Novel cardiovascular biomarkers in unexplained syncopal attacks: the SYSTEMA cohort.

OBJECTIVES: The aim of the study was to investigate the resting levels of novel cardiovascular biomarkers in common types of noncardiac syncope. DESIGN AND SETTING: An observational study was conducted including 255 patients (mean age 60 years, range 15-93; 45% men) with unexplained syncopal attacks. Subjects underwent an expanded head-up tilt test including carotid sinus massage, and nitroglycerin provocation if indicated. Using logistic regression, we explored the associations between specific diagnoses of syncope and resting levels of circulating biomarkers: C-terminal pro-arginine vasopressin (CT-proAVP), C-terminal endothelin-1 precursor fragment (CT-proET-1), midregional fragments of pro-atrial natriuretic peptide (MR-proANP) and pro-adrenomedullin (MR-proADM). RESULTS: A total of 142 (56%) patients were diagnosed with vasovagal syncope (VVS), 85 (33%) with orthostatic hypotension (OH) and 47 (18%) with carotid sinus hypersensitivity (CSH); in addition, 74 (29%) patients had more than one diagnosis. Thirty-five patients (14%) demonstrated a cardioinhibitory reflex. The probability of VVS was highest in the first quartile of MR-proANP [Q1 vs. Q4: odds ratio (OR) 5.57, 95% confidence interval (CI) 1.86-16.74; P < 0.001] and CT-proET-1 (OR 7.17, 95% CI 2.43-21.13; P < 0.001). By contrast, the probability of OH was highest in the fourth quartile of CT-proET-1 (Q4 vs. Q1: OR 8.66, 95% CI 2.49-30.17; P < 0.001). Furthermore, CSH was most frequently observed in the first quartile of MR-proANP (Q1 vs. Q4: OR 6.57, 95% CI 1.62-26.62; P = 0.008) among those over 60 years of age, whereas the cardioinhibitory reflex was strongly associated with low CT-proET-1 levels (Q1 vs. Q4: OR 69.7, 95% CI 6.97-696.6; P < 0.001). Moreover, in patients with VVS, a high concentration of CT-proET-1 was predictive of OH (OR per 1 SD 2.4, 95% CI 1.15-5.02; P = 0.02), whereas low CT-proET-1 suggested involvement of the cardioinhibitory reflex (OR per 1SD 0.42, 95% CI 0.25-0.70; P = 0.001). CONCLUSIONS: The levels of MR-proANP and CT-proET-1 are markedly changed in common forms of syncope, suggesting the involvement of novel neurohormonal mechanisms in syncopal attacks.

A simple tool for stereological assessment of digital images: the STEPanizer.

STEPanizer is an easy-to-use computer-based software tool for the stereological assessment of digitally captured images from all kinds of microscopical (LM, TEM, LSM) and macroscopical (radiology, tomography) imaging modalities. The program design focuses on providing the user a defined workflow adapted to most basic stereological tasks. The software is compact, that is user friendly without being bulky. STEPanizer comprises the creation of test systems, the appropriate display of digital images with superimposed test systems, a scaling facility, a counting module and an export function for the transfer of results to spreadsheet programs. Here we describe the major workflow of the tool illustrating the application on two examples from transmission electron microscopy and light microscopy, respectively.

Subjects heterozygous for genetic loss of function of the thiazide-sensitive cotransporter have reduced blood pressure.

Gitelmans syndrome (GS) is an inherited recessive disorder caused by homozygous or compound heterozygous loss of function mutations of the NaCl cotransporter (NCCT) gene encoding the kidney-expressed NCCT, the pharmacological target of thiazide diuretics. An observational study estimated the prevalence of GS to 19/1,000,000, in Sweden, suggesting that approximately 1% of the population carries one mutant NCCT allele. As the phenotype of GS patients, who always carry two mutant alleles, is indistinguishable from that seen in patients treated with high-dose thiazide diuretics, we aimed at investigating whether subjects carrying one mutated NCCT allele have a phenotype resembling that of treatment with low-dose thiazide diuretics. We screened first-degree relatives of 18 of our patients with an established clinical end genetic diagnosis of GS for NCCT loss of function mutations and identified 35 healthy subjects carrying one mutant allele (GS-heterozygotes). Each GS-heterozygote was assigned a healthy control subject matched for age, BMI and sex. GS-heterozygotes had markedly lower blood pressure (systolic 103.3 +/- 16.4 versus 123.2 +/- 19.4 mmHg; diastolic 62.5 +/- 10.5 versus 73.1 +/- 9.4 mmHg; P < 0.001) than controls. There was no significant difference between the groups either in plasma concentration or urinary excretion rate of electrolytes, however, GS-heterozygotes had higher fasting plasma glucose concentration. Similar to patients being treated with low-dose thiazide diuretics, GS-heterozygotes have markedly lower blood pressure and slightly higher fasting plasma glucose compared with control subjects. Our findings suggest that GS-heterozygotes, the prevalence of which can be estimated to 1%, are partially protected from hypertension through partial genetic loss of function of the NCCT. However, as our study had a case-control design, it is important to underline that any potential effects on population blood pressure and risk of future cardiovascular disease need to be examined in prospective and population-based studies.

Functional respiratory morphology in the newborn quokka wallaby (Setonix brachyurus).

A morphological and morphometric study of the lung of the newborn quokka wallaby (Setonix brachyurus) was undertaken to assess its morphofunctional status at birth. Additionally, skin structure and morphometry were investigated to assess the possibility of cutaneous gas exchange. The lung was at canalicular stage and comprised a few conducting airways and a parenchyma of thick-walled tubules lined by stretches of cuboidal pneumocytes alternating with squamous epithelium, with occasional portions of thin blood-gas barrier. The tubules were separated by abundant intertubular mesenchyme, aggregations of developing capillaries and mesenchymal cells. Conversion of the cuboidal pneumocytes to type I cells occurred through cell broadening and lamellar body extrusion. Superfluous cuboidal cells were lost through apoptosis and subsequent clearance by alveolar macrophages. The establishment of the thin blood-gas barrier was established through apposition of the incipient capillaries to the formative thin squamous epithelium. The absolute volume of the lung was 0.02 +/- 0.001 cm(3) with an air space surface area of 4.85 +/- 0.43 cm(2). Differentiated type I pneumocytes covered 78% of the tubular surface, the rest 22% going to long stretches of type II cells, their precursors or low cuboidal transitory cells with sparse lamellar bodies. The body weight-related diffusion capacity was 2.52 +/- 0.56 mL O(2) min(-1) kg(-1). The epidermis was poorly developed, and measured 29.97 +/- 4.88 microm in thickness, 13% of which was taken by a thin layer of stratum corneum, measuring 4.87 +/- 0.98 microm thick. Superficial capillaries were closely associated with the epidermis, showing the possibility that the skin also participated in some gaseous exchange. Qualitatively, the neonate quokka lung had the basic constituents for gas exchange but was quantitatively inadequate, implying the significance of percutaneous gas exchange.

24-h ambulatory blood pressure is linked to chromosome 18q21-22 and genetic variation of NEDD4L associates with cross-sectional and longitudinal blood pressure in Swedes.

Numerous linkage studies have indicated chromosome 18q21-22 as a locus of importance for blood pressure regulation. This locus harbors the neural precursor cell expressed developmentally downregulated 4-like (NEDD4L) gene, which is instrumental for the regulation of the amiloride-sensitive epithelial sodium channel (ENaC). In a linkage study of 16 markers (including two single nucleotide polymorphism markers located within the NEDD4L gene) on chromosome 18 between 70-104 cM and ambulatory blood pressure (ABP), in 118 families, the strongest evidence of linkage was found for 24 h and day-time systolic ABP at the NEDD4L locus (82.25 cM) (P=0.0014). In a large population sample (n=4001), we subsequently showed that a NEDD4L gene variant (rs4149601), which by alternative splicing leads to varying expression of a functionally crucial C2 domain, was associated with diastolic blood pressure (DBP) (P=0.03) and DBP progression over time (P=0.04). A genotype combination of the rs4149601 and an intronic NEDD4L marker (rs2288774) was associated with systolic blood pressure (SBP) (P=0.01), DBP (P=0.04), and progression of both SBP (P=0.03) and DBP (P=0.05) over time. A quantitative transmission disequilibrium test in the family material of the rs4149601 supported this NEDD4L variant as being at least partially causative of the linkage result. In conclusion, our findings suggest that the chromosome 18 linkage peak at 82.25 cM is explained by genetic NEDD4L variation affecting cross-sectional and longitudinal blood pressure, possibly as a consequence of altered NEDD4L interaction with ENaC.

Turnip rape and oilseed rape are new potential food allergens in children with atopic dermatitis.

BACKGROUND: When skin prick testing (SPT) young children with atopic dermatitis (AD) for suspected food allergy, we frequently found positive reactions with turnip rape (Brassica rapa) and oilseed rape (Brassica napus). We performed food challenge to examine whether these children react clinically to turnip rape. METHODS: A total of 1887 children were screened with SPTs for sensitization to turnip rape and oilseed rape. Twenty-eight children with clearly positive SPT (> or =5 mm) were first subjected to labial challenge with turnip rape seeds followed, if negative, by open oral challenge for up to 7 days. Twenty-five children with AD but negative SPT to turnip rape and oilseed rape served as controls. RESULTS: Two-hundred and six (10.9%) children had positive SPT to turnip rape and/or oilseed rape. Twenty-five (89%) of 28 children showed a positive challenge reaction to turnip rape. Seventeen reacted with labial whealing, and eight in oral challenge with facial urticaria, flare-up of AD or abdominal symptoms. All 25 control children remained negative in the labial challenge. CONCLUSIONS: Turnip rape and oilseed rape seem to be new important food allergens in young children with AD. The modes of exposure to these allergens and the possible routes of sensitization remain to be established.

Human papillomavirus status in advanced cervical cancer: predictive and prognostic significance for curative radiation treatment.

Human papillomavirus (HPV) infection plays a major role in oncogenesis of squamous cell carcinoma of the cervix. This study was performed to investigate if HPV status and E2 gene integrity are prognostic parameters for clinical outcome and predictive for radiation response. Forty women with locally advanced cervical cancer treated with curative radiotherapy were analyzed for HPV infection and E2 gene integrity by multiplex polymerase chain reaction. Statistical analyses were performed for overall survival, disease-free survival (DFS), local progression-free survival, and treatment response (clinical complete remission). Twenty-eight (70%) of 40 carcinomas were HPV positive. The only significant factor for a better overall survival, DFS, and local progression-free survival was HPV positivity (P < 0.02, P= 0.02, and P < 0.05, log-rank, respectively). HPV-positive tumors had a significantly better clinical complete remission (67% vs 33%, P= 0.04, Fisher's exact test). An intact E2 gene region showed a trend for a better DFS (P= 0.1, log-rank). This study reveals HPV as an independent prognostic parameter for outcome and radiation response. Integration of the virus genome into host cell DNA might be a molecular target to determine the treatment response of HPV-positive cancers.

Morphometry and allometry of the postnatal marsupial lung development: an ultrastructural study.

An utrastructural morphometric study of the postnatally remodelling lungs of the quokka wallaby (Setonix brachyurus) was undertaken. Allometric scaling of the volumes of the parenchymal components against body mass was performed. Most parameters showed a positive correlation with body mass in all the developmental stages, except the volume of type II pneumocytes during the alveolar stage. The interstitial tissue and type II cell volumes increased slightly faster than body mass in the saccular stage, their growth rates declining in the alveolar stage. Conversely, type I pneumocyte volumes increased markedly in both the saccular and alveolar stages. Both capillary and endothelial volumes as well as the capillary and airspace surface areas showed highest rates of increase during the alveolar stage, at which time the rate was notably higher than that of the body mass. The pulmonary diffusion capacity increased gradually, the rate being highest in the alveolar stage and the adult values attained were comparable to those of eutherians.

Morphometry and allometry of the postnatal lung development in the quokka wallaby (Setonix brachyurus): a light microscopic study.

The postnatally developing lungs of the quokka wallaby, Setonix brachyurus, were investigated macroscopically and by light microscopic morphometry. Lung, parenchymal and non-parenchymal volumes as well as the components of the latter two were analysed by regression analysis. The lungs comprised a single undivided left lung and a right lung with an adherent accessory lobe. Septal tissue growth was most remarkable in the canalicular and saccular stages. Between mid-canalicular stage and the saccular stage, the lung volume increased 2-fold, mainly due to airspace expansion, coupled with septal tissue thinning. The non-parenchymal vascular volume increase accelerated in the successive developmental stages while the airway and connective tissue volumes progressed in a decreasing order, being highest in the canalicular and saccular stages and lowest in the alveolar stage. Growth and remodelling of the alveolar septa occurred simultaneously with airspace subdivision. Airspace expansion accelerated during the stage of microvascular maturation, when most other parameters showed the least rate of increase.

Comparison of cetirizine, ebastine and loratadine in the treatment of immediate mosquito-bite allergy.

BACKGROUND: People frequently experience whealing and delayed papules from mosquito bites. Whealing is mediated by antisaliva immunoglobulin (Ig)E antibodies and histamine. Cetirizine, ebastine and loratadine have earlier shown effects on mosquito-bite reactions but no comparative studies exist. METHODS: A double-blind, placebo-controlled, cross-over study was performed with cetirizine 10 mg, ebastine 10 mg and loratadine 10 mg in 29 mosquito-bite-sensitive adults exposed to Aedes aegypti mosquito-bites. The size of the bite lesion and the intensity of pruritus (visual analog scale) were measured at 15 min and 2, 6 and 24 h. RESULTS: Cetirizine and ebastine, but not loratadine, decreased significantly the size of whealing (P < 0.01) and accompanying pruritus (P < 0.001) compared to placebo. Cetirizine was most effective on pruritus but caused more often sedation than ebastine or loratadine. The delayed bite symptoms remained too faint for any statistical comparison. CONCLUSION: This comparative study in mosquito-bite-sensitive adults shows that cetirizine and ebastine decrease significantly whealing and accompanying pruritus, and that cetirizine seems to be the most effective against pruritus.

Chorioallantoic membrane capillary bed: a useful target for studying angiogenesis and anti-angiogenesis in vivo.

The chick embryo chorioallantoic membrane (CAM) is an extraembryonic membrane that is commonly used in vivo to study both angiogenesis and anti-angiogenesis. This review 1) summarizes the current knowledge about the structure of the CAM's capillary bed; 2) discusses the controversy about the existence of a single blood sinus or a capillary plexus underlying the chorionic epithelium; 3) describes a new model of the CAM vascular growth, namely the intussusceptive mode; 4) reports findings regarding the role played by endogenous fibroblast growth factor-2 in CAM vascularization; and 5) addresses the use and limitations of the CAM as a model for studying angiogenesis and anti-angiogenesis.

Expression of hypoxia-inducible factor-1alpha: a novel predictive and prognostic parameter in the radiotherapy of oropharyngeal cancer.

Hypoxia has long been recognized as detrimental to the successful treatment of malignant tumors with ionizing radiation. Because hypoxia-inducible factor (HIF)-1alpha plays an essential role in oxygen homeostasis in vitro, we explored the predictive potential of this factor in a cohort of 98 patients with squamous cell cancer of the oropharynx, who were treated by curative radiation therapy. Ninety-four % of the primary tumors showed overexpression of HIF-1alpha, relative to the surrounding tissue, as determined by immunohistochemistry. The degree of HIF-1alpha immunoreactivity correlated inversely with both the rate of complete remission of the primary tumor (odds ratio, 0.33; P = 0.03) and lymph node metastases (odds ratio, 0.34; P = 0.02) as well as with local failure-free survival (risk ratio, 2.15; P = 0.006), disease-free survival (risk ratio, 2.01; P = 0.008), and overall survival (risk ratio, 2.17; P = 0.002). The multivariate analysis revealed the predictive power of HIF-1alpha to be independent of other covariables. We conclude that HIF-1alpha is overexpressed in the vast majority of patients with squamous cell cancer of the oropharynx and that the degree of expression has predictive and prognostic significance in individuals undergoing curative radiation therapy.

Morphological analysis of the postnatally developing marsupial lung: The quokka wallaby.

We investigated the events that take place during the postnatal morphogenesis of the lung of the quokka wallaby, Setonix brachyurus, using the light microscope and both the scanning and transmission electron microscopes. The lung of term, newborn babies (joeys) at 3-days of postnatal life was at late canalicular stage and comprised large airways and tubules separated by thick mesenchymal interstitium. The tubules were lined by a low cuboidal epithelium but had few portions with true gas exchange barrier where capillaries came into close contact with squamous type of epithelium. By the fifth day postpartum, the lung entered the early saccular stage characterised by large air sacs, thinner septa, a better developed double capillary system and conversion of the cuboidal epithelium into a squamous one of type I cells interrupted by groups of cuboidal type II cells with lamellar bodies. Transitory respiratory bronchioles were recognisable toward the end of this stage. Formation of secondary septa started by Day 15, dividing the saccules into several generations of smaller air spaces. There were alternating and concurrent periods of tissue proliferation and air space expansion, followed by septal thinning. Alveolization started from about 125 days postpartum when the first burst of small sized air spaces bounded by septa with a single capillary layer were encountered. By Day 180 the process of alveolization was completed with only occasional septa showing a double capillary system and by Day 210 postnatally, the lung resembled that of an adult. For the first time in a mammal, the canalicular stage was encountered postnatally during lung development.

Intussusceptive arborization contributes to vascular tree formation in the chick chorio-allantoic membrane.

Various reports indicate that the process of intussusceptive microvascular growth (IMG) plays a crucial role in capillary network formation of the chorio-allantoic membrane (CAM). In the present study we demonstrate by methylmethacrylate (Mercox) casting and in vivo time-lapse observations that intussusception, i.e. insertion of transcapillary tissue pillars, is also strongly involved in vascular tree formation, a process we refer to as intussusceptive arborization (IAR). From day 7 to day 14 of incubation, several arterial and venous branching generations arise from the capillary plexus. The process is initiated by pillar formation in rows, which are demarcating future large vessels in the capillary meshwork. In a subsequent step the pillars undergo reshaping to form narrow tissue septa that successively merge, which results in the production of new generations of blood vessels. This is followed by growth and maturation of all vascular components. The process of IAR in the CAM is very active at days 10 and 11 of incubation and takes place in preferentially perfused capillary regions determining "dynamic areas". The process of intussusception may be preceded by endothelial division, but the transcapillary pillar formation itself occurs primarily by rearrangement and attenuation of the endothelial cells without local endothelial cell proliferation. We conclude that after the early sprouting phase, the process of intussusception is the basic mechanism of CAM vascularization. It leads to capillary network growth and expansion (IMG) and, at the same time to feed vessel formation with several branching generations (IAR).

Intussusceptive angiogenesis: its role in embryonic vascular network formation.

Intussusceptive angiogenesis is a novel mode of blood vessel formation and remodeling, which occurs by internal division of the preexisting capillary plexus without sprouting. In this study, the process is demonstrated in developing chicken eye vasculature and in the chorioallantoic membrane by methylmethacrylate (Mercox) casting, transmission electron microscopy, and in vivo observation. In a first step of intussusceptive angiogenesis, the capillary plexus expands by insertion of numerous transcapillary tissue pillars, ie, by intussusceptive microvascular growth. In a subsequent step, a vascular tree arises from the primitive capillary plexus as a result of intussusceptive pillar formation and pillar fusions, a process we termed "intussusceptive arborization." On the basis of the morphological observations, a 4-step model for intussusceptive arborization is proposed, as follows: phase I, numerous circular pillars are formed in rows, thus demarcating future vessels; phase II, formation of narrow tissue septa by pillar reshaping and pillar fusions; phase III, delineation, segregation, growth, and extraction of the new vascular entity by merging of septa; and phase IV, formation of new branching generations by successively repeating the process, complemented by growth and maturation of all components. In contrast to sprouting, intussusceptive angiogenesis does not require intense local endothelial cell proliferation; it is implemented primarily by rearrangement and attenuation of the endothelial cell plates. In summary, transcapillary pillar formation, ie, intussusception, is a central and probably widespread process, which plays a role not only in capillary network growth and expansion (intussusceptive microvascular growth), but also in vascular plexus remodeling and tree formation (intussusceptive arborization).

Do mature pulmonary lobes grow after transplantation into an immature recipient?

BACKGROUND: The use of reduced-size adult lung transplants could help solve the profound pediatric donor lung shortage. However, adequate long-term function of the mature grafts requires growth in proportion to the recipient's development. METHODS: Mature left lower lobes from adult mini-pigs (age: 7 months; mean body weight: 30 kg) were transplanted into 14-week-old piglets (mean body weight: 15 kg). By the end of the 14-week holding period, lungs of the recipients (n = 4) were harvested. After volumetric measurements, the lung morphology was studied using light microscopy, scanning, and transmission electron microscopy. Changes of alveolar airspace volume were determined using a computer aided image analysis system. Comparisons were made to age- and weight-matched controls. RESULTS: Volumetric studies showed no significant differences (p = 0.49) between the specific volume (mL/kg body weight) of lobar grafts and left lower lobes of adult controls. Morphologic studies showed marked structural differences between the grafts and the right native lungs of the recipients, with increased average alveolar diameter of the grafts. On light microscopy and scanning electron microscopy, alveoli appeared dilated and rounded compared to the normal polygonal shape in the controls. The computer generated semi-quantitative data of relative alveolar airspace volume tended to be higher in transplanted lobes. CONCLUSIONS: The mature pulmonary lobar grafts have filled the growing left hemithorax of the developing recipient. Emphysema-like alterations of the grafts were observed without evidence of alveolar growth in the mature lobar transplants. Thus, it can be questioned whether mature pulmonary grafts can guarantee sufficient long-term gas exchange in growing recipients.

Structural considerations. Early intervention in childhood asthma.

Any therapeutic treatment applied to a developing and/or growing organism is complicated by the fact that the treatment window may hit a critical stage of a developing organ. This means that unlike administration in adults, dosage and timing of drug applications are important issues because of their possible damaging effects. In view of the timing of lung developmental phases, it appears that perinatal interferences by diseases, environmental influences or drugs will affect specifically alveolar development and microvascular maturation. Numerous publications report, that the developing lung can be disturbed by a variety of factors, such as temperature, oxygen tension, cigarette smoke, malnutrition, drugs and hormones, in particular glucocorticoids. In well-documented animal experiments perinatal glucocorticoid treatment, even in very low doses, inhibited alveolization. This effect has been analysed in more detail and a hypothesis for its mechanism has been presented. The above effects on lung development may be extremely difficult to assess in human infants by noninvasive techniques. The message, however, remains that potent drugs should be used with great reservation.

Programmed cell death contributes to postnatal lung development.

The rat lung undergoes the phase of maturation of the alveolar septa and of the parenchymal microvascular network mainly during the third postnatal week. Speculating that programmed cell death may contribute to the thinning of the alveolar septa, we searched for the presence of DNA fragmentation in rat lungs between postnatal days 6 and 36 using the TUNEL procedure. The number of positive nuclei was compared at different days. We observed an 8-fold increase of programmed cell death toward the end of the third week as compared to the days before and after this time point. The precise timing of the appearance of the peak depended on the size of the litter. Double-labeling for DNA fragmentation (TUNEL) and for type I and type II epithelial cells (antibodies E11 and MNF-116), as well as morphologic studies at electron microscopic level, revealed that during the peak of programmed cell death mainly fibroblasts and type II epithelial cells were dying. While both dying cell types were TUNEL-positive, nuclear fragments and apoptotic bodies were exclusively observed in the dying fibroblasts. We conclude that programmed cell death is involved in the structural maturation of the lung by reducing the number of fibroblasts and type II epithelial cells in the third postnatal week. We observed that the dying fibroblasts are cleared by neighboring fibroblasts in a later stage of apoptosis, and we hypothesize that type II epithelial cells are cleared by alveolar macrophages in early stages of the programmed cell death process.

Protein cross-linking mediated by tissue transglutaminase correlates with the maturation of extracellular matrices during lung development.

At birth, the mammalian lung is still immature. The alveoli are not yet formed and the interairspace walls contain two capillary layers which are separated by an interstitial core. After alveolarization (first 2 postnatal weeks in rats) the alveolar septa mature: their capillary layers merge, the amount of connective tissue decreases, and the mature lung parenchyma is formed (second and third week). During the first 3 wk of life the role of tissue transglutaminase (tTG) was studied in rat lung by immunostaining of cryostat and paraffin sections, by Northern and Western blotting, and by a quantitative determination of gamma-glutamyl-epsilon-lysine. While enzyme activity and intracellular tTG were already present before term, the enzyme product (gamma-glutamyl-epsilon-lysine-crosslink) and extracellular tTG appeared between postnatal days 10 and 19 in the lung parenchyma. In large blood vessels and large airways, which mature earlier than the parenchyma, both the enzyme product and extracellular tTG had already appeared at the end of the first postnatal week. We conclude that tTG is expressed and externalized into the extracellular matrix of lung shortly before maturation of an organ area. Because tTG covalently and irreversibly crosslinks extracellular matrix proteins, we hypothesize that it may prevent or delay further remodeling of basement membranes and may stabilize other extracellular components, such as microfibrils.