Immunomodulatory effects of mixed hematopoietic chimerism: immune tolerance in canine model of lung transplantation.

Long-term survival after lung transplantation is limited by acute and chronic graft rejection. Induction of immune tolerance by first establishing mixed hematopoietic chimerism (MC) is a promising strategy to improve outcomes. In a preclinical canine model, stable MC was established in recipients after reduced-intensity conditioning and hematopoietic cell transplantation from a DLA-identical donor. Delayed lung transplantation was performed from the stem cell donor without pharmacological immunosuppression. Lung graft survival without loss of function was prolonged in chimeric (n = 5) vs. nonchimeric (n = 7) recipients (p < or = 0.05, Fisher's test). There were histological changes consistent with low-grade rejection in 3/5 of the lung grafts in chimeric recipients at > or =1 year. Chimeric recipients after lung transplantation had a normal immune response to a T-dependent antigen. Compared to normal dogs, there were significant increases of CD4+INFgamma+, CD4+IL-4+ and CD8+ INFgamma+ T-cell subsets in the blood (p < 0.0001 for each of the three T-cell subsets). Markers for regulatory T-cell subsets including foxP3, IL10 and TGFbeta were also increased in CD3+ T cells from the blood and peripheral tissues of chimeric recipients after lung transplantation. Establishing MC is immunomodulatory and observed changes were consistent with activation of both the effector and regulatory immune response.

Optimizing a canine survival model of orthotopic lung transplantation.

INTRODUCTION: While acute models of orthotopic lung transplantation have been described in dogs, the technical considerations of developing a survival model in this species have not been elaborated. Herein, we describe optimization of a canine survival model of orthotopic lung transplantation. METHODS: Protocols of orthotopic left lung transplantation and single lung ventilation were established in acute experiments (n=9). Four dogs, serving as controls, received autologous, orthotopic lung transplants. Allogeneic transplants were performed in 16 DLA-identical and 16 DLA-mismatched unrelated recipient dogs. Selective right lung ventilation was utilized in all animals. A Malecot tube was left in the pleural space connected to a Heimlich valve for up to 24 hours. To date, animals have been followed up to 24 months by chest radiography, pulmonary function tests, bronchoscopy with lavage, and open biopsies. RESULTS: Long-term survival was achieved in 34/36 animals. Two recipients died intraoperatively secondary to cardiac arrest. All animals were extubated on the operating table, and in all cases the chest tube was removed within 24 hours. Major complications included thrombosis of the pulmonary artery and subcritical stenosis of bronchial anastamosis. One recipient underwent successful treatment of a small bowel intussusception. CONCLUSIONS: We report our experience in developing a survival canine model of orthotopic single lung transplantation. While short-term survival following canine lung transplantation is achievable, we report particular considerations that facilitate animal comfort, early extubation, and lung reexpansion in the immediate postoperative period, further optimizing use of this species for experimental modeling of long-term complications after lung transplantation.

Pulmonary function testing prior to hematopoietic stem cell transplantation.

The pretransplant pulmonary function test plays an important role in the management of noninfectious pulmonary complications after hematopoietic stem cell transplantation (HCT). Although these tests are widely used as standard preoperative assessments in the nontransplant population, common conditions associated with the HCT patient requires that particular attention be given to interpretation of pulmonary function testing (PFT) results, such as comparison of serial pulmonary function tests and evaluation of the diffusion capacity. Although their utility in helping to predict the likelihood of developing post transplant pulmonary complications and mortality is not well established, current data indicate that pretransplant PFTs are important as a reference for the interpretation of post transplant PFTs and for identifying patients at high risk for developing pulmonary complications and/or mortality after HCT. Future studies of pretransplant pulmonary function should consider the advances in HCT, so that pretransplant PFTs will become a useful tool in pretransplant risk assessment and help the transplant oncologist to determine the most appropriate conditioning regimen for a patient with compromised lung function.

Incidence, risk factors, and mortality from pneumonia developing late after hematopoietic stem cell transplantation.

The incidence, etiology, outcome, and risk factors for developing pneumonia late after hematopoietic stem cell transplantation (SCT) were investigated in 1359 patients transplanted in Seattle. A total of 341 patients (25% of the cohort) developed at least one pneumonic episode. No microbial or tissue diagnosis (ie clinical pneumonia) was established in 197 patients (58% of first pneumonia cases). Among the remaining 144 patients, established etiologies included 33 viral (10%), 31 bacterial (9%), 25 idiopathic pneumonia syndrome (IPS, 7%), 20 multiple organisms (6%), 19 fungal (6%), and 16 Pneumocystis carinii pneumonia (PCP) (5%). The overall cumulative incidence of first pneumonia at 4 years after discharge home was 31%. The cumulative incidences of pneumonia according to donor type at 1 and 4 years after discharge home were 13 and 18% (autologous/syngeneic), 22 and 34% (HLA-matched related), and 26 and 39% (mismatched related/unrelated), respectively. Multivariate analysis of factors associated with development of late pneumonia after allografting were increasing patient age (RR 0.5 for <20 years, 1.2 for >40 years, P=0.009), donor HLA-mismatch (RR 1.6 for unrelated/mismatched related, P=0.01), and chronic graft-versus-host disease (GVHD; RR 1.5, P=0.007). Our data suggest that extension of PCP prophylaxis may be beneficial in high-risk autograft recipients. Further study of long-term anti-infective prophylaxis based on patient risk factors after SCT appear warranted.

Selective induction of tissue inhibitor of metalloproteinase-1 in bleomycin-induced pulmonary fibrosis.

Tissue inhibitors of metalloproteinases (TIMPs) are multifunctional proteins that have the capacity to modify cellular activities and to modulate matrix turnover. We demonstrate that TIMP-1 messenger RNA (mRNA) and protein expression are selectively and markedly increased in a murine model of bleomycin-induced pulmonary fibrosis. Northern analysis showed that lung steady-state TIMP-1 mRNA levels increased 14-fold after bleomycin administration compared with control mice. Expression of the genes for TIMP-2, TIMP-3, and interstitial collagenase (matrix metalloproteinase-13) was unaltered in the injured lung. In situ hybridization demonstrated that TIMP-1 gene induction was spatially restricted to areas of lung injury. Metalloproteinase inhibitory activity of relative molecular mass of ~ 21 to 28 kD, corresponding to the molecular weights for TIMP-1 and TIMP-2, was identified in lung extracts of bleomycin-injured mice by reverse zymography. Western analysis demonstrated that TIMP-1 protein levels in bronchoalveolar lavage fluid (BALF) of bleomycin-treated mice increased 220- and 151-fold at Days 4 and 28, respectively, compared with control mice. TIMP-2 immunoreactive protein in the BALF increased 20- and 103-fold relative to controls at Days 4 and 28, respectively. These results demonstrate that TIMP-1 gene expression is selectively increased, and that the expression of TIMP-1 and TIMP-2 is differentially regulated in bleomycin-induced pulmonary fibrosis. The profound and durable increase in TIMP-1 and TIMP-2 proteins suggests an important regulatory role for these antiproteases in the inflammatory and fibrotic responses to bleomycin-induced lung injury.

Adherence of adoptively transferred alloreactive Th1 cells in lung: partial dependence on LFA-1 and ICAM-1.

T helper type 1 (Th1) cells are important effectors in a number of immune-mediated lung diseases. We recently described a murine model of lung injury induced by adoptive transfer of cloned alloreactive Th1 cells. To investigate mechanisms that result in injury to the lung, we studied the in vivo distribution of (51)Cr-labeled Th1 cells. One hour after intravenous administration, >85% of injected radioactivity was left in the lung, and at 24 h, 40% of radioactivity was left in the lung. Adherence of Th1 cells in the lung was significantly inhibited by neutralizing antibody to lymphocyte function-associated antigen-1. Th1 cell adherence also was decreased in lungs of mice deficient in intercellular adhesion molecule-1 (ICAM-1). Th1 cell transfer further induced expression of ICAM-1 and vascular cell adhesion molecule-1 in the lung. Vascular cell adhesion molecule-1-immunoreactive protein was markedly induced in lung endothelium by alloreactive Th1 cells. These findings indicate that Th1 cells localize in normal lung by a mechanism involving lymphocyte function-associated antigen-1 and ICAM-1. Alloreactive cells further induce endothelial adhesion molecules that may facilitate recruitment of inflammatory cells to the lung and amplify Th1 cell-induced lung injury.

Chemokine expression in Th1 cell-induced lung injury: prominence of IFN-gamma-inducible chemokines.

Proinflammatory responses generated by T helper type 1 (Th1) cells may contribute significantly to immune-mediated lung injury. We describe a murine model of Th1 cell-induced lung injury in which adoptive transfer of alloreactive Th1 cells produces pulmonary inflammation characterized by mononuclear cell vasculitis, alveolitis, and interstitial pneumonitis. To investigate the link between activation of Th1 cells in the lung and inflammatory cell recruitment, we characterized cytokine and chemokine mRNA expression in Th1 cells activated in vitro and in lung tissue after adoptive transfer of Th1 cells. Activated Th1 cells per se express mRNA for interferon (IFN)-gamma and several members of the tumor necrosis factor family as well as the C-C chemokine receptor-5 ligands regulated on activation normal T cells expressed and secreted and macrophage inflammatory protein-1alpha and -1beta. Additional chemokine genes were induced in the lung after Th1 cell administration, most notably IFN-gamma-inducible protein (IP-10) and monokine induced by IFN-gamma (MIG). Remarkable increases in IP-10- and MIG-immunoreactive proteins were present in inflammatory foci lung and identified in macrophages, endothelium, bronchial epithelium, and alveolar structures. The findings suggest that IFN-gamma-inducible chemokines are an important mechanism for amplifying inflammation initiated by Th1 cells in the lung.

Neutralization of tumor necrosis factor-alpha action delays but does not prevent lung injury induced by alloreactive T helper 1 cells.

BACKGROUND: Lung injury occurs frequently after allogeneic bone marrow transplantation in association with graft-versus-host disease, an immune response that involves both cellular and cytokine components. In a murine model, we recently showed that cloned alloreactive T helper (Th)1 cells can cause lung injury associated with increased production of tumor necrosis factor (TNF)-alpha by alveolar macrophages (J Immunol 1998; 161: 1913). METHODS: To evaluate the role of TNF-alpha in this model, we injected in vitro-activated Th1 cells into the following: (1) recipients deficient in receptors for TNF; (2) C57BL/6 control mice; (3) C57BL/6 mice, pretreated with soluble TNFRIIFc (a dimorphic high-affinity TNF antagonist); (4) mice expressing TNFRIIFc transgene under control of the surfactant apoprotein C promoter (SPCTNFRIIFc); and (5) wild-type littermate controls (C57BL/6) (n=3-6 mice/group). RESULTS: At 1 and 3 days after i.v. Th1 cell transfer, recipients were killed for analysis of lung histology, bronchoalveolar lavage (BAL) protein, and BAL cell counts. Control mice (wild type) at day 1 after injection had a mild to moderate mononuclear perivasculitis and increased interstitial cellularity. At day 3, lesions were more severe and perivasculitis also involved larger veins. TNFR-deficient mice had normal lung or minimal lung inflammation at day 1. At day 3, perivasculitis of medium-sized vessels was present, but there was no apparent involvement of larger veins. Results in mice treated with soluble TNFRIIFc and transgenic mice (SPCsTNFRIIFc) were similar to controls. BAL protein and BAL cell counts did not differ between any of the experimental groups. CONCLUSIONS: We conclude that lung inflammation induced by Th1 cells may be only delayed when TNF-alpha action is blocked. The persistence of abnormalities indicates that other proinflammatory pathways are involved in injury caused by these cells.

Idiopathic pneumonia after bone marrow transplantation: cytokine activation and lipopolysaccharide amplification in the bronchoalveolar compartment.

OBJECTIVE: To determine whether idiopathic pneumonia syndrome (IPS), a form of noninfectious lung injury that follows bone marrow transplantation, is associated with cytokine activation and increased susceptibility to lipopolysaccharide (LPS). DESIGN: Case series. SETTING: Tertiary referral center for marrow transplantation. PATIENTS: Recipients with biopsy-confirmed IPS; normal volunteers and marrow transplant recipients without IPS were analyzed as controls. MEASUREMENTS AND MAIN RESULTS: Levels of lymphocyte and macrophage-derived cytokines as well as components of the LPS, LPS-binding protein (LBP), and CD14 system in bronchoalveolar lavage (BAL) fluid were determined. We found evidence of increased vascular permeability (BAL protein) and inflammatory cytokine activation (interleukin-1, interleukin-2, interleukin-6, and tumor necrosis factor-alpha) in patients with IPS. Patients without IPS had BAL fluid cytokine and protein levels that were similar to levels in BAL fluid from normal volunteers. Moreover, components of the LPS amplification system (LBP and soluble CD14) were increased in patients with IPS but not in patients without IPS. CONCLUSIONS: These results provide direct evidence for proinflammatory cytokine activation in IPS and suggest that these patients might be at increased risk for LPS-mediated injury through the LBP amplification pathway.

Collagen accumulation is decreased in SPARC-null mice with bleomycin-induced pulmonary fibrosis.

Secreted protein acidic and rich in cysteine (SPARC) has been shown to be coexpressed with type I collagen in tissues undergoing remodeling and wound repair. We speculated that SPARC is required for the accumulation of collagen in lung injury and that its absence would attenuate collagen accumulation. Accordingly, we have assessed levels of collagen in SPARC-null mice in an intratracheal bleomycin-injury model of pulmonary fibrosis. Eight- to ten-week-old SPARC-null and wild-type (WT) mice received bleomycin (0.0035 U/g) or saline intratracheally and were subsequently killed after 14 days. Relative levels of SPARC mRNA were increased 2.7-fold (P < 0.001) in bleomycin-treated WT lungs in comparison with saline-treated lungs. Protein from bleomycin-treated WT lung contained significantly more hydroxyproline (191.9 microg/lung) than protein from either bleomycin-treated SPARC-null lungs or saline-treated WT and SPARC-null lungs (147.4 microg/lung, 125.4 microg/lung, and 113. 0 microg/lung, respectively; P < 0.03). These results indicate that SPARC is increased in response to lung injury and that accumulation of collagen, as indicated by hydroxyproline content, is attenuated in the absence of SPARC. The properties of SPARC as a matricellular protein associated with cell proliferation and matrix turnover are consistent with its participation in the development of pulmonary fibrosis.

Mice with a targeted intronic deletion in the Col1a1 gene respond to bleomycin-induced pulmonary fibrosis with increased expression of the mutant allele.

Experiments designed to examine the role of the first intron in regulation of the Col1a1 gene by transfection and in transgenic mice have led to conflicting conclusions. Recently, Hormuzdi et al. [Hormuzdi, S.G., Penttinen, R., Jaenisch, R., Bornstein, P., 1998. A gene-targeting approach identifies a function for the first intron in expression of the alpha1(I) collagen. Mol. Cell. Biol. 18, 3368-3375.] created a targeted deletion in this intron in mice and demonstrated an age-dependent reduction in expression of the mutated allele in lung and skeletal muscle. In this study, intratracheal instillation of bleomycin in mice was used to induce pulmonary fibrosis in control and intron-deleted animals. This stimulus for collagen synthesis was associated with a marked upregulation of the intron-deleted allele in mutant mice. Our results establish that the inhibition of expression of the mutant Col1a1 gene is not fixed, since the gene can still respond to physiological signals. We propose that cis-acting elements, elsewhere in the gene, can compensate for the lack of intronic sequences in the mutated Col1a1 allele and account for the conditional nature of the inhibition. This model has the potential to resolve the conflicting results of previous transfection and transgenic experiments in which different fragments of the Col1a1 gene were used.

Transforming growth factor-alpha deficiency reduces pulmonary fibrosis in transgenic mice.

Despite evidence that implicates transforming growth factor-alpha (TGF-alpha) in the pathogenesis of acute lung injury, the contribution of TGF-alpha to the fibroproliferative response is unknown. To determine whether the development of pulmonary fibrosis depends on TGF-alpha, we induced lung injury with bleomycin in TGF-alpha null-mutation transgenic mice and wild-type mice. Lung hydroxyproline content was 1.3, 1.2, and 1.6 times greater in wild-genotype mice than in TGF-alpha-deficient animals at Days 10, 21, and 28, respectively, after a single intratracheal injection of bleomycin. At Days 7 and 10 after bleomycin treatment, lung total RNA content was 1.5 times greater in wild-genotype mice than in TGF-alpha-deficient animals. There was no significant difference between mice of the two genotypes in lung total DNA content or nuclear labeling indices after bleomycin administration. Wild-genotype mice had significantly higher lung fibrosis scores at Days 7 and 14 after bleomycin treatment than did TGF-alpha-deficient animals. There was no significant difference between TGF-alpha-deficient mice and wild-genotype mice in lung inflammation scores after bleomycin administration. To determine whether expression of other members of the epidermal growth factor (EGF) family is increased after bleomycin-induced injury, we measured lung EGF and heparin-binding- epidermal growth factor (HB-EGF) mRNA levels. Steady-state HB-EGF mRNA levels were 321% and 478% of control values in bleomycin-treated lungs at Days 7 and 10, respectively, but were not significantly different in TGF-alpha-deficient and in wild-genotype mice. EGF mRNA was not detected in normal or bleomycin-treated lungs of mice of either genotype. These results show that TGF-alpha contributes significantly to the pathogenesis of pulmonary fibrosis after bleomycin-induced injury, and that compensatory increases in other EGF family members do not occur in TGF-alpha-deficient mice.

Elevated transforming growth factor-alpha levels in bronchoalveolar lavage fluid of patients with acute respiratory distress syndrome.

The acute respiratory distress syndrome (ARDS) frequently results in a fibroproliferative response that precludes effective alveolar repair. Transforming growth factor-alpha (TGF-alpha), a potent epithelial and mesenchymal cell mitogen, may modulate the response to lung injury. In this study, we determined whether bronchoalveolar lavage fluid (BALF) concentrations of TGF-alpha are increased during the first 2 wk after the onset of ARDS and, if so, whether increased TGF-alpha levels in lavage fluid are associated with increased levels of procollagen peptide III (PCP III), a biological marker of fibroproliferation, and with increased fatality rates. We enrolled 74 consecutive patients with ARDS prospectively identified on admission to the intensive care unit of a tertiary care hospital, and 11 patients with chronic interstitial lung disease. Thirteen healthy volunteers served as control subjects. TGF-alpha concentrations were measured in BALF recovered on Days 3, 7, and 14 after the onset of ARDS (total of 130 lavage samples). TGF-alpha was detected in the lavage fluid of 90% of patients with ARDS (67 of 74), and in 100% of patients with idiopathic pulmonary fibrosis (IPF) (10 of 10), but in none of 13 normal volunteers. At each day tested, the median lavage TGF-alpha level of patients with ARDS was significantly higher than that of normals. The overall fatality rate was 45% (33 of 74 patients). In a univariate analysis, the median TGF-alpha levels in nonsurvivors were 1.5-fold higher at Day 7 (p = 0.06) and 1.8-fold higher at Day 14 (p = 0.048). The fatality rate was 4 times higher (CI 1.6, 17.5) for patients with both increased lavage TGF-alpha and PCP III concentrations at Day 7 than for patients with low TGF-alpha and PCP III values, indicating a synergistic relationship between TGF-alpha and PCP III. We conclude that increased levels of TGF-alpha in BALF are common in patients with ARDS and that lavage TGF-alpha is associated with a marker of the fibroproliferative response in sustained ARDS.

Lung injury induced by alloreactive Th1 cells is characterized by host-derived mononuclear cell inflammation and activation of alveolar macrophages.

We have investigated a murine model of acute lung injury caused by i.v. administration of a T cell clone (CD4+, Th1 phenotype) that recognizes Ly5, a polymorphic cell surface glycoprotein expressed on hemopoietic cells. Alloreactive cloned T cells, specific for host Ly5 Ag, cause a mononuclear cell pulmonary vasculitis and interstitial pneumonitis. In further studies of the cellular mechanisms involved in this model, we found that mature host T cells or B cells are not required, since lung injury was comparable in transgenic host mice that lack these cells (RAG-1 knockout). Cloned T cells labeled in vitro with bromodeoxyuridine were localized in inflammation foci in lung, but the majority of cells in the foci were not labeled. Using transgenic mice that constitutively express lacZ, we determined that the mononuclear cell vasculitis is of host cell origin. Alveolar macrophages (AM) from T cell-treated mice spontaneously secreted TNF-alpha in culture, whereas TNF-alpha was not detected in AM cultures from control mice. TNF-alpha production in response to LPS stimulation was significantly higher in AM cultures derived from T cell-treated mice than in those from control mice. Challenge with sublethal doses of LPS resulted in 50% mortality in T cell-treated mice and was associated with augmented AM TNF-alpha production and protein in bronchoalveolar lavage fluid. We conclude that immune activation of T cells of the Th1 phenotype can initiate lung injury characterized by a host-derived mononuclear cell inflammation and activation of AM.

T cells specific for a polymorphic segment of CD45 induce graft-versus-host disease with predominant pulmonary vasculitis.

To study the character of graft-vs-host disease (GVHD) induced by T cells specific for hemopoietic cells, T cells specific for a polymorphic segment of CD45 were transferred into CD45 congenic mice. C57BL/6 mice that express the CD45b allele were immunized with a 13 mer peptide representing the polymorphic segment (p257-268) of CD45a protein. Conversely, C57BL/6 mice congenic for CD45a were immunized with the CD45b peptide. CD4+ T cells specific for allelic CD45 peptides were elicited. Importantly, T cells specific for CD45 peptides proliferated specifically and vigorously in response to spleen cells expressing the appropriate polymorphic CD45 protein. T cells specific for CD45 induced a substantial graft-vs-host response (GVHR) with predominant early pulmonary vasculitis and later more widespread interstitial mononuclear cell infiltration and alveolitis. No GVHR was induced in bone marrow chimeras expressing only donor hemopoietic cells. Thus, donor T cell recognition of host hemopoietic cells is sufficient to elicit GVHR, but the classical skin, liver, and gut manifestations of GVHD were not observed. The CD45-specific T cells used secreted Th1 cytokines, but without detectable soluble IL-2. Studies using CD45-specific T cells with different effector functions might allow further dissection of donor cell requirements for GVHD syndromes.

Immunolocalization of transforming growth factor-alpha, epidermal growth factor (EGF), and EGF-receptor in normal and injured developing human lung.

The family of growth factors that includes epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) are thought to play a role in the regulation of fetal lung development and epithelial repair after injury. To further elucidate the potential role of these growth factors and their receptor in normal human lung development and in response to injury, their distribution was determined by immunohistochemistry in normal fetal lung, as well as both normal and injured postnatal human lung. We studied 14 specimens of human lung tissue: from three fetuses, four normal infants, two preterm infants with hyaline membrane disease, and five infants with late bronchopulmonary dysplasia (BPD). EGF, TGF-alpha, and EGF receptor (EGF-R) colocalized in airway epithelium in normal fetal and in postnatal human lung. They were also colocalized in scattered alveolar epithelial cells in postnatal lung. Large numbers of alveolar macrophages immunostained for EGF, TGF-alpha, and EGF-R in lungs with late stages of BPD. The colocalization of these growth factors suggests parallel expression of EGF family members. Moreover, the colocalization of these growth factors with their receptor in developing lung suggests that they may act through an autocrine mechanism. The prominent expression of these growth factors in alveolar macrophages in BPD suggests they may be involved with the pathogenesis of this disease.

Expression of transforming growth factor-alpha and epidermal growth factor receptor is increased following bleomycin-induced lung injury in rats.

To investigate the potential role of transforming growth factor-alpha (TGF-alpha) and the epidermal growth factor receptor (EGF-R) in the fibroproliferative response to acute lung injury, we determined lung steady-state TGF-alpha and EGF-R mRNA levels, TGF-alpha protein levels, and the distribution of TGF-alpha and EGF-R immunoreactive protein of bleomycin-injured and control rat lungs. At 2 and 4 days after a single intratracheal injection of bleomycin, TGF-alpha mRNA levels increased to 159% and 184% of control values, respectively. EGF-R mRNA levels increased to 163%, 314%, and 170% of control values at 1, 7, and 14 days after bleomycin instillation. TGF-alpha protein levels in whole lung extracts increased to 230% of control values at 4 days after bleomycin administration. TGF-alpha and EGF-R immunoreactivity was detected in macrophages, alveolar septal cells, and airway epithelium of control and bleomycin-injured animals with an apparent increase in the intensity and number of specifically immunostained cells following lung injury. TGF-alpha and EGF-R immunoreactive proteins were detected in foci of cellular proliferation and in areas of intraalveolar fibrosis. We conclude that TGF-alpha and the EGF-R are present in normal and bleomycin-injured rat lung and that the expression of this growth factor and its receptor are up-regulated following lung injury. These results suggest that increased expression of TGF-alpha and the EGF-R may be an important mechanism that modulates the fibroproliferative response to acute lung injury.

Expression of TGF-alpha, EGF, and EGF receptor in fetal rat lung.

To define the distribution of transforming growth factor-alpha (TGF-alpha) and its relationship to epidermal growth factor (EGF) and EGF receptor in lung development and to determine whether epithelial cells produce TGF-alpha, we studied the expression of TGF-alpha, EGF, and their receptor in late-gestation fetal rat lung and in cultured fetal rat lung cells. TGF-alpha, EGF, and EGF receptor were colocalized in epithelial and smooth muscle cells of bronchioles and bronchi and in epithelial cells of saccules. Epithelial cells cultured from late-gestation fetal rat lung transcribe TGF-alpha and EGF receptor mRNA and produce TGF-alpha and EGF receptor proteins. Cultured fibroblasts contained EGF receptor mRNA, but no detectable TGF-alpha mRNA. These results demonstrate fetal lung epithelial cells are a source for TGF-alpha and suggest that TGF-alpha might act through an autocrine or paracrine mechanism with epithelial and mesenchymal cells. The colocalization of TGF-alpha and EGF suggests that these growth factors might act in parallel in lung development.