Natural porcine surfactant (Curosurf) down-regulates mRNA of tumor necrosis factor-alpha (TNF-alpha) and TNF-alpha type II receptor in lipopolysaccharide-stimulated monocytes

Surfactin reduces particulate matter-induced VCAM-1-dependent monocyte adhesion in human gingival fibroblasts by increasing Nrf2-dependent HO-1 expression

BACKGROUND AND OBJECTIVES

The mechanisms of particulate matter (PM) toxicity involve the generation of ROS and upregulation of proinflammatory molecules. Nrf2 is a multifunctional cytoprotective transcription factor that regulates the expression of various antioxidant, anti-inflammatory, and detoxifying molecules, such as HO-1. As surfactin has potential to induce Nrf2 activation and HO-1 expression, this study aimed to investigate the anti-inflammatory effects of surfactin on PM-exposed human gingival fibroblasts (HGFs) and signaling pathways engaged by surfactin.

MATERIALS AND METHODS

Human gingival fibroblasts were challenged by PM with or without surfactin pretreatment. The expression of Nrf2, HO-1, VCAM-1, and other molecules was determined by western blot, real-time PCR, or ELISA. Human monocytic THP-1 cells labeled with fluorescent reagent were added to HGFs, and the cell adhesion was assessed. ROS generation and NADPH oxidase activity were also measured. The involvement of Nrf2/HO-1 and ROS signaling pathways was investigated by treating HGFs with specific pathway interventions, genetically or pharmacologically. One dose of surfactin was given to mice before PM treatment to explore its in vivo effect on VCAM-1 expression in gingival tissues.

RESULTS

Particulate matter led to VCAM-1-dependent monocyte adhesion in HGFs, which was regulated by PKCα/NADPH oxidase/ROS/STAT1/IL-6 pathway. Surfactin could attenuate monocyte adhesion by disrupting this VCAM-1-dependent pathway. Additionally, surfactin promoted Nrf2-dependent HO-1 expression in HGFs, mitigating VCAM-1 expression. PM-treated mice exhibited the lower expression of IL-6 and VCAM-1 in gingival tissues if they previously received surfactin.

CONCLUSION

Surfactin exerts anti-inflammatory effects against PM-induced inflammatory responses in HGFs by inhibiting VCAM-1-dependent pathway and inducing Nrf2/HO-1 axis.

Impact of the New Generation Reconstituted Surfactant CHF5633 on Human CD4+ Lymphocytes

Background

Natural surfactant preparations, commonly isolated from porcine or bovine lungs, are used to treat respiratory distress syndrome in preterm infants. Besides biophysical effectiveness, several studies have documented additional immunomodulatory properties. Within the near future, synthetic surfactant preparations may be a promising alternative. CHF5633 is a new generation reconstituted synthetic surfactant preparation with defined composition, containing dipalmitoyl-phosphatidylcholine, palmitoyl-oleoyl-phosphatidylglycerol and synthetic analogs of surfactant protein (SP-) B and SP-C. While its biophysical effectiveness has been demonstrated in vitro and in vivo, possible immunomodulatory abilities are currently unknown.

Aim

The aim of the current study was to define a potential impact of CHF5633 and its single components on pro- and anti-inflammatory cytokine responses in human CD4⁺ lymphocytes.

Methods

Purified human CD4⁺ T cells were activated using anti CD3/CD28 antibodies and exposed to CHF5633, its components, or to the well-known animal-derived surfactant Poractant alfa (Curosurf^®). Proliferative response and cell viability were assessed using flow cytometry and a methylthiazolyldiphenyltetrazolium bromide colorimetric assay. The mRNA expression of IFNγ, IL-2, IL-17A, IL-22, IL-4, and IL-10 was measured by quantitative PCR, while intracellular protein expression was assessed by means of flow cytometry.

Results

Neither CHF5633 nor any of its phospholipid components with or without SP-B or SP-C analogs had any influence on proliferative ability and viability of CD4⁺ lymphocytes under the given conditions. IFNγ, IL-2, IL-17A, IL-22, IL-4, and IL-10 mRNA as well as IFNγ, IL-2, IL-4 and IL-10 protein levels were unaffected in both non-activated and activated CD4⁺ lymphocytes after exposure to CHF5633 or its constituents compared to non-exposed controls. However, in comparison to Curosurf^®, expression levels of anti-inflammatory IL-4 and IL-10 mRNA were significantly increased in CHF5633 exposed CD4⁺ lymphocytes.

Conclusion

For the first time, the immunomodulatory capacity of CHF5633 on CD4⁺ lymphocytes was evaluated. CHF5633 did not show any cytotoxicity on CD4⁺ cells. Moreover, our in vitro data indicate that CHF5633 does not exert unintended pro-inflammatory effects on non-activated and activated CD4⁺ T cells. As far as anti-inflammatory cytokines are concerned, it might lack an overall reductive ability in comparison to animal-derived surfactants, potentially leaving pro- and anti-inflammatory cytokine response in balance.

Effects of the New Generation Synthetic Reconstituted Surfactant CHF5633 on Pro- and Anti-Inflammatory Cytokine Expression in Native and LPS-Stimulated Adult CD14+ Monocytes

Background

Surfactant replacement therapy is the standard of care for the prevention and treatment of neonatal respiratory distress syndrome. New generation synthetic surfactants represent a promising alternative to animal-derived surfactants. CHF5633, a new generation reconstituted synthetic surfactant containing SP-B and SP-C analogs and two synthetic phospholipids has demonstrated biophysical effectiveness in vitro and in vivo. While several surfactant preparations have previously been ascribed immunomodulatory capacities, in vitro data on immunomodulation by CHF5633 are limited, so far. Our study aimed to investigate pro- and anti-inflammatory effects of CHF5633 on native and LPS-stimulated human adult monocytes.

Methods

Highly purified adult CD14⁺ cells, either native or simultaneously stimulated with LPS, were exposed to CHF5633, its components, or poractant alfa (Curosurf^®). Subsequent expression of TNF-α, IL-1β, IL-8 and IL-10 mRNA was quantified by real-time quantitative PCR, corresponding intracellular cytokine synthesis was analyzed by flow cytometry. Potential effects on TLR2 and TLR4 mRNA and protein expression were monitored by qPCR and flow cytometry.

Results

Neither CHF5633 nor any of its components induced inflammation or apoptosis in native adult CD14⁺ monocytes. Moreover, LPS-induced pro-inflammatory responses were not aggravated by simultaneous exposure of monocytes to CHF5633 or its components. In LPS-stimulated monocytes, exposure to CHF5633 led to a significant decrease in TNF-α mRNA (0.57 ± 0.23-fold, p = 0.043 at 4h; 0.56 ± 0.27-fold, p = 0.042 at 14h). Reduction of LPS-induced IL-1β mRNA expression was not significant (0.73 ± 0.16, p = 0.17 at 4h). LPS-induced IL-8 and IL-10 mRNA and protein expression were unaffected by CHF5633. For all cytokines, the observed CHF5633 effects paralleled a Curosurf®-induced modulation of cytokine response. TLR2 and TLR4 mRNA and protein expression were not affected by CHF5633 and Curosurf®, neither in native nor in LPS-stimulated adult monocytes.

Conclusion

The new generation reconstituted synthetic surfactant CHF5633 was tested for potential immunomodulation on native and LPS-activated adult human monocytes. Our data confirm that CHF5633 does not exert unintended pro-inflammatory effects in both settings. On the contrary, CHF5633 significantly suppressed TNF-α mRNA expression in LPS-stimulated adult monocytes, indicating potential anti-inflammatory effects.

Pitfalls in flow cytometric analyses of surfactant-exposed human leukocytes

BACKGROUND

Surfactant replacement treatment is the standard of care for the prevention and treatment of neonatal respiratory distress syndrome in preterm infants and may also improve oxygenation in acute respiratory distress syndrome in children, adolescents and adults. Beside surface tension- and mechanical shear-reducing functions, natural surfactants have been ascribed immunomodulatory capacities. Current in vitro studies on immunomodulatory effects of pulmonary surfactant preparations on human leukocytes rely on ELISA, Western blot and polymerase chain reaction. Data obtained by flow cytometry are missing, so far, most likely due to confounding phospholipid residues. Intracellular cytokine flow cytometry in surfactant-exposed immune cells would provide information on pro- and anti-inflammatory immunomodulation at the single-cell level and would allow for integrating detailed immunophenotyping, functional assays and assessment of viability.

AIM

We implemented a flow cytometry protocol for reliable quantitative assessment of in vitro intracellular cytokine production in surfactant-exposed human lymphocytes (CD4(+)) and monocytes (CD14(+)).

METHODS

Two different permeabilization techniques were tested for their ability to provide intracellular cytokine staining in surfactant-exposed CD14(+) monocytes and CD4(+) lymphocytes. Both a commercially available solution containing saponin and ice-cold methanol were used as permeabilization reagents.

RESULTS

For both cell types, flow cytometry following saponin-based permeabilization revealed pronounced unspecific fluorescence signals in surfactant-exposed samples overlapping with the fluorescence spectra of the majority of conjugates. Autofluorescence of surfactant phospholipid particles interfered significantly with reliable quantification of fluorochrome-specific signals and conclusive analysis. Implementation of a methanol-based permeabilization protocol resulted in the elimination of confounding non-cell particle signals allowing for an accurate quantification of intracellular cytokine production.

CONCLUSION

Reliable detection of intracellular cytokines by flow cytometry may be challenging in surfactant-exposed cell samples due to significant autofluorescence of aggregated phospholipid particles. This issue has been addressed for the first time and may be of high relevance for all types of surfactant research. We demonstrate that a methanol-based permeabilization approach completely removes interfering fluorescent surfactant micelles and allows for correct evaluation of data. The successful removal of confounding surfactant phospholipids opens up a wide variety of multiparameter flow cytometry; a method that has not been applied in the field of surfactant research, yet.

Maternal Lipopolysaccharide Exposure Promotes Immunological Functional Changes in Adult Offspring CD4+ T Cells

PROBLEM

Maternal immune activation (MIA) is a risk factor for autism and schizophrenia. However, how MIA affects offspring immune function remains unknown.

METHOD OF STUDY

To investigate the effect of MIA on the offspring, pregnant C57BL/6J mice were given an intraperitoneal injection of 50 μg/kg lipopolysaccharide (LPS) on gestational day 12.5.

RESULTS

Adult LPS-treated offspring were hyper-reactive to LPS, and enhanced tumor necrosis factor-α production was observed. CD4+ T cells from LPS offspring had an elevated percentage of interferon (IFN)-γ(+) CD4+ T cells and interleukin (IL)-17A+ CD4+ T cells in the spleen, IL-17A+ CD4+ T cells in the liver, and CD4+ Foxp3+ T cells in the spleen. LPS offspring CD4+ T cells showed increased proliferation and an enhanced survival rate. DNA microarray analysis of resting LPS offspring CD4+ T cells identified eight up-regulated genes, most of which encoded transcription factors. Quantitative liquid chromatography-mass spectrometry identified 18 up-regulated proteins in resting LPS offspring CD4+ T cells and five up-regulated proteins in activated LPS offspring CD4+ T cells, most of which participated in the PANTHER Gene Ontology metabolic process.

CONCLUSIONS

Our results showed that MIA to LPS up-regulated proteins involved in metabolic process in CD4+ T cells from LPS offspring that might contribute to the hyperactivated immune response of adult LPS offspring.

Immunomodulatory properties of surfactant preparations

Surfactant replacement significantly decreased acute pulmonary morbidity and mortality among preterm neonates with respiratory distress syndrome. Besides improving lung function and oxygenation, surfactant is also a key modulator of pulmonary innate and acquired immunity regulating lung inflammatory processes. In this review, we describe the immunomodulatory features of surfactant preparations. Various surfactant preparations decrease the proinflammatory cytokine and chemokine release, the oxidative burst activity, and the nitric oxide production in lung inflammatory cells such as alveolar neutrophils, monocytes and macrophages; they also affect lymphocyte proliferative response and immunoglobulin production, as well as natural killer and lymphokine-activated killer cell activity. In addition, surfactant preparations are involved in airway remodeling, as they decrease lung fibroblast proliferation capacity and the release of mediators involved in remodeling. Moreover, they increase cell transepithelial resistance and VEGF synthesis in lung epithelial cells. A number of different signaling pathways and molecules are involved in these processes. Because the inhibition of local immune response may decrease lung injury, surfactant therapeutic efficacy may be related not only to its biophysical characteristics but, at least in part, to its anti-inflammatory features and its effects on remodeling processes. However, further studies are required to identify which surfactant preparation ensures the highest anti-inflammatory activity, thereby potentially decreasing the inflammatory process underlying respiratory distress syndrome. In perspective, detailed characterization of these anti-inflammatory effects could help to improve the next generation of surfactant preparations.

Pulmonary surfactant coating of multi-walled carbon nanotubes (MWCNTs) influences their oxidative and pro-inflammatory potential in vitro

Background

Increasing concern has been expressed regarding the potential adverse health effects that may be associated with human exposure to inhaled multi-walled carbon nanotubes (MWCNTs). Thus it is imperative that an understanding as to the underlying mechanisms and the identification of the key factors involved in adverse effects are gained. In the alveoli, MWCNTs first interact with the pulmonary surfactant. At this interface, proteins and lipids of the pulmonary surfactant bind to MWCNTs, affecting their surface characteristics. Aim of the present study was to investigate if the pre-coating of MWCNTs with pulmonary surfactant has an influence on potential adverse effects, upon both (i) human monocyte derived macrophages (MDM) monocultures, and (ii) a sophisticated in vitro model of the human epithelial airway barrier. Both in vitro systems were exposed to MWCNTs either pre-coated with a porcine pulmonary surfactant (Curosurf) or not. The effect of MWCNTs surface charge was also investigated in terms of amino (−NH₂) and carboxyl (−COOH) surface modifications.

Results

Pre-coating of MWCNTs with Curosurf affects their oxidative potential by increasing the reactive oxygen species levels and decreasing intracellular glutathione depletion in MDM as well as decreases the release of Tumour necrosis factor alpha (TNF-α). In addition, an induction of apoptosis was observed after exposure to Curosurf pre-coated MWCNTs. In triple cell-co cultures the release of Interleukin-8 (IL-8) was increased after exposure to Curosurf pre-coated MWCNTs. Effects of the MWCNTs functionalizations were minor in both MDM and triple cell co-cultures.

Conclusions

The present study clearly indicates that the pre-coating of MWCNTs with pulmonary surfactant more than the functionalization of the tubes is a key factor in determining their ability to cause oxidative stress, cytokine/chemokine release and apoptosis. Thus the coating of nano-objects with pulmonary surfactant should be considered for future lung in vitro risk assessment studies.

Poractant alfa (Curosurf®) increases phagocytosis of apoptotic neutrophils by alveolar macrophages in vivo

BACKGROUND

Clearance of apoptotic neutrophils in the lung is an essential process to limit inflammation, since they could become a pro-inflammatory stimulus themselves. The clearance is partially mediated by alveolar macrophages, which phagocytose these apoptotic cells. The phagocytosis of apoptotic immune cells by monocytes in vitro has been shown to be augmented by several constituents of pulmonary surfactant, e.g. phospholipids and hydrophobic surfactant proteins. In this study, we assessed the influence of exogenous poractant alfa (Curosurf®) instillation on the in vivo phagocytosis of apoptotic neutrophils by alveolar macrophages.

METHODS

Poractant alfa (200 mg/kg) was instilled intratracheally in the lungs of three months old adult male C57/Black 6 mice, followed by apoptotic neutrophil instillation. Bronchoalveloar lavage was performed and alveolar macrophages and neutrophils were counted. Phagocytosis of apoptotic neutrophils was quantified by determining the number of apoptotic neutrophils per alveolar macrophages.

RESULTS

Exogenous surfactant increased the number of alveolar macrophages engulfing apoptotic neutrophils 2.6 fold. The phagocytosis of apoptotic neutrophils was increased in the presence of exogenous surfactant by a 4.7 fold increase in phagocytosed apoptotic neutrophils per alveolar macrophage.

CONCLUSIONS

We conclude that the anti-inflammatory properties of surfactant therapy may be mediated in part by increased numbers of alveolar macrophages and increased phagocytosis of apoptotic neutrophils by alveolar macrophages.

Neonatal respiratory distress syndrome: an inflammatory disease?

Surfactant substitution has been a major breakthrough in the treatment of neonatal respiratory distress syndrome (RDS), primarily caused by a lack of pulmonary surfactant; it has significantly reduced mortality and acute pulmonary morbidity in preterm infants. Some very immature infants, however, have a poor response to surfactant replacement or an early relapse. This brief article is based on the hypothesis that neonatal RDS has a complex and multifactorial pathogenesis characterized by an injurious inflammatory sequence in the immature lung. Fetal exposure to chorioamnionitis has been shown to initiate an inflammatory reaction beginning in utero. A 'low-grade' inflammatory stimulus in utero may 'prime' the fetal lung for accelerated maturation of the surfactant system, especially in conjunction with prenatal steroids, and may protect the preterm infant from developing moderate to severe RDS. Depending on the severity of inflammatory injury to the alveolar-capillary unit, however, serum proteins will leak into the airways and induce surfactant inactivation. Following this intrauterine 'first hit', the immature infant may develop severe RDS and have a poor response to surfactant substitution. Secondary insults such as traumatic stabilization techniques, oxygen toxicity, initiation of mechanical ventilation and others injure the immature lung immediately after birth and perpetuate and may aggravate the inflammatory process. Observational studies in preterm infants and animal experiments support this concept. Whenever surfactant inactivation is suspected, higher or repetitive doses of natural surfactant may help to overcome surfactant inactivation and to restore lung function.

Does surfactant type cause a differential proinflammatory response in preterm infants with respiratory distress syndrome?

INTRODUCTION

The objective of this study was to compare the pulmonary inflammatory response of premature infants with respiratory distress following instillation of one of two commonly available surfactant preparations.

METHODS

This was a prospective, randomized investigation of preterm infants who were less than 30 weeks of gestational age, weighed less than 1 kg at birth, and who qualified to receive surfactant. Infants with multiple congenital anomalies or whose mothers were taking anti-inflammatory medications were ineligible. Tracheal aspirates (TAs) were collected on days 1, 3, 5, and 7 and airway cytokines from TAs were assayed for interleukin (IL)-8 and IL-6.

RESULTS

Infants were evenly matched by gestation (26+/-2 days and 26+/-1 days [mean+/-SD], Surfactant A and B, respectively) and birth weight (730+/-141 g and 732+/-167 g). TA cytokine levels were not different between or within groups. Ventilator requirements and clinical outcomes were similar between the two groups.

CONCLUSION

The postnatal airway inflammatory response observed in preterm infants is not altered by the instillation of either surfactant preparation.

CYTOKINE STIMULATION BYPSEUDOMONAS AERUGINOSA—STRAIN VARIATION AND MODULATION BY PULMONARY SURFACTANT

Pulmonary surfactant and its components are part of the first-line immune defense within the lung. Here the authors show that the surfactant protein (SP) SP-D, but not SP-A, agglutinates some clinical isolates of Pseudomonas aeruginosa and Stenotrophomonas maltophilia. No agglutination of Staphylococcus aureus or Burkholderia cepacia was observed. The SP-D-induced agglutination of P. aeruginosa was not dependent on a specific lipopolysaccharide (LPS) serotype. The authors also show that SP-D, but not SP-A, increased the tumor necrosis factor (TNF alpha) release from human monocytic cells in response to a subset of P. aeruginosa and P. aeruginosa LPS. A clinical preparation of surfactant (Alveofact) blocked the TNF alpha release from monocytic cells induced by P. aeruginosa or its LPS. SP-A reversed the inhibitory effect of Alveofact in 6/8 strains of P. aeruginosa and 2/9 preparations of P. aeruginosa LPS. SP-D did not significantly alter the TNF alpha production induced by vital P. aeruginosa in the presence of Alveofact but markedly increased the TNF alpha release induced by a preparation of rough and smooth P. aeruginosa LPS. In summary, this study shows that the immunomodulatory properties of SP-A and SP-D specifically depend on the colonizing strain of P. aeruginosa. In addition, the authors show that the function of SP-A and SP-D is modulated in the presence of surfactant lipids.

The role of surfactant treatment in preterm infants and term newborns with acute respiratory distress syndrome

Surfactant treatment in preterm infants and term newborns with (acute respiratory distress syndrome) ARDS-like severe respiratory failure has become part of an individualized treatment strategy in many intensive care units around the world. These babies constitute heterogeneous groups of gestational ages, lung maturity, as well as of the underlying disease processes and postnatal interventions. The pathophysiology of respiratory failure in preterm infants is characterized by a combination of primary surfactant deficiency and surfactant inactivation as a result of plasma proteins leaking into the airways from areas of epithelial disruption and injury. Various pre- and postnatal factors, such as exposure to chorioamnionitis, pneumonia, sepsis and asphyxia, induce an injurious inflammatory response in the lungs of preterm infants, which may subsequently affect surfactant function, synthesis and alveolar stability. Surfactant inactivation--and dysfunction--is also a hallmark in newborns with meconium aspiration syndrome (MAS), pneumonia and other disorders affecting the pulmonary function. Although for the majority of suggested indications no data from randomized controlled trials exist, a surfactant replacement that counterbalances surfactant inactivation seems to improve oxygenation and lung function in many babies with ARDS without any apparent negative side effects. Newborns with MAS will definitely benefit from a reduced need for extracorporeal membrane oxygenation (ECMO). Clinical experience seems to justify surfactant treatment in neonates with ARDS.

Intravenous lipopolysaccharide-induced pulmonary maturation and structural changes in fetal sheep

BACKGROUND

Antenatal pulmonary inflammation is associated with reduced risk for respiratory distress syndrome but with an increased risk for bronchopulmonary dysplasia (BPD) with impaired alveogenesis.

OBJECTIVE

We hypothesized that fetal systemic inflammation induced by intravenous (IV) lipopolysaccharide (LPS) would affect lung development in utero.

STUDY DESIGN

Twenty-one fetal sheep were instrumented (107 days gestational age). Control fetuses received saline (N = 12) and 9 in the study group received 100 ng of LPS IV 3 days after surgery. Animals were assessed for lung maturation and structure after 3 (N = 5) and 7 (N = 4) days.

RESULTS

Interleukin-6 concentration increased in the bronchoalveolar lavage more than 40-fold 3 days after LPS IV. Processing of pro-surfactant protein (SP)-B to mature SP-B and increased SP-B concentrations were shown 7 days after LPS IV. Deposition of elastin fibers at sites of septation was disturbed within 3 days after LPS IV.

CONCLUSION

Lung maturation and disturbed lung structure occurred after short-term exposure to fetal inflammation and suggests new targeted therapies for BPD.

Antenatal inflammation and lung injury: prenatal origin of neonatal disease

INTRODUCTION

Antenatal inflammation in utero may be associated with lung injury and subsequent aberrant lung development resulting in bronchopulmonary dysplasia (BPD). BPD has become a developmental disease with a uniform arrest in lung development.

STUDY DESIGN

The role of antenatal inflammation in the induction of lung injury was explored in a sheep model suitable for the study of lung development with respect to human development. Chorioamnionitis was induced by a single injection of endotoxin into the amniotic cavity under ultrasound guidance.

RESULT

Endotoxin-induced chorioamnionitis caused a cascade of lung injury, pulmonary inflammation and remodeling in the fetal lung similar to lung injury previously described in adult animal models. The structural changes in the fetal lung after chorioamnionitis showed little to no fibrosis and alveolar/microvascular simplification similar to new BPD. The identified cytokine networks and regulators may explain the absence of fibrosis and lung simplification after strictly intra-uterine inflammation.

CONCLUSION

The mechanisms of antenatal inflammation in the fetal lung were multifactorial and could be antenatally modulated. Fetal pulmonary inflammation was temporarily suppressed by maternal glucocorticoid therapy. However, pulmonary inflammation could be augmented postnatally by resuscitation, oxygen toxicity, mechanical ventilation and pulmonary and systemic infection, which opens a broad window of clinical options.

Exogenous surfactant restores lung function but not peripheral immunosuppression in ventilated surfactant-deficient rats

The authors have previously shown that mechanical ventilation can result in increased pulmonary inflammation and suppressed peripheral leukocyte function. In the present study the effect of surfactant therapy on pulmonary inflammation and peripheral immune function in ventilated surfactant-deficient rats was assessed. Surfactant deficiency was induced by repeated lung lavage, treated rats with surfactant or left them untreated, and ventilated the rats during 2 hours. Nonventilated rats served as healthy control group. Expression of macrophage inflammatory protein (MIP)-2 was measured in bronchoalveolar lavage (BAL), interleukin (IL)-1beta, and heat shock protein 70 (HSP70) were measured in total lung homogenates. Outside the lung phytohemagglutinin (PHA)-induced lymphocyte proliferation, interferon (IFN)-gamma and IL-10 production, and natural killer activity were measured in splenocytes. After 2 hours of mechanical ventilation, expression of MIP-2, IL-1beta, and HSP70 increased significantly in the lungs of surfactant-deficient rats. Outside the lung, mitogen-induced proliferation and production of IFN-gamma and IL-10 reduced significantly. Only natural killer cell activity remained unaffected. Surfactant treatment significantly improved lung function, but could not prevent increased pulmonary expression of MIP-2, IL-1beta, and HSP70 and decreased peripheral mitogen-induced lymphocyte proliferation and IFN-gamma and IL-10 production in vitro. In conclusion, 2 hours of mechanical ventilation resulted in increased lung inflammation and partial peripheral leukocyte suppression in surfactant-deficient rats. Surfactant therapy ameliorated lung function but could not prevent or restore peripheral immunosuppression. The authors postulate that peripheral immunosuppression may occur in ventilated surfactant deficient patients, which may enhance susceptibility for infections.

Onset of mechanical ventilation is associated with rapid activation of circulating phagocytes in preterm infants

OBJECTIVE

In preterm infants with respiratory distress syndrome (RDS), circulating neutrophils are activated. Kinetics and effects of surfactant therapy on this activation are unknown. Therefore, we studied activation of circulating neutrophils and monocytes in newborn preterm infants with and without RDS.

PATIENTS AND METHODS

Preterm infants with RDS who were mechanically ventilated and received surfactant ("ventilated infants": n = 38; mean gestational age +/- SD: 28.3 +/- 2.2 weeks; mean birth weight +/- SD: 1086 +/- 353 g) and preterm infants who received nasal continuous positive airway pressure (n = 8) or no ventilatory support (n = 17) ("control infants": mean gestational age +/- SD: 32.1 +/- 1.2 weeks; mean birth weight +/- SD: 1787 +/- 457 g) were recruited. Blood samples were taken from ventilated infants at birth, before surfactant treatment, at 1 and 2 hours after surfactant, and at 12 to 24 hours of age. Blood samples were taken from control infants at birth, at 2 to 6 hours, and at 12 to 24 hours of age. Phagocyte CD11b expression was analyzed by flow cytometry.

RESULTS

In ventilated infants, phagocyte CD11b expression increased from birth to the first postnatal samples. It increased further by 12 to 24 hours of age. Control infants with or without nasal continuous positive airway pressure showed no significant increase after birth. At 12 to 24 hours of age, phagocyte CD11b expression was higher in ventilated infants than in control infants. In ventilated infants, neutrophil CD11b expression at 1 and 2 hours after surfactant correlated positively with gestational age.

CONCLUSIONS

In preterm infants with RDS, significant activation of circulating phagocytes occurs within 1 to 3 hours of the onset of mechanical ventilation, independent of surfactant administration, which indicates that mechanical ventilation may be the inducer of this systemic inflammatory response.

Bilateral lavage with diluted surfactant improves lung function after unilateral lung contusion in pigs*

OBJECTIVE

This study evaluates the effects of bronchoalveolar lavage with diluted surfactant on unilateral lung contusion-induced lung dysfunction.

DESIGN

Randomized prospective animal study.

SETTING

An animal laboratory.

SUBJECTS

Twenty adult pigs, weighing 25-35 kg.

INTERVENTIONS

Animals were randomly assigned to controls and surfactant treatment. Bilateral lavage with surfactant treatment began 30 mins after unilateral lung contusion. Then 25 mg/kg of body weight diluted Curosurf (5 mg/mL) was applied in a volume of 5 mL/kg of body weight. Observation time was 8 hrs postinjury.

MEASUREMENTS AND MAIN RESULTS

The Pao2/Fio2 ratio fell from 500 to 250 and then recovered gradually in controls and surfactant-treated pigs. After another 4 hrs, the Pao2/Fio2 ratio deteriorated again in controls, but not in surfactant-treated animals. Total compliance fell by 50% after injury but was completely restored by surfactant treatment. Lung contusion increased the median number of neutrophils in bronchoalveolar lavage fluid from 2% to 30% of total cells and peaked >60% at 480 mins in the contused lungs of control pigs. Surfactant-treated pigs had 40% neutrophils at 480 mins without reaching significant difference to controls. The leukocyte neutral proteinase inhibitor increased to 500 ng/mL at 30 mins postinjury in the contused lungs and increased to 2000 ng/mL after surfactant treatment.

CONCLUSIONS

Bilateral bronchoalveolar lavage with diluted surfactant can effectively improve lung function after experimental unilateral lung contusion in pigs.

Decreased expression of angiogenic factors in placentas with chorioamnionitis after preterm birth

Chorioamnionitis and funisitis are associated with neonatal morbidity and mortality. We hypothesized that chorioamnionitis may stress fetal endothelium, activate proinflammatory gene transcription. and affect angiogenic homeostasis in fetal capillaries. Placentas from preterm infants were stained for heat-shock protein 70, nuclear factor-kappaB, hypoxia-inducible factor-1alpha, and vascular endothelial growth factor (VEGF). VEGF receptors (VEGF-R) 1 and 2 as well as the receptor tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (TIE-2), which is involved in vascular remodeling, were quantified. Immunohistochemistry was analyzed by counting positive capillaries in placental terminal villi. Staining intensity was quantified by a three-step semiquantitative scale. The samples were divided into three matched groups according to histology: chorioamnionitis with funisitis ("funisitis"), chorioamnionitis without funisitis ("chorioamnionitis"), and control group with no inflammation. In tissues from the funisitis or chorioamnionitis group, heat-shock protein 70 expression was increased over the control group. More nuclear factor-kappaB-positive nuclei of endothelial cells in capillaries were counted in the funisitis and chorioamnionitis groups. Expression of VEGF and VEGF-R1 and -R2 were reduced in cases of funisitis or chorioamnionitis in comparison with controls. Hypoxia-inducible factor-1alpha expression tended to be slightly lower in the funisitis and chorioamnionitis groups but did not reach statistical significance. We speculate that cellular stress and changes in angiogenic homeostasis induced by proinflammatory activation of fetal endothelium in chorioamnionitis may not be limited to the placenta but may also involve other fetal organs.

Different effects of surfactant and inhaled nitric oxide in modulation of inflammatory injury in ventilated piglet lungs

Septic acute lung injury (ALI) causes high morbidity and mortality in intensive care service as a result of biotrauma and dysfunction in the lungs and other organ systems. We hypothesized that surfactant and/or inhaled nitric oxide (iNO) may have different effects in modulation of inflammatory injury in septic ALI. Twenty-four healthy, 6-9 kg piglets were anesthetized, and intraperitoneally injected with Escherichia coli, followed by a low tidal volume ventilation until sepsis and ALI developed within 4-6 h. They were then randomly treated in groups (n=6 each) as: control (C), inhaled NO at 10 ppm (NO), surfactant at 100mg/kg (Surf), or both surfactant and iNO (SNO). A normal control group (N) was sham-injected and similarly ventilated. Over the 24 h of treatment period, both Surf, and SNO groups had significantly improved PaO2/FiO2, dynamic compliance and resistance of respiratory system. At 24h, the best alveolar aeration and least protein leakage, the lowest wet-to-dry lung weight ratio and lung injury score were found in SNO. Activity of nuclear factor kappa B (NF-kappaB) and myeloperoxidase, interleukin 8 mRNA expression and melondialdehyde were significantly increased, and IL-10 mRNA decreased, in lung tissue of the C group, but were significantly altered in the SNO group, and moderately altered in either NO or Surf group. We conclude that the effects of lung protection by surfactant and/or iNO in this model may be different in modulation of inflammatory cytokine mRNA expression and activity of NF-kappaB, and iNO did not have adverse effects.

Surfactant phospholipid DPPC downregulates monocyte respiratory burst via modulation of PKC

Pulmonary surfactant phospholipids have been shown previously to regulate inflammatory functions of human monocytes. This study was undertaken to delineate the mechanisms by which pulmonary surfactant modulates the respiratory burst in a human monocytic cell line, MonoMac-6 (MM6). Preincubation of MM6 cells with the surfactant preparations Survanta, Curosurf, or Exosurf Neonatal inhibited the oxidative response to either lipopolysaccharide (LPS) and zymosan or phorbol 12-myristate 13-acetate (PMA) by up to 50% ( P < 0.01). Preincubation of MM6 cells and human peripheral blood monocytes with dipalmitoyl phosphatidylcholine (DPPC), the major phospholipid component of surfactant, inhibited the oxidative response to zymosan. DPPC did not directly affect the activity of the NADPH oxidase in a MM6 reconstituted cell system, suggesting that DPPC does not affect the assembly of the individual components of this enzyme into a functional unit. The effects of DPPC were evaluated on both LPS/zymosan and PMA activation of protein kinase C (PKC), a ubiquitous intracellular kinase, in MM6 cells. We found that DPPC significantly inhibited the activity of PKC in stimulated cells by 70% ( P < 0.01). Western blotting experiments demonstrated that DPPC was able to attenuate the activation of the PKCδ isoform but not PKCα. These results suggest that DPPC, the major component of pulmonary surfactant, plays a role in modulating leukocyte inflammatory responses in the lung via downregulation of PKC, a mechanism that may involve the PKCδ isoform.

Mitigation of Meconium-Induced Lung Injury by Surfactant and Inhaled Nitric Oxide Is Associated with Suppression of Nuclear Transcription Factor Kappa B

OBJECTIVE

To investigate whether the mechanism of a combined surfactant and inhaled nitric oxide (iNO) in improvement of oxygenation and mitigation of lung injury is associated with suppression of nuclear transcription factor kappa B (NF-kappaB) in the lung tissue of ventilated rabbits with meconium aspiration.

METHODS

Adult rabbits (weight 2.0-3.5 kg, n = 33) were anesthetized, intratracheally received human meconium, and were subjected to pressure support ventilation for 30-60 min to induce hypoxemic respiratory failure and lung injury. They were then treated for 6 h in groups: control animals; rabbits receiving iNO; animals receiving surfactant (100 mg/kg), and rabbits receiving both iNO and surfactant. iNO was delivered continuously by mass flow controller in sequence at 1, 10, 20, and 40 ppm each for 60 min at 30-min intervals.

RESULTS

Improvement in oxygenation and lung mechanics was found in the animals receiving both iNO and surfactant, associated with a marked response to iNO at 10 and 20 ppm (p < 0.05), a significantly higher ratio of disaturated phosphatidylcholine to total proteins, a lower surface tension of phospholipids from bronchoalveolar lavage fluid, a lower wet-to-dry lung weight ratio and lower lung injury scores, and better alveolar aeration. The iNO- and surfactant-treated groups had only transient or moderate-to-intermediate improvement in the associated parameters. The expression of NF-kappaB in lung tissue was enhanced in the control group, attenuated in the groups treated with either iNO or surfactant, and significantly suppressed in the group receiving both iNO and surfactant.

CONCLUSION

Improvements of lung mechanics and gas exchange and mitigation of lung injury by the combined surfactant and iNO are related to suppression of NF-kappaB expression in lung tissue of ventilated rabbits with hypoxemic respiratory failure.

Nuclear Factor-Kappa B Expression in Alveolar Macrophages of Mechanically Ventilated Neonates with Respiratory Distress Syndrome

BACKGROUND

Inflammatory reaction and injury in mature lungs are associated with activation of nuclear factor-kappaB (NF-kappaB) to trigger proinflammatory cytokine release. In preterm infants with immature lungs, this mechanism is not yet fully understood, therefore we investigated this mechanism in mechanically ventilated neonates with respiratory distress syndrome (RDS).

METHODS

Serial samples of the airway aspirates (AA) were obtained during mechanical ventilation from 21 preterm infants with RDS, of which 12 were survivors (birth weight 1.48 +/- 0.32 kg and gestational age 31 +/- 1.5 weeks) and 9 nonsurvivors (1.34 +/- 0.31 kg and 30 +/- 2 weeks). Seven neonates matched for age and birth weight without respiratory disorders served as controls. Alveolar macrophages (AM) of AA were isolated by differential adherence, some were cultured with lipopolysaccharide (LPS) for 1 h. Then, nuclear extracts of AM were analyzed by electrophoretic mobility shift assay for NF-kappaB expression. The NF-kappaB inhibitor (IkappaB-alpha protein) in cytoplasmic extracts was detected by Western blot, and concentrations of IL-1beta and IL-8 in AA by enzyme-linked immunosorbent assay (ELISA).

RESULTS

On day 2 NF-kappaB expression in AM was significantly increased in the survivors and nonsurvivors at 33.3 +/- 9 and 54.8 +/- 10.2 relative density units (RDU) compared to control infants (11.1 +/- 6.7; p < 0.01). Expression of IkappaB-alpha was significantly higher in controls than that in the survivors and nonsurvivors on days 2 and 4. Moreover, in the nonsurvivors of RDS, expression of NF-kappaB was decreased following LPS stimulation in vitro on day 4. IL-1beta and IL-8 levels in the AA supernatant were higher in the survivors than in controls on days 2 and 4, but lower than those of the nonsurvivors on day 2. There were close correlations between the expression of NF-kappaB and levels of IL-1beta (r = 0.78, p < 0.01), and IL-8 (r = 0.81, p < 0.01) in AA.

CONCLUSION

There were alterations in NF-kappaB activity in the AM of mechanically ventilated preterm neonates with RDS, mediated by decreased synthesis and increased degradation of IkappaB.

Natural Porcine Surfactant Augments Airway Inflammation after Allergen Challenge in Patients with Asthma

There is increasing evidence for a role of pulmonary surfactant in asthma and allergic inflammation. In murine asthma models, recent studies have demonstrated that surfactant components downregulate the allergic inflammation. Therefore, we tested the hypothesis that in individuals with mild asthma, a natural porcine surfactant preparation (Curosurf) given before segmental allergen challenge can reduce the allergic airway inflammation. Ten patients with asthma and five healthy control subjects were treated in two segments with either Curosurf or vehicle followed by local allergen challenge. Six additional patients with asthma received Curosurf before allergen challenge in one segment as above, but the second segment was instilled with Curosurf without allergen challenge. Unexpectedly, surfactant treatment augmented the eosinophilic inflammation 24 hours after allergen challenge. A direct chemotactic effect of Curosurf was excluded. However, levels of eotaxin and interleukin-5 were increased in bronchoalveolar lavage after Curosurf treatment, whereas IFN-gamma-levels and numbers of IFN-gamma(+) T cells were decreased. Curosurf had no influence on spreading and retention of allergen determined by allergen uptake in mice. These findings demonstrate that treatment with a natural porcine surfactant results in an augmentation of the eosinophilic inflammation after allergen challenge that is more likely due to immunomodulatory effects than to biophysical properties of the surfactant.

Neutrophil activation in preterm infants who have respiratory distress syndrome

OBJECTIVE

To study neutrophil activation in circulation as a sign of systemic inflammation in preterm infants with respiratory distress syndrome.

METHODS

The study comprised very low birth weight preterm infants who had respiratory distress syndrome and required intubation and mechanical ventilation (n = 51), 1-day-old preterm infants who had no need for mechanical ventilation (n = 12), term infants (n = 47), and adult volunteers (n = 25). Neutrophil surface expression of CD11b was quantified with flow cytometry.

RESULTS

In preterm infants with respiratory distress syndrome, neutrophil CD11b expression during the first day of life was higher than in cord blood (mean: 165 relative fluorescence units [RFU] [standard deviation [SD]: 53], n = 29 vs 83 RFU [SD: 21], n = 11; 95% confidence interval [CI] for difference: 59-106) or in preterm infants without mechanical ventilation (106 RFU [SD: 33], n = 12; 95% CI for difference: 17-90). CD11b expression decreased by age of 10 days. CD11b expression was lower in preterm cord than in term cord blood (95% CI for difference: 5-53). However, in preterm infants with respiratory distress syndrome aged 2 to 5 days, it was higher than in term infants of that age.

CONCLUSIONS

The observations demonstrate an early transient postnatal neutrophil activation indicative of systemic inflammation that may contribute to the tissue injury in preterm infants with respiratory distress syndrome.

Dipalmitoylphosphatidylcholine modulates inflammatory functions of monocytic cells independently of mitogen activated protein kinases

Phosphatidylcholine (PC) is the major phospholipid of pulmonary surfactant and it is hypothesized that PC and its subspecies modulate the functions of alveolar macrophages. The most abundant of these subspecies is dipalmitoylphosphatidylcholine (DPPC). This study was undertaken to determine the effect of PC on monocyte function using a human monocytic cell line, MonoMac-6 (MM6). This study showed that preincubation of MM6 cells with DPPC at 125 microg/ml for 2 h inhibited the oxidative response to either zymosan or phorbol-12-myristate-13-acetate (PMA) by 30% (P < 0.001). This inhibition with DPPC was independent of LPS priming. When DPPC was replaced with 1-palmitoyl-2-arachidonoyl phosphatidylcholine (PAPC) there was no inhibition and in contrast a significant increase in oxidant production was observed. We also demonstrated that total PC (tPC; a heterogeneous species of PC from egg) and DPPC but not PAPC significantly inhibited the release of TNF-alpha from MM6 cells (P < 0.05). DPPC did not inhibit phosphorylation of the mitogen activated protein kinases (MAPKs) p44/p42 or p38 in stimulated cells. Measurements of membrane fluidity with spin label EPR spectroscopy indicate that DPPC incorporation significantly alters the membrane fluidity of MM6 cells. These results suggest that DPPC, the major component of pulmonary surfactant, may play a role in modulating leucocyte inflammatory responses in the lung. This may in part be related to membrane effects but does not include alterations in p44/p42 or p38 MAPK signalling.

Prostaglandin E(2) and tumour necrosis factor-alpha release by monocytes are modulated by phospholipids

The regulation of pro- and anti-mediator release from cells within the alveolar space would represent a desirable mechanism serving to protect this delicate gas-exchanging region of the lung. This study investigates the effect of alveolar surfactant lipids on the regulation of tumour necrosis factor alpha (TNF-alpha), a potent inflammatory cytokine, and prostaglandin E(2)(PGE(2)), a lipid mediator with anti-inflammatory properties. The results of this investigation reveal a marked effect on the release of these two important mediators from a monocytic cell line, MonoMac 6 (MM6), by phosphatidylcholine (PC), phosphatidylethanolamine (PE), cholesterol (Chol) and sphingomyelin (SM). PC, PE and Chol demonstrated marked downregulation of TNF-alpha production at lipid concentrations of 125 and 250 microg/ml. Interestingly, SM significantly up regulated the release of TNF-alpha at these concentrations. However, the release of PGE(2)in MM6 cells incubated with the same lipids was significantly increased with PC and Chol, and significantly decreased in cells pre-treated with SM. This indicates a role for these lipids in alveolar immunoregulation.

Surfactant modulates intracellular signaling of the adhesion receptor L-selectin

Intraalveolar leukocyte accumulation is one of the hallmarks during respiratory distress. In the intraalveolar space, leukocyte activation is mediated by pathogens, cytokines, and different ligands binding to adhesion molecules. Leukocyte stimulation via the adhesion molecule L-selectin is specifically induced by ligands expressed on leukocytes, platelets, endothelial cells, or lipopolysaccharide. Recently, we have demonstrated that leukocyte activation by L-selectin transmits several intracellular signaling cascades resulting in capping and cytoskeletal changes, the activation of kinases and neutral sphingomyelinase, the recruitment of adaptor proteins to the cell membrane, the activation of the small G-proteins Ras and Rac, and the release of oxygen. In the present study, we examined the effects of surfactant on L-selectin-induced signal transduction in leukocytes. Using fluorescence microscopy, we provide evidence that preincubation of leukocytes with surfactant significantly inhibits receptor capping; 28+/-7% of cells show capping after L-selectin stimulation versus 8+/-5% and 3+/-1% of cells after preincubation with Exosurf and Curosurf, respectively (p < 0.05). The activity of the neutral sphingomyelinase in cell lysates is also modulated by surfactant. In addition, we show that the activation of the tyrosine kinase p56lck is diminished by approximately 50% after surfactant treatment. This results in inhibition in tyrosine phosphorylation of certain intracellular proteins. The interaction of the L-selectin molecule with its antibody was not influenced by surfactant as shown by flow cytometry. Surfactant inhibits intracellular signaling events of the L-selectin receptor in leukocytes and might therefore contribute to the modulatory effects of surfactant on immune function.

In vivo modulation of the allogeneic immune response by human fetal kidneys: the role of cytokines, chemokines, and cytolytic effector molecules

BACKGROUND

We have recently demonstrated that human fetal renal tissue, implanted under the kidney capsule of severe immunodeficient rats, escapes early destruction by intraperitoneal infusion of allogeneic human peripheral blood mononuclear cells, compared with the rapid rejection of implants of human adult kidney tissue. Variable amounts of human mononuclear infiltrates were seen in the transplanted fetal kidney, however, prolonged survival of the fetal tissue (maintenance of graft architecture and significant growth) was independent of the cellular infiltrate.

METHODS

We have used this experimental model to sequentially analyze transcript levels of interferon-gamma and interleukin (IL)-2 (T helper 1 cytokines), IL-4 and IL-10 (T helper 2 cytokines), RANTES, MIP1beta (beta chemokines) and their receptor CCR5, and Fas ligand (cytolytic effector molecule). Analysis was performed by reverse transcriptase-polymerase chain reaction, in both fetal and adult kidney grafts, after infusion of allogeneic human peripheral blood mononuclear cells.

RESULTS

Transcript levels of interferon-gamma and IL-2 in the fetal grafts were markedly reduced throughout follow-up, compared with those observed in the adult implants. Peak levels of these cytokines appeared late in the rejection process. Concomitant with these findings, IL-4 mRNA was up-regulated during the early phase, whereas IL-10 mRNA persisted throughout the rejection process, indicating that a T helper 2 bias occurred in the fetal grafts. In addition, RANTES (after an early peak), MIP1beta, CCR5, and Fas ligand mRNA levels were suppressed in the fetal grafts compared with those in the adult grafts.

CONCLUSIONS

These findings indicate that the immune response of kidney rejection is dependent on whether the target organ is of fetal or adult origin, and suggest that an allogeneic immune system mounts a T helper 2-biased response when the target organ is of fetal origin.

Antenatal dexamethasone suppresses tumor necrosis factor-alpha expression in hypoplastic lung in nitrofen-induced diaphragmatic hernia in rats

The hypoplastic lung in congenital diaphragmatic hernia (CDH) has both a quantitative and qualitative reduction in surfactant. Tumor necrosis factor-alpha (TNF-alpha) drastically decreases surfactant phospholipids synthesis by isolated human type II pneumocytes. Recently, it was shown that TNF-alpha mRNA expression is increased in human hypoplastic CDH lung. Antenatal glucocorticoid therapy demonstrates improved surfactant biochemical immaturity in an animal CDH model. The aim of this study was to investigate the effect of antenatal dexamethasone (Dex) on TNF-alpha protein and gene expression in nitrofen-induced CDH hypoplastic lung in rats. A CDH model was induced in pregnant rats after the administration of nitrofen on d 9.5 of gestation. Dex was given intraperitoneally on d 18.5 and 19.5. Cesarean section was performed on d 21. In situ hybridization was performed with a rat TNF-alpha-specific and digoxigenin-labeled oligonucleotide probe. TNF-alpha level was measured in solubilized lung tissue extracts by ELISA. In control lung, TNF-alpha mRNA expression was weak or absent. In contrast, strong TNF-alpha mRNA expression was demonstrated in type II pneumocytes and bronchiolar epithelium in CDH lung. In Dex-treated CDH lung, TNF-alpha mRNA expression was weak in both type II pneumocytes and the bronchiolar epithelium. The level of TNF-alpha was elevated significantly in CDH lung compared with levels in control lung extracts (p < 0.01). In Dex-treated CDH lung, TNF-alpha protein was significantly decreased compared with CDH lung (p < 0.05). Our findings suggest that the reduction in the local production of TNF-alpha may be one contributing mechanism by which antenatal glucocorticoid therapy improves pulmonary parenchymal immaturity, including surfactant.

Acute cellular rejection of human renal tissue by adoptive transfer of allogeneic human peripheral blood mononuclear cells into chimeric rats: sequential gene expression of cytokines, chemokines and cytolytic effector molecules, and their regulation by CTLA-4-Ig

T(h)1- and T(h)2-related cytokines (IFN-gamma, IL-2, IL-4, IL-10), beta-chemokines (RANTES, macrophage inflammatory protein-1beta) and their receptor [chemotatic cytokine receptor (CCR) 5], and the cytolytic effector molecule [Fas ligand (FasL)] play an essential role in regulating and co-ordinating acute renal allograft rejection. A chimeric model of acute cellular rejection which involves subcapsular grafting of human renal tissue in the kidneys of immunodeficient rats and subsequent i.p. infusion of allogeneic human peripheral blood mononuclear cells (PBMC) was used to study cellular infiltration patterns and sequential intragraft gene expression of these key inflammatory mediators. We found that while all molecules are expressed within the human renal implant at specific time points following infusion of allogeneic human PBMC, peak mRNA expression of IFN-gamma, IL-2, RANTES and CCR5 is associated with a phase of human mononuclear infiltration and accumulation, prior to graft destruction (induction phase). A short burst of FasL gene expression is found at the end of induction and at the onset of graft deterioration. IL-4 mRNA, which is hardly detectable, and IL-10 mRNA, which appears early and persists throughout follow-up at high levels, both peak after the induction phase with the advent of graft destruction. Furthermore, treatment with CTLA-4-Ig, which hardly affects migration of human effector cells into graft tissue, is associated with a temporary reduction in gene transcript levels for all inflammatory mediators, especially IL-2 and IL-4, reduced apoptosis in the graft and amelioration of tissue injury. Thus, development of acute cellular rejection in our chimeric model involves a co-ordinated pattern of gene expression, in which CTLA-4-Ig promotes its effects by transient inactivation of infiltrating human cells.