Diminished transcription of interleukin-8 by monocytes from preterm neonates.

Developmental delays, which impair antibacterial host defense, are present in the neutrophil system of human preterm neonates. We hypothesized that diminished production of interleukin-8 (IL-8), a neutrophil chemotactic peptide, might in part be responsible for these defects. To test this, monocytes from the blood of preterm neonates, term neonates, and adults were isolated immunologically by "negative panning" and subsequently stimulated with interleukin-1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF-alpha), or lipopolysaccharide (LPS), after which IL-8 levels in the supernatants were measured by ELISA. Total cellular RNA was extracted and IL-8 mRNA was assessed by Northern blotting and by competitive polymerase chain reaction (PCR) analyses. After stimulation with IL-1 alpha, IL-8 accumulation was lowest in supernatants of monocytes from preterm neonates, intermediate in supernatants of monocytes from term neonates and greatest from monocytes of adults. Similarly, when stimulated with TNF-alpha or LPS, monocytes from preterm neonates produced less IL-8 than cells from term neonates and adults. These differences in IL-8 concentrations paralleled differences in IL-8 mRNA expression.

A randomized, placebo-controlled trial of granulocyte colony-stimulating factor administration to newborn infants with neutropenia and clinical signs of early-onset sepsis.

OBJECTIVE: To determine whether recombinant human granulocyte colony-stimulating factor (G-CSF) administration: 1) accelerates production of neutrophils; 2) increases bone marrow stored and precursor neutrophils; and 3) is safe in newborn infants with neutropenia and clinical signs of early-onset sepsis. STUDY DESIGN: We randomized 20 infants with neutropenia and clinical signs of early-onset sepsis in the first 3 days of life to receive G-CSF (10 microg/kg/d) or placebo for 3 days. Entry criteria included neutropenia as defined by Manroe criteria, an elevated immature to total neutrophil ratio [(I/T) >/=0.25], and a requirement for ventilatory support. Cultures were obtained and antibiotics initiated on all study infants. Circulating absolute neutrophil count (ANC), I/T ratio, bone marrow neutrophil storage pool (NSP) and neutrophil proliferative pool (NPP), and plasma G-CSF concentrations were evaluated. Also, severity of illness as determined using the Score for Neonatal Acute Physiology (SNAP), morbidity, and mortality were recorded. RESULTS: Circulating ANC increased in both G-CSF and placebo recipients by day 1. Also, the I/T neutrophil ratio decreased in both G-CSF and placebo recipients. There were no significant differences in the ANC or I/T ratio between the two groups during the study period. Similarly, bone marrow NSP and NPP did not differ between G-CSF and placebo recipients at study entry or day 2. No differences were observed in the secondary outcome measures including severity of illness, morbidity, and mortality. CONCLUSIONS: Administration of recombinant G-CSF to infants with neutropenia and clinical signs of early-onset sepsis did not increase circulating ANC, or bone marrow NSP and NPP compared with placebo. No differences were observed between G-CSF and placebo recipients in severity of illness, morbidity, or mortality. No adverse effects of G-CSF administrations were noted.

Congenital bone marrow failure syndromes associated with protean developmental defects and leukemia.

Congenital bone marrow failure syndromes are associated with a number of congenital abnormalities affecting a wide range of organ systems. The underlying molecular abnormalities that cause these disorders affect normal embryonic development during the critical organogenesis phase (weeks 4 to 8). These syndromes predispose patients to leukemia and other malignancies, and these genetic disorders may represent the first hit of at least two hits necessary for malignant transformation. The molecular defects underlying these diseases are just beginning to be understood; mechanisms suggested by recent research include DNA repair (FA-A, FA-G); abnormalities of the ribosomes (DBA, DC); to disorders of electron transport (FA-C, Pearson's syndrome, Barth's syndrome). Understanding these molecular mechanisms provides the knowledge necessary to develop better therapy, possibly including gene therapy, offering for the first time the potential for curing the hematologic manifestations of these illnesses.

Developmental biology of the dendritic cell system.

AIM: To determine whether an imbalance of dendritic cell subsets might contribute to diminished adaptive host responses observed in newborn infants. It was hypothesized that the proportion of lymphoid dendritic cells would be greater than that of myeloid dendritic cells in cord blood. METHODS: To investigate this, dendritic cell subsets were evaluated in whole cord blood by flow cytometry. Circulating dendritic cells were also isolated from cord blood based on CD1c and BDCA-2 expression. Myeloid dendritic cells were also obtained by culturing cord and adult blood monocytes. Surface phenotypes of these cells were determined by flow cytometry using monoclonal antibodies directed against lineage, major histocompatibility, adhesion, co-stimulation and cytokine receptor molecules. Antigen-presenting functions of dendritic cell subsets were determined by mixed leukocyte reactions. RESULTS: Circulating myeloid dendritic cells were higher in cord blood than previously reported in adult blood, whereas lymphoid dendritic cell numbers were similar between cord and adult blood. Expression of CD11c, CD45RA and CD45RO did not accurately differentiate between dendritic cell subsets circulating in cord blood. Fresh and culture-derived cord blood myeloid dendritic cells stimulated adult allogeneic leukocyte proliferation, while lymphoid dendritic cells were less effective inducers of an adult allogeneic leukocyte response. Culture-derived dendritic cells induced modest autologous cord blood leukocyte proliferation, but freshly isolated myeloid and lymphoid dendritic cells did not stimulated autologous leukocytes. CONCLUSION: Contrary to the hypothesis, an imbalance in the ratio of circulating myeloid to lymphoid dendritic cell subsets does not exist and, therefore, does not contribute to diminished adaptive immune responses in newborn infants.

Evaluating retinopathy of prematurity screening guidelines for 24- to 27-week gestational age infants.

OBJECTIVE: To determine whether current retinopathy of prematurity (ROP) screening guidelines adequately identify treatable ROP in a contemporary cohort of extremely low gestation infants. STUDY DESIGN: Data from the Surfactant, Positive Pressure, and Pulse Oximetry Randomized Trial were used. Inborn infants of 24 (0)/7 to 27 (6)/7 weeks gestational age (GA) with consent before delivery were enrolled in 2005 to 2009. Severe ROP (type 1 ROP or treatment with laser, cryotherapy or bevacizumab) or death was the primary outcome for the randomized trial. Examinations followed the then current AAP (American Academy of Pediatrics) screening recommendations, beginning by 31 to 33 weeks postmenstrual age (PMA). RESULT: One thousand three hundred and sixteen infants were enrolled in the trial. Nine hundred and ninety-seven of the 1121 who survived to first eye exam had final ROP outcome determined. One hundred and thirty-seven (14% of 997) met criteria for severe ROP and 128 (93%) of those had sufficient data (without missing or delayed exams) to determine age of onset of severe ROP. PMA at onset was 32.1 to 53.1 weeks. In this referral center cohort, 1.4% (14/997) developed severe ROP after discharge. CONCLUSION: Our contemporary data support the 2013 AAP screening guidelines for ROP for infants of 24 (0)/7 to 27 (6)/7 weeks GA. Some infants do not meet treatment criteria until after discharge home. Post-discharge follow-up of infants who are still at risk for severe ROP is crucial for timely detection and treatment.

Fetal and postnatal brain MRI in premature infants with twin-twin transfusion syndrome.

OBJECTIVE: To describe the findings on fetal and postnatal magnetic resonance imaging (MRI) in premature infants with twin-twin transfusion syndrome (TTTS) and to determine whether currently used staging systems and other fetal and postnatal factors correlate with brain injury in this population. STUDY DESIGN: We performed a prospective study of 22 premature infants with TTTS whose mothers had fetal MRIs. Postnatal brain MRI was performed at term equivalent age (38 to 44 weeks) and medical records were reviewed. Brain injury was scored on fetal and postnatal MRIs using an injury scale incorporating hemorrhagic and nonhemorrhagic injury. RESULT: The median (range) gestational age (GA) was 31 weeks (26 to 35) and birth weight (BW) was 1296 g (762 to 2330). In all, 5/22 patients (23%) had brain injury seen on fetal MRI and 15/22 patients (68%) had brain injury seen on postnatal MRI. Quintero stage was the only predictor variable that was significantly correlated with the total brain injury score (P=0.05). CONCLUSION: Postnatal brain injury in premature infants with TTTS is correlated with Quintero stage. GA and BW are not predictive of brain injury in this cohort of infants.

Donor human milk largely replaces formula-feeding of preterm infants in two urban hospitals.

OBJECTIVE: To determine acceptance of donor human milk (DM) for feeding preterm infants and whether offering DM, alters mothers' milk (MM) feeding. STUDY DESIGN: Infant feeding data were collected from medical records of 650 very preterm infants enrolled between 2006-2011 in two hospital level III neonatal intensive care units (NICUs) in Cincinnati, Ohio. The study was conducted during the implementation of a program offering 14 days of DM. RESULT: From 2006-2011, any DM use increased from 8 to 77% of infants, largely replacing formula for the first 2 weeks of life; provision of MM did not change. DM was more likely to be given in the first 2 weeks of life, if infants never received MM or were >1000 g birth weight, but DM use did not differ by sociodemographic factors. CONCLUSION: Offering DM dramatically increased human milk feeding and decreased formula use, but did not alter MM feeding in hospital.

Hospital and neurodevelopmental outcomes of extremely low-birth-weight infants with necrotizing enterocolitis and spontaneous intestinal perforation.

OBJECTIVE: We sought to determine the incidence of necrotizing enterocolitis (NEC) and spontaneous intestinal perforation (SIP) in surviving extremely low-birth-weight (ELBW, <1000 g birth weight) infants and to establish the impact of NEC on outcomes by hospital discharge and at 18 to 22 months adjusted age in a large, contemporary, population-based practice. STUDY DESIGN: Hospital outcome data for all ELBW infants born in the greater Cincinnati region from 1998 to 2009 were extracted from the National Institute of Child Health Neonatal Research Network Database. Neurodevelopmental outcome at 18 to 22 months was assessed using Bayley Scales of Infant Development-II scores for Mental Developmental Index and Psychomotor Developmental Index. Multivariable logistic regression was used and adjusted odds ratios reported to control for confounders. RESULT: From 1998 to 2009, ELBW infants accounted for 0.5% of the 352 176 live-born infants in greater Cincinnati. The incidence of NEC was 12%, with a 50% case-fatality rate. Death before discharge, morbid complications of prematurity and neurodevelopmental impairment were all increased among infants diagnosed with NEC. Infants with surgical NEC and SIP had a higher incidence of death, but long-term neurodevelopmental outcomes were not different comparing surviving ELBW infants with medical NEC, surgical NEC and SIP. CONCLUSION: Although ELBW infants comprise a very small proportion of live-born infants, those who develop NEC and SIP are at an increased risk for death, morbid complications of prematurity and neurodevelopmental impairment. No significant differences in neurodevelopmental outcomes were observed between the medical and surgical NEC and SIP groups.

Effect of interleukin-11 on cycling status and clonogenic maturation of fetal and adult hematopoietic progenitors.

A recently cloned human cytokine, interleukin-11 (IL-11), has functional similarities to IL-6. We tested the hypothesis that the hematopoietic actions of IL-11 in vitro also resemble those of IL-6. The effect of IL-11 on the cell cycle status of fetal and adult hematopoietic progenitors was assessed using serum-free incubations followed by tritiated thymidine suicide studies. Its effect on clonogenic maturation was assessed by including IL-11, either as a single agent or with subplateau or plateau concentrations of other recombinant cytokines, in cultures that contained neutralizing monoclonal antibodies directed against relevant growth factors. Similar to IL-6, IL-11 resulted in accelerated cycling of fetal colony-forming units-mixed (CFU-MIX), CFU-granulocyte macrophage (CFU-GM), and erythroid burst-forming units (BFU-E). This effect was additive to that of submaximal, but not to plateau, concentrations of IL-6. However, no effect of IL-11 was observed on cycling status of adult progenitors. As a single agent, IL-11 failed to support clonal maturation of either fetal or adult progenitors. IL-11 was additive to GM-CSF in supporting clonal maturation of CFU-GM from adult marrow but not from fetal blood. We conclude that the in vitro hematopoietic actions of IL-11 on cell cycle status of hematopoietic progenitors resemble those of IL-6. However, unlike IL-6, IL-11 as a single agent failed to support clonal maturation of fetal CFU-GM, BFU-E, and CFU-MIX.

The effect of erythropoietin on the transfusion requirements of preterm infants weighing 750 grams or less: a randomized, double-blind, placebo-controlled study.

BACKGROUND: Clinical trials of erythropoietin (EPO) administration to preterm infants have not focused on infants weighing 750 gm or less, the population most likely to receive multiple transfusions because of large phlebotomy losses. It is unknown whether preterm infants weighing 750 gm or less will respond to EPO by accelerating erythropoiesis, or whether EPO administered to this population will decrease blood transfusions. METHODS: We randomly assigned 28 extremely low birth weight preterm infants (mean +/- SEM: 24.7 +/- 0.3 weeks' gestation, 662 +/- 14 gm birth weight), in the first 72 hours of life, to receive either EPO (200 U/kg/day) or placebo for 14 days and administered transfusions only according to protocol over a 21-day study period. All infants received 1 mg/kg/day iron dextran in their total parenteral nutrition solution during the 14-day treatment period. RESULTS: During the 21-day study period, a lower number and volume of transfusions were received by the EPO recipients (4.7 +/- 0.7 transfusions per patient and 70 +/- 11 ml/kg per patient) than by the placebo recipients (7.5 +/- 1.1 transfusions per patient and 112 +/- 17 ml/kg per patient; p < 0.05, EPO vs placebo), whereas hematocrits remained similar in the two groups. Reticulocyte counts were similar in both groups on day 1 but were greater in the EPO recipients on day 14 (EPO day 1, 351 +/- 53; EPO day 14, 359 +/- 40 x 10(3)/microl; placebo day 1, 334 +/- 64; placebo day 14, 120 +/- 10 x 10(3)/microl; p < 0.01, EPO vs placebo). Serum ferritin concentrations were similar in both groups at the beginning of the study but were greater in the placebo recipients by day 14 (EPO, 262 +/- 44 microg/L; placebo, 593 +/- 92 microg/L; p < 0.01). No adverse effects of EPO or iron were noted. CONCLUSION: The combination of EPO and parenteral iron stimulates erythropoiesis in preterm infants weighing 750 gm or less and results in fewer transfusions during their first 3 weeks of life.

Regulation of interleukin-10 gene expression: possible mechanisms accounting for its upregulation and for maturational differences in its expression by blood mononuclear cells.

Interleukin-10 (IL-10) downmodulates phagocytic immune responses and accentuates humoral responses. Human neonates exhibit broad immune deficits that parallel actions of IL-10. We postulated that IL-10 production would be diminished in neonatal blood cells. We found that IL-10 production by lipopolysaccharide-stimulated peripheral blood mononuclear cells (PBMNCs) in vitro was greater by adult cells than by term cells and preterm cells. Additional studies were undertaken to identify mechanisms responsible for the developmental differences in IL-10 gene expression. IL-10 transcription was present in freshly isolated adult and neonatal cells in the absence of detectable levels of transcript. Transcription rates were not different between adult and neonatal cells. IL-10 transcripts were approximately 40% more abundant in adult cells than in term cells and were consistent with differences in secreted protein; however, no differences were noted in mRNA stability. IL-10 half-life was 60 minutes for both adult and term PBMNCs. We conclude that up-regulation of IL-10 gene expression in PBMNCs is modulated at the post-transcriptional level, that IL-10 protein production and mRNA content are greater in activated cells from adults compared with those from neonates, and that maturational differences in IL-10 expression are not due to differences in transcription rate or mRNA stability. Maturational differences in IL-10 expression might be due to differences in subpopulations of cytokine-producing cells or differences in nucleo-cytoplasmic transport.

Effect of recombinant stem cell factor on clonogenic maturation and cycle status of human fetal hematopoietic progenitors.

Studies were undertaken to delineate the actions of stem cell factor (SCF) on human fetal hematopoietic progenitors in vitro. Mononuclear cells from umbilical cord blood of term fetuses were "panned" immunologically, and the resulting hematopoietic progenitors were grown in methylcellulose culture containing various concentrations of SCF alone or in combination with other recombinant hematopoietic growth factors. Neutralizing antibodies to IL-3 and granulocyte-macrophage colony-stimulating factor were added to all plates to which recombinant IL-3 or granulocyte-macrophage colony-stimulating factor were not included to decrease any confounding effect resulting from production of small quantities of these factors within the culture plates. SCF, as a single agent, supported clonogenic maturation of fetal granulocyte-macrophage progenitors (granulocyte-macrophage colony-forming unit, p < 0.05), multipotent progenitors (CFU-MIX, p < 0.05), and erythroid progenitors (erythroid burst-forming unit, p < 0.05). When combined with subplateau concentrations (0.1 microgram/L) of IL-3 or granulocyte-macrophage colony-stimulating factor, SCF had an additive or synergistic effect on clonogenic maturation of granulocyte-macrophage colony-forming unit and CFU-MIX. When combined with higher concentrations (5.0 micrograms/L) of IL-3 or granulocyte-macrophage colony-stimulating factor, SCF generally did not enhance colony formation but did increase the number of cells per colony. Like other pleiotropic cytokines such as IL-6, IL-9, and IL-11, SCF had a broad spectrum of action of fetal hematopoietic progenitors.

Defective production of interleukin-6 by monocytes: a possible mechanism underlying several host defense deficiencies of neonates.

Several deficiencies in antibacterial defense have been described in neonates. Among those best characterized are delayed maturation of B cells into antibody producing cells, deficient T-cell maturation, and delayed cycling of hematopoietic progenitor cells after an infectious challenge. No unifying theory has been forwarded, however, to explain the concomitance of these three developmental deficiencies. IL-6, a cytokine produced primarily by monocytes and macrophages in response to stimulation by IL-1, is involved in the regulation of these three processes. Thus, we postulated that defective production of IL-6 could be a mechanism underlying these immune deficiencies of neonates. Indeed, we observed that a peak production, cells of five term neonates produced only one half as much IL-6 (14 120 +/- 2590 pg IL-6/10(6) monocytes) as those of five adults (28 940 +/- 1680 pg, p less than 0.001). Peak production was lower still by monocytes of six preterm neonates (7190 +/- 1400 pg, p less than 0.001 versus term). Production of IL-6 protein was inhibited by actinomycin D and the IL-6 mRNA content of monocytes from neonates, as assessed by competitive polymerase chain reaction, was less than that of adult monocytes. We speculate that defective IL-6 transcription might underlie some of the defects in immune regulation observed in neonates.

Production of granulocyte colony-stimulating factor in vitro by monocytes from preterm and term neonates.

We postulated that defective generation of granulocyte colony-stimulating factor (G-CSF) by cells of newborn infants might underlie their deficiencies in upregulating neutrophil production and function during bacterial infection. To test this, we isolated monocytes from the blood of preterm neonates, term neonates, and adults and, after stimulation with various concentrations of interleukin-1 alpha (IL-1 alpha) or lipopolysaccharide (LPS), quantified G-CSF concentrations in cell supernatants and G-CSF mRNA in cell lysates. When stimulated with plateau concentrations of IL-1 alpha for 24 hours, G-CSF concentrations were higher in supernatants of adult cells (8,699 +/- 5,529 pg/10(6) monocytes) than in those from term infants (2,557 +/- 442 pg, P < .05) or from preterm infants (879 +/- 348 pg, P < .05 v adults). When stimulated with plateau concentrations of LPS, supernatants of monocytes from preterm neonates had less G-CSF than did those from term neonates or adults. G-CSF mRNA content was low in cells from preterm infants, higher in those from term infants, and highest in those from adults. On the basis of the in vitro studies, we speculated that serum G-CSF concentrations might be less elevated in neutropenic neonates than in neutropenic adults. Indeed, serum concentrations were relatively low in all nonneutropenic subjects; 92 +/- 34 pg/mL (mean +/- SEM) in 10 preterm neonates, 114 +/- 21 pg/mL in 16 term neonates, and 45 +/- 13 pg/mL in 11 healthy adults. Serum concentrations were not elevated in 7 neutropenic neonates (39 +/- 17 pg/mL) but were in 8 neutropenic adults (2101 +/- 942 pg/mL, P < .05 v healthy adults). Other studies suggested that the lower G-CSF production in neonates is not counterbalanced by a heightened sensitivity of G-CSF--responsive progenitors to G-CSF. Therefore, we speculate that newborn infants, particularly those delivered prematurely, generate comparatively low quantities of G-CSF after inflammatory stimulation, and that this might constitute part of the explanation for their defective upregulation of neutrophil production and function during infection.

Administration of erythropoietin to newborn rats results in diminished neutrophil production.

Very high concentrations of erythropoietin (epo), in clonogenic cultures, result in reduced production of neutrophils, and fetal progenitors are more sensitive to this effect of epo than are those of adults. However, the significance of this observation is unclear because no evidence of reduced neutrophil production has been presented following administration of recombinant epo to human or animal subjects. In the present study we injected newborn rats, beginning on the first day of life, with 20, 200, or 2,000 U epo/kg body weight, and measured serum epo concentrations after 2, 8, 24, or 48 hours. After selecting a dose that resulted in serum concentrations greater than 1,000 mU/mL (a concentration that resulted in down-modulation of neutrophil production from neonatal rat progenitors in vitro) other newborn rats were treated for 3 days with that dose (1,000 U epo/kg) or a vehicle control. Administration of epo resulted in increased hematocrits (P less than .001), reticulocyte counts (P less than .001), normoblasts/femur (P less than .05), and normoblasts/spleen (P less than .001). Recipients of epo also had more erythroid colony-forming units (CFU-E) (P less than .001) and higher CFU-E tritiated thymidine suicide rates (P less than .01) than did controls. However, femurs and spleens of epo recipients contained fewer postmitotic neutrophils (femur, P less than .01; spleen, P less than .01), proliferative neutrophils (femur, P less than .01; spleen, P less than .02), granulocyte-macrophage colony-forming units (CFU-GM) (P less than .005), and lower CFU-GM tritiated thymidine suicide rates (P less than .01). Seven and nine days after twice-daily administration of 2,000 U epo/kg, blood neutrophil concentrations had diminished (P less than .05). Thus, administration of high doses of recombinant epo to newborn rats resulted in diminished neutrophil production accompanying accelerated erythropoiesis.

Effect of interleukin-9 on clonogenic maturation and cell-cycle status of fetal and adult hematopoietic progenitors.

We assessed the effect of interleukin-9 (IL-9) on clonogenic maturation and cell-cycle status of hematopoietic progenitors of fetal (umbilical cord blood) and adult (bone marrow) origin. As a single agent IL-9 supported, in a concentration-dependent fashion, maturation of burst-forming units-erythroid (BFU-E) of adult and fetal origin. However, only 1/3 the number of adult BFU-E colonies developed, as did in response to granulocyte-macrophage colony-stimulating factor (GM-CSF), and only 1/6 the number developed as did in response to IL-3. In contrast, the effect of IL-9 on fetal BFU-E colonies was equal to that of GM-CSF and IL-3. Synergistic effects of IL-9 with low concentrations (0.1 ng/mL) of GM-CSF and IL-3 were seen on adult BFU-E colony formation, but no effect was apparent at higher concentrations (1.0 ng/mL). In contrast, using fetal cells, synergistic effects of IL-9 with low and high concentrations of GM-CSF and IL-3 were apparent. Addition of IL-9 to plates containing fetal cells plus GM-CSF and IL-3 not only resulted in more BFU-E colonies, but also in more multicentered (greater than or equal to 10 individual centers) colonies, and more cells per colony. IL-9 had a wider spectrum of action on progenitors of fetal origin than on progenitors of adult origin, supporting the generation of fetal multipotent colony-forming unit (CFU)-Mix and CFU-GM colonies. Incubation with IL-9 did not accelerate cycling of adult or fetal BFU-E, CFU-Mix, or CFU-GM to the extent observed after incubation with IL-6. Thus, IL-9 primarily supported maturation of erythroid progenitors of adult origin, and its addition to plates containing GM-CSF and IL-3 (1.0 ng/mL) did not result in maturation of additional clones. In contrast, IL-9 had a wider spectrum of action on fetal progenitors and, when combined with IL-3 and GM-CSF, resulted in clonogenic maturation of progenitors that did not undergo maturation after stimulation with IL-3 and GM-CSF.

The failure of newborn mice infected with Escherichia coli to accelerate neutrophil production correlates with their failure to increase transcripts for granulocyte colony-stimulating factor and interleukin-6.

We quantified circulating and storage neutrophils, their precursors and progenitors, and mRNA for some of the cytokines involved in granulocytopoiesis, in newborn and adult mice following intrapulmonary inoculation of Escherichia coli. Four hours following inoculation of adult and newborn mice with a quantity of organisms 2 logs below the LD100, all animals were neutropenic. After 24 h, adults had recovered from the neutropenia but neonates had not (p < 0.001). Accelerated neutrophil production was evident in the infected adults, and correlated with the appearance of granulocyte colony-stimulating factor (G-CSF) transcripts in the liver, spleen, and lung, and interleukin-6 (IL-6) transcripts in the spleen and lung. An increase in neutrophil production was not observed in the neonates, and none of their organs tested had transcripts for either G-CSF or IL-6, but they did have transcripts for cytokines not involved in granulocytopoiesis; macrophage colony-stimulating factor and its receptor (c-fms). We speculate that the failure to increase neutrophil production in infected neonatal mice is the result of failure to increase production of relevant cytokines.