Diminished chemiluminescent responses of polymorphonuclear leukocytes in severely and moderately preterm neonates

Cord blood hematopoietic cells from preterm infants display altered DNA methylation patterns

Background

Premature infants are highly vulnerable to infection. This is partly attributable to the preterm immune system, which differs from that of the term neonate in cell composition and function. Multiple studies have found differential DNA methylation (DNAm) between preterm and term infants’ cord blood; however, interpretation of these studies is limited by the confounding factor of blood cell composition. This study evaluates the epigenetic impact of preterm birth in isolated hematopoietic cell populations, reducing the concern of cell composition differences.

Methods

Genome-wide DNAm was measured using the Illumina 450K array in T cells, monocytes, granulocytes, and nucleated red blood cells (nRBCs) isolated from cord blood of 5 term and 5 preterm (<31 weeks gestational age) newborns. DNAm of hematopoietic cells was compared globally across the 450K array and through site-specific linear modeling.

Results

Nucleated red blood cells (nRBCs) showed the most extensive changes in DNAm, with 9258 differentially methylated (DM) sites (FDR < 5%, |Δβ| > 0.10) discovered between preterm and term infants compared to the <1000 prematurity-DM sites identified in white blood cell populations. The direction of DNAm change with gestational age at these prematurity-DM sites followed known patterns of hematopoietic differentiation, suggesting that term hematopoietic cell populations are more epigenetically mature than their preterm counterparts. Consistent shifts in DNAm between preterm and term cells were observed at 25 CpG sites, with many of these sites located in genes involved in growth and proliferation, hematopoietic lineage commitment, and the cytoskeleton. DNAm in preterm and term hematopoietic cells conformed to previously identified DNAm signatures of fetal liver and bone marrow, respectively.

Conclusions

This study presents the first genome-wide mapping of epigenetic differences in hematopoietic cells across the late gestational period. DNAm differences in hematopoietic cells between term and <31 weeks were consistent with the hematopoietic origin of these cells during ontogeny, reflecting an important role of DNAm in their regulation. Due to the limited sample size and the high coincidence of prematurity and multiple births, the relationship between cause of preterm birth and DNAm could not be evaluated. These findings highlight gene regulatory mechanisms at both cell-specific and systemic levels that may be involved in fetal immune system maturation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-017-0339-1) contains supplementary material, which is available to authorized users.

Age-Appropriate Functions and Dysfunctions of the Neonatal Neutrophil

Neonatal and adult neutrophils are distinctly different from one another due to well-defined and documented deficiencies in neonatal cells, including impaired functions, reduced concentrations of microbicidal proteins and enzymes necessary for pathogen destruction, and variances in cell surface receptors. Neutrophil maturation is clearly demonstrated throughout pregnancy from the earliest hematopoietic precursors in the yolk sac to the well-developed myeloid progenitor cells in the bone marrow around the seventh month of gestation. Notable deficiencies of neonatal neutrophils are generally correlated with gestational age and clinical condition, so that the least functional neutrophils are found in the youngest, sickest neonates. Interruption of normal gestation secondary to preterm birth exposes these shortcomings and places the neonate at an exceptionally high rate of infection and sepsis-related mortality. Because the fetus develops in a sterile environment, neonatal adaptive immune responses are deficient from lack of antigen exposure in utero. Newborns must therefore rely on innate immunity to protect against early infection. Neutrophils are a vital component of innate immunity since they are the first cells to respond to and defend against bacterial, viral, and fungal infections. However, notable phenotypic and functional disparities exist between neonatal and adult cells. Below is review of neutrophil ontogeny, as well as a discussion regarding known differences between preterm and term neonatal and adult neutrophils with respect to cell membrane receptors and functions. Our analysis will also explain how these variations decrease with postnatal age.

Does IVIg administration yield improved immune function in very premature neonates?

Intravenous immunoglobulin (IVIg) has been evaluated as an adjunctive therapy for neonatal sepsis with modest clinical success despite strong biological plausibility. Multiple factors contribute to this outcome, but perhaps none greater than the limited immune system function in newborns, especially in the very premature neonates. For very premature neonates (<30 weeks gestational age), understanding the effects of IVIg on specific immature immune system functions is particularly relevant given their preponderance to develop sepsis and therefore potentially benefit from IVIg-mediated immunoenhancement. Here, we review the available evidence for enhanced immune function after IVIg administration in very premature neonates and highlight areas for future research.

Differential maturation of the innate immune response in human fetuses

Newborns and especially preterm infants show a unique susceptibility to severe bacterial infections that cause significant morbidity and mortality. As very few data are available on innate immune functions in human fetuses, we conducted a comprehensive study to investigate the expression of several adhesion molecules essentially involved in migration (CD11a, CD11b, CD11c, CD18, and CD62L). Furthermore, phagocytic activity, generation of respiratory burst products, and production of several proinflammatory cytokines were assessed. Various functions of the fetal innate immune system were demonstrated to be essentially different from those observed in term neonates or adults. Expression of several surface markers was significantly diminished on fetal granulocytes. Furthermore, a significantly reduced phagocytic activity of fetal granulocytes and monocytes was found, contrasted by an enhanced generation of reactive oxygen products. In addition, we demonstrate that significant numbers of fetal monocytes are capable of the production of proinflammatory cytokines in response to stimulation. However, the pattern of cytokine production is different from the more mature individuals: the number of IL-6- and tumor necrosis factor-alpha-positive monocytes were significantly diminished, whereas more IL-8-producing monocytes were found compared with adults. The results of our study add significantly to our understanding of the maturation and impairment of the innate immune response.

Pulmonary fluorodeoxyglucose uptake in infants of very low birth weight with and without intrauterine inflammation

OBJECTIVE

We compared early pulmonary (18)fluorodeoxyglucose ((18)FDG) uptake in infants who had very low birth weight with and without exposure to intrauterine inflammation by using positron emission tomography (PET). A secondary goal was to correlate (18)FDG uptake with later death or bronchopulmonary dysplasia.

METHODS

Within 72 hours of birth, 22 singleton infants between 25 and 30 weeks of gestation had a thoracic PET scan after intravenous (18)FDG. Influx constants (K(i)) for (18)FDG were determined. Placental histology assessed exposure to intrauterine inflammation.

RESULTS

Chorioamnionitis was found in 13 infants. Seven of these infants also had evidence of funisitis. No inflammation was detected in the remaining nine infants. Median (minimum, maximum) thoracic K(I) was 0.008 (0.006, 0.011) mL/min/mL in infants with funisitis, 0.006 (0.002, 0.008) in infants with chorioamnionitis only, and 0.006 (0.001, 0.015) in infants with no evidence of intrauterine inflammation (P=.16). No relation was found between K(i) and later death or bronchopulmonary dysplasia. Cord blood interleukin-6 was elevated in newborns with placental inflammation (P=.014).

CONCLUSION

Early thoracic PET scanning for metabolically active inflammatory cells does not differ between infants with and without exposure to intrauterine inflammation. Evidence of early intrapulmonary sequestration of inflammatory cells in some infants without chorioamnionitis points to the complex etiology of postnatal inflammation.

The characterization of superoxide production of human neonatal neutrophil

To assess the role of neutrophil in neonatal host defense against microbial infection, we characterized the superoxide anion (O(2-)) production of neonatal neutrophil on a biochemical basis. After taking an appropriate informed consent, neutrophils were obtained from cord blood immediately after transvaginal delivery and divided into two groups: the Preterm group, 15 neonates (27-36 weeks' gestation) and the Term group, 15 neonates (37-41 weeks' gestation). Eleven healthy adults served as controls in the Adult group. The value of N-formyl-methionyl-leucyl-phenylalanin (fMLP)-induced O(2-) production activity of neutrophils in the Preterm group using chemiluminescence assay was significantly lower than those values in both the Term and Adult groups (5.77+/-0.53x10(6) vs. 11.1+/-0.94x10(6) and 10.7+/-0.63x10(6) cpm; mean+/-S.E.M., p<0.05). In phorbol 12-myristate 13-acetate (PMA)-stimulation, the values of O(2-) production activity of neutrophils in both the Preterm and Term groups were significantly lower than that in the Adult group (13.0+/-1.66x10(6) and 18.0+/-1.44x10(6) vs. 27.3+/-1.45x10(6) cpm, p<0.05). Scatchard analysis of [(3)H]fMLP binding to neutrophil demonstrated a two-receptor model in each group, and the number of high-affinity receptors per neutrophil in the Preterm group was significantly lower than those in other groups (p<0.05). However, cord blood levels of proinflammatory cytokines, such as interleukin (IL)-6, -8, and tumor necrosis factor-alpha (TNF-alpha) did not differ in either neonatal group. These results indicated that the fMLP-induced O(2-)production activity of neutrophils in the term neonates was enhanced at the level of the receptor and suggested that this enhanced production contribute to the neonatal host defense against microbial infection.

Plasma effects on phagocytic activity and hydrogen peroxide production by polymorphonuclear leukocytes in neonates

To elucidate the defense mechanism in neonates against bacterial infections, phagocytic activity and hydrogen peroxide (H2O2) production by polymorphonuclear leukocytes (PMNs) in the whole blood and the effects of plasma on these functions were investigated on 44 healthy mature neonates (term 37 to 41 weeks) and 15 premature neonates (term 30 to 36 weeks) using two color flow cytometric analysis. The results were compared to those of a healthy adult control group (n = 10). PMN phagocytic activity was low in both mature and premature neonates. H2O2 production of PMN with phorbol myristate acetate (PMA) stimulation and following phagocytosis was augmented in both mature and premature neonates. When plasma and PMNs of adults and neonates were separated and combined differently, phagocytic activity and H2O2 production of PMNs appeared to be principally regulated by the plasma employed. This finding indicates that plasma has major effects on both phagocytosis and H2O2 production by PMNs of newborn neonates.

Chemiluminescent and flow cytometric analysis of gamma interferon preincubation on neonatal and adult rat polymorphonuclear leukocytes

Gamma interferon (IFN-gamma) has multiple immunomodulating effects and has been postulated as a possible immunopotentiating agent for the prevention or treatment of neonatal infections. This report describes the effect of rat recombinant IFN-gamma on the oxidative burst activity and CD11b expression of neonatal and adult rat polymorphonuclear leukocytes (PMNL). Oxidative burst activity was assessed by chemiluminescence and dihydrorhodamine flow cytometry. Neonatal PMNL exhibited significantly less oxidative burst activity than did adult PMNL. IFN-gamma mildly enhanced the chemiluminescence response of PMNL from both the rat pups and adults, but this effect was not statistically significant when analyzed by a multivariate model of repeated-measures analysis of variance for both chemiluminescence and dihydrorhodamine flow cytometry. CD11b expression was also not significantly enhanced by IFN-gamma.

Phagocyte chemiluminescence in pre-term infants

Intact phagocyte function is a pre-requisite for successful defence against infection, but paradoxically, these cells may also play a major role in the pathogenesis of the infant respiratory distress syndrome. Phagocyte function is known to be deficient in pre-term infants, who are at risk of infection as a result, but these infants are also at risk of respiratory distress syndrome as a result of surfactant deficiency. Despite this, few longitudinal studies of phagocyte function have been performed in pre-term infants. We have used lucigenin-enhanced chemiluminescence to examine the respiratory burst of mixed samples containing polymorphonuclear leucocytes and monocytes of 100 pre-term infants at 48- to 72-h intervals during their admission to a neonatal care unit. Increased polymorphonuclear leucocyte chemiluminescence was associated with respiratory distress syndrome and the use of intermittent positive pressure ventilation. Multiple linear regression analysis revealed a slight, but significant depression of chemiluminescence in association with the use of gentamicin and penicillin when stronger influencing factors such as the presence of respiratory distress syndrome were taken into consideration. Measurement of phagocyte function by sensitive luminescence assays requires very little blood and may be useful in pre-term infants to follow the severity of respiratory distress syndrome. However, it is probable that other factors such as antioxidant capacity also have an important influence on the degree of tissue damage.

Photon emission of phagocytes in relation to stress and disease

Phagocytes, the first-line cells of the body's defence mechanisms against invading pathogens, kill microorganisms by means of lysosomal degradative enzymes and highly toxic reactive oxygen intermediates. The reactive oxygen compounds are produced, in a process called the 'respiratory burst', by the NADPH oxidase complex in plasma membranes, and by myeloperoxidase in phagolysosomes after degranulation. These processes generate electronically excited states which, on relaxation, emit photons, giving rise to phagocyte chemiluminescence (CL). This paper describes the conditions for the measurement of CL, and reviews the activity of phagocytes from individuals undergoing stress or disease. The capability of phagocytes to emit photons reflects remarkably well the pathophysiological state of the host. In many cases even the magnitude of the stress, the presence of a pathogen in the body, or the activity of the disease can be estimated. Physiological changes, e.g. in the reproductive cycle, can also be predicted.

Decreased adherence, chemotaxis and phagocytic activities of neutrophils from preterm neonates

Using microanalytic assays various phagocytic functions of separated neutrophils from preterm neonates (mean birthweight 1,506 g, n = 13) were simultaneously studied. Adherence of neutrophils to nylon fibre was decreased in cells from preterm infants (77.1 +/- 3.1%) when compared with adult controls (86.9 +/- 2.1%, mean +/- 1 SD, p less than 0.05). In addition neutrophil chemotaxis in response to zymosan activated serum was reduced in preterm neonates (131.9 +/- 19.7, adults 166.6 +/- 11.1, p less than 0.001); directed migration towards Formyl-Methionyl-Leucyl-Phenylalanine was also decreased (preterm neonates 93.4 +/- 15, adults 111.1 +/- 16.8, p less than 0.05). Preterm infants had a higher percentage of slow moving neutrophils when compared with adults (p less than 0.001). Phagocytosis of Candida albicans was reduced in neutrophils from preterm neonates (phagocytic index: preterm neonates 41.4 +/- 12.7, adults 83 +/- 7.2). Adult neutrophils ingested more Candida per cell (p less than 0.001). Chemiluminescence, exocytosis of elastase and lactoferrin during uptake of opsonized zymosan was also reduced in neutrophils from preterm neonates. However, random migration, phagocytosis of Staphylococcus aureus and production of O2- in response to Phorbol myristate acetate or opsonized zymosan were identical in cells from either source. We conclude, that these abnormalities of neutrophils could predispose the preterm infant to serious and often overwhelming bacterial and fungal infections.

Longitudinal evaluation of polymorphonuclear leukocyte chemiluminescence in premature infants

A chemiluminescence (CL) microassay was used to evaluate polymorphonuclear leukocyte (PMN) function in premature newborn infants longitudinally during a 2-month period and in healthy adult control subjects. At postnatal ages of 12, 26, 40 and 54 days the infants' mean peak CL activity was significantly lower than that of the adults. Infants with one or more low CL responses were more severely ill than those with normal CL activity. The infants with low CL responses had longer hospital stays and a higher frequency of serious infections, as well as more days of level 3 care, antimicrobial therapy, supplemental oxygen, assisted ventilation, and total parenteral nutrition. The PMN CL activity before, during, and after episodes of serious infection did not differ. In addition, a high frequency of depressed CL activity was observed at the time of infection. Our findings are consistent with previous studies suggesting that defective PMN oxidative metabolic responses are more common in neonates undergoing stress. Our results further suggest that defective PMN function may persist for the first 2 months of life and during the course of serious infection. Enhancement of PMN host defense may be an important strategy in the management of neonatal sepsis.

Ontogeny of inflammatory cell responsiveness: superoxide anion generation by phorbol ester-stimulated fetal, neonatal, and adult bovine neutrophils

Newborn calves, like human infants, are uniquely susceptible to bacterial infections. Part of this increased susceptibility may be related to defects in newborn polymorphonuclear leukocyte (PMN) defensive functions. It remains unclear whether reported deficits in newborn PMN function represent maturational disorders or are manifestations of some form of perinatal suppression phenomenon. We therefore compared the ability of bovine newborn PMNs (less than 24 h old), newborn PMNs (7-10 days of age), fetal PMNs (210-220 days gestational age), and adult PMNs to generate superoxide anion (O2-) as an indicator of respiratory burst activity. Citrated blood was collected, and PMNs were isolated to greater than 95% purity and 98% viability. O2- generation was measured as the superoxide dismutase-inhibitable (10 micrograms/ml) reduction of ferricytochrome c (2 mg/ml) after activation of PMNs with phorbol myristate acetate (PMA, 2 micrograms/ml) to directly stimulate protein kinase C. The reaction kinetics were measured (37 degrees C, 550 nm) using a spectrophotometer and chart recorder for continuous monitoring. O2- generation was measured for 5 min after the initial lag period and the total nanomoles of O2- generated calculated using the extinction coefficient for ferricytochrome c. Newborn PMNs (N = 10) generated significantly less O2- (5.7 +/- 0.8 nmol O2-/10(6) cells/5 min, P less than 0.01) than did adult PMNs (N = 14) (9.6 +/- 2.1 nmol O2-/10(6) cells/5 min) or fetal PMNs (N = 4) (10.7 +/- 0.7 nmol O2-/10(6) cells/5 min). PMNs from 7- to 10-day-old calves (N = 9) generated almost identical amounts of O2- as newborn PMNs (5.7 +/- 1.6 nmol O2-/10(6) cells/5 min). There was no difference in measured lag time period between newborn and adult PMNs, but fetal PMNs had significantly reduced (P less than 0.01) mean lag time. The data indicated that bovine newborn PMNs have a decreased ability to generate O2- in response to PMA stimulation, which persists for at least 7-10 days, and that this functional decrement may be a manifestation of some form of perinatal PMN suppression phenomenon rather than a developmental abnormality since fetal PMNs produced O2- as well as adult PMNs.

Ontogeny of inflammatory cell responsiveness: superoxide anion generation by phorbol ester-stimulated fetal, neonatal, and adult bovine neutrophils

Newborn calves, like human infants, are uniquely susceptible to bacterial infections. Part of this increased susceptibility may be related to defects in newborn polymorphonuclear leukocyte (PMN) defensive functions. It remains unclear whether reported deficits in newborn PMN function represent maturational disorders or are manifestations of some form of perinatal suppression phenomenon. We therefore compared the ability of bovine newborn PMNs (less than 24 h old), newborn PMNs (7-10 days of age), fetal PMNs (210-220 days gestational age), and adult PMNs to generate superoxide anion (O2-) as an indicator of respiratory burst activity. Citrated blood was collected, and PMNs were isolated to greater than 95% purity and 98% viability. O2- generation was measured as the superoxide dismutase-inhibitable (10 micrograms/ml) reduction of ferricytochrome c (2 mg/ml) after activation of PMNs with phorbol myristate acetate (PMA, 2 micrograms/ml) to directly stimulate protein kinase C. The reaction kinetics were measured (37 degrees C, 550 nm) using a spectrophotometer and chart recorder for continuous monitoring. O2- generation was measured for 5 min after the initial lag period and the total nanomoles of O2- generated calculated using the extinction coefficient for ferricytochrome c. Newborn PMNs (N = 10) generated significantly less O2- (5.7 +/- 0.8 nmol O2-/10(6) cells/5 min, P less than 0.01) than did adult PMNs (N = 14) (9.6 +/- 2.1 nmol O2-/10(6) cells/5 min) or fetal PMNs (N = 4) (10.7 +/- 0.7 nmol O2-/10(6) cells/5 min). PMNs from 7- to 10-day-old calves (N = 9) generated almost identical amounts of O2- as newborn PMNs (5.7 +/- 1.6 nmol O2-/10(6) cells/5 min). There was no difference in measured lag time period between newborn and adult PMNs, but fetal PMNs had significantly reduced (P less than 0.01) mean lag time. The data indicated that bovine newborn PMNs have a decreased ability to generate O2- in response to PMA stimulation, which persists for at least 7-10 days, and that this functional decrement may be a manifestation of some form of perinatal PMN suppression phenomenon rather than a developmental abnormality since fetal PMNs produced O2- as well as adult PMNs.