Electron Signatures of Reconnection in a Global eVlasiator Simulation.

Geospace plasma simulations have progressed toward more realistic descriptions of the solar wind-magnetosphere interaction from magnetohydrodynamic to hybrid ion-kinetic, such as the state-of-the-art Vlasiator model. Despite computational advances, electron scales have been out of reach in a global setting. eVlasiator, a novel Vlasiator submodule, shows for the first time how electromagnetic fields driven by global hybrid-ion kinetics influence electrons, resulting in kinetic signatures. We analyze simulated electron distributions associated with reconnection sites and compare them with Magnetospheric Multiscale (MMS) spacecraft observations. Comparison with MMS shows that key electron features, such as reconnection inflows, heated outflows, flat-top distributions, and bidirectional streaming, are in remarkable agreement. Thus, we show that many reconnection-related features can be reproduced despite strongly truncated electron physics and an ion-scale spatial resolution. Ion-scale dynamics and ion-driven magnetic fields are shown to be significantly responsible for the environment that produces electron dynamics observed by spacecraft in near-Earth plasmas.

Apolipoprotein A-I inhibits experimental colitis and colitis-propelled carcinogenesis.

In both humans with long-standing ulcerative colitis and mouse models of colitis-associated carcinogenesis (CAC), tumors develop predominantly in the distal part of the large intestine but the biological basis of this intriguing pathology remains unknown. Herein we report intrinsic differences in gene expression between proximal and distal colon in the mouse, which are augmented during dextran sodium sulfate (DSS)/azoxymethane (AOM)-induced CAC. Functional enrichment of differentially expressed genes identified discrete biological pathways operating in proximal vs distal intestine and revealed a cluster of genes involved in lipid metabolism to be associated with the disease-resistant proximal colon. Guided by this finding, we have further interrogated the expression and function of one of these genes, apolipoprotein A-I (ApoA-I), a major component of high-density lipoprotein. We show that ApoA-I is expressed at higher levels in the proximal compared with the distal part of the colon and its ablation in mice results in exaggerated DSS-induced colitis and disruption of epithelial architecture in larger areas of the large intestine. Conversely, treatment with an ApoA-I mimetic peptide ameliorated the phenotypic, histopathological and inflammatory manifestations of the disease. Genetic interference with ApoA-I levels in vivo impacted on the number, size and distribution of AOM/DSS-induced colon tumors. Mechanistically, ApoA-I was found to modulate signal transducer and activator of transcription 3 (STAT3) and nuclear factor-κB activation in response to the bacterial product lipopolysaccharide with concomitant impairment in the production of the pathogenic cytokine interleukin-6. Collectively, these data demonstrate a novel protective role for ApoA-I in colitis and CAC and unravel an unprecedented link between lipid metabolic processes and intestinal pathologies.

Descending phlebography in patients with venous ulceration: hemodynamic implications.

AIM: The aim of this paper is to report on the hemodynamic significance of the various degrees reflux as demonstrated on descending phlebography, by comparing the phlebographic findings with ambulatory venous pressure (AVP) measurements. METHOD: Thirty-two patients (45 affected limbs) with active or healed venous ulceration were admitted to the study. Descending phlebography with grading of reflux (0-4 using Herman's grading), AVP and refilling time 90 (RT90) were performed in all patients. In addition, the presence of deep to superficial reflux into the great saphenous vein at the sapheno-femoral junction, thigh incompetent perforating veins, small saphenous vein at the saphenopopliteal junction and incompetent calf perforating veins was recorded using ascending functional phlebography. The examined limbs were separated into two groups according to the Grade of reflux. Group I consisted of limbs in which popliteal valve incompetence was not demonstrated on descending phlebography, i.e., Grades 0-2 (18 limbs). Group II consisted of limbs with popliteal reflux as demonstrated by descending venography, i.e., grades 3 and 4 (27 limbs). RESULTS: In Group I the mean AVP ± SD was 47.2 ± 9.3 mmHg (range 31-67 mmHg). After the application of the ankle tourniquet to exclude the effects of the superficial venous incompetence on the pressure recordings, the mean AVP ± SD became 28.1 ± 9.9 mmHg (range 11-44) (paired t test: P < 0.001). In Group II (limbs with incompetent popliteal valves) the mean AVP ± SD was 71.6 ± 12.7 mmHg (range 49-95 mmHg) before the tourniquet. This was significantly higher than in Group I (t test: P < 0.001). The application of the ankle tourniquet in this group produced a small but significant decrease in the AVP (mean AVP ± SD: 66 ± 14.5 mmHg) (paired t test: P < 0.001). CONCLUSION: Incompetence of the femoral valves in the presence of competent popliteal valves adds very little to the hemodynamic abnormality produced by superficial venous reflux. In the majority of these patients, there is co-existing reflux from deep to superficial veins with associated superficial valve incompetence which is responsible for the venous hypertension, skin changes and ulceration. The hemodynamic changes which in the past had been associated with deep venous insufficiency (AVP >45 mmHg and RT90 < 14 seconds despite the application of an ankle tourniquet) occur only when there is popliteal incompetence.

Treatment of experimental murine colitis with CD40 antisense oligonucleotides delivered in amphoteric liposomes.

BACKGROUND AND AIMS: CD40-CD40L interactions appear to play an important role in the pathogenesis of experimental colitis. We tested the effect and investigated the underlying mechanism of action of systemically administered antisense oligonucleotide (ASO) targeting CD40 formulated in amphoteric liposomes (nov038/CD40). The charge characteristics of the amphoteric liposomes (anionic surface charge at physiological pH that becomes cationic at low pH), facilitate efficient sequestration of the ASO inside the liposomes at low pH and the direction of the carriers towards macrophages and dendritic cells under physiological conditions. METHODS: Colitis was induced in Balb/c mice using 2,4,6-Trinitrobenzene sulphonic acid (TNBS) and treated with nov038/CD40. Disease was monitored by body weight, histology, cytokine profiling and changes in immune cell populations. CD40 expression on different cell subsets was analyzed by flow cytometry. An antigen challenge model was used to determine neoimmunity under CD40 modulation. RESULTS: Administration of nov038/CD40 inhibited the development of TNBS colitis as assessed by weight loss, histology and cytokine profiles; unformulated CD40 ASO or nov038 encapsulating an unrelated ASO (nov038/SCR) were ineffective. The novel agent is potent as it completely suppressed even established colitis with a single treatment and significantly reduced T-cell activation as well as levels of pro-inflammatory mediators in serum. The inhibition of CD40 specifically occurred in macrophages, but not in B-cells. In contrast to prednisolone, standard treatment for inflammatory bowel diseases (IBD) that is effective in a single administration and involves extensive immunosuppression, nov038/CD40 did not affect the number of B- or Treg cells. Eventually, we observed a largely intact neoimmunity under conditions of a CD40 inhibition. CONCLUSIONS: Administration of nov038/CD40, but neither naked CD40 ASO nor nov038/SCR, prevents the development and treats established colitis in mice. Delivery of CD40 ASO in nov038 is highly cell-specific as it selectively suppresses CD40 on macrophages, but not on B-cells; the novel agent has strong anti-inflammatory characteristics without being immunosuppressive.

Thiopurine methyltransferase activity combined with 6-thioguanine metabolite levels predicts clinical response to thiopurines in patients with inflammatory bowel disease.

BACKGROUND/AIMS: 6-Mercaptopurine and its prodrug azathioprine are effective for the treatment of inflammatory bowel disease. Thiopurine methyltransferase is important for the metabolism of thiopurines. However, there is controversy as to the clinical utility of measuring thiopurine methyltransferase enzyme activity and 6-thioguanine nucleotide levels. Our aim was to determine if thiopurine methyltransferase enzyme activity and 6-thioguanine nucleotide level monitoring would predict response to therapy with thiopurines in patients with inflammatory bowel disease. METHODS: Baseline thiopurine methyltransferase enzyme activity prior to initiation of therapy with either 6-mercaptopurine or azathioprine was determined in 39 patients with inflammatory bowel disease. The association between clinical response and thiopurine methyltransferase activity and 6-thioguanine nucleotide levels singly or in combination were analysed. RESULTS: Seventeen of 39 patients (44%) responded to 6-mercaptopurine or azathioprine therapy. Thiopurine methyltransferase enzyme activity below the mean of 30.5 U was significantly associated with clinical response. The thiopurine methyltransferase low phenotype was associated with response in 65% vs. 29% in individuals with thiopurine methyltransferase enzyme activity above 30.5 U (p = 0.05). There was no correlation between thiopurine methyltransferase activity and 6-thioguanine nucleotide levels. The maximal 6-thioguanine nucleotide levels did not predict clinical response. When combining thiopurine methyltransferase enzyme activity and 6-thioguanine nucleotide levels, the combination of thiopurine methyltransferase low/6-thioguanine nucleotide high was associated with response in 7/7 (100%) vs. only 2/8 (25%) with the combination of thiopurine methyltransferase high/6-thioguanine nucleotide low (p=0.01). CONCLUSIONS: Thiopurine methyltransferase activity inversely correlated with clinical response to thiopurine treatment in inflammatory bowel disease. Thiopurine methyltransferase enzyme activity below 30.5 U combined with a post-treatment 6-thioguanine nucleotide level > 230 pmol/8 x 10(8) erythrocytes was the best predictor of response.

Diagnostic yield of capsule endoscopy in ulcerative colitis and inflammatory bowel disease of unclassified type (IBDU).

BACKGROUND AND STUDY AIMS: Capsule endoscopy is increasingly reported as an important diagnostic procedure in patients with known or suspected Crohn's disease, but its clinical utility in patients with ulcerative colitis or unclassified type inflammatory bowel disease (IBDU) is unclear. The aim of our study was to determine the diagnostic yield of capsule endoscopy for small-bowel disease in patients with ulcerative colitis and IBDU. PATIENTS AND METHODS: All data from patients with a history of ulcerative colitis or IBDU who underwent capsule endoscopy between October 2001 and August 2005 were analyzed for procedure indications and findings. Images were reviewed by an experienced capsule endoscopist. The finding of multiple ulcerations (three or more) on capsule endoscopy was classified as diagnostic of small-bowel Crohn's disease. RESULTS: 120 patients had undergone 122 capsule endoscopy procedures. Overall, 19 of 120 patients (15.8 %) had capsule endoscopy findings consistent with the diagnosis of Crohn's disease. The proportion of patients with small-bowel disease was significantly higher among patients with a history of colectomy (7 of 21 patients, 33 %) compared with those without colectomy (12/99, 12 %) ( P = 0.04). Among patients with positive findings on capsule endoscopy, 18 had also previously undergone a small-bowel follow-through study and only one showed findings consistent with Crohn's disease. CONCLUSIONS: Many patients with a diagnosis of ulcerative colitis and atypical features or IBDU may have small-bowel findings on capsule endoscopy that are consistent with Crohn's disease. Capsule endoscopy should be considered in ulcerative colitis patients with atypical clinical features particularly after colectomy.

Infliximab in the treatment of medically refractory indeterminate colitis.

AIM: To examine the outcome of infliximab intervention in refractory indeterminate colitis. METHODS: Twenty patients with severe, medically refractory indeterminate colitis were treated with infliximab. All patients initially received infliximab, 5 mg/kg, intravenously and, in some patients, the dose was subsequently increased to 10 mg/kg. The number of infusions ranged from one to 16 per patient. Indeterminate colitis was defined as colitis that could not be classified with certainty as Crohn's disease or ulcerative colitis based on traditional clinical, endoscopic and histopathological criteria. The clinical response to infliximab was classified as complete response, partial response or non-response. RESULTS: Fourteen of the 20 patients (70%) showed a complete response to infliximab treatment, two showed a partial response and four showed no response. The four non-responders underwent colectomy with ileal pouch-anal anastomosis. The resected colon specimen was consistent with ulcerative colitis in all four cases, although two were subsequently re-classified as Crohn's disease. Eight additional patients were subsequently re-classified as having Crohn's disease on longer follow-up evaluation, whilst eight continued to have features of indeterminate colitis. The response rate to infliximab treatment was similar in both groups. CONCLUSIONS: Infliximab is effective in approximately two-thirds of patients with indeterminate colitis, and thus may be considered for patients with refractory disease prior to colectomy. The follow-up time afforded by infliximab treatment may allow for more accurate classification of the disease in a significant proportion of patients whose colitis has indeterminate features at initial presentation.

CCR9-positive lymphocytes and thymus-expressed chemokine distinguish small bowel from colonic Crohn's disease.

BACKGROUND & AIMS: Thymus-expressed chemokine (TECK) or CCL25) is selectively expressed in the small bowel (SB), where lamina propria lymphocytes (LPL) and intraepithelial leukocyte expressing the cognate chemokine receptor CCR9 predominate. We characterize the role of TECK and CCR9-expresing lymphocytes in small intestinal Crohn's disease. METHODS: CCR9 expression on lymphocytes from lamina propria, mesenteric lymph node, and peripheral blood was analyzed by flow cytometry and by Northern blotting for LPL. TECK expression was analyzed in inflamed SB and colon by reverse-transcription polymerase chain reaction and immunohistochemistry. RESULTS: The fraction of CCR9(+) T cells in inflamed SB was significantly lower than in uninvolved SB mucosa. In contrast, in peripheral blood lymphocytes, CCR9(+) lymphocytes were markedly elevated in patients with small bowel Crohn's or celiac disease, but not in patients with purely colonic Crohn's. Also, TECK expression is altered in inflamed small bowel, being intensely expressed in a patchy distribution in crypt epithelial cells in proximity to lymphocytic infiltrates. TECK is not expressed in either normal or inflamed colon. CONCLUSIONS: In SB immune-mediated diseases, there is repartitioning of CCR9(+) lymphocytes between SB and blood and an altered pattern of TECK expression in SB Crohn's. The TECK/CCR9 ligand/receptor pair may play an important role in the pathogenesis of SB Crohn's disease.

Outcome of cytomegalovirus infections in patients with inflammatory bowel disease.

OBJECTIVE: The aim of this study was to determine the outcome of cytomegalovirus (CMV) infections complicating the course of inflammatory bowel disease (IBD). METHODS: The records and clinical courses were reviewed for all IBD patients who were evaluated at the IBD Center of the Cedars-Sinai Medical Center and who developed CMV infection. RESULTS: Ten patients with severe, medically refractory IBD (five ulcerative colitis, three Crohn's colitis, and two indeterminate colitis) developed CMV infection. All but two were hospitalized with exacerbation of their underlying disease and were receiving immunosuppressive treatment with steroids, thiopurines, and/or cyclosporine at the time CMV infection was recognized. Eight patients had documented colonic CMV (one had concurrent upper GI tract involvement), one developed interstitial CMV and Pneumocystis carinii pneumonia, and one developed primary CMV mononucleosis. Prompt treatment with ganciclovir and withdrawal of immunosuppressive treatment resulted in gradual improvement and induction of remission of the underlying IBD in five patients. The patient with concomitant CMV and P. carinii pneumonitis died. In two patients, treatment with ganciclovir did not alter the clinical course of their IBD, and one of them underwent colectomy. In one patient CMV was found on the resected colonic specimen. One patient with primary CMV infection responded also to ganciclovir treatment. CONCLUSIONS: CMV infection may aggravate the course of seemingly refractory IBD in patients who either fail to respond or experience worsening of symptoms despite immunosuppressive therapy. Expedient evaluation, prompt treatment intervention with ganciclovir, and withdrawal of immunosuppressive treatment may avoid complications and mortality. This regimen leads to improvement of the underlying IBD in most patients.

The role of thymus-expressed chemokine and its receptor CCR9 on lymphocytes in the regional specialization of the mucosal immune system.

Chemokines play an important role in the migration of leukocytes at sites of inflammation, and some constitutively expressed chemokines may direct lymphocyte trafficking within lymphoid organs and peripheral tissues. Thymus-expressed chemokine (TECK or Ckbeta-15/CCL25), which signals through the chemokine receptor CCR9, is constitutively expressed in the thymus and small intestine but not colon, and chemoattracts a small fraction of PBLs that coexpress the integrin alpha(4)beta(7). Here we show that TECK is expressed in the human small bowel but not colon by endothelial cells and a subset of cells in intestinal crypts and lamina propria. CCR9 is expressed in the majority of freshly isolated small bowel lamina propria mononuclear cells (LPMC) and at significantly higher levels compared with colonic LPMC or PBL. TECK was selectively chemotactic for small bowel but not colonic LPMC in vitro. The TECK-induced chemotaxis was sensitive to pertussis toxin and partially inhibited by Abs to CCR9. TECK attracts predominantly the T cell fraction of small bowel LPMC, whereas sorted CD3(+)CCR9(+) and CD3(+)CCR9(-) lymphocytes produce similar Th1 or Th2 cytokines at the single cell level. Collectively, our data suggest that the selective expression of TECK in the small bowel underlie the homing of CCR9(+) intestinal memory T cells to the small bowel rather than to the colon. This regional specialization implies a segregation of small intestinal from colonic immune responses.

Late-gestation tracheal occlusion in the fetal lamb causes rapid lung growth with type II cell preservation.

BACKGROUND: Fetal tracheal occlusion (TO) results in varying degrees of lung growth. This study examines whether gestational age influences lung growth response following TO. MATERIALS AND METHODS: Fetal lambs (term = 145 days) underwent TO early (108 days, n = 6) or late (122 days, n = 6) in gestation. Aspirated lung fluid volume (LFV) and intratracheal pressure (ITP) were recorded daily. Two weeks after TO, the fetuses were sacrificed. Lung growth was assessed by lung weight and stereologic volumetry. Type II cellular density was assessed by computer-assisted morphometry using antisurfactant protein B antibody. RESULTS: After early TO, ITP remained below 2 mm Hg for all but one of the first 5 days. In late TO, ITP rose to 4.8 +/- 1.7 mm Hg by Day 1 and remained elevated. LFV remained lower after early than after late TO (P < 0.05) for 8 days. Thereafter, pressure and volume reached similar levels in both TO groups; both were significantly higher than their respective controls (P < 0.05). Parenchymal fraction (1 - air-space fraction) was significantly smaller after late TO (22.8 +/- 1.2%) than after early TO (31.3 +/- 0.5%). Type II density was 38.0 +/- 12.4 x 10(6)/mL after early TO and 84.0 +/- 24.3 x 10(6)/mL in control (P < 0.05); the difference between late TO and control was not significant. CONCLUSIONS: Late tracheal occlusion in fetal lambs caused more rapid lung growth than earlier TO, although ultimate lung size was similar in both groups. Late TO also resulted in greater air-space fraction and better preservation of the type II cell population than early TO. Late-gestation tracheal occlusion may therefore be preferable to prolonged occlusion initiated earlier.

Role of cytokines in the pathogenesis of inflammatory bowel disease.

Recent advances in the drug treatment of inflammatory bowel disease (IBD) have paralleled our understanding of the pathophysiology of ulcerative colitis and Crohn's disease. Several proinflammatory and immune-regulatory cytokines are upregulated in the mucosa of patients with IBD, and differences and similarities in the cytokine profiles of ulcerative colitis and Crohn's disease have been elucidated. Several clinical trials involving a chimeric anti-TNF-alpha (tumor necrosis factor-alpha) antibody have shown marked clinical benefit in the majority of patients with Crohn's disease, verifying the importance of TNF-alpha in the pathogenesis of Crohn's disease. In preliminary studies, treatment with recombinant human interleukin-10 has been beneficial in Crohn's disease but not in ulcerative colitis. Future treatment of IBD may include combination or sequential cytokine and anticytokine administration in defined groups of patients based on their mucosal cytokine profiles.

The role of chemokines and chemokine receptors in mucosal inflammation.

Chemokines represent a large family of small cytokines, the main function of which is the attraction of leukocytes to different tissues. Several chemokines and their receptors have been shown to play a critical role in lymphoid development, mucosal immunity, and inflammation. In this article we review recent advances in chemokine physiology and their potential role in the pathogenesis of mucosal inflammation. We also discuss the potential for the use of chemokine or chemokine receptor antagonists as novel therapies for inflammatory bowel disease.

The clinical spectrum of stenotrophomonas (xanthomonas) maltophilia respiratory infection.

During a 15-month retrospective clinical study in an academic referral-based cancer center, 26 patients with S. maltophilia respiratory tract infections were identified (which were associated with bacteremia in 13 patients). Five of these 26 patients had previously undescribed sinopulmonary involvement. The infections were typically nosocomial. Nine patients with solid tumors had malignant involvement of the respiratory tract (five with obstruction). In two patients, the infection co-existed with pulmonary aspergillosis. Fifteen patients (58%) died of the infection. The factors that correlated with a poor outcome included bacteremic pneumonia, persistent neutropenia, presence of obstruction, development of septic shock or multiple organ dysfunction, and delay in institution of appropriate antibiotic therapy. In multivariate analysis, only septic shock and delayed therapy remained significant. Trimethoprim-sulfamethoxazole and/or ticarcillin-clavulanate were most commonly associated with a favorable outcome.

An open-label pilot study of low-dose thalidomide in chronically active, steroid-dependent Crohn's disease.

BACKGROUND & AIMS: Thalidomide decreases production of tumor necrosis factor alpha, a proinflammatory cytokine associated with Crohn's disease (CD). In this study the safety, tolerance, and efficacy of low-dose thalidomide were evaluated for treatment of moderate-to-severe, steroid-dependent CD. METHODS: Twelve adult male patients with Crohn's Disease Activity Index (CDAI) scores of > or = 250 and < or = 500 despite > or = 20 mg prednisone/day were enrolled. The first 6 patients received 50 mg thalidomide every night, the next 6 received 100 mg every night. Steroid doses were stable during the first 4 weeks of treatment, then tapered during weeks 5-12. CDAI was used to assess response. RESULTS: (1) Disease activity improved consistently in all patients during weeks 1-4: 58% response, 17% remission. (2) Clinical improvement was generally maintained despite steroid taper during weeks 5-12. All patients were able to reduce steroids by >/=50%. Forty-four percent discontinued steroids entirely. In weeks 5-12, 70% of patients responded and 20% achieved remission. (3) Side effects were mild and mostly transient, with the most common being drowsiness, peripheral neuropathy, edema, and dermatitis. CONCLUSIONS: Low-dose thalidomide appears to be well tolerated and effective over a 12-week period. Results of this pilot study support the need for controlled multicenter trials of thalidomide for treatment of CD.

Lung growth response after tracheal occlusion in fetal rabbits is gestational age-dependent.

In utero tracheal occlusion (TO) is a potent stimulus of fetal lung growth, and is currently being applied in clinical trials to treat severe forms of pulmonary hypoplasia. The aim of this study was to examine the effect of timing of TO on pulmonary growth and maturation rates. Fetal rabbits (term = 31 d) were subjected to in utero tracheal clipping at 24 (late pseudoglandular stage) or 27 d of gestation (late canalicular/early terminal sac stage). Sham-operated littermates served as controls (C). Animals were killed at time intervals ranging from 1 to 6 d (early group) or 1 to 3 d (late group) after occlusion. Lung growth was measured by computerized stereologic volumetry and 5'-bromo-2'-deoxyuridine (BrdU) pulse labeling. Pneumocyte II population kinetics were analyzed using a combination of anti-surfactant protein-A and BrdU immunohistochemistry and computer-assisted morphometry. Statistical analysis was performed using unpaired Student's t test. Early TO was followed by an initial 3-d stagnation of growth and subsequently a dramatic acceleration of growth (BrdU-labeling index [LI] 10.1 +/- 0. 6% in TO versus 2.7 +/- 0.5% in C at 29 d, P < 0.001). In contrast, late TO induced an immediate and sustained moderate increase of lung growth (BrdU-LI 2.8 +/- 0.9% in TO versus 1.1 +/- 0.2% in C at 30 d, P < 0.05), associated with relatively more pronounced air-space distension. Whereas late TO caused no significant alterations in type II cell density or proliferation, early TO was followed by a marked increase in type II cell proliferation, paradoxically associated with dramatic reduction of type II cell density after 29 d. The effects of intrauterine TO on fetal lung growth and type II cell kinetics critically depend on the gestational age, and thus on the maturity of the lungs at the time of surgery. These findings have important clinical implications with respect to the timing of fetal interventions aimed at promoting lung growth. The fetal rabbit provides an invaluable model to study the mechanics and age dependency of TO-induced lung growth.

The role of apoptosis in normal and accelerated lung development in fetal rabbits.

BACKGROUND/PURPOSE: During fetal development, the mammalian lung undergoes progressive parenchymal involution. Intrauterine tracheal occlusion induces accelerated architectural maturation of the fetal lungs associated with depletion of the surfactant-producing type II cells. This study investigates the spatiotemporal pattern of apoptosis during normal fetal lung development and its modulation in tracheal occlusion-induced accelerated fetal lung growth. METHODS: Fetal rabbit lungs were studied at 25 to 31 days' gestational age (DGA; term, 31 DGA), corresponding to late pseudoglandular through terminal air sac stages of fetal lung development. Intrauterine tracheal ligation (TL) was performed at 24 DGA. TL fetuses were monitored until 29 DGA, a time-point previously shown to coincide with significant type II cell depletion. Apoptotic cells were identified by light and electron microscopy, as well as terminal deoxynucleotidyl transferase-mediated dUTP-FITC nick-end labeling (TUNEL). Epithelial (type I and II) cell apoptosis was studied by TUNEL labeling in conjunction with antisurfactant protein and anticytokeratin immunohistochemistry. DNA fragmentation was analyzed by gel electrophoresis. Sham-operated littermates served as controls. RESULTS: The number of apoptotic cells progressively increased with advancing lung growth and architectural maturation (apoptotic index [Al] 1.2 +/- 0.7 x 10(-3) at 25 DGA v 4.2 +/- 1.4 x 10(-3) at 31 DGA; P< .05, analysis of variance). In TL fetuses, the apoptotic rate was significantly higher than in non-TL fetuses from the third postligation day on, coinciding with the onset of significantly increased airspace distension (Al 4.9 +/- 1.3 x 10(-3) in TL v2.6 +/- 0.4 x 10(-3) in controls at 29 DGA; P< .05, Student's ttest). Apoptosis occurred in parenchymal cells and in isolated cells within the airspaces. The apoptotic activity of type II cells was significantly higher in TL fetuses than C fetuses at 29 DGA (type II Al 25.5 +/- 6.3 x 10(-3) in TL v2.3 +/- 0.8 x 10(-3) in C; P< .001). Electron microscopic studies confirmed the presence of apoptotic nuclei in interstitial macrophages and in degenerating intraluminal type II cells. DNA analysis showed nucleosomal bands. CONCLUSIONS: Normal fetal lung development is associated with a progressive increase of epithelial and interstitial apoptotic activity, a process enhanced by TL. Tracheal occlusion induces a significant increase of type II cell apoptosis, which likely contributes to the observed type II cell depletion after TL. We speculate that fetal type II cell apoptosis after TL may be induced by mechanical distension (stretch) of the airspaces.