Mononuclear cell subpopulations in preterm and full-term neonates: independent effects of gestational age, neonatal infection, maternal pre-eclampsia, maternal betamethason therapy, and mode of delivery

Flow Cytometry: An Important Diagnostic Tool in Critically Ill Preterm Neonates with Suspected Sepsis

OBJECTIVE

Sepsis is a major cause of neonatal mortality. The gold standard for diagnosis is blood culture which suffers from low sensitivity and huge turn-around time. Flow cytometry has been extensively applied to malignant disorders and is an upcoming tool for diagnosis of nonmalignant disorders due to its rapidity and accuracy in detecting cells, cell products, and their functional states. The aim of this study was to investigate the utility of flow cytometric expression of neutrophil CD64, monocyte human leukocyte antigen (HLA-DR) and CD16 in diagnosis in suspected preterm neonates.

STUDY DESIGN

In total, 100 preterm neonates with clinical signs of sepsis were enrolled in the study. Blood culture, C-reactive protein (CRP) and flow cytometry for nCD64, mHLA-DR, and mCD16 were performed. The neonates were divided into two groups: culture positive and culture negative and CRP and flow cytometric findings compared. ROC analysis was performed to determine the best cut-off for nCD64, mHLA-DR, and mCD16 values along with estimation of sensitivity, specificity, and predictive values. Probability of <0.05 was taken as significant.

RESULTS

Out of the 100 enrolled neonates, 34 (34%) were culture positive. CRP was not found to be significantly different in the two groups. Expression of nCD64 (p = 0.03) was significantly upregulated in the blood culture positive cases with a cut-off mean fluorescence intensity (MFI) value = 4.72 and sensitivity of 92% and specificity of 52%. Expression of mCD16 (p = 0.02) was also upregulated in the blood culture positive cases with a cut-off MFI value = 4.9, with sensitivity of 41%, specificity of 83%.

CONCLUSION

The study concluded that nCD64 and mCD16 can be potential biomarkers for early diagnosis of neonatal sepsis with a high sensitivity and specificity.

KEY POINTS

· Neutrophil CD64 significantly upregulated in septic neonates.. · Monocyte CD16 significantly upregulated in septic neonates.. · C-reactive protein values were not significantly different in septic versus nonseptic neonates..

Zinc homeostasis in immunity and its association with preterm births

Preterm birth is among the most common adverse pregnancy outcomes and is the leading cause of neonatal mortality and morbidity. While trace elements are essential for humans, their specific roles in the prenatal period remain unexplored. Zinc, a ubiquitous element plays a pivotal role in protein synthesis, cell division, nucleic acid metabolism, apoptosis, ageing, reproduction, immunological as well as antioxidant defense mechanism. Although zinc quantities are very small in body tissue, it is involved in every conceivable biochemical pathway which is critical for the performance of various functions necessary to sustain life. Owing to the multifactorial role of zinc, it is not possible to attribute a certain zinc dependent mechanism in pre-term births. Although the effect of zinc deficiency on immunity, its impact on maternal function and health as well as its role in the developing foetus is well documented, much less attention has been given to the understanding of micronutrient zinc homeostasis in immunity and its association with preterm births. Despite extensive research, the pathway by which zinc regulates pregnancy outcomes as well as the function of immune cells in controlling the delivery status (term/ preterm) is still obscure. The present review aims to focus on the understanding of relationship of micronutrient zinc homeostasis in immunity and its association with preterm births.

Prenatal and Perinatal Environmental Influences Shaping the Neonatal Immune System: A Focus on Asthma and Allergy Origins

It is suggested that programming of the immune system starts before birth and is shaped by environmental influences acting during critical windows of susceptibility for human development. Prenatal and perinatal exposure to physiological, biological, physical, or chemical factors can trigger permanent, irreversible changes to the developing immune system, which may be reflected in cord blood of neonates. The aim of this narrative review is to summarize the evidence on the role of the prenatal and perinatal environment, including season of birth, mode of delivery, exposure to common allergens, a farming environment, pet ownership, and exposure to tobacco smoking and pollutants, in shaping the immune cell populations and cytokines at birth in humans. We also discuss how reported disruptions in the immune system at birth might contribute to the development of asthma and related allergic manifestations later in life.

Imbalance between inflammatory and regulatory cord blood B cells following pre-term birth

Preterm birth (PTB) is one of the most frequent pregnancy complications. It affects millions of babies each year worldwide and is associated with increased morbidity and mortality. PTB-associated alterations in the maternal immune response may have a direct effect on the developing fetal immune system. Having recently shown that B regulatory (Breg) cells are decreased in number and functionally impaired in maternal blood from women delivering preterm, we now addressed the question whether the adaptive immune system is also altered in cord blood (CB) after the onset of PTB. PTB was associated with increased concentrations of IL-6, TNF-α and IL-21 in CB and enhanced IL-6, but decreased IFN-γ and IL-4 in amniotic fluid (AF) samples compared to term delivery (TD). We found no differences in the frequency of CD19 + B cells, CD4 + T cells or CD4+Foxp3+CD25+ T regulatory (Treg) cells in CB cells in PTB vs TD. The frequency of CD86 + B cells was increased, while the percentage of CD24^hiCD38^hiCD19 + Breg and CD1d^hiCD5+ Breg cells and the ability of B cells to convert into Breg cells was diminished in PTB compared to TD. CB B cells from PTB secreted more IL-6, TNF-α, IL-9 and IL-2 compared to B cells obtained from term samples. We conclude that, after PTB onset, a shift from immunoregulation towards inflammation takes place in CB cells that are reportedly representative of the fetal compartment. B cells have a substantial contribution herein. This phenomenon might account for the observed enhanced mortality and morbidity in prematurely born infants. Further studies will clarify how to employ this easy-to-obtain information for closely monitoring newborns at risk.

Immune System Remodelling by Prenatal Betamethasone: Effects on β-Cells and Type 1 Diabetes

Type 1 diabetes (T1D) is a multifactorial disease of unknown aetiology. Studies focusing on environment-related prenatal changes, which might have an influence on the development of T1D, are still missing. Drugs, such as betamethasone, are used during this critical period without exploring possible effects later in life. Betamethasone can interact with the development and function of the two main players in T1D, the immune system and the pancreatic β-cells. Short-term or persistent changes in any of these two players may influence the initiation of the autoimmune reaction against β-cells. In this review, we focus on the ability of betamethasone to induce alterations in the immune system, impairing the recognition of autoantigens. At the same time, betamethasone affects β-cell gene expression and apoptosis rate, reducing the danger signals that will attract unwanted attention from the immune system. These effects may synergise to hinder the autoimmune attack. In this review, we compile scattered evidence to provide a better understanding of the basic relationship between betamethasone and T1D, laying the foundation for future studies on human cohorts that will help to fully grasp the role of betamethasone in the development of T1D.

Maternal pregnancy-induced hypertension increases the subsequent risk of neonatal candidiasis: A nationwide population-based cohort study

OBJECTIVE

Neonatal candidiasis is a leading infectious cause of significant morbidity and mortality in premature birth mainly due to impaired physical barriers and immature immune system of fetus. Maternal pregnancy-induced hypertension (PIH) has been reported to be able to disturb the neonatal immune system, which could cause the increased possibility of neonatal infection. Therefore, we hypothesized that maternal PIH may increase the risk of neonatal candidiasis. The aim of this study was to evaluate whether PIH increased the risk of neonatal candidiasis and identify the predictive risk factors.

MATERIALS AND METHODS

Patients with newly diagnosed PIH between January 1, 2000, and December 31, 2013 were selected from the Taiwan National Health Insurance Research Database (NHIRD). For each patient in the PIH cohort, 4 subjects without PIH, matched for age and year of delivery, were randomly selected as the comparison cohort. A Cox proportional regression model was used to estimate the risks of neonatal candidiasis in both cohorts.

RESULTS

Among the 23.3 million individuals registered in the NHIRD, 29,013 patients with PIH and 116,052 matched controls were identified. Patients with PIH had a higher incidence of neonatal candidiasis than did those without PIH. According to the multivariate analysis, PIH (odds ratio [OR] = 2.08, 95% confidence interval [CI] = 1.11-3.19, p < 0.0228), single parity (OR = 1.91, 95% CI = 1.00-3.65, p < 0.0499), and preterm birth (OR = 3.57, 95% CI = 1.84-6.93, p = 0.0002) were independent risk factors for the development of neonatal candidiasis.

CONCLUSION

Patients who had a history of PIH was associated with an increased risk of having infants who develop neonatal candidiasis compared with those without PIH. Additionally, preterm birth was an independent risk factor for the development of neonatal candidiasis.

Term vs. preterm cord blood cells for the prevention of preterm brain injury

BACKGROUNDWhite matter brain injury in preterm infants can induce neurodevelopmental deficits. Umbilical cord blood (UCB) cells demonstrate neuroprotective properties, but it is unknown whether cells obtained from preterm cord blood (PCB) vs. term cord blood (TCB) have similar efficacy. This study compared the ability of TCB vs. PCB cells to reduce white matter injury in preterm fetal sheep.METHODSHypoxia-ischemia (HI) was induced in fetal sheep (0.7 gestation) by 25 min umbilical cord occlusion. Allogeneic UCB cells from term or preterm sheep, or saline, were administered to the fetus at 12 h after HI. The fetal brain was collected at 10-day post HI for assessment of white matter neuropathology.RESULTSHI (n=7) induced cell death and microglial activation and reduced total oligodendrocytes and CNPase+myelin protein in the periventricular white matter and internal capsule when compared with control (n=10). Administration of TCB or PCB cells normalized white matter density and reduced cell death and microgliosis (P<0.05). PCB prevented upregulation of plasma tumor necrosis factor (TNF)-a, whereas TCB increased anti-inflammatory interleukin (IL)-10 (P<0.05). TCB, but not PCB, reduced circulating oxidative stress.CONCLUSIONSTCB and PCB cells reduced preterm HI-induced white matter injury, primarily via anti-inflammatory actions. The secondary mechanisms of neuroprotection appear different following TCB vs. PCB administration.

Immune responses in perinatal brain injury

The perinatal period has often been described as immune deficient. However, it has become clear that immune responses in the neonate following exposure to microbes or as a result of tissue injury may be substantial and play a role in perinatal brain injury. In this article we will review the immune cell composition under normal physiological conditions in the perinatal period, both in the human and rodent. We will summarize evidence of the inflammatory responses to stimuli and discuss how neonatal immune activation, both in the central nervous system and in the periphery, may contribute to perinatal hypoxic-ischemic brain injury.

Lymphocyte subpopulations in premature infants: an observational study

BACKGROUND AND OBJECTIVES

The infant's immune system evolves over the first months and years of life. Strong correlation exists between lymphocyte count, lymphocyte subpopulations and gestational age at birth. Associations with antenatal and postnatal steroid treatment, infection and chronic lung disease have also been described. Few published studies report the effect of increasing postnatal age (PNA) and comorbidities on lymphocyte subpopulations in premature infants beyond the first 4 months of life. This study aimed to describe changes in lymphocyte subpopulations in preterm infants up to 13 months PNA.

METHODS

Premature infants (23-34 weeks completed gestation) from five centres had lymphocyte subpopulations measured at 2, 5 or 7, 12 and 13 months PNA alongside their vaccine responses in a vaccination trial.

RESULTS

393 blood samples from 151 babies were analysed. There was an increase in absolute numbers of total lymphocytes (median cell count 6.21×10⁹/L at 13 months compared with 4.9×10⁹/L at 2 months PNA) and CD3⁺, CD4⁺, CD8⁺, natural killer and B cells with increasing age. At 2 months PNA, there was a positive correlation between gestation and CD3⁺ and CD4⁺ counts (r=0.32 and 0.46, respectively) and proportions (r=0.22 and 0.41, respectively), and CD4⁺:CD8⁺ ratios (r=0.57), but a negative correlation with CD8⁺ proportions (r=-0.32).

CONCLUSIONS

This longitudinal study describes the distribution of lymphocyte subpopulations in premature infants and provides reference ranges for the major lymphocyte subsets to help guide clinicians when assessing premature infants for immunodeficiency in the first year of life.

TRIAL REGISTRATION NUMBER

EudraCT 2007-007535-23.

[Effect of perinatal factors on postnatal development of lymphocyte subsets in early preterm infants]

OBJECTIVE

To study the postnatal changes in lymphocyte subsets in early preterm infants and the effect of perinatal factors on lymphocyte subsets.

METHODS

A total of 61 early preterm infants were enrolled. Flow cytometry was used to measure the absolute counts of lymphocytes and lymphocyte subsets at 1, 7, 14, and 28 days after birth, as well as at 6 months after birth for 17 of these early preterm infants. The effects of perinatal factors, such as antepartum use of hormone, intrauterine infection, gestational age at birth, and Ureaplasma urealyticum (UU) colonization, on lymphocyte subsets were analyzed.

RESULTS

The absolute counts of lymphocyte subsets except natural killer (NK) cells were lowest at birth, increased rapidly at 1 week after birth, and reached the levels in healthy infants at 6 months; the count of NK cells remained at a low level and increased significantly at 6 months after birth. Compared with those with a gestational age of <28 weeks, the early preterm infants with a gestational age of ≥28 weeks had significantly higher absolute counts of T cells, T helper (Th) cells, and NK cells at 7 days after birth, a significantly higher absolute count of T cells at 14 days after birth, and significantly higher absolute counts of lymphocytes and Th cells at 28 days after birth (P<0.05). Compared with the group not using hormone, the group using hormone showed a significantly higher absolute count of T cells at 7 days after birth and significantly higher absolute counts of lymphocytes and all subsets at 14 days after birth (P<0.05). There was no significant difference in lymphocyte subsets at 1 day after birth between the intrauterine infection and non-infection groups (P>0.05); the intrauterine infection group had significantly higher absolute counts of B cells at 7 and 14 days after birth than the non-infection group. Compared those without UU colonization, the infants with UU colonization had significantly higher absolute counts of lymphocytes, T cells, Th cells, and Ts cells at 1 day after birth and a significantly higher absolute count of B cells at 14 days after birth.

CONCLUSIONS

Early preterm infants have deficiencies in innate immune cells at birth and normal levels at about 6 months after birth. Various perinatal factors including antepartum use of hormone, gestational age at birth, intrauterine infection, and UU colonization have long-term effects on lymphocyte subsets in early preterm infants.

Expression of lymphocyte activation markers of preterm neonates is associated with perinatal complications

Background

Inappropriate activation of T lymphocytes plays an important role in perinatal complications. However, data on T lymphocyte activation markers of preterm infants is scarce. We investigated the association between gender, gestational and postnatal age, preeclampsia (PE), premature rupture of membranes (PROM) as well as prenatal steroid treatment (PS) and the frequency of activated T lymphocyte subsets (HLA-DR+, CD69+, CD25+, CD62L+) and major T lymphocyte subpopulations (CD4, CD8, Th1, Th2, naïve, memory) in peripheral blood during the first postnatal week in preterm infants.

Results

Cord blood and peripheral blood samples were collected from 43 preterm infants on the 1st, 3rd, and 7th days of life. We assessed the frequency of the above T lymphocyte subsets using flow cytometry. The ‘mixed effect model’ was used to analyze the effects of clinical parameters on T lymphocyte markers. The frequency of CD25+ T lymphocytes was higher in PROM. The frequency of CD4+ and CD8+ cells and the CD4+/CD8+ cell ratio was decreased in PE. The frequency of CD62L+ T lymphocytes was higher in male compared with female infants. PS did not affect the frequency of the investigated markers. CD4+ CD25+ cells had a lower frequency at birth than on day 7. Th2 lymphocytes had a lower frequency on postnatal days 1 and 3 when compared to day 7.

Conclusions

Our observations indicate that alterations affecting the expression of T lymphocyte activation markers are associated with the above factors and may play a role in the development of perinatal complications.

Postnatal Infections and Immunology Affecting Chronic Lung Disease of Prematurity

Premature infants suffer significant respiratory morbidity during infancy with long-term negative consequences on health, quality of life, and health care costs. Enhanced susceptibility to a variety of infections and inflammation play a large role in early and prolonged lung disease following premature birth, although the mechanisms of susceptibility and immune dysregulation are active areas of research. This article reviews aspects of host-pathogen interactions and immune responses that are altered by preterm birth and that impact chronic respiratory morbidity in these children.

The ontogeny of naïve and regulatory CD4(+) T-cell subsets during the first postnatal year: a cohort study

As there is limited knowledge regarding the longitudinal development and early ontogeny of naïve and regulatory CD4(+) T-cell subsets during the first postnatal year, we sought to evaluate the changes in proportion of naïve (thymic and central) and regulatory (resting and activated) CD4(+) T-cell populations during the first postnatal year. Blood samples were collected and analyzed at birth, 6 and 12 months of age from a population-derived sample of 130 infants. The proportion of naïve and regulatory CD4(+) T-cell populations was determined by flow cytometry, and the thymic and central naïve populations were sorted and their phenotype confirmed by relative expression of T cell-receptor excision circle DNA (TREC). At birth, the majority (94%) of CD4(+) T cells were naïve (CD45RA(+)), and of these, ~80% had a thymic naïve phenotype (CD31(+) and high TREC), with the remainder already central naïve cells (CD31(-) and low TREC). During the first year of life, the naïve CD4(+) T cells retained an overall thymic phenotype but decreased steadily. From birth to 6 months of age, the proportion of both resting naïve T regulatory cells (rTreg; CD4(+)CD45RA(+)FoxP3(+)) and activated Treg (aTreg, CD4(+)CD45RA(-)FoxP3(high)) increased markedly. The ratio of thymic to central naïve CD4(+) T cells was lower in males throughout the first postnatal year indicating early sexual dimorphism in immune development. This longitudinal study defines proportions of CD4(+) T-cell populations during the first year of postnatal life that provide a better understanding of normal immune development.

Macrophage phenotype is associated with disease severity in preterm infants with chronic lung disease

BACKGROUND

The etiology of persistent lung inflammation in preterm infants with chronic lung disease of prematurity (CLD) is poorly characterized, hampering efforts to stratify prognosis and treatment. Airway macrophages are important innate immune cells with roles in both the induction and resolution of tissue inflammation.

OBJECTIVES

To investigate airway innate immune cellular phenotypes in preterm infants with respiratory distress syndrome (RDS) or CLD.

METHODS

Bronchoalveolar lavage (BAL) fluid was obtained from term and preterm infants requiring mechanical ventilation. BAL cells were phenotyped by flow cytometry.

RESULTS

Preterm birth was associated with an increase in the proportion of non-classical CD14(+)/CD16(+) monocytes on the day of delivery (58.9 ± 5.8% of total mononuclear cells in preterm vs 33.0 ± 6.1% in term infants, p = 0.02). Infants with RDS were born with significantly more CD36(+) macrophages compared with the CLD group (70.3 ± 5.3% in RDS vs 37.6 ± 8.9% in control, p = 0.02). At day 3, infants born at a low gestational age are more likely to have greater numbers of CD14(+) mononuclear phagocytes in the airway (p = 0.03), but fewer of these cells are functionally polarized as assessed by HLA-DR (p = 0.05) or CD36 (p = 0.05) positivity, suggesting increased recruitment of monocytes or a failure to mature these cells in the lung.

CONCLUSIONS

These findings suggest that macrophage polarization may be affected by gestational maturity, that more immature macrophage phenotypes may be associated with the progression of RDS to CLD and that phenotyping mononuclear cells in BAL could predict disease outcome.

T-cell subpopulations αβ and γδ in cord blood of very preterm infants: the influence of intrauterine infection

Preterm infants are very susceptible to infections. Immune response mechanisms in this group of patients and factors that influence cord blood mononuclear cell populations remain poorly understood and are considered insufficient. However, competent immune functions of the cord blood mononuclear cells are also described. The aim of this work was to evaluate the T-cell population (CD3⁺) with its subpopulations bearing T-cell receptor (TCR) αβ or TCR γδ in the cord blood of preterm infants born before 32 weeks of gestation by mothers with or without an intrauterine infection. Being a pilot study, it also aimed at feasibility check and assessment of an expected effect size. The cord blood samples of 46 infants age were subjected to direct immunofluorescent staining with monoclonal antibodies and then analyzed by flow cytometry. The percentage of CD3⁺ cells in neonates born by mothers with diagnosis of intrauterine infection was significantly lower than in neonates born by mothers without infection (p = 0.005; Mann–Whitney U test). The number of cells did not differ between groups. Infection present in the mother did not have an influence on the TCR αβ or TCR γδ subpopulations. Our study contributes to a better understanding of preterm infants’ immune mechanisms, and sets the stage for further investigations.

Toll-like receptor signaling in neonatal sepsis and inflammation: a matter of orchestration and conditioning

Altered neonatal Toll-like receptor (TLR) function is hypothesized to contribute to the heightened susceptibility to infection and perpetuated inflammation in term and preterm neonates, clinically evident in neonatal sepsis and increased rates of inflammatory disorders. Current data indicate that basal TLR expression in term neonates equals adult expression patterns, while expression in preterm infants seems to increase, depending on gestational age. Regarding TLR signaling, some studies suggest TLR incompetence in neonates associated with impaired pro-inflammatory responses, others describe neonatal TLR function well developed and allude to its hyper-inflammation tendency. We discuss the competing positions and considerable limitations of research approaches and conclude that neonatal innate immunity is not generally less able to respond to TLR stimulation. Moreover, we describe pre-conditioning factors other than immaturity having a comparable impact. In the long term, better understanding of the complex interplay of pre- and postnatal conditions and maturation-dependent neonatal TLR function may provide new therapeutic approaches.

Association of in utero sensitization to Schistosoma haematobium with enhanced cord blood IgE and increased frequencies of CD5- B cells in African newborns

This study investigated in utero priming as a consequence of maternal parasitic infections. Cord blood plasma samples of 63 African newborns were assessed by enzyme-linked immunosorbent assay for their content of total and schistosome-specific or filaria-specific IgE and IgG4. The frequencies of lymphocyte phenotypes in cord blood were also determined by using flow cytometry, and were compared with those of European newborns. We found significantly increased schistosome soluble egg antigen (SEA)-specific IgE in cord plasma of those born to mothers with schistosome infections and correlations between fetal and maternal SEA-specific and filaria antigen-specific IgE. These data are evidence for in utero priming of the fetal immune system to maternal helminth infections. Furthermore, we show significantly enhanced percentages of CD5- B cells in African newborns cord blood compared with Europeans, which is consistent with earlier maturation of the African fetal immune system.

Immune status in very preterm neonates

OBJECTIVES

Preterm neonates are at increased risk of sepsis compared with those born at term. We investigated immune status at birth and early neonatal life in very preterm neonates and its association with short-term outcomes.

METHODS

Prospective observational study conducted at a university hospital recruiting 113 preterm neonates (23-32 weeks) and 78 controls. Monocyte major histocompatibility complex (MHC) class II expression, serum, and ex vivo lipopolysaccharide stimulated levels of six cytokines (tumor necrosis factor α, interleukin (IL)-1β, IL-6, IL-8, IL-10, and IL-12p70) were measured in umbilical cord blood and over the first 7 days. The presence of neonatal sepsis and histologic chorioamnionitis was recorded.

RESULTS

Prematurity (preterm labor and preterm premature rupture of membranes cohorts), neonatal sepsis, and histologic chorioamnionitis were associated with significant reduction in monocyte MHC class II expression. Neonates who had evidence of subsequent protracted sepsis had low levels of MHC class II expression at birth. Serial monocyte MHC class II expression revealed a fall by day 2, in all preterm neonates, with the degree being influenced by both prematurity and sepsis, and incomplete recovery by day 7, suggesting immunoparalysis in preterm premature rupture of membranes and preterm labor cohorts. Whole blood lipopolysaccharide stimulation assay showed significantly lower tumor necrosis factor α, values in preterm neonates who subsequently developed sepsis indicating a degree of immunoparalysis.

CONCLUSIONS

Our data support the concept that fetal exposure to inflammation before preterm delivery leads to subsequent endotoxin hyporesponsiveness (immunoparalysis), which increases the risk of subsequent sepsis and associated organ dysfunction.

Immune response to Haemophilus influenzae type b conjugate vaccine in preterm infants

BACKGROUND

Haemophilus influenzae type b (Hib) vaccine became available for use in Japan in December 2008. The aim of the present study was to evaluate the immunogenicity of Hib vaccine in Japanese preterm infants.

METHODS

Serum samples were obtained from 54 preterm infants before the first vaccination and 1 month after the third. Anti-polyribosylribitol phosphate (PRP) antibodies were measured using an enzyme-linked immunosorbent assay method. Antibody positivity was defined as levels >1 µg/mL.

RESULTS

Of the 54 preterm infants, 46 (85.2%) achieved antibody levels >1 µg/mL. This compares with the 92.4% reported in full-term infants. The antibody seroconversion rate of infants starting vaccination at 2 months of age was close to being significantly lower than when vaccination was started at 3 months of age (P= 0.060). In addition, the percentage of infants achieving a positive response in the group with a history of antenatal steroid exposure was significantly higher than in those not exposed (P= 0.046). Thus, risk factors for lower Hib antibody concentrations after three doses of vaccine were age at first vaccination and lack of use of antenatal steroids.

CONCLUSIONS

There is a possibility that perinatal factors and the environment unique to preterm infants are related to their lower antibody positivity rates compared to full-term infants. It may therefore be preferable to modify the proposed immunization schedule.

Prenatal programming of the innate immune response following in utero exposure to inflammation: a sexually dimorphic process?

Maternal infection and inflammation are common events during pregnancy. This article documents evidence that suggests such inflammation compromises the development of the fetal innate immune response, in support of an in utero origins hypothesis of neonatal and childhood inflammatory disease. The potential for this response to exhibit sex specificity is also explored, based on evidence of sexually dimorphic placental responses to maternal inflammation.

Tracking changes of lymphocyte subsets and pre-inflammatory mediators in full-term neonates with suspected or documented infection

Investigation was made of changes in immune system parameters during the course of neonatal infection. The study population consisted of 95 full-term neonates matched for chronological age and sex, divided into three groups: suspected infection (n=20), sepsis (n=25), infection-free control subjects (n=50). Serial measurements were made of the cytokines interleukin-6 (IL-6), interleukin-1b (IL-1b) and tumour necrosis factor-α (TNF-α), lymphocyte subsets [CD3+, CD4+, CD8+, natural killer (NK) cells and B cells], the immunoglobulins (Ig) (IgG, IgM and IgA), C-reactive protein (CRP), and the total blood count, before, 2 days after initiation of treatment and after stopping treatment (time periods first, second and third, respectively). IL6, TNF-α, IL1-b and CRP were higher at the first time period in the sepsis group, and IL6 and TNF-α continued to be higher in this group at the second period. IL-6 and TNF-α were precise sepsis predictors with sensitivity and specificity of 0.92, 0.98 and 0.91, 0.92, respectively. NK cells, B cells, CD3+, CD4+, CD8+ were higher in the sepsis and suspected infection groups, but the ratios CD3+/CD4+, CD3+/CD8+, CD4+/CD8+ showed no difference from the controls. IgG was lower and IgM higher in the sepsis group. In the control subjects CD3+, CD4+, CD8+ lymphocytes increased with increasing age. It is concluded that IL-6 and TNF are good diagnostic markers of sepsis in full-term neonates. Lymphocyte subsets were affected by both the clinical condition and the chronological age. NK and B cells may be elevated in suspected and documented sepsis, and further studies are needed to determine their clinical significance.

Development of lymphocyte subpopulations in preterm infants

In preterm neonates the immune system is thought to be less developed at birth, but very little is known about the actual size of lymphocyte subpopulations, and even less about the maturation of these subpopulations during the first months after a premature birth. To evaluate the development of lymphocyte subpopulations in preterm infants during the first 3 months after birth, we performed a prospective longitudinal study in two hospitals in the Netherlands. Preterm neonates (n = 38) of all post-menstrual ages were included and blood samples were taken from cord blood, and at 1 week, 6 weeks, and 3 months. Lymphocyte subpopulations were measured by four-colour flow cytometry. The data were compared with follow-up data obtained in healthy term neonates (n = 8), and with single samples from school age children (n = 5) and adults (n = 5). Overall, we found a similar pattern of post-natal development of lymphocyte subpopulations in the term and preterm infants. Both B lymphocytes and helper and cytotoxic T lymphocytes mainly consist of naive cells at birth and during the 3 months of follow-up in all neonatal age groups. So, the preterm immune system seems to be able to generate an outburst of naive T and B lymphocytes from the thymus and bone marrow within the same time span after the start of post-natal antigenic stimulation from the environment as the term immune system, but, with lower post-menstrual age, the absolute counts of naive helper T lymphocytes are lower.

Arachidonic and docosahexaenoic acid deficits in preterm neonatal mononuclear cell membranes. Implications for the immune response at birth

Preterm neonates are more susceptible to infection than term neonates. Arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3) are biologically active components of cell membrane phospholipids. Arachidonic acid is a substrate for the synthesis of eicosanoids, potent regulators of immune function. Preterm babies may have a deficiency of arachidonic acid and docosahexaenoic acid, but the impact of this deficit on maturation of the immune system is unknown. To address this we explored links between placental provision of fatty acids to cord blood mononuclear cell (CBMC) membranes using gas chromatography (GC), and maturation of the immune response with gestational age by analysing lymphocyte subsets by flow cytometry. This is the first study to examine the lipid profile of the phosphatidylcholine (PC) and phosphatidylethanolamine (PE) fractions of CBMC membranes from preterm neonates. The long chain polyunsaturated fatty acid (LCPUFA) composition of CBMC membranes was dominated by arachidonic acid in both PE (34%) and PC (15%) fractions in healthy term neonates (> or =37 weeks, n=9), whilst in healthy preterm neonates (<37 weeks, n=10) the level of arachidonic acid was significantly lower at 28.8% and 12.5% respectively (p<0.05). Preterm neonates (<37 weeks, n=23) also had significantly lower absolute numbers of CD4+ (p<0.05) leukocytes and CD4+ (p<0.01) and CD8+ (p<0.05) naïve T-cells than term (> or =37 weeks, n=24) neonates that correlated with gestational age (p<0.01-0.05).

Comparison of immunological status of African and European cord blood mononuclear cells

The cellular aspects of the immunologic development of the fetus during pregnancy have been studied mainly in populations living in economically well developed countries, and there is no data concerning variation of the neonatal cellular immune system in geographically distinct areas with different environments. Here, we report a comparative immunologic marker analysis of the circulating mononuclear cell subsets in unstimulated cord blood of newborns from Gabon and Austria, assessing the activation and maturation status of T and B lymphocytes as well as antigen-presenting cells. Cells and markers hypothesized to be modulated by frequent exposure to microorganisms and parasites such as regulatory T cells and the expression of toll-like receptor 2 on antigen-presenting cells were also studied. We found marked differences in terms of expression of immunologic markers between the two populations, pointing to a comparatively enhanced maturation status of the neonatal immune system in general in the African setting. The observations suggest that environmental factors, including differential exposure to pathogens as well as nutritional differences, may have substantial impact on the development of the fetal immune system.

Perinatal stress influences lymphocyte subset counts in neonates. The generation R study

In the general population, it is unknown whether stress-related perinatal factors influence lymphocyte subset counts in neonates. The aim of this study was to assess the associations of perinatal factors related to stress and hypoxia (mode of delivery, Apgar scores, and umbilical cord blood pH) with absolute lymphocyte subset counts (T, B, NK, helper T, cytotoxic T, naïve, memory T) in cord blood of 571 neonates. This study was embedded in a population-based prospective cohort study from fetal life onwards. All models were adjusted for gestational age, birth weight, gender, maternal fever, and each of the other perinatal stress-relating factors. Our results showed that increasing stress-related mode of delivery was positively associated with NK and memory T-lymphocyte subset counts (all p < 0.01). Effects of Apgar scores on lymphocyte subsets were explained by umbilical cord blood pH. Lower umbilical cord blood pH was associated with higher B, NK, and memory T-lymphocyte counts (all p < 0.05). Effects of mode of delivery and umbilical cord blood pH on other lymphocyte subsets were not observed. We conclude that, in the general population, lymphocyte subset counts in neonates increase with increasing stress- and hypoxia-related perinatal factors.

Active immunization of premature and low birth-weight infants: a review of immunogenicity, efficacy, and tolerability

Preterm infants are at increased risk of disease and hospitalization from a number of vaccine-preventable diseases. However, these same infants have immunologic immaturities that may impact vaccine responses. Larger premature infants mount immune responses to vaccines similar to those of full-term infants, but very premature infants (<28-32 weeks' gestation at birth) may have specific defects in vaccine responsiveness. Although there are minor differences in immunogenicity, the immune responses to diphtheria, tetanus, pertussis, and polio antigens are similar enough between full-term and premature infants that clinical consequences are unlikely to result. However, the immunogenicity of Haemophilus influenzae type b conjugate vaccines varies widely among studies of premature infants, and may be affected by the choice of conjugate protein, inclusion in a combination vaccine, and by an infant's overall health. Pneumococcal conjugate vaccine is efficacious in larger premature infants, but little information is available about immunogenicity in smaller premature infants. Meningococcal group C conjugate vaccine appears immunogenic in even very premature infants, but the duration of immunity may be limited. Hepatitis B vaccine given at birth appears poorly immunogenic in infants with birth weights <1500-2000 g, with delay in the administration of the first dose yielding improved immunogenicity. Few data on influenza vaccine in premature infants are available, but infants with pulmonary disease may respond less robustly than others. Bacille Calmette Guérin vaccine appears to be most immunogenic if delayed until at least 34-35 weeks' postmenstrual age in very premature infants, although there may be non-specific advantages to its earlier administration. Premature infants may have persistently lower antibody titers than full-term infants, even years after initial immunization. Sick premature infants experience increased episodes of apnea or cardiorespiratory compromise following vaccine administration, necessitating careful monitoring. Specific factors that impair immune response, quality of the immune response, and safety and immunogenicity evaluation of new vaccines in premature infants are topics needing further research. Premature infants are at significant risk for decisions from healthcare providers that delay beginning and completing their vaccine regimens. A major challenge facing those who care for these infants is the provision of timely immunization.

NK cell increase in neonates from the preterm to the full-term period of gestation

BACKGROUND

Several studies have reported differences in lymphocyte phenotype in preterm and full-term neonates as compared to children and adults. However, a detailed description of the immunologic cell populations of neonates corresponding to the gestational age is needed. This will be helpful for clinical practice to find the best way to prevent neonatal infections or strengthen the immune system of newborns with some kind of immunodeficiency.

OBJECTIVE

To study maturation of the immune system throughout gestation, describing the variations of the lymphocyte populations in function of the gestational week when born.

METHODS

We performed a descriptive study in 134 healthy newborns (gestation age 25-42 weeks), quantifying the relative and absolute counts of cell populations in umbilical cord blood obtained during delivery, by a four-color flow cytometry single platform.

RESULTS

We first compared the very-preterm (25-30 weeks), preterm (31-36 weeks) and full-term (37-42 weeks) neonates. We found higher absolute counts of all cell populations in the full-term group and lower absolute and relative values of NK cells in the very-preterm group. After that, we analyzed the lymphocyte populations week to week (from week 31 to 41) and found the lowest values of T cells (CD4+ and CD8+) for week 36. However, lower percentages of CD4+ T cells and higher percentages of NK cells were observed in week 38 and 41.

CONCLUSION

We found an increase in cord blood NK cells with gestational age, both in terms of absolute counts and of percentage values. Moreover, the %NK cells showed a pattern opposite to %CD4+ T cells along the studied period.

Class II MHC antigen presentation defect in neonatal monocytes is not correlated with decreased MHC-II expression

Neonates are at increased risk of infections compared to adults. To dissect the mechanisms that contribute to neonatal immune deficiency, we compared MHC-II antigen processing and presentation by monocytes from umbilical cord blood and unrelated adult controls. Antigen-specific, co-stimulation-independent murine T hybridoma cells were used to detect peptide:HLA-DR complexes. Relative to adult monocytes, neonatal monocytes were significantly defective in processing and presentation of protein antigens and presentation of exogenous peptide. Defects in responses to protein antigens and exogenous peptide were of similar magnitude (56-81% decrease), indicating that the defect lies in antigen presentation as opposed to intracellular antigen processing. Average surface MHC-II levels on neonatal monocytes were 38% less than on adult monocytes. However, there was no correlation between decreased MHC-II expression on individual neonatal monocyte samples and reduced T cell responses. We demonstrate for the first time that neonatal monocytes are defective in MHC-II antigen presentation by a mechanism not correlated with decreased MHC-II expression.

Genetic susceptibility to neonatal infection

PURPOSE OF REVIEW

To review current data on genetic factors contributing to the striking susceptibility of neonates to infectious diseases and other adverse outcomes.

RECENT FINDINGS

Although few studies address genetic determinants of neonatal infectious disease susceptibility, several variants in genes involved in the innate immune response have been associated with differential risk for neonatal infection. The most consistent results relate to polymorphisms of tumour necrosis factor-alpha, whereas other gene polymorphisms, such as those of interleukin-6, have yielded conflicting findings. Similar genetic factors may be involved in other inflammatory neonatal diseases. Recent data suggest that genetic variation may influence the pace of immunologic maturation.

SUMMARY

Despite the enormous human and financial costs of infection for neonatal mortality and morbidity worldwide, it remains unclear why neonates are so susceptible. Genetic epidemiologic studies may assist in the identification of critical protective and pathogenic pathways. Despite the current relative lack of robust data, such studies are likely to facilitate the development of interventions that ultimately decrease the significant morbidity and mortality of this highly vulnerable population.

Flow cytometric assessment of hematopoietic cell subsets in cryopreserved preterm and term cord blood, influence of obstetrical parameters, and availability for transplantation

OBJECTIVE

The aim of this study was to characterize the lymphocyte and the hematopoietic stem and progenitor cell (HPC) subsets of cryopreserved premature cord blood (PCB) compared to term cord blood (TCB) by flow cytometry, to study the influence of birth conditions, and to assess its availability for transplantation.

MATERIALS AND METHODS

Four-color flow cytometric analysis was performed on 43 PCB and 40 TCB cryopreserved samples using a panel of 24 different mAbs, directed against lymphoid and HPC surface markers. The CB volume was estimated by the weight of the newborn to determine the absolute MNC and CD34(+) cell content/CB sample. Clinical and obstetrical data were recovered. Statistical comparisons and a multiple regression analysis were performed.

RESULTS

No consistent differences were found in the mononuclear cell (MNC) or CD34(+) cell concentration (x10(6)/L) between PCB and TCB. The percentage of primitive HPC (CD34(+)CD38(-), CD34(+)CD38(-)CD90(-)HLA-DR(-), CD34(+)CD38(-)CD90(-)HLA-DR(+)) and primitive lymphoid progenitors (CD34(+)CD7(+), CD34(+)CD7(+)CD19(-)CD117(-)) were higher in PCB than in TCB. Correspondingly, TCB had an increased percentage of committed HPC. No sample of PCB contained >2 x 10(7) MNC/kg (and only 48% had >1 x 10(5) CD34(+) cells) for a recipient of 20 kg body wt, as the minimum threshold recommended for CB transplantation. Obstetrical factors modulated mainly lymphocyte subsets and fewer HPC subpopulations. Acute fetal distress increased CD34(+) cells, especially the immature subsets. Maternal treatment with dexamethasone and intrauterine growth retardation decreased CD3(+) cells. No other obstetrical factors played a detrimental effect on CB cells if used for transplantation.

CONCLUSION

PCB is richer in immature cells both in lymphocyte and HPC populations, and its use for transplantation, at least in special cases, should be reconsidered.

Lymphocyte subsets in term and significantly preterm UK infants in the first year of life analysed by single platform flow cytometry

This observational study describes the ranges observed for lymphocyte subsets for significantly preterm infants (<32 weeks) in the first year of life, measured by single platform flow cytometry and compared to identically determined subsets in term infants. After ethical approval 39 term and 28 preterm infants had lymphocyte subset analysis before and after their primary immunization series. Median values with 5th and 95th percentiles of absolute counts and percentages are presented for total lymphocytes, T cells, NK cells, B cells, cytotoxic T cells, helper T cells, dual positive T cells, activated T cells, activated T helper cells (including T regulatory cells), pan memory T cells, pan naive T cells, memory helper T cells, naive helper T cells and the T helper/suppressor ratio. The lymphocyte profile of the preterm infants differed from that of the term infants.

Influence of perinatal risk factors on CD3+/TCR alphabeta and CD3+/TCR gammadelta lymphocytes in cord blood of preterm neonates

BACKGROUND

The aim of the study was the evaluation of CD3+/TCR alphabeta and CD3+/TCR gammadelta lymphocytes in the cord blood of the preterm neonates.

METHODS

The study included 26 term neonates as a control group delivered both by spontaneous labor and by cesarean section and 41 preterm neonates: (i) by cesarean section due to abruptio placentae, (ii) by cesarean section due to the danger of intrauterine asphyxia, (iii) by cesarean section due to preterm rupture of membrane (PROM), and (iv) by spontaneous labor. Immunological analysis was performed in the flow cytometer FACScan, using anti-CD3, anti-TCR alphabeta and anti-TCR gammadelta monoclonal antibodies from Becton Dickinson (San Jose, California USA).

RESULTS

It was shown that the way of delivery does not influence the value of CD3+/TCR alphabeta lymphocytes. A decrease of the percentage and number of CD3+/TCR gammadelta lymphocytes was found in neonates delivered by elective cesarean section. However, the danger of intrauterine fetal asphyxia, as a reason for preterm delivery, influenced a considerable increase of the number of CD3+/TCR alphabeta and CD3+/TCR gammadelta lymphocytes. Perinatal risk factors (abruptio placentae, PROM) were related to the lowest number of CD3+/TCR gammadelta lymphocytes in the blood of the preterm neonates.

CONCLUSION

The obtained results suggest that in spite of considerable immaturity, both a term and preterm neonate is prepared for the immune response and is able to activate cell mechanisms. The precise mechanism that links CD3+/TCR alphabeta and CD3+/TCR gammadelta lymphocytes and pathological condition of preterm birth remains unclear.

Dexamethasone effects on group B streptococcal infection in newborn rats

BACKGROUND

We previously published that human neutrophil-mediated bacterial killing of group B Streptococcus (GBS) in vitro was dependent on the timing and concentration of dexamethasone exposure.

HYPOTHESIS

Dexamethasone treatment would affect neutrophil mediated killing of GBS in an animal model.

METHODS

Wistar rat pups were randomly allocated to receive placebo or dexamethasone before, early or late after GBS infection. Suckling rats were infected with 104 or 105 colony-forming units of GBS or nothing. Pups were followed for survival, quantitative bacteremia, growth and neutrophil-mediated bacterial killing. Neutrophils for bacterial killing were obtained via cardiac puncture before infection. Statistics included chi square for survival, Mann-Whitney U test for bacteremia, analysis of variance for growth and paired Student's t test for bacterial killing analyses.

RESULTS

Dexamethasone treatment before invasive GBS infection decreases quantitative bacteremia, improves survival and improves neonatal neutrophil-mediated bacterial killing in suckling rats, whereas dexamethasone treatment after infection increases bacteremia and decreases survival. Regardless of timing of dexamethasone treatment, before or after invasive GBS infection, growth was significantly impaired in all suckling rats receiving dexamethasone compared with controls.

CONCLUSION

Treatment with dexamethasone before invasive GBS infection improves survival and decreases bacteremia in suckling rats; this appears in part to be mediated by improved neonatal neutrophil-mediated bacterial killing. We speculate that this improvement in outcome may be a result of improved number or function of neutrophil cell surface receptors.

Rat peripheral CD4+CD8+ T lymphocytes are partially immunocompetent thymus-derived cells that undergo post-thymic maturation to become functionally mature CD4+ T lymphocytes

CD4+CD8+ double-positive (DP) T cells represent a minor subpopulation of T lymphocytes found in the periphery of adult rats. In this study, we show that peripheral DP T cells appear among the first T cells that colonize the peripheral lymphoid organs during fetal life, and represent approximately 40% of peripheral T cells during the perinatal period. Later their proportion decreases to reach the low values seen in adulthood. Most DP T cells are small size lymphocytes that do not exhibit an activated phenotype, and their proliferative rate is similar to that of the other peripheral T cell subpopulations. Only 30-40% of DP T cells expresses CD8beta chain, the remaining cells expressing CD8alphaalpha homodimers. However, both DP T cell subsets have an intrathymic origin since they appear in the recent thymic emigrant population after injection of FITC intrathymically. Functionally, although DP T cells are resistant to undergo apoptosis in response to glucocorticoids, they show poor proliferative responses upon CD3/TCR stimulation due to their inability to produce IL-2. A fraction of DP T cells are not actively synthesizing the CD8 coreceptor, and they gradually differentiate to the CD4 cell lineage in reaggregation cultures. Transfer of DP T lymphocytes into thymectomized SCID mice demonstrates that these cells undergo post-thymic maturation in the peripheral lymphoid organs and that their CD4 cell progeny is fully immunocompetent, as judged by its ability to survive and expand in peripheral lymphoid organs, to proliferate in response to CD3 ligation, and to produce IL-2 upon stimulation.

Pre-eclampsia affects the immunophenotype of neonates

OBJECTIVE

We tried to estimate whether immunological changes are present in neonates born to mothers who had been suffering from pre-eclampsia.

STUDY DESIGN

Eighteen neonates born to mothers with severe pre-eclampsia (between 35 and 40 weeks of gestation) and 20 full-term healthy newborns (between 38 and 40 weeks of gestation) were included in the study. The lymphocytes were isolated from umbilical cord blood. The specific lymphocyte antigens were determined using direct staining with monoclonal antibodies and analysed by flow-cytometry.

RESULTS

We observed that neonates born to pre-eclamptic mothers had decreased percentage of T CD 3(+), CD 4(+) and T CD 8(+)28(+) (cytotoxic) lymphocytes and increased percentage CD 3(-)16/56(+) cells and CD 8(+)28(-) (suppressor) lymphocytes in comparison with newborns of healthy women. Furthermore, we found decreased CD 4: CD 8 lymphocyte ratio in the study group in comparison with the control group. We also observed that the percentage of CD 19(+)5(+), CD 4(+)8(+), CD 19(+)40(+) and CD 3(+)40L(+) lymphocytes did not differ in both studied groups. The percentage of CD 4(+)45RO(+), CD 8(+)45RO(+) memory cells was higher in neonates born to pre-eclamptic mothers when compared to controls. Moreover, the expression of CD 25 molecule was higher on T CD 8(+) and B CD 19(+) lymphocytes of neonates of pre-eclamptic mothers.

CONCLUSION

The alterations in the immunological parameters of neonates born to pre-eclamptic mothers can be associated with the maternal disease.

Flow cytometric measurement of HLA-DR expression on circulating monocytes in healthy and sick neonates using monocyte negative selection

The aim of this study was to investigate the effect of prematurity, neonatal sepsis, respiratory distress syndrome (RDS) and perinatal asphyxia on monocyte HLA-DR expression of neonates using a flow cytometric method based on monocyte negative selection. The subjects were one hundred and thirty-one neonates (59 healthy, 44 septicaemic, 20 with RDS and eight with perinatal asphyxia) and 20 healthy adults. Monocyte HLA-DR expression was measured using one-colour HLA-DR labelling in a gate for monocytes obtained using the combination of CD3-CD19--PE/CD15--FITC MoAbs. In addition, the common dual staining method using MoAbs against two CD14 epitopes (TUK4, MO2) was evaluated. With the one-colour HLA-DR labelling higher purity and recovery values of monocytes were achieved than with the dual labelling

METHOD

Healthy neonates had significantly lower percentages of HLA-DR(+) monocytes than adults (69 +/- 13% versus 91.5 +/- 2.5%) and comparable mean fluorescence intensity (MFI) (119 +/- 25 versus 131 +/- 26). Values did not differ significantly between healthy term and preterm neonates. Preterm neonates with RDS had a significantly lower percentage of HLA-DR(+) monocytes than the healthy preterm neonates. In neonates with asphyxia both parameters were comparable to those of the healthy ones. Septicaemic neonates presented significantly lower values of both parameters than the healthy, RDS and asphyxiated neonates. Monocyte negative selection provides a reliable estimation of HLA-DR expression on monocytes. Expression of monocyte HLA-DR is lower in healthy neonates in comparison with adults and is further decreased in neonates with sepsis and RDS, but it is not influenced by prematurity and perinatal asphyxia.

Prematurity at birth reduces the long-term risk of atopy

BACKGROUND

Antigen exposure in early life has long-lasting effects on atopic sensitization. Thus the predisposition to atopy of children born preterm can be assumed to differ from that of children born at term.

OBJECTIVE

The aim of this study was to evaluate the association between premature birth and atopy.

METHODS

At an outpatient clinic, we examined 2 groups of 10-year-old children, 72 who were born preterm (birth weight < 1500 g) and 65 who were born at term (birth weight > 2500 g). The atopy data were collected with a questionnaire, by performing skin prick testing, and by measuring the serum total IgE level, 3 allergen-specific IgE levels, the eosinophil cationic protein level, and the blood eosinophil level. The data on perinatal and neonatal events affecting the preterm children were collected from the hospital records.

RESULTS

By the age of 10 years, the children born preterm had significantly less atopy than the children born at term: 15% versus 31% of children in the 2 groups were defined as having had obvious atopy (P = .03, odds ratio 0.41, 95% CI 0.18-0.93). The mean value of total IgE level was significantly higher in the term group, 74 kU/L versus 41 kU/L (P = .02). By skin prick testing, the children born at term had positive reactions 2 to 3 times more often; 37% versus 17% of children in the groups had at least 1 positive reaction (P = .007).

CONCLUSION

Our data show that prematurity at birth is linked with a decreased long-term risk of atopic sensitization.

Two-color flow cytometric analysis of preterm and term newborn lymphocytes

Immune system maturation proceeds postnatally in humans. Therefore, newborns, especially those of a lower gestational age, are not fully immunocompetent and are more likely to acquire perinatal infections. In order to investigate the neonatal immune system status, the major lymphocyte subpopulations were studied in newborns of different gestational age, comparing term newborns and adults. The cord blood from 66 newborns and the peripheral blood from 23 adults were analyzed using fluorochrome labelled monoclonal antibodies and two-color flow cytometry. The newborns were divided into three groups according to their gestational age. Ten prematures were under 32 weeks of gestation, 35 were of 32-37 weeks and there were 21 term newborns. The percentage of cytotoxic T lymphocytes (CD4 CD8+) was lower in term newborns as compared to the adult controls (17.8 versus 30.3%), and so were the percentages of activated T lymphocytes (CD3+Ia+; 0.3 versus 3.7%), cytotoxic non-MHC restricted T lymphocytes (CD3+CD16+CD56+; 0.2 versus 1.8%) and NK cells (CD3-CD16+CD56+; 4.8 versus 15.5%). On the contrary, the proportions of unlabelled cells were increased in term cord blood. The expression of CD45R0 marker on neonatal lymphocytes was very low (1%). In comparison to the higher-gestation newborns, the lower gestation prematures had reduced percentages of T lymphocytes (CD3+; 43 versus 65%), mostly helper T lymphocytes (CD4+CD8-; 35 versus 50%), and increased percentages of unlabelled cells. The percentages of NK cells (CD3+CD16+CD56+) and B lymphocytes (CD3-CD19+; CD3-Ia+) did not differ among the tested newborn groups. There were no significant differences in major lymphocyte subpopulations between the group of highest-gestation prematures and the group of term newborns that differed significantly when compared to adults. The lowest-gestation newborns showed the most immature lymphocyte phenotype with the highest percentages of unlabelled cells.

Analysis of the human neonatal thymus: evidence for a transient thymic involution

The neonatal period is marked by the impairment of the major components of both innate and adaptive immunity. We report a severe depletion of cortical CD4+CD8+ double-positive thymocytes in the human neonatal thymus. This drastic reduction in immature double-positive cells, largely provoked by an increased rate of cell death, could be observed as early as 1 day after birth, delaying the recovery of the normal proportion of this thymocyte subset until the end of the first month of postnatal life. Serum cortisol levels were not increased in newborn donors, indicating that the neonatal thymic involution is a physiological rather than a stress-associated pathological event occurring in the perinatal period. Newborn thymuses also showed increased proportions of both primitive CD34+CD1- precursor cells and mature TCRalphabetahighCD69-CD1-CD45RO+/RAdull and CD45ROdull/RA+ cells, which presumably correspond to recirculating T lymphocytes into the thymus. A notable reinforcement of the subcapsular epithelial cell layer as well as an increase in the intralobular extracellular matrix network accompanied modifications in the thymocyte population. Additionally neonatal thymic dendritic cells were found to be more effective than dendritic cells isolated from children's thymuses at stimulating proliferative responses in allogeneic T cells. All these findings can account for several alterations affecting the peripheral pool of T lymphocytes in the perinatal period.