Pascal M. Lavoie

Neonatal Innate TLR-Mediated Responses Are Distinct from Those of Adults

The human neonate and infant are unduly susceptible to infection with a wide variety of microbes. This susceptibility is thought to reflect differences from adults in innate and adaptive immunity, but the nature of these differences is incompletely characterized. The innate immune response directs the subsequent adaptive immune response after integrating information from TLRs and other environmental sensors. We set out to provide a comprehensive analysis defining differences in response to TLR ligation between human neonates and adults. In response to most TLR ligands, neonatal innate immune cells, including monocytes and conventional and plasmacytoid dendritic cells produced less IL-12p70 and IFN-α (and consequently induced less IFN-γ), moderately less TNF-α, but as much or even more IL-1β, IL-6, IL-23, and IL-10 than adult cells. At the single-cell level, neonatal innate cells generally were less capable of producing multiple cytokines simultaneously, i.e., were less polyfunctional. Overall, our data suggest a robust if not enhanced capacity of the neonate vs the adult white-blood cell TLR-mediated response to support Th17- and Th2-type immunity, which promotes defense against extracellular pathogens, but a reduced capacity to support Th1-type responses, which promote defense against intracellular pathogens.

Heritability of bronchopulmonary dysplasia, defined according to the consensus statement of the national institutes of health.

OBJECTIVE. The goal was to determine the magnitude of genetic effects on susceptibility and risk factors for bronchopulmonary dysplasia by using the clinically validated National Institutes of Health consensus definition as a demonstrated proxy for long-term respiratory and neurodevelopmental outcomes in extremely low birth weight infants. METHODS. We analyzed clinical data from twin pairs born at ≤30 completed weeks of gestation in British Columbia, Canada, between 1993 and 2006. Differences in correlations between monozygotic and dizygotic twin pairs and model-fitting approaches were used to quantify the relative contributions of genetic, shared environmental, and nonshared environmental effects. RESULTS. Among 318 twins of known zygosity, monozygotic twin pair similarities were greater than those observed for dizygotic pairs, which suggests significant heritability for bronchopulmonary dysplasia. Model-fitting analyses confirmed that genetic effects accounted for 82% and 79% of the observed variance in bronchopulmonary dysplasia susceptibility, defined on the basis of the need for supplemental oxygen at 36 weeks or the National Institutes of Health consensus definition, respectively. Variations in rates of hemodynamically significant patent ductus arteriosus were largely accounted for by genetic effects, whereas the observed variability in susceptibility to blood-borne bacterial infections was largely attributable to environmental factors, both common and unique to each infant. CONCLUSIONS. Susceptibility to bronchopulmonary dysplasia and persistence of patent ductus arteriosus are both significantly heritable. Our study strengthens the case for investigating genetic risk stratification markers useful for predicting the most significant long-term respiratory and neurodevelopmental consequences of bronchopulmonary dysplasia in premature neonates.

Ontogeny of Toll-Like Receptor Mediated Cytokine Responses of Human Blood Mononuclear Cells

Newborns and young infants suffer increased infectious morbidity and mortality as compared to older children and adults. Morbidity and mortality due to infection are highest during the first weeks of life, decreasing over several years. Furthermore, most vaccines are not administered around birth, but over the first few years of life. A more complete understanding of the ontogeny of the immune system over the first years of life is thus urgently needed. Here, we applied the most comprehensive analysis focused on the innate immune response following TLR stimulation over the first 2 years of life in the largest such longitudinal cohort studied to-date (35 subjects). We found that innate TLR responses (i) known to support Th17 adaptive immune responses (IL-23, IL-6) peaked around birth and declined over the following 2 years only to increase again by adulthood; (ii) potentially supporting antiviral defense (IFN-α) reached adult level function by 1 year of age; (iii) known to support Th1 type immunity (IL-12p70, IFN-γ) slowly rose from a low at birth but remained far below adult responses even at 2 years of age; (iv) inducing IL-10 production steadily declined from a high around birth to adult levels by 1 or 2 years of age, and; (v) leading to production of TNF-α or IL-1β varied by stimuli. Our data contradict the notion of a linear progression from an ‘immature’ neonatal to a ‘mature’ adult pattern, but instead indicate the existence of qualitative and quantitative age-specific changes in innate immune reactivity in response to TLR stimulation.

The developing human preterm neonatal immune system: A case for more research in this area

Neonates, particularly those born prematurely, are among the most vulnerable age group for morbidity and mortality due to infections. Immaturity of the innate immune system and a high need for invasive medical procedures in the context of a preterm birth make these infants highly susceptible to common neonatal pathogens. Preterm infants who survive may also suffer permanent disabilities due to organ damage resulting from either the infection itself or from the inflammatory response generated under an oxidative stress. Infections in preterm infants continue to pose important healthcare challenges. Yet, developmental maturation events in the innate immune system that underlie their excessively high vulnerability to infection remain largely understudied. In this review article, we identify pertinent knowledge gaps that must be filled in order to orient future translational research.

Understanding the mechanism of action of bacterial superantigens from a decade of research

Summary: In the face of the unique diversity and plasticity of the immune system pathogenic organisms have developed multiple mechanisms in adaptation to their hosts, including the expression of a particular class of molecules called superantigens. Bacterial superantigens are the most potent stimulators of T cells. The functional consequences of the expression of superantigens by bacteria can be extended not only to T lymphocytes, but also to B lymphocytes and to cells of the myeloid compartment, including antigen‐presenting cells and phagocytes. The biological effects of bacterial superantigens as well as their molecular aspects have now been studied for a decade. Although there is still a long way to go to clearly understand the role these molecules play in the establishment of disease, recently acquired knowledge of their biochemistry now offers unique experimental opportunities in defining the molecular rules of T‐cell activation. Here, we present some of the most recent functional and molecular aspects of the interaction of bacterial superantigens with MHC class II molecules and the T‐cell receptor.

Role of the T Cell Receptor α Chain in Stabilizing TCR-Superantigen-MHC Class II Complexes

Superantigens (SAGs) activate T cells by simultaneously binding the Vbeta domain of the TCR and MHC class II molecules on antigen-presenting cells. The preferential expression of certain Valpha regions among SAG-reactive T cells has suggested that the TCR alpha chain may modulate the level of activation through an interaction with MHC. We demonstrate that the TCR alpha chain is required for maximum stabilization of the TCR-SAG-MHC complex and that the alpha chain increases the half-life of the complex to match those of TCR-peptide/MHC complexes. The site on the TCR alpha chain responsible for these effects is CDR2. Thus, the overall stability of the TCR-SAG-MHC complex is determined by the combination of three distinct interactions: TCR-SAG, SAG-MHC, and MHC-TCR.

Neonatal Sepsis due to Coagulase-Negative Staphylococci

Neonates, especially those born prematurely, are at high risk of morbidity and mortality from sepsis. Multiple factors, including prematurity, invasive life-saving medical interventions, and immaturity of the innate immune system, put these infants at greater risk of developing infection. Although advanced neonatal care enables us to save even the most preterm neonates, the very interventions sustaining those who are hospitalized concurrently expose them to serious infections due to common nosocomial pathogens, particularly coagulase-negative staphylococci bacteria (CoNS). Moreover, the health burden from infection in these infants remains unacceptably high despite continuing efforts. In this paper, we review the epidemiology, immunological risk factors, diagnosis, prevention, treatment, and outcomes of neonatal infection due to the predominant neonatal pathogen CoNS.

Attenuation of Respiratory Syncytial Virus-Induced and RIG-I-Dependent Type I IFN Responses in Human Neonates and Very Young Children

Newborn infants, including those born at term without congenital disorders, are at high risk of severe disease from respiratory syncytial virus (RSV) infection. Indeed, our current local surveillance data demonstrate that approximately half of children hospitalized with RSV were ≤3 mo old, and 74% were born at term. Informed by this clinical epidemiology, we investigated antiviral innate immune responses in early life, with the goal of identifying immunological factors underlying the susceptibility of infants and young children to severe viral lower respiratory tract infections. We compared RSV-induced innate cytokine production in blood mononuclear cells from neonates, young children aged 12–59 mo, and healthy adults. RSV-induced IFN-α production was primarily mediated by plasmacytoid dendritic cells (pDCs), and was significantly lower in term infants and young children < 5 y of age than in adults (p < 0.01). RSV-induced IFN-α production in human pDCs proceeded independently of endosomal TLRs, and human pDCs from healthy adult donors produced IFN-α in a retinoic acid–inducible gene I protein (RIG-I)–dependent manner. Of interest, young age and premature birth were independently associated with attenuated RIG-I–dependent IFN-α responses (p < 0.01). In contrast to IFN-α production, proinflammatory IL-6 responses to RSV were mediated by monocytes, appeared less dependent on RIG-I, and were significantly impaired only among preterm infants, not in term infants and young children. Our results suggest that human pDCs are less functional in early life, which may contribute to the increased susceptibility of infants and young children to severe RSV disease.

Neonatal Pain-Related Stress and NFKBIA Genotype Are Associated with Altered Cortisol Levels in Preterm Boys at School Age

Neonatal pain-related stress is associated with elevated salivary cortisol levels to age 18 months in children born very preterm, compared to full-term, suggesting early programming effects. Importantly, interactions between immune/inflammatory and neuroendocrine systems may underlie programming effects. We examined whether cortisol changes persist to school age, and if common genetic variants in the promoter region of the NFKBIA gene involved in regulation of immune and inflammatory responses, modify the association between early experience and later life stress as indexed by hair cortisol levels, which provide an integrated index of endogenous HPA axis activity. Cortisol was assayed in hair samples from 128 children (83 born preterm ≤32 weeks gestation and 45 born full-term) without major sensory, motor or cognitive impairments at age 7 years. We found that hair cortisol levels were lower in preterm compared to term-born children. Downregulation of the HPA axis in preterm children without major impairment, seen years after neonatal stress terminated, suggests persistent alteration of stress system programming. Importantly, the etiology was gender-specific such that in preterm boys but not girls, specifically those with the minor allele for NFKBIA rs2233409, lower hair cortisol was associated with greater neonatal pain (number of skin-breaking procedures from birth to term), independent of medical confounders. Moreover, the minor allele (CT or TT) of NFKBIA rs2233409 was associated with higher secretion of inflammatory cytokines, supporting the hypothesis that neonatal pain-related stress may act as a proinflammatory stimulus that induces long-term immune cell activation. These findings are the first evidence that a long-term association between early pain-related stress and cortisol may be mediated by a genetic variants that regulate the activity of NF-κB, suggesting possible involvement of stress/inflammatory mechanisms in HPA programming in boys born very preterm.

Genetics of bronchopulmonary dysplasia in the age of genomics.

Purpose of review According to recent evidence, susceptibility to bronchopulmonary dysplasia (BPD) in preterm infants is predominantly inherited. The purpose of this review is to discuss current published genetic association studies in light of the accumulated knowledge in genomics. Recent findings Major advances in the development of next-generation genotyping and sequencing platforms, statistical methodologies, inventories of functional outcome of some common genetic polymorphisms and large-scale cataloguing of genetic variability among many of the worlds ethnic populations have greatly facilitated the study of polygenic conditions. For BPD, genetic-association studies have primarily focused on components of innate (e.g. first-line) immune and antioxidant defences, mechanisms of vascular and lung remodelling, and surfactant proteins. However, studies have been limited in sample size and therefore fraught with a high probability of false-positive and false-negative associations. Nonetheless, candidate gene associations have indicated some novel biological pathways and provide a conceptual framework for the design of larger, collaborative population-based studies. Summary Although studies to date have not been able to identify reproducible genetic risk markers for BPD, they have directed us towards new, promising research avenues.