Complement system in healthy term newborns: reference values in umbilical cord blood

External quality assurance program for diagnostic complement laboratories: evaluation of the results of the past seven years

Introduction

The complement external quality assurance (EQA) program was first organized in 2010 by a group of researchers working in diagnostic complement laboratories. Starting in 2016, INSTAND e.V., a German, non-profit interdisciplinary scientific medical society dedicated to providing expert EQA programs for medical laboratories, started organizing the EQAs for complement diagnostic laboratories together with the same group of experienced scientists and doctors who also work as EQA experts. The aim of the current work is to provide descriptive analysis of the past seven years' complement EQA results and evaluate timeline changes in proficiency testing.

Methods

Each year, in March and October, blinded samples (normal, pathological) were sent to the participating diagnostic laboratories, where complement parameters were evaluated exactly as in daily routine samples. Since no reference method/target values exist for these parameters, and participants used different units for measurement, the reported results were compared to the stable mean (Algorithm A) of the participants using the same method/measurement units. A reported result was qualified as "passed" if it fell into the 30-50% evaluation/target range around the mean of reported results (depending on the given parameter).

Results

While the number of participating laboratories has increased in the past years (from around 120 to 347), the number of complement laboratories providing multiple determinations remained mostly unchanged (around 30 worldwide). C3, C4, C1-inhibitor antigen and activity determinations provided the best proficiency results, with >90% passing quotas in the past years, independent of the applied method. Determination of the functional activity of the three activation pathways was good in general, but results showed large variance, especially with the pathological samples. Complement factor C1q and regulators FH and FI are determined by only a few laboratories, with variable outcomes (in general in the 85-90% pass range). Activation products sC5b-9 and Bb were determined in 30 and 10 laboratories, respectively, with typical passing quotas in the 70-90% range, without a clear tendency over the past years.

Conclusion

With these accumulated data from the past seven years, it is now possible to assess sample-, method-, and evaluation related aspects to further improve proficiency testing and protocolize diagnostic complement determinations.

Variation of Complement Protein Levels in Maternal Plasma and Umbilical Cord Blood during Normal Pregnancy: An Observational Study

The complement system constitutes a crucial part of the innate immunity, mediating opsonization, lysis, inflammation, and elimination of potential pathogens. In general, there is an increased activity of the complement system during pregnancy, which is essential for maintaining the host’s defense and fetal survival. Unbalanced or excessive activation of the complement system in the placenta is associated with pregnancy complications, such as miscarriage, preeclampsia, and premature birth. Nonetheless, the actual clinical value of monitoring the activation of the complement system during pregnancy remains to be investigated. Unfortunately, normal reference values specifically for pregnant women are missing, and for umbilical cord blood (UCB), data on complement protein levels are scarce. Herein, complement protein analyses (C1q, C3, C4, C3d levels, and C3d/C3 ratio) were performed in plasma samples from 100 healthy, non-medicated and non-smoking pregnant women, collected during different trimesters and at the time of delivery. In addition, UCB was collected at all deliveries. Maternal plasma C1q and C3d/C3 ratio showed the highest mean values during the first trimester, whereas C3, C4, and C3d had rising values until delivery. We observed low levels of C1q and C4 as well as increased C3d and C3d/C3 ratio, particularly during the first trimester, as a sign of complement activation in some women. However, the reference limits of complement analyses applied for the general population appeared appropriate for the majority of the samples. As expected, the mean complement concentrations in UCB were much lower than in maternal plasma, due to the immature complement system in neonates.

Quantification of human complement C2 protein using an automated turbidimetric immunoassay

BACKGROUND

The measurement of complement components is clinically useful where a deficiency is suspected, or where excessive activation and consumption are present in disease. C2 deficiency carries an increased risk of developing systemic lupus erythematosus, recurrent infections and atherosclerosis. In this study, we have evaluated The Binding Site's Human Complement C2 SPAPLUS® assay.

METHODS

Linearity was tested using 13 sample dilutions covering the standard measuring range. Within- and between-assay variabilities were calculated using five samples with different C2 concentrations. The correlation between C2 concentrations in EDTA-plasma and serum was assessed, as was the correlation between C2 measurements by the automated assay and radial immunodiffusion. C2 concentrations were compared with CH50 activity, and quantified in individuals with homozygous or heterozygous C2 deficiency, acquired angioedema and patients with chronic inflammatory conditions.

RESULTS

The assay was linear across the measuring range (3.8-42.3 mg/L). Intra- and interassay variability were 2.3%-3.8% and 0%-3.3%, respectively. Comparison between C2 measurements in EDTA-plasma and serum provided a strong correlation (p<0.0001, R2=0.82, slope 0.92), as did the correlation between the automated and radial immunodiffusion methods (p<0.0001, R2=0.89, slope 1.07). A positive correlation between C2 concentration and CH50 activity was demonstrated (p<0.0001, R2=0.48). Significant differences were observed between the median C2 concentrations obtained in healthy controls and the patient clinical samples, with homozygous C2-deficient patients giving below detectable results.

CONCLUSIONS

This C2 SPAPLUS® assay allows the automated, rapid and precice quantification of complement C2 protein and could therefore be considered as a replacement for older, more time-consuming methods.

The role of properdin in complement-mediated renal diseases: a new player in complement-inhibiting therapy?

Properdin is known as the only positive regulator of the complement system. Properdin promotes the activity of this defense system by stabilizing its key enzymatic complexes: the complement alternative pathway (AP) convertases. Besides, some studies have indicated a role for properdin as an initiator of complement activity. Though the AP is a powerful activation route of the complement system, it is also involved in a wide variety of autoimmune and inflammatory diseases, many of which affect the kidneys. The role of properdin in regulating complement in health and disease has not received as much appraisal as the many negative AP regulators, such as factor H. Historically, properdin deficiency has been strongly associated with an increased risk for meningococcal disease. Yet only recently had studies begun to link properdin to other complement-related diseases, including renal diseases. In the light of the upcoming complement-inhibiting therapies, it is interesting whether properdin can be a therapeutic target to attenuate AP-mediated injury. A full understanding of the basic concepts of properdin biology is therefore needed. Here, we first provide an overview of the function of properdin in health and disease. Then, we explore its potential as a therapeutic target for the AP-associated renal diseases C3 glomerulopathy, atypical hemolytic uremic syndrome, and proteinuria-induced tubulointerstitial injury. Considering current knowledge, properdin-inhibiting therapy seems promising in certain cases. However, knowing the complexity of properdin's role in renal pathologies in vivo, further research is required to clarify the exact potential of properdin-targeted therapy in complement-mediated renal diseases.

Reference Intervals of Factor H and Factor H-Related Proteins in Healthy Children

Complement is activated as part of the innate immune defense against invading pathogens. Also, it helps to remove apoptotic debris and immune complexes from the circulation. Impaired complement function due to aberrant plasma levels of complement proteins may be indicative for complement-mediated diseases or can be involved in susceptibility for infections. To determine whether plasma levels are abnormal, reference intervals (RIs) are used from adult healthy donors. Since many complement-mediated diseases have an onset during childhood, it is important to know whether these RIs can be extrapolated to children. RIs of Factor H (FH), the crucial fluid-phase regulator, and the FH-related proteins (FHRs), its homologous counterparts, are unknown in healthy children. While FH is measured to diagnose and monitor therapy of patients with atypical hemolytic uremic syndrome, recent studies also implicated increased plasma levels of FHRs in disease. Here, we investigated the levels of FH and FHRs in healthy children using recently developed specific ELISAs. We found that levels of FH, FHR-2, and FHR-3 were equal to those found in healthy adults. Levels of FHR-4A and FHR-5 were lower in children than in adults. However, only the FHR-5 levels associated with age. The RIs of these FH family proteins now serve to support the interpretation of plasma levels in prospective and retrospective studies that can be used for routine diagnostic and monitoring purposes including pediatric patient samples.

Granulocyte and monocyte CD11b expression during plasma separation is dependent on complement factor 5 (C5) - an ex vivo study with blood from a C5-deficient individual

The aim of the study was to investigate the role of complement factor 5 (C5) in reactions elicited by plasma separation using blood from a C5-deficient (C5D) individual, comparing it to C5-deficient blood reconstituted with C5 (C5DR) and blood from healthy donors. Blood was circulated through an ex vivo plasma separation model. Leukocyte CD11b expression and leukocyte-platelet conjugates were measured by flow cytometry during a 30-min period. Other markers were assessed during a 240-min period. Granulocyte and monocyte CD11b expression did not increase in C5D blood during plasma separation. In C5DR samples granulocytes CD11b expression, measured by mean fluorescence intensity (MFI), increased from 10481 ± 6022 (SD) to 62703 ± 4936, and monocytes CD11b expression changed from 13837 ± 7047 to 40063 ± 713. Granulocyte-platelet conjugates showed a 2.5-fold increase in the C5DR sample compared to the C5D sample. Monocyte-platelet conjugates increased independently of C5. In the C5D samples, platelet count decreased from 210 × 10⁹ /L (201-219) (median and range) to 51 × 10⁹ /L (50-51), and C3bc increased from 14 CAU/mL (21-7) to 198 CAU/mL (127-269), whereas TCC formation was blocked during plasma separation. In conclusion, up-regulation of granulocyte and monocyte CD11b during plasma separation was C5-dependent. The results also indicate C5 dependency in granulocyte-platelet conjugates formation.

Complement analysis 2016: Clinical indications, laboratory diagnostics and quality control

In recent years, complement analysis of body fluids and biopsies, going far beyond C3 and C4, has significantly enhanced our understanding of the disease process. Such expanded complement analysis allows for a more precise differential diagnosis and for critical monitoring of complement-targeted therapy. These changes are a result of the growing understanding of the involvement of complement in a diverse set of disorders. To appreciate the importance of proper complement analysis, it is important to understand the role it plays in disease. Historically, it was the absence of complement as manifested in severe infection that was noted. Since then complement has been connected to a variety of inflammatory disorders, such as autoimmune diseases and hereditary angioedema. While the role of complement in the rejection of renal grafts has been known longer, the significant impact of complement. In certain nephropathies has now led to the reclassification of some rare kidney diseases and an increased role for complement analysis in diagnosis. Even more unexpected is that complement has also been implicated in neural, ophtalmological and dermatological disorders. With this level of involvement in some varied and impactful health issues proper complement testing is clearly important; however, analysis of the complement system varies widely among laboratories. Except for a few proteins, such as C3 and C4, there are neither well-characterized standard preparations nor calibrated assays available. This is especially true for the inter-laboratory variation of tests which assess classical, alternative, or lectin pathway function. In addition, there is a need for the standardization of the measurement of complement activation products that are so critical in determining whether clinically relevant complement activation has occurred in vivo. Finally, autoantibodies to complement proteins (e.g. anti-C1q), C3 and C4 convertases (C3 and C4 nephritic factor) or to regulatory proteins (e.g. anti-C1inhibitor, anti-factor H) are important in defining autoimmune processes and diseases based on complement dysregulation. To improve the quality of complement laboratory analysis a standardization commmittee of the International Complement Society (ICS) and the International Union of Immunological Societies (IUIS) was formed to provide guidelines for modern complement analysis and standards for the development of international testing programs.

Emerging and Novel Functions of Complement Protein C1q

Complement protein C1q, the recognition molecule of the classical pathway, performs a diverse range of complement and non-complement functions. It can bind various ligands derived from self, non-self, and altered self and modulate the functions of immune and non-immune cells including dendritic cells and microglia. C1q involvement in the clearance of apoptotic cells and subsequent B cell tolerance is more established now. Recent evidence appears to suggest that C1q plays an important role in pregnancy where its deficiency and dysregulation can have adverse effects, leading to preeclampsia, missed abortion, miscarriage or spontaneous loss, and various infections. C1q is also produced locally in the central nervous system, and has a protective role against pathogens and possible inflammatory functions while interacting with aggregated proteins leading to neurodegenerative diseases. C1q role in synaptic pruning, and thus CNS development, its anti-cancer effects as an immune surveillance molecule, and possibly in aging are currently areas of extensive research.

Complement profile in neonates of different gestational ages

Blood levels of regulators of the complement system in preterm babies were reported in few studies only. The aim of this study was to set up a complement profile in premature and term babies focusing on the development of blood levels of MBL, key regulatory proteins and on classical pathway activity, which may allow an estimation of potential susceptibility to infection. Complement activity (CH50), levels of mannan-binding lectin (MBL), complement regulators (factors H and I, C1 inhibitor, properdin) and C3a as marker of complement activation were assessed in three groups of healthy newborns: (1) prematures (≤34 weeks); (2) late prematures (>34-<37 weeks) and (3) term neonates (≥37 weeks). CH50 increased with gestational age with lower titres in cord blood than in day 5 post-delivery venous blood. MBL concentrations were not significantly different among groups. Quantitative and functional C1 inhibitor were below adult normal range in prematures <34 weeks and lower in cord blood as compared to day 5. Factor I, factor H and properdin remained below adult values in all groups. Low C3a levels excluded that low complement titres were due to activation-induced consumption. These results demonstrate the relative immaturity of the complement system and its regulation, especially in premature infants.

Staphylococcus epidermidis biofilms induce lower complement activation in neonates as compared with adults

BACKGROUND

Staphylococcus epidermidis (SE) is an important cause of late-onset sepsis in neonates. SE frequently produces a polysaccharide intercellular adhesin (PIA) biofilm, important in the pathogenesis of these infections. Little is known about how the neonatal innate immune system reacts to SE biofilm-associated infections. Our hypothesis was that SE biofilms induce a lower complement activation in neonates as compared with adults.

METHODS

Cord blood from term infants (n = 15) and blood from adults (n = 6) were studied in an ex vivo whole-blood sepsis model. A PIA biofilm-producing strain (SE1457) and its isogenic mutant (M10), producing a non-PIA biofilm, were used.

RESULTS

Both SE biofilms induced stronger complement activation in adult than in cord blood (P ≤ 0.033). We found lower levels of antibodies toward both PIA (P = 0.002) and the whole bacterium (P = 0.001) in cord vs. adult blood. By contrast, the interleukin-8 (IL-8) and IL-6 secretion were higher in cord than in adult blood (P ≤ 0.002). The PIA biofilm induced stronger complement activation than the non-PIA biofilm.

CONCLUSION

We conclude that the neonatal complement system exhibits a maturational deficiency. This may reduce the ability of neonates to combat biofilm-associated SE infections.

Humanized mice, a new model to study the influence of drug treatment on neonatal sepsis

Bacterial infection with group B Streptococcus (GBS) represents a prominent threat to neonates and fetuses in the Western world, causing severe organ damage and even death. To improve current therapeutic strategies and to investigate new approaches, an appropriate in vivo model to study the immune response of a human immune system is needed. Therefore, we introduced humanized mice as a new model for GBS-induced sepsis. Humanized mice feature deficiencies similar to those found in neonates, such as lower immunoglobulin levels and myeloid cell dysfunction. Due to the husbandry in specific-pathogen-free (SPF) facilities, the human immune cells in these mice also exhibit a naive phenotype which mimics the conditions in fetuses/neonates. Following infection, cytokine release and leukocyte trafficking from the bone marrow to the lymphoid organ (spleen) and into the peritoneum (site of infection) as well as bacterial spreading and clearance were traceable in the humanized mice. Furthermore, we investigated the effects of betamethasone and indomethacin treatment using this novel sepsis model. Although both drugs are commonly used in perinatal care, little is known about their effects on the neonatal immune system. Treatment of infected humanized mice not only induced the reduction of human leukocytes in the spleen but also increased the bacterial load in all analyzed organs, including the brain, which did not show infiltration of live GBS in untreated controls. These studies demonstrate the utility of the humanized mice as a new model to study an immature human immune response during bacterial infection and allow the investigation of side effects induced by various treatments.

Decreased expression of complement 3a receptor (C3aR) in human placentas from severe preeclamptic pregnancies

OBJECTIVES

The aim of this study was to determine the expression of the anaphylatoxin receptors complement C3a receptor (C3aR) and C5a receptor (C5aR) in the placentas of pregnancies complicated by severe early onset preeclampsia.

STUDY DESIGN

We recruited women with pregnancies complicated by severe early-onset preeclampsia (n=19, 11 of which were further complicated with IUGR) and women with preterm pregnancies not affected by preeclampsia (n=8). Gene and protein expression of C3aR and C5aR was analysed by quantitative RT-PCR and Western blotting, respectively.

RESULTS

C3aR was detected in the Hofbauer cells in the villous stroma of the placenta. C5aR staining was detected in the syncytiotrophoblast and endothelial cells. We found significantly decreased expression of C3aR mRNA and protein expression in placentas with preeclampsia compared to controls. However, C5aR expression was not significantly different between preeclamptic and control placentas at either the mRNA or protein level.

CONCLUSIONS

Decreased C3aR expression indicates a dysregulation of the complement system in the placentas of preeclamptic women. Further studies would elucidate the exact mechanisms that complement has in preeclampsia.

Factors of the lectin pathway of complement activation and their clinical associations in neonates

This paper summarizes the data concerning soluble defense lectins (mannan-binding lectin, M-ficolin, L-ficolin, and H-ficolin) with the unique ability to activate complement and their associated serine proteases (MASPs) in neonates. The clinical importance of deficiencies of these immune factors is presented in aspects of perinatal mortality, premature births, and low birthweight. Prenatal serum concentrations of L-ficolin, H-ficolin, and MASP-2 (and probably M-ficolin) correlate with gestational age and birthweight. The relationship of serum MBL to gestational age is controversial. The MBL2 genotypes XA/O and O/O (associated with low-serum MBL) are associated with perinatal infections, whereas the high serum MBL-conferring A/A genotypes may be associated with prematurity. Low-serum L-ficolin concentrations, but not low-serum H-ficolin concentrations, are also associated with perinatal infections. Much of the literature is inconsistent, and the relationships reported so far require independent confirmation at both gene and protein levels. Our preliminary conclusion is that these soluble defense lectins play a protective role in the neonate, and that insufficiency of such factors contributes to the adverse consequences of prematurity and low birthweight.

Off to a slow start: under-development of the complement system in term newborns is more substantial following premature birth

Complement represents a keystone to the innate immune system, with three activation pathways that utilise foreign microbial pattern recognition as well as activation by the host's specific antibodies. However, innate immunity is not synonymous with neonatal immunity. The complement system in healthy term (38-42 weeks gestation) newborns is under-developed and, with only a few exceptions (e.g. C7 and factor D), the circulating complement component concentrations are between 10 and 80% of adult levels. Complement activation is tightly regulated and the circulating regulator levels are also low relative to adults, sometimes at almost undetectable levels (e.g. C4b-binding protein). For premature newborns, these relative deficiencies are even more marked. Newborns are known to be more susceptible to infection, and the importance of complement, not only through its decreased ability to directly lyse bacteria with the common terminal pathway, but also its reduced ability to recruit (chemotaxis) innate and adaptive leukocytes to sites of microbial invasion and reduced ability to enhance phagocytosis (opsonisation) will be discussed. Complement also holds a key role in enhancing and directing refinement of the specific antibody response to pathogens (as an adjuvant) that likely plays a role in the well-known under-performance of the humoral immune response in newborns.

Evidence for complement activation in the amniotic fluid of women with spontaneous preterm labor and intra-amniotic infection

OBJECTIVE

The complement system plays an important role in host defense against infection. Concentrations of complement split products or anaphylatoxins (C3a, C4a, and C5a) in biological fluids are considered to reflect complement activation. The purpose of this study was to determine if term and preterm parturition are associated with evidence of complement activation in the amniotic fluid.

STUDY DESIGN

Amniotic fluid (AF) samples were collected from 270 women in the following groups: (1) normal pregnant women in midtrimester (n = 70), (2) term not in labor (n = 23), (3) term in labor (n = 48), and (4) preterm labor (PTL) (n = 129). PTL was categorized into: (a) PTL without microbial invasion of the amniotic cavity (MIAC) who delivered at term (n = 42), (b) PTL who delivered preterm without MIAC (n = 57), and (c) PTL with MIAC (n = 30). C5a, C4a, and C3a concentrations in amniotic fluid were determined by ELISA. Nonparametric tests were used for statistical analysis.

RESULTS

(1) The median AF C5a concentration was higher in women at term than that of those in the midtrimester (p = 0.02); (2) Spontaneous labor at term was not associated with changes in AF concentrations of anaphylatoxins C3a, C4a, and C5a (all p > 0.05); (3) Among patients with PTL who delivered preterm, those with MIAC had higher AF C4a and C5a concentrations than those without infection (p < 0.01); and (4) AF C3a, C4a, and C5a concentrations were higher in patients with PTL with MIAC than in those with PTL without MIAC who delivered at term.

CONCLUSION

Patients with spontaneous preterm labor and intact membranes with microbial invasion of the amniotic cavity had higher median amniotic fluid concentration of complement split products C3a, C4a, and C5a than patients without intra-amniotic infection. These findings suggest that preterm labor in the context of infection is associated with activation of the complement system.

Fragment Bb in amniotic fluid: evidence for complement activation by the alternative pathway in women with intra-amniotic infection/inflammation

OBJECTIVE

Fragment Bb is an activator of the alternative pathway of the complement system. Recently, increased first trimester maternal plasma concentrations of this fragment were reported in patients destined to have a spontaneous preterm delivery before 34 weeks of gestation. The aim of this study was to determine whether the amniotic fluid (AF) concentrations of fragment Bb change with gestational age, spontaneous labor (term and preterm) and in the presence of intra-amniotic infection/inflammation (IAI).

STUDY DESIGN

This cross-sectional study included patients in the following groups: (1) mid-trimester (n = 64); (2) term in spontaneous labor (n = 70); (3) term not in labor (n = 43); (4) spontaneous preterm labor (PTL) who delivered at term (n = 76); (5) PTL without IAI who delivered preterm (n = 73); (6) PTL with IAI (n = 76); (7) preterm prelabor rupture of membranes (PROM) without IAI (n = 71); and (8) preterm PROM with IAI (n = 71). Fragment Bb concentration in AF was determined by an enzyme-linked immunoassay. Non-parametric statistics were used for analyses.

RESULTS

(1) Fragment Bb was detected in all AF samples (n = 544); (2) The median AF concentration of fragment Bb in patients at term not in labor was significantly higher than that of those in the mid-trimester [2.42 microg/ml, interquartile range (IQR) 1.78-3.22 vs. 1.64 microg/ml, IQR 1.06-3.49; p < 0.001]; (3) Among patients with PTL, those with IAI had a higher median AF fragment Bb concentration than that of woman without IAI, who delivered preterm (4.82 microg/ml, IQR 3.32-6.08 vs. 3.67 microg/ml, IQR 2.35-4.57; p < 0.001) and than that of women with an episode of PTL, who delivered at term (3.21 microg/ml, IQR 2.39-4.16; p < 0.001); (4) Similarly, among patients with preterm PROM, the median AF fragment Bb concentration was higher in individuals with IAI than in those without IAI (4.24 microg/ml, IQR 2.58-5.79 vs. 2.79 microg/ml, IQR 2.09-3.89; p < 0.001). (5) Among patients at term, the median AF fragment Bb concentration did not differ between women with spontaneous labor and those without labor (term in labor: 2.47 microg/ml, IQR 1.86-3.22; p = 0.97).

CONCLUSIONS

(1) Fragment Bb, an activator of the alternative complement pathway, is a physiologic constituent of the AF, and its concentration increases with advancing gestational age; (2) AF concentrations of fragment Bb are higher in pregnancies complicated with IAI; and (3) labor at term is not associated with changes in the AF concentrations of fragment Bb. These findings suggest a role for fragment Bb in the host immune response against IAI.

Pathway-specific complement activity in pigs evaluated with a human functional complement assay

BACKGROUND

The complement system is an important part of innate immunity. Complement deficiencies or inappropriate activation of complement may cause severe diseases. The complement functional test, Wielisa, assesses all three complement activation pathways in humans. It is important to have assays available to determine the functional complement activity in research animals. Since the pig is a relevant animal in experimental research, the aim of the present study was to evaluate the applicability of this human complement assay in pigs.

METHODS

Normal pig serum was serially diluted and assayed in the Wielisa test which is based on the activation of complement detected with an antibody against activated C9. The specificity of the three pathways was assessed using purified human MBL and mouse monoclonal antibodies against human C1q and pig factor D. Sera from 103 pigs and 38 newborn pigs were analyzed. Finally, functional activity of all pathways was assessed in vitro and in vivo in the absence and presence of complement inhibitors.

RESULTS

The detection antibody showed cross-reactivity against pig. Normal pig serum showed activity in all pathways however about 10-fold more serum was required to obtain values comparable to human serum. Anti-human C1q and anti-pig factor D antibodies abolished classical and alternative pathway activity, respectively. Sera with low lectin pathway activity reconstituted with purified human MBL, fully recovered this activity. No deficiencies were found in classical or alternative pathway, whereas the lectin pathway showed reduced activity in a substantial number of pigs, similar to the situation in humans. Finally, the assay was successfully used to evaluate and monitor inhibition of pig complement in vitro and in vivo.

CONCLUSIONS

The human complement Wielisa test can be used for functional evaluation of all complement pathways in pig serum.

Two factors of the lectin pathway of complement, l-ficolin and mannan-binding lectin, and their associations with prematurity, low birthweight and infections in a large cohort of Polish neonates

Ficolins and one collectin, mannan-binding lectin (MBL), are the only factors known to activate the lectin pathway (LP) of complement. There is considerable circumstantial evidence that MBL insufficiency can increase susceptibility to various infections and influence the course of several non-infectious diseases complicated by infections. Much less information is available concerning l-ficolin. We report the results of a prospective study to investigate any association between either MBL deficiency or l-ficolin deficiency with prematurity, low birthweight or perinatal infections in a large cohort of Polish neonates, representing an ethnically homogenous population (n=1832). Cord blood samples were analysed to determine mbl-2 gene variants, MBL concentrations and MBL-MASP-2 complex activities (MBL-dependent lectin pathway activity) as well as l-ficolin levels. Median concentrations of l-ficolin and MBL were 2500 and 1124 ng/ml, respectively, while median LP activity was 272 mU/ml. After genotyping, 60.6% of babies were mbl-2 A/A, 35.4% were A/O and 4% were O/O genotypes. We found relative l-ficolin deficiency to be associated with prematurity, low birthweight and infections. l-Ficolin concentration correlated with gestational age and with birthweight, independently of gestational age. Preterm deliveries (<38 weeks) occurred more frequently among neonates with low LP activity but not with those having low serum MBL levels. Similarly, no association of serum MBL deficiency with low birthweight was found, but there was a correlation between LP activity and birthweight. Genotypes conferring very low serum MBL concentrations were associated with perinatal infections, and high-MBL-conferring genotypes were associated with prematurity. Our findings suggest that l-ficolin participates in host defence during the perinatal period and constitute the first evidence that relative l-ficolin deficiency may contribute to the adverse consequences of prematurity. Some similar trends were found with facets of MBL deficiency, but the observed relationships were weaker and less consistent.

Role of complement and CD14 in meconium-induced cytokine formation

OBJECTIVE

Meconium aspiration syndrome has a complex, poorly defined pathophysiology. Meconium is a potent activator of complement in vitro and in vivo; the latter is associated with a systemic inflammatory response. The complement system and Toll-like receptors are 2 important upstream components of the innate immune system that act partly independently in the inflammatory network. The aim of this study was to investigate the relative role of complement and CD14 in meconium-induced cytokine production.

METHODS

Human adult (n = 6) and cord whole blood (n = 6) anticoagulated with lepirudin was collected and distributed into tubes that contained inhibitory antibodies (anti-CD14, anti-C2, anti-factor D, or combinations thereof). The tubes were preincubated for 5 minutes before addition of meconium or buffer and then incubated for 4 hours at 37 degrees C. Complement activation was measured by quantification of the terminal sC5b-9 complement complex by enzyme-linked immunosorbent assay. A panel of 27 inflammatory mediators (cytokines, chemokines, and growth factors) was measured by using multiplex technology.

RESULTS

Fourteen of the 27 mediators measured were induced by meconium both in cord and adult blood. In cord blood, 2 additional chemokines were induced and the inflammatory response was, in general, more potent. Blocking of complement or CD14 differentially reduced the formation of most mediators, anti-CD14 being more effective. Notably, the combined inhibition of complement and CD14 almost completely abolished meconium-induced formation of the cytokines and the chemokines and markedly reduced the formation of growth factors. The endogenous lipopolysaccharide content of meconium could not explain the CD14-mediated response.

CONCLUSIONS

Meconium-induced triggering of the cytokine network is differentially mediated by complement and CD14. A combined inhibition of these effector mechanisms may be an alternative approach to reduce the inflammatory reaction in meconium aspiration syndrome.

Perinatal asphyxia may present with features of neonatal atypical hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) is the consequence of platelet consumption at sites of endothelial injury. Perinatal asphyxia (PA) may cause renal failure after birth and can be associated with disseminated intravascular coagulopathy (DIC) with platelet consumption. No biological investigation permits us to distinguish clearly between neonatal HUS and DIC. We report on three neonates with renal failure due to different degrees of PA. They presented biological features compatible with HUS, such as fragmentocytes ( approximately 2%), thrombopenia (<50,000/mm(3)), and anemia (<8 g/dl). One patient required peritoneal dialysis. Haptoglobin was undetectable for all three patients. Factor H and factor I, as well as components of the complement system (C3 and C4) and ADAMTS13 activity, were decreased. Two patients received daily fresh frozen plasma infusions over the first 4 weeks. Renal function improved in two patients; one patient had chronic renal failure. No neurological sequelae were noted. All blood parameters suggestive of thrombotic microangiopathy (TMA) were normal on days 12, 30, and 60. We hypothesize that endothelial cell damage concomitant with PA may lead to a vicious circle that results in consumption of platelets and plasma factors involved in hemostasis and/or fibrinolysis. In conclusion, PA, DIC and HUS are difficult to distinguish, and endothelial cell damage may be their common pathophysiological pathway.

Complement analysis in the 21st century

Complement analysis in the clinic is usually associated with the quantification of C3 and C4, measurement of C1-inhibitor and screening for complement activity. These analyses have been available in routine diagnostic laboratories for decades. In recent years, however, the field of complement analysis has expanded considerably, with the introduction of novel assays to detect complement activation products, and spreading still further towards genetic analysis to reveal the basis of complement deficiencies and identify mutations and polymorphisms associated with defined diseases such as atypical haemolytic uraemic syndrome and age related macular degeneration. Here we review the current status of complement analysis, including assays for the quantification of complement activity and complement activation products, together with genetic methods for the detection of deficiencies, mutations and polymorphisms. This is an area where significant developments have been made recently, paralleling the research advances into the role of complement in human disease. It is clear, however, that there is a need for consensus and standardisation of analytical methods. This will be a major challenge for the complement society in the future.

Dysfunction of innate immunity and associated pathology in neonates

The neutrophils and complement system are the critical elements of innate immunity mainly due to participation in the first line of defense against microorganisms by means of phagocytosis, lysis of bacteria and activation of naive B-lymphocytes. In this report we provide an overview of the up to date information regarding the neutrophil and complement system's functional ability in newborn infants in association with the maternal conditions that exist during the intrauterine stage, gestational age and post-neonatal pathology. The neonates' capacity to control the neutrophil and complement protein activation process has also been discussed because of the evidence that uncontrolled activation of these immune elements provides a significant contribution to the tissue damage and subsequent pathology. The authors are confident that despite the many unanswered questions this review updates their knowledge and points the need for further research to clarify the role of the age-associated dysfunction of neutrophils and complement system in the infection and inflammation related pathology of newborn infants.

Synthesis of complement proteins in the human chorion is differentially regulated by cytokines

The aim of the current paper was to determine the chorion's contribution to complement synthesis in the placenta and its regulation by cytokines. Biosynthetic labeling followed by immunoprecipitation with polyclonal antibodies was performed in chorionic tissue and chorion-derived cells. Eight complement proteins, factor B, C3, C1r, C1s, C1 inhibitor, factor H, C4 and C2 were detected in chorionic tissue and were secreted extracellularly. In chorion-derived cells, IL-1beta stimulated factor B synthesis but had no effect on C1r, C1 inhibitor, C1s, factor H and C4. TNFalpha had no stimulative effect on any of the complement proteins tested. In contrast, both IL-1beta and TNFalpha highly induced IL-6 secretion in chorion-derived cells, demonstrating the overall responsiveness of these cells to these stimuli. Interestingly, IFN-gamma increased the synthesis of C1s, C1r, C1 inhibitor, C4 and factor H in chorion-derived cells. The fact that the latter two complement proteins have opposing effects on immune activation of the complement cascade demonstrates the complex balance required to both maintain an ability to ward off infections but simultaneously suppress the immune response to enable tolerance of the allograft fetus.

Passive and active components of neonatal innate immune defenses

Innate immune defenses are crucial for survival in the first days and weeks of life. At birth, newborns are confronted with a vast array of potentially pathogenic microorganisms that were not encountered in utero. At this age, cellular components of the adaptive immune system are in a naive state and are slow to respond. Antibodies received from the dam are essential for defense, but represent a finite and dwindling resource. Innate components of the immune system detect pathogen-associated molecular patterns (PAMPs) on microorganisms (and their products) by means of pattern-recognition receptors (PRRs). Soluble mediators of the innate system such as complement proteins, pentraxins, collectins, ficolins, defensins, lactoferrin, lysozyme etc. can bind to structures on pathogens, leading to agglutination, interference with receptor binding, opsonization, neutralization, direct membrane damage and recruitment of additional soluble and cellular elements through inflammation. Cell-associated receptors such as the Toll-like receptors (TLRs) can activate cells and coordinate responses (both innate and adaptive). In this paper, accumulated knowledge of the receptors, soluble and cellular elements that contribute to innate defenses of young animals is reviewed. Research interest in this area has been intermittent, and the literature varies in quantity and quality. It is hoped that documentation of the limitations of our knowledge base will lead to more extensive and enlightening studies.

Characterization of cord blood natural killer cells: implications for transplantation and neonatal infections

The role of natural killer (NK) cells in hematopoietic stem cell transplantation and in the control of neonatal infections is not yet clear. Donor-versus-recipient NK cell alloreactivity was found to improve outcome in some settings of hematopoietic stem cell transplantation. We hypothesized that the role of NK cells in cord blood (CB) transplantation and neonatal infections may depend on CB NK cell maturation stage. We therefore analyzed the expression of NK cell differentiation/phenotypic markers in human CB, as well as functional properties of purified CB NK cells. CD8 and CD57 expression was lower in CB than in adult NK cells. However, the expression of other differentiation markers was similar, as was cell surface density of CD56, the percentage of late NK cell precursors, interferon-gamma production, and the proliferative response of purified NK cells to IL-2. Spontaneous cytotoxic activity of purified CB NK cells against NK-sensitive targets was low but reached adult levels after treatment with IL-15. Expression of perforin and granzyme B was higher in CB NK cells (90 versus 58% and 86 versus 69%, respectively). intercellular adhesion molecule-1 and CD161 expression was lower in CB. Surprising, fewer CB NK cells expressed L-selectin, a marker of immature NK cells. Taken together, our results suggest that CB NK cells are phenotypically and functionally mature.

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.

Complement activation by in vivo neonatal and in vitro extracorporeal membrane oxygenation

Complment activation during extracorporeal membrane oxygenation (ECMO) in newborns can be caused by both the underlying disease processes and by blood contact with the ECMO circuit. We investigated the relative importance of these mechanisms by measuring C3a, C5a and sC5b-9 before, during and after neonatal ECMO in six consecutive newborn patients using enzyme-linked immunoassay. In addition complement activation during in vitro ECMO with repeated flow of the same blood volume was measured using blood from healthy adult donors. C3a increased significantly in vivo after 1 h (from 1035+/-193 to 1865+/-419 microg/l) and in vitro ECMO (from 314+/-75 to 1962+/-1062 microg/l). C5a increased during ECMO without significant differences between in vivo and in vitro activation. In neonatal patients, sC5b-9 rose faster than in vitro, but the rapid increase was also significant for in vitro experiments (in vivo: from 328+/-63 to 1623+/-387 microg/l after 2 h; and in vitro: from 78+/-32 to 453+/-179 microg/l after 8 h). After this initial peak at 1-2 h, complement activation decreased gradually until 2-3 days after the initiation of ECMO. We conclude that in newborns the rapid activation of the complement system after the start of ECMO is predominantly caused by contact with artificial surfaces rather than the patient's underlying disease.

In-vitro activation of complement system by lactic acidosis in newborn and adults

INTRODUCTION

Complement activation occurs secondary to a variety of external stimuli. Lactic acidosis has been previously shown to activate the complement factors C3a and C5a. In the present investigation we examined the differential effect of lactic acidosis on anaphylatoxin levels in cord and adult blood. Furthermore we aimed to determine if the entire complement cascade could be activated by lactic acidosis.

METHODS

Cord and adult blood samples (n = 20 each) were collected and incubated for one hour in either untreated condition or with the addition of lactate in two concentrations (5.5 mmol/l vs. 22 mmol/l). Following incubation, levels of C3a, C5a and sC5b-9, and blood gas parameters were determined.

RESULTS

Anaphylatoxin (C3a and C5a) and sC5b-9 levels increased with the addition of lactate in a dose-dependent manner in cord and adult blood (C3a: 1 h, 5.5 mmo/l, 22 mmol/l: 418/498/622 microg/l in cord blood; 1010/1056/1381 microg/l in adult blood, p<0,05; similar results were found for C5a and sC5b-9).

CONCLUSION

Lactic acidosis leads to an activation of the entire complement system in neonates and in adults. This activation is dose-dependent and more pronounced in adults as compared to neonates.

The analysis of the complement activation product SC5 b-9 is applicable in neonates in spite of their profound C9 deficiency

Native complement factors and complement activation products were measured in healthy neonates (n = 72) and in a group of infants with premature prolonged rupture of the membranes (PPROM) without sepsis (n = 10). Vitronectin concentration in normal cord blood was not correlated with gestational age, and the median value was 86.0% of adult values. This was markedly higher than other native complement factors studied (factor B: 35.9%, C4: 45.1%, C3: 56.2%). The concentration of C9 showed a positive correlation with gestational age and was very low, 10.8% of normal adult values in cord blood and 8.3% in the patients. Fifteen percent of the neonates had C9 levels lower than 2% of adult values. The complement activation products Bb and SC5 b-9 were significantly elevated in the patients (159% and 130% of control values, respectively), indicating alternative and terminal pathway activation. In contrast, C4 bc and C3 bc levels were not increased. The maximum amount of SC5 b-9 which could be generated in the neonatal sera by cobra venom factor was highly correlated with C9 concentration (rs = 0.86, p = 0.0001) The profound C9 deficiency found in neonates is correlated with gestational age, limits the capacity to form bacteriolytic C5 b-9 (m) and may predispose for severe invasive bacterial infection. The plasma level of SC5 b-9 under normal conditions was very low, only 0.3% (0.1%-3.0%) of the values obtained after CVF activation of the same samples. Therefore, we suggest that the analysis of SC5 b-9 is applicable also in neonates, in spite of their extremely low C9 levels.