Reduced expression of C5a receptors on neutrophils from cord blood

Histological chorioamnionitis shapes the neonatal transcriptomic immune response

BACKGROUND

Histologic chorioamnionitis (HCA) is commonly associated with preterm birth and deleterious post-natal outcomes including sepsis and necrotizing enterocolitis. Transcriptomic analysis has been used to uncover gene signatures that permit diagnosis and prognostication, show new therapeutic targets, and reveal mechanisms that underlie differential outcomes with other complex disease states in neonates such as sepsis.

AIMS

To define the transcriptomic and inflammatory protein response in peripheral blood among infants with exposure to histologic chorioamnionitis.

STUDY DESIGN

Prospective, observational study.

SUBJECTS

Uninfected preterm neonates retrospectively categorized based on placental pathology with no HCA exposure (n=18) or HCA exposure (n=15).

OUTCOMES MEASURES

We measured the transcriptomic and inflammatory mediator response in prospectively collected whole blood.

RESULTS

We found 488 significant (p<0.001), differentially expressed genes in whole blood samples among uninfected neonates with HCA exposure that collectively represented activated innate and adaptive immune cellular pathways and revealed a potential regulatory role for the pleotropic microRNA molecule miR-155. Differentially secreted plasma cytokines in patients with HCA exposure compared to patients without HCA included MCP-1, MPO, and MMP-9 (p<0.05).

CONCLUSIONS

Exposure to HCA distinctively activates the neonatal immune system in utero with potentially long-term health consequences.

Platelet-Dependent Neutrophil Function Is Dysregulated by M Protein from Streptococcus pyogenes

Platelets are rapidly responsive sentinel cells that patrol the bloodstream and contribute to the host response to infection. Platelets have been reported to form heterotypic aggregates with leukocytes and may modulate their function. Here, we have investigated platelet-neutrophil complex formation and neutrophil function in response to distinct agonists. The endogenous platelet activator thrombin gave rise to platelet-dependent neutrophil activation, resulting in enhanced phagocytosis and bacterial killing. Streptococcus pyogenes is an important causative agent of severe infectious disease, which can manifest as sepsis and septic shock. M1 protein from S. pyogenes also mediated platelet-neutrophil complex formation; however, these neutrophils were dysfunctional and exhibited diminished chemotactic ability and bacterial killing. This reveals an important agonist-dependent neutrophil dysfunction during platelet-neutrophil complex formation and highlights the role of platelets during the immune response to streptococcal infection.

Decreased pattern recognition receptor signaling, interferon-signature, and bactericidal/permeability-increasing protein gene expression in cord blood of term low birth weight human newborns

Background

Morbidity and mortality rates of low birth weight (LBW) newborns at term are higher than rates in normal birth weight (NBW) newborns. LBW newborns are at greater risk to acquire recurrent bacterial and viral infections during their first few weeks of life possibly as an outcome of compromised innate immune functions. As adaptive immunity is in a naive state, increased risk of infection of LBW as compared to NBW newborns may reflect impairments in innate immunity.

Methodology

To characterize the increased susceptibility to infections in LBW newborns we used microarray technology to identify differences in gene expression in LBW newborns (n = 8) compared to NBW newborns (n = 4) using cord blood. The results obtained from the microarray study were validated on a larger number of samples using real time RT-PCR (LBW = 22, NBW = 18) and western blotting (LBW = 12, NBW = 12). The Interferome database was used to identify interferon (IFN) signature genes and ingenuity pathway analysis identified canonical pathways and biological functions associated with the differentially expressed genes in LBW newborns. ELISAs for IFNs and bactericidal/permeability-increasing protein were performed in both LBW and NBW newborns and in adults (LBW = 18, NBW = 18, Adults  = 8).

Principal Findings

Upon microarray analysis, we identified 1,391 differentially expressed genes, of which, 1,065 genes were down-regulated and 326 genes were up-regulated in the LBW compared to NBW newborns. Of note, 70 IFN-signature genes were found to be significantly down-regulated in LBW compared to NBW newborns. Ingenuity pathway analysis revealed pattern recognition receptors signaling including Toll-Like Receptors (TLRs) -1, -5, and -8 genes and IFN signaling as the most significantly impacted pathways. Respiratory infectious diseases were the most significantly affected bio-functions in LBW newborns.

Conclusion and Significance

Diminished PRRs, IFN-signature, and BPI gene expression raises the possibility that impairments in these pathways contribute to the susceptibility of LBW term infants to infection.

Peptidylarginine deiminases present in the airways during tobacco smoking and inflammation can citrullinate the host defense peptide LL-37, resulting in altered activities

Bacterial colonization of the lower respiratory tract is frequently seen in chronic obstructive pulmonary disease (COPD), and may cause exacerbations leading to disease progression. Antimicrobial peptides comprise an important part of innate lung immunity, and not least the cathelicidin human cationic antimicrobial protein-18/LL-37. Peptidylarginine deiminases (PADIs) post-translationally modify proteins by converting cationic peptidylarginine residues to neutral peptidylcitrulline. An increased presence of PADI2 and citrullinated proteins was demonstrated in the lungs of smokers. In this study, preformed PADI4, stored in granulocytes and extracellularly in the lumina of bronchi, was found in lung tissue of individuals suffering from COPD. In vitro, recombinant human PADI2 and PADI4 both caused a time- and dose-dependent citrullination of LL-37. The citrullination resulted in impaired antibacterial activity against Staphylococcus aureus, Streptococcus pneumoniae, and nontypable Haemophilus influenzae, but less so against Pseudomonas aeruginosa. Using artificial lipid bilayers, we observed discrete differences when comparing the disrupting activity of native and citrullinated LL-37, suggesting that differences in cell wall composition are important during interactions with whole bacteria. Furthermore, citrullinated LL-37 showed higher chemotactic activity against mononuclear leukocytes than did native LL-37, but was less efficient at neutralizing lipolysaccharide, and also in converting apoptotic neutrophils into a state of secondary necrosis. In addition, citrullinated LL-37 was more prone to degradation by proteases, whereas the V8 endopetidase of S. aureus cleaved the modified peptide at additional sites, compared with native LL-37. Together, these findings demonstrate novel mechanisms whereby the inflammation-dependent deiminases PADI2 and PADI4 can alter the activites of antibacterial polypeptides, affecting the course of inflammatory disorders such as COPD.

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.

Streptococcal pyogenic exotoxin B (SpeB) boosts the contact system via binding of α-1 antitrypsin

The Streptococcus pyogenes cysteine protease SpeB (streptococcal pyrogenic exotoxin B) is important for the invasive potential of the bacteria, but its production is down-regulated following systemic infection. This prompted us to investigate if SpeB potentiated the host immune response after systemic spreading. Addition of SpeB to human plasma increased plasma-mediated bacterial killing and prolonged coagulation time through the intrinsic pathway of coagulation. This effect was independent of the enzymatic activity of SpeB and was mediated by a non-covalent medium-affinity binding and modification of the serpin A1AT (α-1 antitrypsin). Consequently, addition of A1AT to plasma increased bacterial survival. Sequestration of A1AT by SpeB led to enhanced contact system activation, supported by increased bacterial growth in prekallikrein deficient plasma. In a mouse model of systemic infection, administration of SpeB reduced significantly bacterial dissemination. The findings reveal an additional layer of complexity to host–microbe interactions that may be of benefit in the treatment of severe bacterial infections.

Pathophysiology and treatment of septic shock in neonates

Neonatal septic shock is a devastating condition associated with high morbidity and mortality. Definitions for the sepsis continuum and treatment algorithms specific for premature neonates are needed to improve studies of septic shock and assess benefit from clinical interventions. Unique features of the immature immune system and pathophysiologic responses to sepsis, particularly those of extremely preterm infants, necessitate that clinical trials consider them as a separate group. Keen clinical suspicion and knowledge of risk factors will help to identify those neonates at greatest risk for development of septic shock. Genomic and proteomic approaches, particularly those that use very small sample volumes, will increase our understanding of the pathophysiology and direct the development of novel agents for prevention and treatment of severe sepsis and shock in the neonate. Although at present antimicrobial therapy and supportive care remain the foundation of treatment, in the future immunomodulatory agents are likely to improve outcomes for this vulnerable population.

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.

Injury is a major inducer of epidermal innate immune responses during wound healing

We examined the importance of injury for the epidermal innate immune response in human skin wounds. We found that injury, independent of infiltrating inflammatory cells, generated prominent chemotactic activity toward neutrophils in injured skin because of IL-8 production. Furthermore, injury was a major inducer of the expression of antimicrobial (poly)peptides (AMPs) in skin wounds. In human skin, these injury-induced innate immune responses were mediated by activation of the epidermal growth factor receptor (EGFR). Consequently, inhibition of the EGFR blocked both the chemotactic activity generated in injured skin and the expression of the majority of the AMPs. The importance of injury was confirmed in mouse experiments in vivo, in which injury independent of infection was a potent inducer of AMPs in skin wounds. To our knowledge, these data thereby provide a previously unreported molecular link between injury and neutrophil accumulation and identify the molecular background for the vast expression of IL-8 and AMPs in wounded epidermis. Conceptually, these data show that the growth factor response elicited by injury is important for the recruitment of neutrophils in skin wounds.

Bench-to-bedside review: Developmental influences on the mechanisms, treatment and outcomes of cardiovascular dysfunction in neonatal versus adult sepsis

Sepsis is a significant cause of morbidity and mortality in neonates and adults, and the mortality rate doubles in patients who develop cardiovascular dysfunction and septic shock. Sepsis is especially devastating in the neonatal population, as it is one of the leading causes of death for hospitalized infants. In the neonate, there are multiple developmental alterations in both the response to pathogens and the response to treatment that distinguish this age group from adults. Differences in innate immunity and cytokine response may predispose neonates to the harmful effects of pro-inflammatory cytokines and oxidative stress, leading to severe organ dysfunction and sequelae during infection and inflammation. Underlying differences in cardiovascular anatomy, function and response to treatment may further alter the neonate's response to pathogen exposure. Unlike adults, little is known about the cardiovascular response to sepsis in the neonate. In addition, recent research has demonstrated that the mechanisms, inflammatory response, response to treatment and outcome of neonatal sepsis vary not only from that of adults, but vary among neonates based on gestational age. The goal of the present article is to review key pathophysiologic aspects of sepsis-related cardiovascular dysfunction, with an emphasis on defining known differences between adult and neonatal populations. Investigations of these relationships may ultimately lead to 'neonate-specific' therapeutic strategies for this devastating and costly medical problem.

Effect of morphine sulfate on neonatal neutrophil chemotaxis

BACKGROUND

Opioids have been increasingly used for pain control in the neonatal intensive care unit. Data from adult human studies have demonstrated suppressive effects of morphine sulfate on the immune system, owing in part to its inhibition of chemotaxis.

OBJECTIVE

To study the effect of morphine exposure on chemotaxis of newborn neutrophils compared with adult neutrophils.

METHODS

Blood samples were collected from adult controls and from the umbilical cord of healthy full-term newborns. Neutrophils were isolated and then exposed to morphine sulfate. Chemotaxis assays were performed using interleukin (IL)-8 as the chemoattractant. The migrated neutrophils were quantitated by flow cytometry. IL-8 receptor expression was evaluated by staining with an anti-IL-8 receptor-specific antibody. Chemotaxis and IL-8 receptor expression were compared between newborn and adult neutrophils.

RESULTS

There was no difference in random migration between adult (n=10) and newborn neutrophils (n=14). IL-8 efficiently induced chemotaxis of both adult and newborn neutrophils, although newborn neutrophils exhibited significantly decreased chemotaxis compared with adult neutrophils: 389+/-197 newborn cells versus 731+/-190 adult cells (P=0.025). Exposure to morphine sulfate did not decrease chemotaxis of adult neutrophils but did modestly impair chemotaxis of newborn neutrophils. After exposure to morphine sulfate, adult neutrophils showed no difference in IL-8 receptor expression, whereas newborn neutrophils expressed fewer IL-8 receptors.

CONCLUSIONS

Newborn neutrophils had reduced chemotaxis toward IL-8. Exposure to morphine sulfate further decreased their chemotactic function. The differential effect may be explained in part by the reduction of IL-8 receptors of newborn neutrophils after morphine exposure.

Generation of reactive oxygen species by umbilical blood cells and immune status of newborns at risk of infectious inflammatory diseases

We carried out a comparative clinical and immunological examination of newborns whose mothers were at risk of infectious inflammatory diseases. Umbilical blood cell phenotype was evaluated by flow cytofluorometry. ROS level was evaluated by chemiluminescence intensity. Spontaneous production of ROS and phagocytic activity of cells in the whole umbilical blood was reduced in newborns born after complicated pregnancy. Low immunoregulatory index indicating changed CD4+/CD8+ ratio and low percentage of natural killer cells were observed in children with manifestations of bacterial infection. ROS production by isolated granulocytes and the effects of PI3K and p38 MAPK (kinases involved in the regulation of activity of NADPH oxidase responsible for the production of ROS) in the risk group infants differed from the corresponding parameters in the control group. The results indicate shifts in the phagocytosis system, immune status, and the receptor-conjugated regulatory systems of ROS generation by granulocytes in newborns at risk of infectious inflammatory diseases.

LPS-induced lung injury in neonatal rats: changes in gelatinase activities and consequences on lung growth

Postnatal lung growth disorders may involve imbalance between metalloproteinases and their inhibitors. Inflammatory cell 92-kDa gelatinase overactivity has been reported in adults with lung injury but has not been looked for in neonates. We compared gelatinase activity in neonatal and adult rats and evaluated postnatal lung growth after lipopolysaccharide (LPS)-induced lung injury. Significant intra-alveolar inflammatory cell recruitment occurred in adults and neonates; cell counts increased 16-fold in adults and 2.7-fold in neonates. Total 92-kDa gelatinase activity was increased in neonates and adults and was significantly correlated to inflammatory cell counts. For a given cell count, 92-kDa gelatinase increased more in neonates than in adults. Morphometric neonatal lung analysis showed that LPS-injured lungs had decreases in absolute values of lung volume (P < 0.03), alveolar surface (P < 0.004), and air space volume (P < 0.03). Doxycycline, a nonspecific metalloproteinase inhibitor, partly inhibited LPS-induced 92-kDa gelatinase overactivity but did not improve LPS-induced alveolar growth disorders. LPS-mediated lung injury in neonatal rats induced both gelatinase B overactivity and alveolar growth disorders, although no causal link between these two effects was demonstrated.