Alternative pathway activation of the complement system in preterm infants with early onset infection

Epigenetic scores derived in saliva are associated with gestational age at birth

BACKGROUND

Epigenetic scores (EpiScores), reflecting DNA methylation (DNAm)-based surrogates for complex traits, have been developed for multiple circulating proteins. EpiScores for pro-inflammatory proteins, such as C-reactive protein (DNAm CRP), are associated with brain health and cognition in adults and with inflammatory comorbidities of preterm birth in neonates. Social disadvantage can become embedded in child development through inflammation, and deprivation is overrepresented in preterm infants. We tested the hypotheses that preterm birth and socioeconomic status (SES) are associated with alterations in a set of EpiScores enriched for inflammation-associated proteins.

RESULTS

In total, 104 protein EpiScores were derived from saliva samples of 332 neonates born at gestational age (GA) 22.14 to 42.14 weeks. Saliva sampling was between 36.57 and 47.14 weeks. Forty-three (41%) EpiScores were associated with low GA at birth (standardised estimates |0.14 to 0.88|, Bonferroni-adjusted p-value < 8.3 × 10-3). These included EpiScores for chemokines, growth factors, proteins involved in neurogenesis and vascular development, cell membrane proteins and receptors, and other immune proteins. Three EpiScores were associated with SES, or the interaction between birth GA and SES: afamin, intercellular adhesion molecule 5, and hepatocyte growth factor-like protein (standardised estimates |0.06 to 0.13|, Bonferroni-adjusted p-value < 8.3 × 10-3). In a preterm subgroup (n = 217, median [range] GA 29.29 weeks [22.14 to 33.0 weeks]), SES-EpiScore associations did not remain statistically significant after adjustment for sepsis, bronchopulmonary dysplasia, necrotising enterocolitis, and histological chorioamnionitis.

CONCLUSIONS

Low birth GA is substantially associated with a set of EpiScores. The set was enriched for inflammatory proteins, providing new insights into immune dysregulation in preterm infants. SES had fewer associations with EpiScores; these tended to have small effect sizes and were not statistically significant after adjusting for inflammatory comorbidities. This suggests that inflammation is unlikely to be the primary axis through which SES becomes embedded in the development of preterm infants in the neonatal period.

Oxidative and Inflammatory Markers Are Higher in Full-Term Newborns Suffering Funisitis, and Higher Oxidative Markers Are Associated with Admission

The aim of this study was to assess whether oxidative and inflammatory mediators in the cord blood of newborns with funisitis and chorioamnionitis can serve as indicators of their inflammatory status, and whether there is a positive association between higher mediator levels and an increased risk of admission to the neonatal intensive care unit (NICU). This study was conducted prospectively in a neonatology department of a university hospital. In total, 52 full-term newborns were evaluated, including 17 funisitis cases, 13 chorioamnionitis cases, and 22 control newborns without funisitis or chorioamnionitis. Cord blood samples were measured for oxidative stress and inflammatory status markers. The oxidative stress markers included the total nitric oxide (NO), total hydroperoxide (TH), biological antioxidant potential (BAP), and TH/BAP ratio, comprising the oxidative stress index (OSI). Inflammatory markers included interleukin (IL)-1b, IL-6, IL-8, IL-10, tumor necrosis factor alpha (TNFα), interferon γ (IFNγ), and complement component C5a. TH, OSI, IL-1b, IL-6, and IL-8 concentrations were higher in the funisitis group than in the chorioamnionitis and control groups. C5a was higher in the funisitis and chorioamnionitis groups than in the control group. Among all enrolled newborns, 14 were admitted to the NICU. Multiple logistic regression analysis showed that elevated umbilical cord blood levels of OSI and TH were associated with a higher risk of admission to the NICU (OSI: R = 2.3, 95% CI 1.26–4.29, p = 0.007 and TH: R = 1.02, 95%CI = 1.004–1.040, p = 0.015). In conclusion, OSI and TH in cord blood from full-term newborns can provide an index of inflammatory status, and higher levels are associated with the risk of admission to the NICU and, therefore, could serve as an early indicator of inflammatory conditions in newborns.

Increased Alternative Complement Pathway Function and Improved Survival during Critical Illness

Rationale: Complement is crucial for host defense but may also drive dysregulated inflammation. There is limited understanding of alternative complement function, which can amplify all complement activity, during critical illness.Objectives: We examined the function and key components of the alternative complement pathway in a series of critically ill patients and in a mouse pneumonia model.Methods: Total classical (CH50) and alternative complement (AH50) function were quantified in serum from 321 prospectively enrolled critically ill patients and compared with clinical outcomes. Alternative pathway (AP) regulatory factors were quantified by ELISA (n = 181) and examined via transcriptomics data from external cohorts. Wild-type, Cfb-/-, and C3-/- mice were infected intratracheally with Klebsiella pneumoniae (KP) and assessed for extrapulmonary dissemination.Measurements and Main Results: AH50 greater than or equal to median, but not CH50 greater than or equal to median, was associated with decreased 30-day mortality (adjusted odds ratio [OR], 0.53 [95% confidence interval (CI), 0.31-0.91]), independent of chronic liver disease. One-year survival was improved in patients with AH50 greater than or equal to median (adjusted hazard ratio = 0.59 [95% CI, 0.41-0.87]). Patients with elevated AH50 had increased levels of AP factors B, H, and properdin, and fewer showed a "hyperinflammatory" subphenotype (OR, 0.30 [95% CI, 0.18-0.49]). Increased expression of proximal AP genes was associated with improved survival in two external cohorts. AH50 greater than or equal to median was associated with fewer bloodstream infections (OR, 0.67 [95% CI, 0.45-0.98). Conversely, depletion of AP factors, or AH50 less than median, impaired in vitro serum control of KP that was restored by adding healthy serum. Cfb-/- mice demonstrated increased extrapulmonary dissemination and serum inflammatory markers after intratracheal KP infection compared with wild type.Conclusions: Elevated AP function is associated with improved survival during critical illness, possibly because of enhanced immune capacity.

Comparative Analysis of Global Gene Expression and Complement Components Levels in Umbilical Cord Blood from Preterm and Term Neonates: Implications for Significant Downregulation of Immune Response Pathways related to Prematurity

Background: Preterm birth is the most frequent cause of neonatal death, but its aetiology remains unclear. It has been suggested that the imbalance of immunological mechanisms responsible for maintaining pregnancy is contributing to preterm birth pathogenesis. We aimed to investigate global gene expression and the levels of several complement system components in umbilical cord blood samples from preterm neonates and compare them to term newborns. We sought to examine how differentially expressed genes could affect various immune-related pathways that are believed to be crucial factors in preterm birth. Material and methods: We enrolled 27 preterm infants (<37 weeks GA) and 52 term infants (>37 weeks GA), from which umbilical cord blood samples were collected. From these samples, peripheral blood mononuclear cells were isolated and subsequent RNA isolation was performed. We used Affymetrix Human Gene 2.1 ST Array Strip for microarray experiment and DAVID resources for bioinformatics analysis of the obtained data. Concentrations of C2, C3a, C5/C5a, C9, FactorD, Properdin were measured in umbilical cord blood plasma samples using multiplex fluorescent bead-based immunoassays using Luminex technology. Results: The levels of C3a and C5/5a were significantly elevated in preterm neonates compared to term babies, whereas C9 concentration was evidently increased in term infants. The expression of 250 genes was upregulated at least 2-fold and 3781 genes were downregulated at least 2-fold in preterm neonates in comparison with term infants. Functional annotation analysis revealed that in preterm infants in comparison to term babies there was a significant downregulation of genes encoding several Toll-like receptors, interleukins and genes involved in major signalling pathways (e.g. NF-κB, MAPK, TNF, Notch, JAK) and vital cellular processes (e.g. intracellular signal transduction, protein ubiquitination, protein transport, RNA splicing, DNA-templated transcription). Conclusions: Preterm birth results in immediate and long-term complications. Our results indicate that infants born prematurely show significant differences in complement components concentration and a downregulation of over 3,000 genes, involved mainly in various immune-related pathways, including innate immune response, phagocytosis and TLR function, when compared to full-term babies. Further studies on larger cohorts are needed to elucidate the role of immunity in prematurity.

The terminal complement pathway is activated in septic but not in aseptic shoulder revision arthroplasties

BACKGROUND

The early diagnosis of suspected periprosthetic low-grade infections in shoulder arthroplasties is important for the outcome of the revision surgical procedures. The aim of this study was to investigate new biomarkers of infection in revision shoulder arthroplasties, taking into account the implant design, patient age, and comorbidities.

METHODS

The study included 33 patients with shoulder arthroplasties undergoing revision surgical procedures. Microbiological diagnostic testing was performed in all cases. C-reactive protein serum levels and white blood cell counts were evaluated, and the periprosthetic tissue was stained immunohistologically for the terminal complement pathway components (C3, C5, and C9) and for CD68 and α-defensin.

RESULTS

Microbiological diagnostic testing detected a periprosthetic infection in 10 reverse shoulder arthroplasties and in 4 anatomic shoulder arthroplasties, while the remaining 19 shoulder arthroplasties were classified as aseptic. We observed more Staphylococcus epidermidis infections in reverse shoulder arthroplasties and more Staphylococcus aureus infections in anatomic shoulder arthroplasties. The revision rate correlated with pre-existing comorbidities and number of previous surgical procedures. The C-reactive protein values and the incidence of specific periprosthetic radiolucent lines were significantly increased in septic revision cases. We found increased staining for all tested complement factors (C3, C5, and C9) but not for α-defensin and CD68 in septic tissue. The most interesting finding was that C9 separated septic from aseptic tissue with a predictive specificity of 100% and a sensitivity of 88.89%.

CONCLUSION

We observed a strong correlation between C9 expressions in septic revision tissue. We propose that the terminal complement pathway, especially C9 deposition, may be a potential biomarker to identify septic complications using tissue biopsy specimens.

Immunomodulation to Prevent or Treat Neonatal Sepsis: Past, Present, and Future

Despite continued advances in neonatal medicine, sepsis remains a leading cause of death worldwide in neonatal intensive care units. The clinical presentation of sepsis in neonates varies markedly from that in older children and adults, and distinct acute inflammatory responses results in age-specific inflammatory and protective immune response to infection. This review first provides an overview of the neonatal immune system, then covers current mainstream, and experimental preventive and adjuvant therapies in neonatal sepsis. We also discuss how the distinct physiology of the perinatal period shapes early life immune responses and review strategies to reduce neonatal sepsis-related morbidity and mortality. A summary of studies that characterize immune ontogeny and neonatal sepsis is presented, followed by discussion of clinical trials assessing interventions such as breast milk, lactoferrin, probiotics, and pentoxifylline. Finally, we critically appraise future treatment options such as stem cell therapy, other antimicrobial protein and peptides, and targeting of pattern recognition receptors in an effort to prevent and/or treat sepsis in this highly vulnerable neonatal population.

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.

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.

Role of innate host defenses in susceptibility to early-onset neonatal sepsis

Neonatal sepsis continues to take a devastating toll globally. Although adequate to protect against invasive infection in most newborns, the distinct function of neonatal innate host defense coupled with impairments in adaptive immune responses increases the likelihood of acquiring infection early in life, with subsequent rapid dissemination and death. Unique differences exist between neonates and older populations with respect to the capacity, quantity, and quality of innate host responses to pathogens. Recent characterization of the age-dependent maturation of neonatal innate immune function has identified novel translational approaches that may lead to improved diagnostic, prophylactic, and therapeutic modalities.

Immunologic and infectious consequences of immediate versus delayed umbilical cord clamping in premature infants: a prospective, randomized, controlled study

AIM

To evaluate the immunologic and infectious consequences of delayed versus immediate cord clamping in premature infants (<35 weeks) during the neonatal period.

METHODS

This was a prospective, masked, randomized, controlled, single-center study. Prior to delivery 35 infants were randomly assigned to immediate cord clamping (ICC) at 5-10 s and 30 infants to delayed cord clamping (DCC), at 30-45 s (14 and 15 infants in each group were <1500 g, respectively).

RESULTS

Neonatal characteristics of the ICC and DCC groups were comparable. There was no significant difference between the ICC and DCC groups in the complement or in the immunoglobulin levels. All were within the normal range for age. All infectious parameters (events of sepsis or "rule-out sepsis", days of antibiotic therapy, and number of antibiotic courses during hospitalization and infections within the first month of life in cases of earlier discharge) were comparable in both groups. Similar results were found in the subgroup of infants <1500 g. Gender analysis showed only modest differences.

CONCLUSIONS

Delayed compared to immediate cord clamping did not affect the immunologic or the infectious status of infants born at <35 weeks during the neonatal period.

Respiratory Deleted in Malignant Brain Tumours 1 (DMBT1) levels increase during lung maturation and infection

Deleted in Malignant Brain Tumours 1 (DMBT1) is a secreted scavenger receptor cysteine-rich protein that binds and aggregates various bacteria and viruses in vitro. Studies in adults have shown that DMBT1 is expressed mainly by mucosal epithelia and glands, in particular within the respiratory tract, and plays a role in innate immune defence. We hypothesized that respiratory DMBT1 levels may be influenced by various developmental and clinical factors such as maturity, age and bacterial infection. DMBT1 levels were studied in 205 tracheal aspirate samples of 82 ventilated preterm and full-term infants by enzyme-linked immunosorbent assay. Possible effects of various clinical parameters were tested by multiple regression analysis. DMBT1 levels increased significantly with lung maturity (P < 0.0001 for both gestational and postnatal age) and in small-for-gestational-age infants (P = 0.0179). An increase of respiratory DMBT1 levels was detected in neonatal infections (P < 0.0001). These results were supported by Western blotting. Immunohistochemical analyses of archived newborn lung sections (n = 17) demonstrated high concentrations of DMBT1 in lungs of neonates with bacterial infections. Our data show that preterm infants are able to up-regulate DMBT1 in infection as an unspecific immune reaction.

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.

SIRS and group-B streptococcal sepsis in newborns: pathogenesis and perspectives in adjunctive therapy

Clinical signs of systemic inflammation and suspected systemic infection are common in neonatal medicine. Yet, causative infectious organisms can only infrequently be isolated. In previously healthy infants at low risk of sepsis, group B streptococcus (GBS) is the most common isolate. In vitro and in vivo data suggest that immune cells from newborn infants have impaired antimicrobial properties against GBS. In contrast large amounts of inflammatory mediators are formed upon GBS challenge and Toll-like receptors (TLR) are critical host molecules in this context. Thus, the immune balance tilts towards inflammation, SIRS and sepsis. Adjunctive therapy of neonatal sepsis needs to adjust the inflammatory response without further impairing bacterial clearance. This article summarises the pathophysiological events leading to sepsis and suggests molecular targets for adjunctive therapy.

Newer approaches to the diagnosis of early onset neonatal sepsis

Accurate and timely diagnosis of early onset neonatal sepsis remains challenging to the clinician and the laboratory. A test with a rapid turnaround time with 100% sensitivity, rather than high specificity, which allows accurate diagnosis and appropriate antimicrobial treatment or which allows antibiotics to be safely withheld in non-infected infants, is desirable. Many potential markers (acute phase reactants, cell surface markers, cytokines) are not routinely available to the laboratory, and most likely combinations of markers will ensure greater diagnostic accuracy. In the future, molecular biology techniques offer the prospect of rapid identification of both pathogens and antimicrobial resistance markers.

Diagnostic markers of infection in neonates

Diagnostic markers of infection are useful indicators of neonatal sepsis. Serial measurements of infection markers can improve diagnostic sensitivity, and the use of multiple markers can enhance diagnostic accuracy. Current evidence suggests that promising markers may be useful for early termination of antimicrobial treatment, but none of the current diagnostic tests are sensitive and specific enough to influence the clinical decision for withholding antibiotic treatment at the onset of suspected infection.

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.

Complement and contact activation related to surfactant response in respiratory distress syndrome

The activation of inflammation and coagulation cascades is part of the pathogenesis of adult respiratory distress syndrome (RDS). Previous studies have demonstrated contact activation in preterm infants with RDS, whereas no concordant results have been found with complement activation. In this study, both systems were investigated in preterm infants with severe RDS and related to surfactant response. Thirty preterm newborns with severe respiratory distress (FiO2 > 0.5), but with no evidence of infection or fetal acidosis, were studied. Eighteen healthy preterm newborns of similar gestational age and birth weight served as controls. The study group was divided into two subgroups, according to their response to a porcine natural surfactant 6 h after administration: responders (FiO2 reduction > 50%) and poor responders (FiO2 reduction < or = 50%). C1q, C4, factor B, C3a, C5a, complement, and C1-inhibitor activity, as well as factor XIIa, were determined in blood samples, drawn 24 h after birth. Except for C1-inhibitor concentration and C1-inhibitor activity, all parameters for infants with severe RDS were different from controls. Complement precursor proteins were lower, and activated split products of the complement and contact system were higher. Infants with a poor response after application of surfactant showed higher amounts of C3a, C5a, and factor XIIa but lower C1q and C4 levels compared with infants with a good response to surfactant. Activation of the complement and the contact system was demonstrated in all respiratory distress patients. This activation was more pronounced in poor responders to exogenous surfactant.