Multipotent adult progenitor cells: their role in wound healing and the treatment of dermal wounds.

The use of cellular therapy in the treatment of dermal wounds is currently an active area of investigation. Multipotent adult progenitor cells (MAPC) are an attractive choice for cytotherapy because they have a large proliferative potential, the ability to differentiate into different cell types and produce a variety of cytokines and growth factors important to wound healing. Whole bone marrow (BM) was one of the initial attempts to treat impaired wounds. While it has shown some promise, the low frequency of progenitor cell populations in BM and the large number of inflammatory cells make it less attractive. Multipotent mesenchymal stromal cells (MSC) and endothelial progenitor cells are populations of BM-derived progenitor cells that have been isolated and used to treat chronic wounds with some success. Skin-derived MAPC are another heterogeneous population of progenitor cells present in the skin with the potential to differentiate into skin elements and participate in wound healing. All of these progenitor cell populations are potential sources for cytotherapy of wounds. This review focused on the contribution of adult progenitor cell populations to dermal wound healing and their potential for use in cytotherapy.

Human mesenchymal stem cells engraft and demonstrate site-specific differentiation after in utero transplantation in sheep.

Mesenchymal stem cells are multipotent cells that can be isolated from adult bone marrow and can be induced in vitro and in vivo to differentiate into a variety of mesenchymal tissues, including bone, cartilage, tendon, fat, bone marrow stroma, and muscle. Despite their potential clinical utility for cellular and gene therapy, the fate of mesenchymal stem cells after systemic administration is mostly unknown. To address this, we transplanted a well-characterized human mesenchymal stem cell population into fetal sheep early in gestation, before and after the expected development of immunologic competence. In this xenogeneic system, human mesenchymal stem cells engrafted and persisted in multiple tissues for as long as 13 months after transplantation. Transplanted human cells underwent site-specific differentiation into chondrocytes, adipocytes, myocytes and cardiomyocytes, bone marrow stromal cells and thymic stroma. Unexpectedly, there was long-term engraftment even when cells were transplanted after the expected development of immunocompetence. Thus, mesenchymal stem cells maintain their multipotential capacity after transplantation, and seem to have unique immunologic characteristics that allow persistence in a xenogeneic environment. Our data support the possibility of the transplantability of mesenchymal stem cells and their potential utility in tissue engineering, and cellular and gene therapy applications.

Fetal wound repair results in scar formation in interleukin-10-deficient mice in a syngeneic murine model of scarless fetal wound repair.

BACKGROUND: Fetal dermal wound healing is characterized by minimal inflammation, restoration of normal dermal architecture, and scarless repair. The authors have shown that proinflammatory cytokines interleukin-6 (IL-6) and interleukin-8 (IL-8) are diminished during fetal wound repair. Interleukin-10 (IL-10) is an antiinflammatory cytokine that decreases production of IL-6 and IL-8. The authors hypothesized that diminished IL-6 and IL-8 and minimal inflammation may be caused by IL-10. METHODS: To test this hypothesis, the authors developed a new syngeneic murine model of fetal wound repair in which 15-day-gestation skin from either normal C57BL/6 or transgenic C57BL/6 IL-10 knockout mice was grafted to the back of the same strain adult mice. The grafts were incisionally wounded after 5 days, harvested at 1 week, and analyzed for inflammatory response and scar formation. RESULTS: Wounds in normal fetal skin grafts showed minimal inflammation and normal dermal reticular collagen pattern at the site of the wound, consistent with scarless repair. In contrast, wounds in IL-10 knockout fetal skin grafts showed significant inflammation and scar formation. CONCLUSIONS: Fetal skin grafts on adult syngeneic mice heal without inflammation or scar formation. The absence of IL-10 in fetal skin results in scar formation. Intrinsic lack of IL-10 may result in continued amplification of the inflammatory cytokine cascade, continued stimulation of fibroblasts, and abnormal collagen deposition. IL-10 is necessary for scarless wound repair to occur.

Diminished interleukin 6 (IL-6) production during scarless human fetal wound repair.

Fetal wound healing is characterized by minimal inflammation and scarless repair. IL-6 stimulates inflammation in postnatal wound healing. We hypothesized that fetal skin has a diminished IL-6 response and that exogenous IL-6 will result in scar formation. Human adult or fetal skin was placed subcutaneously in SCID mice and incisionally wounded. Wounds were excised after 4, 12, 24 or 72 h for IL-6 mRNA quantification by RT-PCR. In other grafts, 5 microgram of IL-6 was injected at wounding and then harvested at 7 days for analysis of scar formation. IL-6 production was examined in primary cultures of human fetal or adult dermal fibroblasts incubated for 8 h with 0, 0.1, 1 or 10 ng/ml of PDGF-BB. IL-6 mRNA was detected 4 h after wounding in fetal and adult wounds, but by 12 h there was no IL-6 mRNA in the fetal wounds. Adult wounds had IL-6 mRNA persisting to 72 h. IL-6 administration to fetal wounds resulted in scar formation. Fetal fibroblasts produced less IL-6 protein and mRNA at all points examined (P<0.01 vs adult). Diminished production of inflammatory cytokines such as IL-6 may be responsible for the lack of inflammation seen during fetal wound healing. Diminished inflammation may provide a permissive environment for scarless wound healing.

Adenoviral-mediated overexpression of platelet-derived growth factor-B corrects ischemic impaired wound healing.

Chronic wounds represent a major clinical problem with significant morbidity and healthcare expenditures, but no effective therapies. Topical platelet-derived growth factor-BB trials have required large and repeated doses to achieve only a modest effect. We examined the ability of an adenovirus containing the platelet-derived growth factor-B transgene to improve the rate of wound healing through induction of platelet-derived growth factor-B overexpression in cells participating in the wound healing response. We treated excisional wounds in the ischemic rabbit ear, which have a 60% delay in healing, with vehicle, 106, or 108 plaque-forming units of an adenovirus containing the platelet-derived growth factor-B per wound (n = 19). At 7 d this resulted in a decrease in the epithelial gap from 3.4 +/- 1 mm (mean +/- SD) in vehicle-treated wounds to 1.9 +/- 1.8 mm (mean +/- SD, p < 0.05) when treated with 106 plaque-forming units of an adenovirus containing the platelet-derived growth factor-B, and 0.7 +/- 1.1 mm (mean +/- SD, p < 0.001) when treated with 108 plaque-forming units of an adenovirus containing the platelet-derived growth factor-B. Ischemic excisional wounds treated with 108 plaque-forming units of an adenovirus containing the platelet-derived growth factor-B even healed more rapidly than non-ischemic excisional wounds treated with vehicle (p < 0.05). In contrast, 5 microg of platelet-derived growth factor-BB protein (n = 2) resulted in only modest granulation tissue at the margin, but no significant differences in epithelial gap (3 +/- 0.6 mm, mean +/- SD). Plaque-forming units (106 or 108) of an adenovirus containing the beta-galactosidase transgene (n = 4) impaired wound re-epithelialization with an epithelial gap of 5.11 +/- 0.69 mm, mean +/- SD, p < 0.004, and 3.8 +/- 0.57 mm, mean +/- SD, p < 0.07, respectively. Adenoviral-mediated gene transfer of platelet-derived growth factor-B overcame the ischemic defect in wound healing and offers promise in the treatment of chronic nonhealing wounds. The vulnerary effects of platelet-derived growth factor-B overexpression were sufficient to overcome the adverse effects of the adenovirus or transgene on wound healing.

Recombinant adenoviral mediated gene transfer in ischemic impaired wound healing.

Chronic nonhealing wounds represent a large clinical problem resulting in severe disabilities and large healthcare expenditures. Despite the scope of this problem, effective new therapies are lacking. The deficiency of growth factors in chronic wounds has brought attention to the topical application of growth factors, but initial clinical trials have resulted in only modest improvements in healing despite large, repetitive doses. The modest improvement in healing observed in these trials show that growth factors can improve chronic wound healing, but a better means of growth factor delivery is needed. We hypothesized that gene therapy using a recombinant adenoviral vector could be used to induce transgene production directly by cells in the wound. An adenovirus containing the beta-galactosidase reporter transgene (Ad-LacZ) was used in the ischemic rabbit ear model to test this hypothesis. Ad-LacZ resulted in efficient transgene delivery to cells participating in the wound healing response, with expression up to 2 weeks. However, wound reepithelialization was impaired in Ad-LacZ treated wounds compared to vehicle control wounds. Adenoviral mediated gene transfer is a promising efficient means of growth factor delivery to chronic wounds. However, selection of the proper transgene with appropriate biologic activity in wound healing may be essential to overcome the potential adverse effects of adenoviral infection.

TGF-beta2 is increased after fetal tracheal occlusion.

BACKGROUND/PURPOSE: Fetal tracheal occlusion (TO) accelerates lung growth in normal and hypoplastic fetal lung. The mechanism of accelerated lung growth remains unknown but may be a result of growth factor induction. Previous studies of growth factors induced by tracheal ligation have characterized mRNA rather than protein expression. Although the transforming growth factor-beta (TGF-beta) family participates in normal lung morphogenesis, its role in lung growth after TO is unclear. The authors hypothesize that TGF-beta expression is increased with TO and may contribute to the accelerated lung growth seen after TO. METHODS: Diaphragmatic hernia (DH) was created in 80-day-gestation sheep (n = 6; term, 145) by excising the left diaphragm. At 110 days, the trachea was occluded (n = 4) with a clip. DH controls (n = 2) were not occluded. Fetuses were killed at 139 days, and lung samples were snap frozen for tissue analysis. Non-DH control lungs were harvested from full-term animals (n = 2). TGF-beta mRNA was analyzed by semiquantitative reverse transcriptionase-polymerase chain reaction (RT-PCR). TGF-beta protein was assessed by Western blot analysis. RESULTS: TGF-beta1 mRNA and protein were not increased with tracheal ligation compared with either non-DH or DH controls. TGF-beta2, however, was markedly increased, at both the mRNA and protein level, in ligated lungs compared with nonligated controls. CONCLUSIONS: TGF-beta2 protein, but not TGF-beta1, is increased in the hypoplastic lungs of fetal sheep after tracheal occlusion. Increased TGF-beta2 expression appears to result from increased or prolonged expression of mRNA transcripts. This is the first study to document a change in growth factor protein levels after TO. Increased TGF-beta2 expression may contribute to accelerated lung growth and decreased surfactant production observed after tracheal occlusion.

Elevated platelet-derived growth factor-B in congenital cystic adenomatoid malformations requiring fetal resection.

BACKGROUND: During lung development, platelet-derived growth factor-BB (PDGF-BB) is maximal during the canalicular stage and decreases by the saccular stage. PDGF-BB stimulates lung growth by increasing cell proliferation. Fetal CCAMs have been shown to have an elevated proliferative index, but it is not known why some CCAMs rapidly enlarge in utero and cause fetal hydrops. The authors hypothesized that the high proliferative index and rapid enlargement of some fetal CCAMs may be caused by persistently elevated PDGF-BB production compared with normal fetal lung. METHODS: To test this hypothesis, tissue was obtained at the time of resection from two fetal CCAMs (22 weeks), three full-term CCAMs, and three normal fetal lungs (21 to 22 weeks). PDGF-BB production by fetal CCAMs was compared with normal age-matched fetal lung using immunohistochemistry, reverse transcriptionase-polymerase chain reaction (RT-PCR), and Western blot analysis. RESULTS: CCAMs resulting in fetal hydrops and requiring fetal resection had strong mesenchymal immunostaining for PDGF-BB next to epithelial lined cysts, increased PDGF-B gene expression by RT-PCR, and elevated PDGF-BB protein by Western blot, compared with normal age-matched fetal lung. Term CCAMs had minimal PDGF-BB staining, PDGF-B gene expression, and PDGF-BB protein production. CONCLUSIONS: CCAMs that grew rapidly and progressed to hydrops, requiring in utero resection, demonstrated increased mesenchymal PDGF-B gene expression and PDGF-BB protein production compared with age-matched normal fetal lung, which may, in part, be responsible for the autonomous growth and proliferation seen in hydropic fetal CCAMs.

The ex utero intrapartum treatment procedure for a large fetal neck mass in a twin gestation.

BACKGROUND: Large fetal neck masses can make it difficult or impossible to secure airways at birth, with associated risks of hypoxia, brain injury, and death. Based on a MEDLINE search from 1966 to June 1998, using the keywords EXIT procedure, placental support, twins, and neck mass, we report the first ex utero intrapartum treatment procedure performed in a twin gestation complicated by a large fetal neck mass. CASE: A giant fetal cervical mass was diagnosed in one fetus of a 20-week twin gestation by sonography and magnetic resonance imaging. At 35 weeks' gestation, the ex utero intrapartum treatment procedure was performed successfully for delivery of the normal twin, followed by intrapartum airway access of the twin with the neck mass. CONCLUSION: Even in twin gestations, the ex utero intrapartum treatment procedure is the delivery method of choice for fetuses with giant neck masses.

Management of fetal airway obstruction.

Fetal airway obstruction can make it difficult if not impossible to secure the airway at birth, before hypoxia, brain injury, or death results. Fetal airway obstruction can result from an intrinsic defect in the airway, such as the congenital high airway obstruction syndrome or extrinsic compression of the airway caused by a cervical mass, most commonly a cervical teratoma or lymphangioma. As fetuses with fetal airway obstruction reach viability, they should be monitored closely for the development or progression of hydrops in intrinsic obstruction cases or polyhydramnios in extrinsic obstruction cases. The fetus should be delivered by using the ex utero intrapartum treatment procedure, with maintenance of uteroplacental circulation and gas exchange. This approach provides time to perform procedures such as direct laryngoscopy, bronchoscopy, or tracheostomy to secure the fetal airway, thereby converting an emergent airway crisis into a controlled situation.

Microchimerism and tolerance after in utero bone marrow transplantation in mice.

BACKGROUND: Donor-specific tolerance has been induced after both fetal and neonatal hematopoietic stem cell (HSC) transplantation in mice. However, the relationship between hematopoietic microchimerism and tolerance in these models has not been defined due to the insensitivity of donor cell detection methodology. To address this problem we developed a semiquantitative polymerase chain reaction (PCR)-based assay for detection of microchimerism after major histocompatibility (MHC) class I disparate HSC transplantation. This assay was used to examine the relationship between microchimerism and tolerance after fetal and neonatal transplantation of fully allogeneic bone marrow cells. MATERIALS AND METHODS: C57BL/6 mice (H2-Kb) were used as adult bone marrow donors and Balb/c mice (H2-Kd) were used as fetal or newborn recipients. A dose of 10(10) BM cells/kg was injected intraperitoneally into recipient animals. Peripheral blood of animals which survived beyond 3 weeks of age was analyzed by PCR for the presence of donor MHC class I DNA. Tolerance was tested by placement of donor-specific skin grafts after determination of chimerism status. RESULTS: Our assay was found to be specific for H2-Kb donor cells in an H2-Kd background with a sensitivity of <0.0001%. Of 49 animals injected in utero 19 (38%) had donor DNA present in peripheral blood at low levels (<0.1%) whereas only 1 of 18 neonatally injected animals had detectable donor cells (P < 0.01). Tolerance to donor-specific skin grafts was found in 6 of 9 animals which were chimeric after in utero HSC transplantation whereas none of the 18 neonatally injected animals including the chimeric animal were tolerant. CONCLUSIONS: Our results indicate the following. (1) Hematopoietic microchimerism can be detected by PCR in peripheral blood after in utero injection of fully allogeneic HSCs. (2) Fetal injections yield a higher incidence of microchimerism than newborn injections. (3) Tolerance can be induced across a fully allogeneic barrier by in utero HSC transplantation and this is associated with the presence of peripheral blood microchimerism.

Diminished interleukin-8 (IL-8) production in the fetal wound healing response.

BACKGROUND: Fetal skin wound healing results in scarless repair with minimal cellular inflammatory response. Interleukin-8 (IL-8) stimulates inflammation in postnatal wound healing but little is known about its role in fetal wounds. We hypothesized that fetal tissues have diminished IL-8 during wound repair and in response to platelet-derived growth factor (PDGF), a growth factor central to wound healing. MATERIALS AND METHODS: To examine the IL-8 response of fibroblasts to PDGF, cultures of human fetal (17-18 weeks) and adult dermal fibroblasts were incubated 8 h with PDGF (0, 0.1, 1, or 10 ng/mL) and supernatants and cells were collected for IL-8 ELISA and IL-8 RT-PCR. To evaluate the IL-8 response to wounding, human adult and fetal skin was placed subcutaneously in the SCID mouse, wounded, and the wound cleft excised after 4, 12, 24, or 72 h for IL-8 RT-PCR. RESULTS: Fetal fibroblasts produced less IL-8 protein at baseline (50 +/- 6 pg/mL versus 450 +/- 115 pg/mL, P < 0.001) and in response to all concentrations of PDGF examined (P < 0.001). IL-8 mRNA was detected in unstimulated adult fibroblasts but not in fetal fibroblasts. Much less IL-8 mRNA was detected in stimulated fetal fibroblasts than in adult fibroblasts. IL-8 mRNA was detected 4 h after wounding in fetal and adult wounds. By 12 h no IL-8 mRNA was detected in fetal wounds, whereas adult wounds had IL-8 mRNA persisting to 72 h. CONCLUSIONS: Diminished inflammatory cytokine response by fetal tissues may be responsible for the lack of cellular recruitment and inflammation seen in fetal wound healing and may contribute to scarless wound repair.

Increased cell proliferation and decreased apoptosis characterize congenital cystic adenomatoid malformation of the lung.

BACKGROUND/PURPOSE: Congenital cystic adenomatoid malformations (CCAM) are lung lesions that demonstrate abnormalities of both mesenchymal and epithelial tissues. The pathogenesis of these tumors remains unknown. Because normal organogenesis requires a balance between cell proliferation and programmed cell death (apoptosis), the authors hypothesized that CCAM results from an increase in cell proliferation or a decrease in apoptosis within the developing lung, possibly mediated by keratinocyte growth factor (KGF). METHODS: To examine cell cycle control in CCAM, we measured indices of cell proliferation and apoptosis in lesions requiring fetal (n = 4) or neonatal (n = 8) resection compared with those of normal fetal (14 to 28 weeks' gestation; n = 14) and neonatal (n = 3) human lung. Cell proliferation was analyzed by immunostaining for a proliferation marker (Ki-67). Apoptosis was examined using an in situ digoxigenin end-labeling technique to localize apoptotic bodies. The expression of KGF protein and KGF mRNA in CCAM and normal lung was examined using immunohistochemistry and semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR). RESULTS: CCAM lesions in general showed a twofold increase in cell proliferation index (19.2% +/- 1.4% v 9.6% +/- 0.7%, P < .00005) and a fivefold decrease in apoptotic bodies (0.9 +/- 0.2 v 4.5 +/- 0.5, P < .0005) compared with age-matched normal lung. CCAMs that required resection before birth had the highest cell proliferation index. There were no differences in the expression of KGF protein or KGF mRNA in CCAM and normal lung. CONCLUSIONS: These results demonstrate that CCAM differs from normal lung by increased cell proliferation and decreased apoptosis. The increased proliferation does not appear to be mediated by the pneumocyte mitogen KGF. An examination of factors that control cell proliferation and apoptosis in CCAM may provide further insight into the pathogenesis of this tumor.

Intrapartum airway management for giant fetal neck masses: the EXIT (ex utero intrapartum treatment) procedure.

OBJECTIVE: Our goal was to review our experience with the EXIT (ex utero intrapartum treatment) procedure in the management of five cases with life-threatening fetal neck masses. STUDY DESIGN: We present a retrospective review of prenatal presentation and course, diagnostic accuracy of imaging studies, intraoperative management, complications, and outcomes. RESULTS: Polyhydramnios was the initial presenting symptom in three of five fetuses with a mean gestational age of 25 +/- 6 weeks. Preterm labor occurred in two patients. Fetal magnetic resonance imaging provided accurate diagnosis in all four cases whereas conventional ultrasonography led to the diagnosis in four of five cases. The mean duration of EXIT was 28 +/- 22 minutes. The mean venous cord blood gas values were pH 7.22 +/- 0.05, PCO2 61 +/- 11 mm Hg, and PO2 42 +/- 8 mm Hg. In four of five cases an airway was successfully secured. CONCLUSIONS: The EXIT procedure provides up to 1 hour of good uteroplacental support and is the procedure of choice to secure an airway in the fetus with a giant neck mass.

Possible mechanisms accounting for the growth factor independence of hematopoietic progenitors from umbilical cord blood.

Hematopoietic progenitors obtained from the bone marrow of healthy adults fail to undergo clonogenic maturation in vitro if a source of hematopoietic growth factors is not included in the culture dishes. In contrast, a fraction of similarly purified progenitors obtained from umbilical cord blood undergo clonogenic maturation even in the absence of added growth factors. We postulated that production of hematopoietic growth factors within the culture dishes containing the progenitors of umbilical cord blood origin might be responsible. We postulated further, that this production might be by non-progenitor cells co-plated along with the progenitors, or alternatively by CD34+ cells themselves, or by cells clonally derived from CD34+ cells. To test these possibilities we first assessed the effect of including in the cultures neutralizing antibody directed against various growth factors. Inclusion of anti-granulocyte macrophage colony-stimulating factor (GM-CSF) and anti-interleukin-3 (IL-3) (but not anti-IL-2) significantly reduced the growth factor independence of cord blood progenitors (P < .005 and P < .01). Inclusion of both anti-GM-CSF and anti-IL-3 almost completely ablated the spontaneous colony growth (P < .001). Inclusion of IL-10 also reduced, in a concentration-dependent fashion, the spontaneous generation of umbilical cord blood-derived colonies. Transcripts for GM-CSF and IL-3 were detected, by reverse transcriptase-polymerase chain reaction (RT-PCR), in the CD34+ cells from cord blood and from adult marrow. When plated without added growth factors, however, the CD34+ cells of adult marrow origin failed to produce colonies, whereas 6% of cord blood CD34+ cells similarly cultured did so. When these growth factor independent colonies were plucked from culture, transcripts for GM-CSF and IL-3 were identified in all. We conclude that production of GM-CSF and IL-3 occurs within culture dishes containing hematopoietic progenitors of umbilical cord origin, and that this explains some of their apparently unique features of in vitro growth.

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.

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.

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.

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.

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.