Deficiency of human complement factor I associated with lowered factor H

Complement factor I: Regulatory nexus, driver of immunopathology, and therapeutic

Complement factor I (FI) is the nexus for classical, lectin and alternative pathway complement regulation. FI is an 88 kDa plasma protein that circulates in an inactive configuration until it forms a trimolecular complex with its cofactor and substrate whereupon a structural reorganization allows the catalytic triad to cleave its substrates, C3b and C4b. In keeping with its role as the master complement regulatory enzyme, deficiency has been linked to immunopathology. In the setting of complete FI deficiency, a consumptive C3 deficiency results in recurrent infections with encapsulated microorganisms. Aseptic cerebral inflammation and vasculitic presentations are also less commonly observed. Heterozygous mutations in the factor I gene (CFI) have been demonstrated to be enriched in atypical haemolytic uraemic syndrome, albeit with a very low penetrance. Haploinsufficiency of CFI has also been associated with decreased retinal thickness and is a strong risk factor for the development of age-related macular degeneration. Supplementation of FI using plasma purified or recombinant protein has long been postulated, however, technical difficulties prevented progression into clinical trials. It is only using gene therapy that CFI supplementation has reached the clinic with GT005 in phase I/II clinical trials for geographic atrophy.

The Nonbacterial Microbiome: Fungal and Viral Contributions to the Preterm Infant Gut in Health and Disease

The intestinal microbiome is frequently implicated in necrotizing enterocolitis (NEC) pathogenesis. While no particular organism has been associated with NEC development, a general reduction in bacterial diversity and increase in pathobiont abundance has been noted preceding disease onset. However, nearly all evaluations of the preterm infant microbiome focus exclusively on the bacterial constituents, completely ignoring any fungi, protozoa, archaea, and viruses present. The abundance, diversity, and function of these nonbacterial microbes within the preterm intestinal ecosystem are largely unknown. Here, we review findings on the role of fungi and viruses, including bacteriophages, in preterm intestinal development and neonatal intestinal inflammation, with potential roles in NEC pathogenesis yet to be determined. In addition, we highlight the importance of host and environmental influences, interkingdom interactions, and the role of human milk in shaping fungal and viral abundance, diversity, and function within the preterm intestinal ecosystem.

Antifungal Immunological Defenses in Newborns

Newborns are prone to fungal infections, largely due to Candida species. The immunological basis for this vulnerability is not yet fully understood. However, useful insights can be gained from the knowledge of the maturation of immune pathways during ontogeny, particularly when placed in context with how rare genetic mutations in humans predispose to fungal diseases. In this article, we review these most current data on immune functions in human newborns, highlighting pathways most relevant to the response to Candida. While discussing these data, we propose a framework of why deficiencies in these pathways make newborns particularly vulnerable to this opportunistic pathogen.

An ELISA assay with two monoclonal antibodies allows the estimation of free factor H and identifies patients with acquired deficiency of this complement regulator

Complement factor H (FH) serum levels can be affected by the presence of immune complexes of FH with autoantibodies like in autoimmune forms of atypical haemolytic uraemic syndrome (aHUS) or with C3b in homozygous factor I (FI) deficiency. These complexes reduce the amount of free functional circulating FH. In this study we aimed to determine whether FH levels measurement is disturbed in some pathological conditions and to establish a method for quantifying free and total FH in serum. For that purpose, FH levels were measured in serum samples from aHUS patients having anti-FH autoantibodies or mutations in FH gene, in patients with homozygous FI deficiency, and in healthy controls. Two anti-FH monoclonal antibodies, OX24 and A229, recognizing different functional regions in FH, were used as capture antibodies in an ELISA assay. In the control group and in the group of patients with FH mutations, the FH levels obtained with the two monoclonal antibodies were similar. In patients with anti-FH autoantibodies or with homozygous FI deficiency, however, FH levels measured with both antibodies were significantly different. As these patients had complexes of FH with autoantibodies or C3b, we interpreted that OX24 was detecting total FH and A229 was recognising free FH. Therefore, quantification of FH in plasma using these two monoclonal antibodies provides not only total FH level but also gives an estimation of how much FH circulates free and is thus available to properly control complement activation.

Mutations of complement factor I and potential mechanisms of neuroinflammation in acute hemorrhagic leukoencephalitis

PURPOSE

Acute Hemorrhagic Leukoencephalitis (AHLE) is a rare demyelinating disorder of acute onset, rapid deterioration and significant morbidity and mortality. Most often described as a post-infectious complication of an upper respiratory illness, its precise pathophysiology remains unclear. We describe two pediatric patients with AHLE with partial complement factor I (FI) deficiency whose successful treatment included the interleukin-1 (IL-1) receptor antagonist, anakinra, implicating a role for FI and IL-1 in this disorder.

METHODS

Extensive clinical workup of two patients presenting with AHLE revealed complement abnormalities, specifically related to the alternative pathway and its regulator, FI. Aggressive management with steroids, immunoglobulin, and anakinra ultimately led to improvement of clinical status and near return to neurologic baseline in both patients. Genetic sequencing of the FI coding regions of the patients and their families was performed. In vitro protein expression studies and immunohistochemistry of fixed brain tissue was used to investigate pathogenic mechanisms.

RESULTS

Two novel mutations in FI were identified in our patients, which result in failure to secrete FI. Immunohistochemical evaluation of brain tissue demonstrated positive staining for C3, membrane attack complex (MAC) and IL-1.

CONCLUSIONS

We propose AHLE is an unreported, rare phenotype for partial FI deficiency. The upregulation of C3, MAC and IL-1 with subsequent demyelination support a pathologic role for complement activation in AHLE, and suggest anakinra as an important adjunctive therapy in this disease.

Factor I autoantibodies in patients with atypical hemolytic uremic syndrome: disease-associated or an epiphenomenon?

BACKGROUND AND OBJECTIVES

Atypical hemolytic uremic syndrome is a disease associated with mutations in the genes encoding the complement regulators factors H and I. In addition, factor H autoantibodies have been reported in ∼10% of patients with atypical hemolytic uremic syndrome. This study searched for the presence of factor I autoantibodies in atypical hemolytic uremic syndrome.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study screened 175 atypical hemolytic uremic syndrome patients for factor I autoantibodies using ELISA with confirmatory Western blotting. Functional studies using purified immunoglobulin from one patient were subsequently undertaken.

RESULTS

Factor I autoantibodies were detected in three patients. In one patient with a high titer of autoantibody, the titer was tracked over time and was found to have no association with disease activity. This study found evidence of an immune complex of antibody and factor I in this patient, but purified IgG, isolated from current serum samples, had only a minor effect on fluid phase and cell surface complement regulation. Genetic analysis of the three patients with factor I autoantibodies revealed that they had two copies of the genes encoding factor H-related proteins 1 and 3 and therefore, did not have a deletion commonly associated with factor H autoantibodies in atypical hemolytic uremic syndrome. Two patients, however, had functionally significant mutations in complement factor H.

CONCLUSIONS

These findings reinforce the concept of multiple concurrent risk factors being associated with atypical hemolytic uremic syndrome but question whether autoantibodies per se predispose to atypical hemolytic uremic syndrome.

Peripheral administration of human adrenomedullin and its binding protein attenuates stroke-induced apoptosis and brain injury in rats

Stroke is a leading cause of death and the primary medical cause of acquired adult disability worldwide. The progressive brain injury after acute stroke is partly mediated by ischemia-elicited inflammatory responses. The vasoactive hormone adrenomedullin (AM), upregulated under various inflammatory conditions, counterbalances inflammatory responses. However, regulation of AM activity in ischemic stroke remains largely unknown. Recent studies have demonstrated the presence of a specific AM binding protein (that is, AMBP-1) in mammalian blood. AMBP-1 potentiates AM biological activities. Using a rat model of focal cerebral ischemia induced by permanent middle cerebral artery occlusion (MCAO), we found that plasma levels of AM increased significantly, whereas plasma levels of AMBP-1 decreased significantly after stroke. When given peripherally early after MCAO, exogenous human AM in combination with human AMBP-1 reduced brain infarct volume 24 and 72 h after MCAO, an effect not observed after the treatment by human AM or human AMBP-1 alone. Furthermore, treatment of human AM/AMBP-1 reduced neuron apoptosis and morphological damage, inhibited neutrophil infiltration in the brain and decreased serum levels of S100B and lactate. Thus, human AM/AMBP-1 has the ability to reduce stroke-induced brain injury in rats. AM/AMBP-1 can be developed as a novel therapeutic agent for patients with ischemic stroke.

Human adrenomedullin and its binding protein ameliorate sepsis-induced organ injury and mortality in jaundiced rats

Sepsis is a serious complication for patients with obstructive jaundice. Although administration of adrenomedullin (AM) in combination with its binding protein (AMBP-1) is protective after injury, it remains unknown whether AM/AMBP-1 ameliorates sepsis-induced organ injury and mortality in the setting of biliary obstruction. The aim of this study is, therefore, to test the efficacy of human AM/AMBP-1 in a rat model of obstructive jaundice and polymicrobial sepsis. To study this, obstructive jaundice was induced in male adult rats (275-325g) by common bile duct ligation (BDL). One week after BDL, the rats were subjected to sepsis by cecal ligation and puncture (CLP). Plasma levels of AM and AMBP-1 were measured at 20h after CLP. In additional groups of BDL+CLP rats, human AM/AMBP-1 (24/80microg/kg body weight (BW)) or vehicle (i.e., human albumin) was administered intravenously at 5h after CLP. Blood and tissue samples were collected at 20h after CLP for various measurements. To determine the long-term effect of human AM/AMBP-1 after BDL+CLP, the gangrenous cecum was removed at 20h after CLP and 7-day survival was recorded. Our results showed that plasma levels of AM were significantly increased while AMBP-1 levels were markedly decreased after BDL+CLP (n=8, P<0.05). Administration of human AM/AMBP-1 attenuated tissue injury and inflammatory responses after BDL+CLP. Moreover, human AM/AMBP-1 significantly increased the survival rate from 21% (n=14) to 53% (n=15). Thus, human AM/AMBP-1 ameliorates sepsis-induced organ injury and mortality in jaundiced rats. Human AM/AMBP-1 can be further developed as a novel treatment for sepsis in jaundiced patients.

Attenuation of renal ischemia and reperfusion injury by human adrenomedullin and its binding protein

BACKGROUND

Acute renal failure secondary to ischemia and reperfusion (I/R) injury poses a significant burden on both surgeons and patients. It carries a high morbidity and mortality rate and no specific treatment currently exists. Major causes of renal I/R injury include trauma, sepsis, hypoperfusion, and various surgical procedures. We have demonstrated that adrenomedullin (AM), a novel vasoactive peptide, combined with AM binding protein-1 (AMBP-1), which augments the activity of AM, is beneficial in various disease conditions. However, it remains unknown whether human AM/AMBP-1 provides any beneficial effects in renal I/R injury. The objective of our study therefore was to determine whether administration of human AM/AMBP-1 can prevent and/or minimize damage in a rat model of renal I/R injury.

METHODS

Male adult rats were subjected to renal I/R injury by bilateral renal pedicle clamping with microvascular clips for 60 min followed by reperfusion. Human AM (12 microg/kg BW) and human AMBP-1 (40 microg/kg BW) or vehicle (52 microg/kg BW human albumin) were given intravenously over 30 min immediately following the clip removal (i.e., reperfusion). Rats were allowed to recover for 24 h post-treatment, and blood and renal tissue samples were collected. Plasma levels of AM were measured using a radioimmunoassay specific for rat AM. Plasma AMBP-1 was measured by Western analysis. Renal water content and serum levels of systemic markers of tissue injury were measured. Serum and renal TNF-alpha levels were also assessed.

RESULTS

At 24 h after renal I/R injury, plasma levels of AM were significantly increased while plasma AMBP-1 was markedly decreased. Renal water content and systemic markers of tissue injury (e.g., creatinine, BUN, AST, and ALT) were significantly increased following renal I/R injury. Serum and renal TNF-alpha levels were also increased post injury. Administration of human AM/AMBP-1 decreased renal water content, and plasma levels of creatinine, BUN, AST, and ALT. Serum and renal TNF-alpha levels were also significantly decreased after AM/AMBP-1 treatment.

CONCLUSION

Treatment with human AM/AMBP-1 in renal I/R injury significantly attenuated organ injury and the inflammatory response. Thus, human AM combined with human AMBP-1 may be developed as a novel treatment for patients with acute renal I/R injury.

Complement in human diseases: Lessons from complement deficiencies

Complement deficient cases reported in the second half of the last century have been of great help in defining the role of complement in host defence. Surveys of the deficient individuals have been instrumental in the recognition of the clinical consequences of the deficiencies. This review focuses on the analysis of the diseases associated with the deficiencies of the various components and regulators of the complement system and their therapeutic implications. The diagnostic approach leading to the identification of the deficiency is discussed here as a multistep process that starts with the screening assays and proceeds in specialized laboratories with the characterization of the defect at the molecular level. The organization of a registry of complement deficiencies is presented as a means to collect the cases identified in and outside Europe with the aim to promote joint projects on treatment and prevention of diseases associated with defective complement function.

Human adrenomedullin and its binding protein attenuate organ injury and reduce mortality after hepatic ischemia-reperfusion

OBJECTIVE

To determine whether administration of a vasoactive peptide, human adrenomedullin (AM), in combination with its binding protein (ie, AMBP-1), prevents or minimizes hepatic ischemia-reperfusion (I/R) injury.

SUMMARY BACKGROUND DATA

Hepatic I/R injury results from tissue hypoxia and subsequent inflammatory responses. Even though numerous pharmacological modalities and substances have been studied to reduce I/R-induced mortality, none have been entirely successful. We have shown that administration of AM/AMBP-1 produces significant beneficial effects under various pathophysiological conditions. However, it remains unknown if human AM/AMBP-1 has any protective effects on hepatic I/R-induced tissue damage and mortality.

METHODS

Seventy percent hepatic ischemia was induced in male adult rats by placing a microvascular clip across the hilum of the left and median lobes for 90 minutes. After removing the clip, human AM alone, human AMBP-1 alone, human AM in combination with human AMBP-1 or vehicle was administered intravenously over a period of 30 minutes. Blood and tissue samples were collected 4 hours after reperfusion for various measurements. In additional groups of animals, the nonischemic liver lobes were resected at the end of 90-minute ischemia. The animals were monitored for 7 days and survival was recorded.

RESULTS

After hepatic I/R, plasma levels of AM were significantly increased, whereas AMBP-1 levels were markedly decreased. Likewise, gene expression of AM in the liver was increased significantly, whereas AMBP-1 expression was markedly decreased. Administration of AM in combination with AMBP-1 immediately after the onset of reperfusion down-regulated inflammatory cytokines, decreased hepatic neutrophil infiltration, inhibited liver cell apoptosis and necrosis, and reduced liver injury and mortality in a rat model of hepatic I/R. On the other hand, administration of human AM alone or human AMBP-1 alone after hepatic I/R failed to produce significant protection.

CONCLUSIONS

Human AM/AMBP-1 may be a novel treatment to attenuate tissue injury after an episode of hepatic ischemia.

Role of complement in host defense against pneumococcal otitis media

Strategies to limit complement deposition on Streptococcus pneumoniae are established as virulence features for invasive disease, but their role in respiratory tract infection requires further analysis. We evaluated complement C3 protein deposition on discordant S. pneumoniae isolates of the same serotype (6A) and their capacity to cause nasopharyngeal (NP) colonization and experimental otitis media (EOM) in an animal model. We compared C3 binding to five 6A isolates from asymptomatic NP carriers with five 6A strains that caused invasive disease, and we observed less C3 ( approximately 10-fold less fluorescence) binding to invasive isolates. We selected two high-level C3-binding carriage and two low-level C3-binding invasive 6A isolates for further study. In the EOM model, 11/12 (92%) ears challenged with a low-level C3-binding 6A strain became infected. Only 2/8 (25%) ears challenged with the discordant high-level C3-binding 6A isolate developed disease (P = 0.005). Results with the second discordant 6A isolate pair were comparable. Cobra venom factor (CoVF) treatment, which depletes C3 and consumes complement, restored virulence of the high-level C3-binding strain; 8/8 (100%) ears in CoVF-treated animals developed EOM compared to only 25% of ears in naïve animals (P = 0.007). These studies demonstrate the critical role for complement evasion in pneumococcal EOM. Colonization with carriage isolates that bound high levels of C3 caused EOM in fewer animals compared to low-level C3-binding invasive strains. Thus, limiting C3 deposition on the surface of S. pneumoniae correlates with increased incidence of EOM following NP colonization and barotrauma in the animal model.

Reversing established sepsis in rats with human vasoactive hormone adrenomedullin and its binding protein

We recently demonstrated that early administration of rat adrenomedullin (AM), a vasoactive peptide, in combination with its binding protein (human AMBP-1) produces various beneficial effects in sepsis. Human AM is a 52-amino acid peptide, but rat AM differs from human AM, having only 50 amino acid residues, with two amino acid deletions and six substitutions. It remains unknown whether a combination of human AM and human AMBP-1 (AM/AMBP-1) is also beneficial in sepsis and, if so, whether human AM/AMBP-1 reverses established sepsis in rats. To test the effects of human AM/AMBP-1, we induced sepsis in male adult rats by cecal ligation and puncture (CLP). At 10 h after CLP (i.e., severe sepsis), human AM (12-48 microg/kg body weight) was administered in combination with human AMBP-1 (40-160 microg/kg body weight). Vehicle-treated animals received a nonspecific human plasma protein (albumin). Blood and intestinal samples were collected at 20 h for various measurements. In additional groups of septic animals, the gangrenous cecum was surgically excised at 20 h after CLP. The 10-day survival was recorded. Our results showed that tissue injury, as evidenced by increased levels of transaminases and lactate, was present at 20 h after CLP. Proinflammatory cytokines tumor necrosis factor-alpha and interleukin-6 were significantly elevated. Gut barrier dysfunction, manifested by increased mucosal permeability to hydrophilic macromolecules and increased bacterial translocation to mesenteric lymph nodes, also occurred at 20 h after CLP. Administration of human AM/AMBP-1 in established sepsis markedly attenuated tissue injury, reduced proinflammatory cytokine levels, ameliorated intestinal-barrier dysfunction, and improved the survival rate from 47% to 67%-80%. Thus, human AM/AMBP-1 can be further developed as a safe and effective therapy for patients with established sepsis.

Translational mini-review series on complement factor H: renal diseases associated with complement factor H: novel insights from humans and animals

Factor H is the major regulatory protein of the alternative pathway of complement activation. Abnormalities in factor H have been associated with renal disease, namely glomerulonephritis with C3 deposition including membranoproliferative glomerulonephritis (MPGN) and the atypical haemolytic uraemic syndrome (aHUS). Furthermore, a common factor H polymorphism has been identified as a risk factor for the development of age-related macular degeneration. These associations suggest that alternative pathway dysregulation is a common feature in the pathogenesis of these conditions. However, with respect to factor H-associated renal disease, it is now clear that distinct molecular defects in the protein underlie the pathogenesis of glomerulonephritis and HUS. In this paper we review the associations between human factor H dysfunction and renal disease and explore how observations in both spontaneous and engineered animal models of factor H dysfunction have contributed to our understanding of the pathogenesis of factor H-related renal disease.

Factor I is required for the development of membranoproliferative glomerulonephritis in factor H-deficient mice

The inflammatory kidney disease membranoproliferative glomerulonephritis type II (MPGN2) is associated with dysregulation of the alternative pathway of complement activation. MPGN2 is characterized by the presence of complement C3 along the glomerular basement membrane (GBM). Spontaneous activation of C3 through the alternative pathway is regulated by 2 plasma proteins, factor H and factor I. Deficiency of either of these regulators results in uncontrolled C3 activation, although the breakdown of activated C3 is dependent on factor I. Deficiency of factor H, but not factor I, is associated with MPGN2 in humans, pigs, and mice. To explain this discordance, mice with single or combined deficiencies of these factors were studied. MPGN2 did not develop in mice with combined factor H and I deficiency or in mice deficient in factor I alone. However, administration of a source of factor I to mice with combined factor H and factor I deficiency triggered both activated C3 fragments in plasma and GBM C3 deposition. Mouse renal transplant studies demonstrated that C3 deposited along the GBM was derived from plasma. Together, these findings provide what we believe to be the first evidence that factor I-mediated generation of activated C3 fragments in the circulation is a critical determinant for the development of MPGN2 associated with factor H deficiency.

Enhanced Analysis of the Mouse Plasma Proteome Using Cysteine-Containing Tryptic Glycopeptides

A comprehensive understanding of the mouse plasma proteome is important for studies using mouse models to identify protein markers of human disease. To enhance our analysis of the mouse plasma proteome, we have developed a method for isolating low-abundance proteins using a cysteine-containing glycopeptide strategy. This method involves two orthogonal affinity capture steps. First, glycoproteins are coupled to an azlactone copolymer gel using hydrazide chemistry and cysteine residues are then biotinylated. After trypsinization and extensive washing, tethered N-glycosylated tryptic peptides are released from the gel using PNGase F. Biotinylated cysteinyl-containing glycopeptides are then affinity selected using a monomeric avidin gel and analyzed by LC-MS/MS. We have applied the method to a proteome analysis of mouse plasma. In two independent analyses using 200 muL each of C57BL mouse plasma, 51 proteins were detected. Only 42 proteins were seen when the same plasma sample was analyzed by glycopeptides only. A total of 104 N-glycosylation sites were identified. Of these, 17 sites have hitherto not been annotated in the Swiss-Prot database whereas 48 were considered probable, potential, or by similarity - i.e., based on little or no experimental evidence. We show that analysis by cysteine-containing glycopeptides allows detection of low-abundance proteins such as the epidermal growth factor receptor, the Vitamin K-dependent protein Z, the hepatocyte growth factor activator, and the lymphatic endothelium-specific hyaluronan receptor as these proteins were not detected in the glycopeptide control analysis.

Clinical aspects and molecular basis of primary deficiencies of complement component C3 and its regulatory proteins factor I and factor H

The complement system participates in both innate and acquired immune responses. Deficiencies in any of the protein components of this system are generally uncommon and require specialized services for diagnosis. Consequently, complement deficiencies are clinically underscored and may be more common than is normally estimated. As C3 is the major complement component and participates in all three pathways of activation, it is fundamental to understand all the clinical consequences observed in patients for which this protein is below normal concentration or absent in the serum. C3 deficiencies are generally associated with higher susceptibility to severe infections and in some cases with autoimmune diseases such as systemic lupus erythematosus. Here, we review the main clinical aspects and the molecular basis of primary C3 deficiency as well as the mutations in the regulatory proteins factor I and factor H that result in secondary C3 deficiencies. We also discuss the use of animal models to study these deficiencies.

Recurrent infections in partial complement factor I deficiency: evaluation of three generations of a Brazilian family

We report here on the evaluation of a factor I-deficient Brazilian family (three generations, 39 members) with strong consanguinity. The complete factor I-deficient patients (n = 3) presented recurrent respiratory infections, skin infections and meningitis; one of them died after sepsis. They presented an impaired total haemolytic activity (CH50), low C3, low factor H and undetectable C3dg/C3d. Partial factor I deficiency was detected in 16 family members (normal low cut-off value was 25 microg/ml). Respiratory infections were the most common clinical occurrence among partial factor I-deficient relatives. Two of them were submitted to nephrectomy following recurrent urinary tract infections. An additional two heterozygous relatives presented with arthritis and rheumatic fever. Apparently, patients with partial factor I deficiency are also at higher risk for recurrent infections. Vaccination against capsulated bacteria and the eventual use of prophylactic antibiotics should be considered individually in this patient group.

Complement factor I deficiency associated with recurrent infections, vasculitis and immune complex glomerulonephritis

Here we report complement factor I deficiency in an 11-y-old girl from a consanguineous Turkish family, who presented with recurrent pyogenic infections, vasculitic eruptions and immune complex glomerulonephritis. A moderately low C3 level together with the clinical picture suggested a deficiency affecting regulation of complement activation. Analysis of haemolytic activity revealed absence of alternative pathway activity and subsequent analysis showed no detectable factor I (<2%) together with a low level of factor B and a moderately low level of factor H, indicating consumption secondary to the factor I deficiency. Factor I inhibits complement activation beyond C3 by cleavage of C3b in the presence of cofactors. Complement factor I deficiency is frequently associated with recurrent pyogenic infections mainly affecting the upper and lower respiratory tract, or presenting as meningitis or septicaemia, while rheumatic disorders have not been a prominent feature. The patient's sister also suffered from recurrent pyogenic infections and had a low C3 level clearly suggesting the same deficiency.

Ontogeny of complement regulatory proteins - concentrations of factor h, factor I, c4b-binding protein, properdin and vitronectin in healthy children of different ages and in adults

Previous studies of human in vivo complement protein levels have only compared data for neonates with that from adult sera. Here, we establish the normal concentration ranges of the following complement regulatory proteins in healthy Brazilian children of different age groups (neonates: 1 month-1 year, 1-6 years and 6-13 years) and in adults: factor H (fH), factor I (fI), C4b-binding protein (C4 BP), properdin and vitronectin. We found that the concentrations of fH, fI, properdin and vitronectin in neonates are significantly lower than in adults. Remarkably, the concentration of C4 BP is below the method resolution (<50 micro g/ml) in 76% of the sera from neonates, while adults presented 199-532 microg/ml of C4 BP in their sera. The concentration of properdin in the sera from neonates and up to 1-year-old children was less than that observed in older children. Adults presented vitronectin levels significantly higher than all the other age groups in the study. No significant sex differences in the concentrations of all the studied regulatory proteins were detected. This study reveals the ontogeny of complement system in greater detail than previously available and may point to the reasons why neonates have higher susceptibility to develop life-threatening pyogenic infections. These reference values will be of use in clinical and laboratory investigations of disorders associated with low levels of these regulatory proteins.

Simple method to distinguish between primary and secondary C3 deficiencies

Due to the increasing numbers of reported clinical cases of complement deficiency in medical centers, clinicians are now more aware of the role of the complement system in the protection against infections caused by microorganisms. Therefore, clinical laboratories are now prepared to perform a number of diagnostic tests of the complement system other than the standard 50% hemolytic component assay. Deficiencies of alternative complement pathway proteins are related to severe and recurrent infections; and the application of easy, reliable, and low-cost methods for their detection and distinction are always welcome, notably in developing countries. When activation of the alternative complement pathway is evaluated in hemolytic agarose plates, some but not all human sera cross-react to form a late linear lysis. Since the formation of this linear lysis is dependent on C3 and factor B, it is possible to use late linear lysis to routinely screen for the presence of deficiencies of alternative human complement pathway proteins such as factor B. Furthermore, since linear lysis is observed between normal human serum and primary C3-deficient serum but not between normal human serum and secondary C3-deficient serum caused by the lack of factor H or factor I, this assay may also be used to discriminate between primary and secondary C3 deficiencies.

Molecular characterization of homozygous hereditary factor I deficiency

We have studied the molecular basis of factor I (fI) deficiency in two Brazilian sisters from a consanguineous family. By reverse transcription-polymerase chain reaction we observed that all fI cDNA amplified products from one sister had the same size as those of normal cDNA, however, they were significantly less intense. Sequencing analysis of subcloned cDNA revealed a dinucleotide insertion (AT) between positions 1204 and 1205 in the 11th exon that creates a stop codon 13 bp downstream of the insertion site. Genomic DNA sequencing and heteroduplex analysis confirmed that both probands are homozygous for this mutation, whereas their parents are heterozygous. The stop codon and the diminished amounts of fI cDNA could indicate increased fI mRNA instability, perhaps due to a mechanism of nonsense-mediated decay. This hypothesis is consistent with our observation that treatment with the translation inhibitor cycloheximide stabilized fI mRNA expression in proband's fibroblasts.

Mechanisms of the beneficial effect of adrenomedullin and adrenomedullin-binding protein-1 in sepsis: down-regulation of proinflammatory cytokines

OBJECTIVE

Our recent study indicates that administration of adrenomedullin (AM) in combination with AM-binding protein-1 (AMBP-1) before sepsis (i.e., pretreatment) maintains cardiovascular stability and reduces the mortality rate. The aim of the present study was to determine whether administration of AM/AMBP-1 after the onset of sepsis (posttreatment) has any salutary effects on the septic host, and if so, whether AM/AMBP-1 down-regulates proinflammatory cytokines, such as tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6.

DESIGN

Prospective, controlled, randomized animal study.

SETTING

A university research laboratory.

SUBJECTS

Male adult Sprague-Dawley rats.

INTERVENTIONS

Rats were subjected either to polymicrobial sepsis by cecal ligation and puncture or to sham operation followed by the administration of normal saline solution (i.e., fluid resuscitation).

MEASUREMENTS AND MAIN RESULTS

At 5 hrs after cecal ligation and puncture, AM (12 microg/kg body weight) and AMBP-1 (40 microg/kg body weight) were administered intravenously over 1 hr. At 20 hrs after cecal ligation and puncture (i.e., the late, hypodynamic stage of sepsis), cardiac output, stroke volume, total peripheral resistance, systemic oxygen delivery, and organ blood flow were determined by radioactive microspheres, and circulating concentrations of proinflammatory cytokines were measured using enzyme-linked immunosorbent assay kits. Moreover, plasma concentrations of transaminases and lactate were measured. The results indicated that administration of AM/AMBP-1 at 5 hrs after cecal ligation and puncture prevented the decrease in measured systemic and regional hemodynamic variables and reduced plasma concentrations of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 at 20 hrs after the onset of sepsis. Moreover, administration of AM/AMBP-1 attenuated hepatic damage and the increase in plasma lactate and prevented hemoconcentration.

CONCLUSION

Administration of AM/AMBP-1 may provide a novel approach to the treatment of sepsis. Moreover, because AM/AMBP-1 significantly reduced circulating concentrations of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6, down-regulation of those proinflammatory cytokines by AM/AMBP-1 appears to play an important role for the beneficial effects of these agents in polymicrobial sepsis.

Inherited complete factor I deficiency associated with systemic lupus erythematosus, higher susceptibility to infection and low levels of factor H

Here we describe two new cases of complete deficiency of factor I (fI) in two sisters from a consanguineous Brazilian family. The eldest sibling (20-year-old) developed systemic lupus erythematosus (SLE) early during childhood while the youngest had been committed on several occasions owing to repeated infections although she was asymptomatic for auto-immune diseases. We also detected lower concentrations of C3 and factor B in both sisters. Biological functions dependent on complement activation such as the production of opsonins and killing of phagocytozed micro-organisms, chemotactic factors and haemolytic activity were all significantly reduced in both probands. Consistent with the absence of fI and low levels of fH, a deregulated production of C3b was observed by bidimensional electrophoresis in sera of both the probands.

Hereditary human complement C3 deficiency owing to reduced levels of C3 mRNA

An 8-year-old son (L.A.S.) of consanguineous parents, presented recurrent bacterial infections, vasculitis and extremely low levels of serum C3 (0.15 microg/ml). The classical and alternative pathway haemolytic activities and the generation of opsonins and chemotactic factors derived from the activation of the complement system were markedly affected in the proband's serum. An in vitro addition of purified C3 restored the classical pathway-dependent haemolytic activity of his serum. Autoradiographs of the proband's lipopolysaccharide (LPS)-stimulated and 35S-labelled fibroblast supernatants after that the SDS-PAGE revealed no C3 alpha or beta chains. The amount of C3 mRNA synthesized by the proband's fibroblasts, as evaluated by reverse transcription-polymerase chain reaction (RT-PCR) assays, was greatly reduced.