Inhibiting complement anaphlytoxin C5a during sepsis may prevent sepsis mortality. Although human anti-C5 antibodies exist, their therapeutic use in microbial sepsis has been avoided because of the hypothesis that inhibiting C5b will prevent formation of the bactericidal membrane attack complex (MAC) and worsen clinical outcome. We wished to test the hypothesis that inhibition of C5 would improve outcomes in sepsis. Sepsis was induced in rats by laparotomy and cecal ligation and puncture (CLP) by an IACUC-approved protocol. Sham animals underwent laparotomy without CLP. Following CLP rats were randomized to receive a single IV dose of purified IgG ant-C5 antibody (Ab) or control IgG Ab. Anti-C5 Ab treated rats ( n = 20 ) had significantly lower mortality vs. controls ( n = 21 ) , 20% vs. 52% ( P = 0.019 , log-rank). Analysis of bacterial load by culture of spleen and liver homogenates showed a reduction in colony forming units in anti-C5 Ab treated rats vs. control IgG ( P = 0.003 and 0.009, respectively). Anti-C5 treatment reduced lung injury as measured by total MPO content of lung tissue ( P = 0.024 ) . Finally, rats genetically deficient in C6 production, unable to form MAC but capable of producing C5a and C5b, were protected from CLP-induced sepsis mortality. Our results show that an anti-C5 antibody therapy prevents CLP sepsis-induced mortality and improves lung injury. Inhibition of the complement MAC does not increase bacterial load or mortality, therefore, the use of anti-C5 therapy may be beneficial rather than detrimental in sepsis.

Tissue and organ replacement have quickly outpaced available supply. Tissue bioengineering holds the promise for additional tissue availability. Various scaffolds are currently used, whereas polyglycolic acid (PGA), which is currently used in absorbable sutures and orthopedic pins, provides an excellent support for tissue development. Unfortunately, PGA can induce a local inflammatory response following implantation. Therefore, we investigated the molecular mechanism of inflammation in vitro and in vivo . Degraded PGA induced an acute peritonitis, characterized by neutrophil (PMN) infiltration following intraperitoneal injection in mice. Similar observations were observed using the metabolite of PGA, glycolide. Dissolved PGA or glycolide, but not native PGA, activated the classical complement pathway in human sera, as determined by classical complement pathway hemolytic assays, C3a and C5a production, and C3 and immunoglobulin deposition. To investigate whether these in vitro observations translated to in vivo findings, we used genetically engineered mice. Intraperitoneal administration of glycolide or dissolved PGA in mice deficient in C1q, factor D, C1q and factor D, or C2 and factor B demonstrated significantly reduced PMN infiltration compared to congenic controls (WT). Mice deficient in C6 also demonstrated acute peritonitis. However, treatment of WT or C6 deficient mice with a monoclonal antibody against C5 prevented the inflammatory response. These data suggest that the hydrolysis of PGA to glycolide activates the classical complement pathway. Furthermore, complement is amplified via the alternative pathway and inflammation is induced by C5a generation. Inhibition of C5a may provide a potential therapeutic approach to limit the inflammation associated with PGA-derived materials following implantation.

The complement system is thought to be a major physiological mediator of injury in a number of diseases including rheumatoid arthritis (RA). The membrane attack complex (MAC) of complement has been detected in RA tissue, suggesting that the MAC may be relevant to the pathogenesis of the disease. Deposition of sublytic concentrations of the MAC has been shown to promote the expression of proinflammatory mediators. In the present study, we utilized rabbits deficient in the complement protein C6 to elucidate the role of the MAC in mediating the pathogenesis of antigen-induced arthritis. Swelling, leukocyte accumulation, IL-8 expression, proteoglycan, and hydroxyproline content were assessed. Analysis of synovial tissue demonstrated a significant decrease in leukocyte influx and a parallel decrease in tissue associated IL-8 in joints of C6-deficient animals as compared to C6-sufficient animals. However, this did not correlate with the preservation of connective tissue. The results derived from this study provide evidence that the MAC has an important function in mediating leukocyte recruitment in antigen-induced arthritis but does not play a direct role in connective tissue breakdown.

Candida activates complement via all three pathways leading to opsonisation and anaphylaxis. The aim of the study was to investigate the influence of the terminal complement system on Candida infections. Thus, fungal cell growth, mitochondrial activity and phagocytosis by polymorphonuclear leukocytes (PMNLs) as well as specific virulence factors, such as release of secreted aspartic protease (Sap) and adherence to epithelial cells, were assessed under the influence of normal or C6/C7-depleted serum. Candida (C.) dubliniensis was used in all experiments as prototype because of its known increased expression of Saps and its strong geno- and phenotypical similarity to the most abundant Candida species C. albicans. Being exposed to sufficient quantities of complement, fungal growth decreased and phagocytosis increased but mitochondrial activities of the yeast increased as well. Concerning the virulence factors, both adhesion and especially Sap release were markedly reduced in the presence of high serum concentrations. Interestingly, at low serum concentrations some opposite effects (an augmented cell growth, a higher Sap release and a stronger adhesion) were observed. In particular, it was shown that the presence of terminal complement factors, and thus the generation of the membrane attack complex, clearly induced a higher fungal mitochondrial activation and has an effect on host defence against yeast cells by augmenting phagocytosis.

Patients whose blood is deficient in the terminal component of complement have an increased susceptibility to meningococcal infection. However, mortality from meningococcal infection is lower in these patients than in immunocompetent subjects. We studied a C6-deficient patient with meningococcal sepsis who received fresh frozen plasma (FFP). The patient's initial plasma endotoxin, C6, and terminal-complement-complex concentrations were low, but rose sharply after treatment with FFP. Samples of the patient's serum taken shortly after admission did not cause endotoxin release from Escherichia coli J5 in vitro, but endotoxin-releasing activity was restored in serum samples taken after infusion of FFP. It is possible that C6-deficient patients have reduced mortality from meningococcal infection because their serum cannot cause acute release of endotoxin from the invading organism and extensive tissue damage is thus avoided.