Intralobular pulmonary lymphatic distribution in normal human lung using D2-40 antipodoplanin immunostaining

Effects of different degrees of anthracosis on pleural structure: A preliminary exploratory study

BACKGROUND

Pleural anthracosis (PA) appears as superficial black discoloration or scattered focal black spots on the surface of the pleura. Few studies have investigated the relationship between PA and changes in pleural structure. The aim of this study is to perform a detailed morphometric characterization of pleura in patients with different degrees of PA at both macroscopic and microscopic levels.

METHODS

Preoperative, intraoperative, and postoperative data were collected for all patients. Lung tissue (far away from the tumor) was obtained from patients with pulmonary nodules who required surgical treatment. According to different degrees of PA, the pleura were classified into four degrees. In addition to using grade data, we also calculated the ratio of PA. Slices were stained with Hematoxylin-eosin (HE) and D2-40 to obtain the results of pleural structures.

RESULTS

We prospectively evaluated 48 subjects between March 12, 2024 and August 17, 2024. There was no significant difference in PA levels between people living in urban and rural areas (P = 0.32). However, the proportion of rural population in patients with PA level 3 was 2.6 times that of urban population. Patients who were male demonstrated significantly higher level of PA (P = 0.01). With the increase of the smoking index, the patients with PA levels increased. PA levels increased with age (P = 0.02). With the decrease of the FEV1/FVC, the patients with PA levels also increased (P = 0.03), and the patients with PA ratio also increased (P = 0.007). With the continuous improvement of PA ratio and upgrading of PA level, the pleural thickness continued to decrease(R = -0.75, P < 0.01), the number of subpleural lymphatic vessels (SLVs) increased (P < 0.01), cross-sectional area of SLVs increased (P < 0.01), length of SLVs increased (P < 0.01), and SLVs density increased (P < 0.01).

CONCLUSIONS

The current study demonstrated that the proportion of PA is negatively correlated with pleural thickness and positively correlated with the number of SLVs, cross-sectional area of SLVs, length of SLVs, and SLVs density. This study provides us with new evidence for the subpleural lymphatic metastasis pathways.

Comparative oncological features of centrally and peripherally located small-sized radiologically solid-dominant non-small-cell lung cancer

OBJECTIVES

This study aimed to compare the oncological features of centrally and peripherally located small-sized (≤2 cm), radiologically solid-dominant, cN0 non-small-cell lung cancer (NSCLC).

METHODS

We retrospectively reviewed 1240 patients who underwent lobectomy or segmentectomy for radiologically solid-dominant cN0 NSCLC tumours ≤2 cm in size. Tumours were categorized as centrally (inner two-thirds of the pulmonary parenchyma) or peripherally (outer one-third) located. Clinicopathological characteristics and prognoses were compared between the 2 groups.

RESULTS

Among the 1240 patients, 299 had centrally located and 941 had peripherally located tumours. Centrally located tumours showed a significantly higher proportion of pure solid tumours and pathological lymph node upstaging than peripherally located tumours (P = 0.018 and P = 0.038, respectively). Multivariable logistic regression analysis identified central location as an independent predictor for pN1 (odds ratio, 1.91; 95% confidence interval, 1.09-3.36; P = 0.024), but not for pN2, upstaging. The cumulative incidence of loco-regional and distant recurrences did not significantly differ between the 2 groups (P = 0.455 and P = 0.383, respectively). Overall survival and recurrence-free survival rates were also similar among patients with central and peripheral tumours (P = 0.267 and P = 0.269, respectively).

CONCLUSIONS

Patient prognosis following complete anatomical resection was comparable between centrally and peripherally located radiologically solid-dominant cN0 NSCLC tumours ≤2 cm in size. However, centrally located tumours were associated with a higher risk of pN1 upstaging, highlighting the importance of thorough hilar lymph node dissection in these patients.

Diseases Involving the Lung Peribronchovascular Region: A CT Imaging Pathologic Classification

TOPIC IMPORTANCE

Chest CT imaging holds a major role in the diagnosis of lung diseases, many of which affect the peribronchovascular region. Identification and categorization of peribronchovascular abnormalities on CT imaging can assist in formulating a differential diagnosis and directing further diagnostic evaluation.

REVIEW FINDINGS

The peribronchovascular region of the lung encompasses the pulmonary arteries, airways, and lung interstitium. Understanding disease processes associated with structures of the peribronchovascular region and their appearances on CT imaging aids in prompt diagnosis. This article reviews current knowledge in anatomic and pathologic features of the lung interstitium composed of intercommunicating prelymphatic spaces, lymphatics, collagen bundles, lymph nodes, and bronchial arteries; diffuse lung diseases that present in a peribronchovascular distribution; and an approach to classifying diseases according to patterns of imaging presentations. Lung peribronchovascular diseases can appear on CT imaging as diffuse thickening, fibrosis, masses or masslike consolidation, ground-glass or air space consolidation, and cysts, acknowledging that some diseases may have multiple presentations.

SUMMARY

A category approach to peribronchovascular diseases on CT imaging can be integrated with clinical features as part of a multidisciplinary approach for disease diagnosis.

Three-dimensional visualization of the lymphatic, vascular and neural network in rat lung by confocal microscopy

In order to demonstrate the intricate interconnection of pulmonary lymphatic vessels, blood vessels, and nerve fibers, the rat lung was selected as the target and sliced at the thickness of 100 μm for multiply immunofluorescence staining with lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), alpha smooth muscle actin (α-SMA), phalloidin, cluster of differentiation 31 (CD31), and protein gene product 9.5 (PGP9.5) antibodies. Taking the advantages of the thicker tissue section and confocal microscopy, the labeled pulmonary lymphatic vessels, blood vessels, and nerve fibers were demonstrated in rather longer distance, which was more convenient to reconstruct a three-dimensional (3D) view for analyzing their spatial correlation in detail. It was clear that LYVE-1+ lymphatic vessels were widely distributed in pulmonary lobules and closely to the lobar bronchus. Through 3D reconstruction, it was also demonstrated that LYVE-1+ lymphatic vessels ran parallel to or around the α-SMA+ venules, phalloidin+ arterioles and CD31+ capillaries, with PGP9.5+ nerve fibers traversing alongside or wrapping around them, forming a lymphatic, vascular and neural network in the lung. By this study, we provide a detailed histological view to highlight the spatial correlation of pulmonary lymphatic, vascular and neural network, which may help us for insight into the functional role of this network under the physiological and pathological conditions.

Subpleural sparing: Clinical, physiological, and radiological implications

The term "subpleural sparing" refers to computed tomography (CT) images that indicate that there is limited disease/infiltrate in the immediate subpleural location. This observation is often associated with nonspecific interstitial pneumonitis and is a characteristic that distinguishes this pathology from usual interstitial pneumonitis (idiopathic pulmonary fibrosis). Subpleural sparing can also occur in acute respiratory disorders, including pulmonary contusion in children, acute lung disease associated with electronic cigarettes (vaping), and aspiration of exogenous lipids. Potential explanations for this observation include nonuniform distribution of lung injury/inflammation, nonuniform clearing/resolution of injury, and variations in CT image acquisition and presentation. The subpleural region contains lymphatic structures on the interior surface of the visceral pleura and in interlobular septa. The density of subpleural lymphatics decreases in more interior zones of the lung that largely contain alveolar-capillary units. These lymphatics transfer fluid and other inflammatory mediators from the peripheral lung into central lymphatics and veins. Consequently, the density and distribution of lymphatics could explain preferential clearing of the subpleural regions during acute injury. The acquisition of CT images also depends on the configuration of detectors, slice thickness, and the energy of the electron beam. Clinicians should carefully consider the disease process, lymphatic function and other clearance mechanisms, and the vagaries in CT image acquisition when they evaluate patients with subpleural sparing.

Acute Respiratory Distress Syndrome: Focus on Viral Origin and Role of Pulmonary Lymphatics

Acute respiratory distress syndrome (ARDS) is a serious affection of the lung caused by a variety of pathologies. Great interest is currently focused on ARDS induced by viruses (pandemic influenza and corona viruses). The review describes pulmonary changes in ARDS and specific effects of the pandemic viruses in ARDS, and summarizes treatment options. Because the known pathogenic mechanisms cannot explain all aspects of the syndrome, the contribution of pulmonary lymphatics to the pathology is discussed. Organization and function of lymphatics in a healthy lung and in resorption of pulmonary edema are described. A future clinical trial may provide more insight into the role of hyaluronan in ARDS but the development of promising pharmacological treatments is unlikely because drugs play no important role in lymphedema therapy.

Lymphatic Endothelial Cell Defects in Congenital Cardiac Patients With Postoperative Chylothorax

Objectives

Chylothorax following cardiac surgery for congenital cardiac anomalies is a complication associated with severe morbidities and mortality. We hypothesize that there are intrinsic defects in the lymphatics of congenital cardiac patients.

Methods

Postsurgical chylothorax lymphatic endothelial cells (pcLECs) (n = 10) were isolated from the chylous fluid from congenital cardiac defect patients, and characterized by fluorescent-activated cell sorting, immunofluorescent staining, and quantitative RT-PCR. Results were compared to normal human dermal lymphatic endothelial cells (HdLECs). pcLECs (n = 3) and HdLECs were xenografted into immunocompromised mice. Implants and postoperative chylothorax patient's pulmonary tissues were characterized by immunostaining for lymphatic endothelial proteins.

Results

pcLECs expressed endothelial markers VECADHERIN, CD31, VEGFR2, lymphatic endothelial markers PROX1, podoplanin, VEGFR3, and progenitor endothelial markers CD90 and CD146. However, pcLECs had key differences relative to HdLECs, including altered expression and mislocalization of junctional proteins (VECADHERIN and CD31), and essential endothelial proteins, VEGFR2, VEGFR3, and PROX1. When xenografted in mice, pcLECs formed dilated lymphatic channels with poor cell-cell association. Similar to congenital lymphatic anomalies, the pulmonary lymphatics were dilated in a patient who developed postoperative chylothorax after cardiac surgery.

Conclusions

Recent studies have shown that some postoperative chylothoraces in congenital cardiac anomalies are associated with anatomical lymphatic defects. We found that pcLECs have defects in expression and localization of proteins necessary to maintain lymphatic specification and function. This pcLEC phenotype is similar to that observed in lymphatic endothelial cells from congenital lymphatic anomalies. Co-existence of lymphatic anomalies should be considered as a feature of congenital cardiac anomalies.

"Pulmonary target sign" as a diagnostic feature in chest computed tomography of COVID-19

BACKGROUND

In chest computed tomography (CT) scan, bilateral peripheral multifocal ground-glass opacities, linear opacities, reversed halo sign, and crazy-paving pattern are suggestive for coronavirus disease 2019 (COVID-19) in clinically suspicious cases, but they are not specific for the diagnosis, as other viral pneumonias, like influenza and some viral pneumonia may show similar imaging findings.

AIM

To find a specific imaging feature of the disease would be a welcome guide in diagnosis and management of challenging cases.

METHODS

Chest CT imaging findings of 650 patients admitted to a university Hospital in Tehran, Iran between January 2020 and July 2020 with confirmed COVID-19 infection by RT-PCR were reviewed by two expert radiologists. In addition to common non-specific imaging findings of COVID-19 pneumonia, radiologic characteristics of "pulmonary target sign" (PTS) were assessed. PTS is defined as a circular appearance of non-involved pulmonary parenchyma, which encompass a central hyperdense dot surrounded by ground-glass or alveolar opacities.

RESULTS

PTS were presented in 32 cases (frequency 4.9%). The location of the lesions in 31 of the 32 cases (96.8%) was peripheral, while 4 of the 31 cases had lesions both peripherally and centrally. In 25 cases, the lesions were located near the pleural surface and considered pleural based and half of the lesions (at least one lesion) were in the lower segments and lobes of the lungs. 22 cases had multiple lesions with a > 68% frequency. More than 87% of cases had an adjacent bronchovascular bundle. Ground-glass opacities were detectable adjacent or close to the lesions in 30 cases (93%) and only in 7 cases (21%) was consolidation adjacent to the lesions.

CONCLUSION

Although it is not frequent in COVID-19, familiarity with this feature may help radiologists and physicians distinguish the disease from other viral and non-infectious pneumonias in challenging cases.

Pathophysiology of the Lymphatic System in Patients With Heart Failure: JACC State-of-the-Art Review

The removal of interstitial fluid from the tissues is performed exclusively by the lymphatic system. Tissue edema in congestive heart failure occurs only when the lymphatic system fails or is overrun by fluid leaving the vascular space across the wall of the capillaries into the interstitial space. This process is driven by Starling forces determined by hydrostatic and osmotic pressures and organ-specific capillary permeabilities to proteins of different sizes. In this review, we summarize current knowledge of the generation of lymph in different organs, the mechanics by which lymph is returned to the circulation, and the consequences of the inadequacy of lymph flow. We review recent advances in imaging techniques that have allowed for new research, diagnostic, and therapeutic approaches to the lymphatic system. Finally, we review how efforts to increase lymph flow have demonstrated potential as a viable therapeutic approach for refractory heart failure.

Clinical variability in multifocal lymphangioendotheliomatosis with thrombocytopenia: a review of the literature

Multifocal lymphangioendotheliomatosis with thrombocytopenia (MLT) is a recently recognized disorder characterized by vascular lesions marked by distinct endothelial proliferation. Lesions affect multiple tissues, and MLT can be associated with refractory thrombocytopenia resulting in life-threatening bleeding. Diagnosing MLT may be challenging given its rarity and phenotypic variability. There is no consensus on the optimal management or treatment duration. We report a 4-month-old male who presented with multiple vascular malformations involving the gastrointestinal tract, lung, bones, choroid plexus, and spleen, with minimal cutaneous involvement and no thrombocytopenia. Wedge resection of a pulmonary nodule was strongly positive for lymphatic vessel endothelial hyaluronan receptor 1 favoring MLT despite the lack of thrombocytopenia. The patient's clinical symptoms and vascular lesions improved on sirolimus therapy. We review the literature to highlight the clinical variability of MLT and discuss the diagnostic and therapeutic options for MLT.

Lymphatic Proliferation Ameliorates Pulmonary Fibrosis after Lung Injury

Despite many reports about pulmonary blood vessels in lung fibrosis, the contribution of lymphatics to fibrosis is unknown. We examined the mechanism and consequences of lymphatic remodeling in mice with lung fibrosis after bleomycin injury or telomere dysfunction. Widespread lymphangiogenesis was observed after bleomycin treatment and in fibrotic lungs of prospero homeobox 1-enhanced green fluorescent protein (Prox1-EGFP) transgenic mice with telomere dysfunction. In loss-of-function studies, blocking antibodies revealed that lymphangiogenesis 14 days after bleomycin treatment was dependent on vascular endothelial growth factor (Vegf) receptor 3 signaling, but not on Vegf receptor 2. Vegfc gene and protein expression increased specifically. Extensive extravasated plasma, platelets, and macrophages at sites of lymphatic growth were potential sources of Vegfc. Lymphangiogenesis peaked at 14 to 28 days after bleomycin challenge, was accompanied by doubling of chemokine (C-C motif) ligand 21 in lung lymphatics and tertiary lymphoid organ formation, and then decreased as lung injury resolved by 56 days. In gain-of-function studies, expansion of the lung lymphatic network by transgenic overexpression of Vegfc in club cell secretory protein (CCSP)/VEGF-C mice reduced macrophage accumulation and fibrosis and accelerated recovery after bleomycin treatment. These findings suggest that lymphatics have an overall protective effect in lung injury and fibrosis and fit with a mechanism whereby lung lymphatic network expansion reduces lymph stasis and increases clearance of fluid and cells, including profibrotic macrophages.

Vascular permeability in the fibrotic lung

Idiopathic pulmonary fibrosis (IPF) is thought to result from aberrant tissue repair processes in response to chronic or repetitive lung injury. The origin and nature of the injury, as well as its cellular and molecular targets, are likely heterogeneous, which complicates accurate pre-clinical modelling of the disease and makes therapeutic targeting a challenge. Efforts are underway to identify central pathways in fibrogenesis which may allow targeting of aberrant repair processes regardless of the initial injury stimulus. Dysregulated endothelial permeability and vascular leak have long been studied for their role in acute lung injury and repair. Evidence that these processes are of importance to the pathogenesis of fibrotic lung disease is growing. Endothelial permeability is increased in non-fibrosing lung diseases, but it resolves in a self-limited fashion in conditions such as bacterial pneumonia and acute respiratory distress syndrome. In progressive fibrosing diseases such as IPF, permeability appears to persist, however, and may also predict mortality. In this hypothesis-generating review, we summarise available data on the role of endothelial permeability in IPF and focus on the deleterious consequences of sustained endothelial hyperpermeability in response to and during pulmonary inflammation and fibrosis. We propose that persistent permeability and vascular leak in the lung have the potential to establish and amplify the pro-fibrotic environment. Therapeutic interventions aimed at recognising and "plugging" the leak may therefore be of significant benefit for preventing the transition from lung injury to fibrosis and should be areas for future research.

Aerosol Pirfenidone Pharmacokinetics after Inhaled Delivery in Sheep: a Viable Approach to Treating Idiopathic Pulmonary Fibrosis

PURPOSE

Inhaled delivery of pirfenidone to the lungs of patients with idiopathic pulmonary fibrosis holds promise to eliminate oral-observed side effects while enhancing efficacy. This study aimed to comprehensively describe the pulmonary pharmacokinetics of inhaled aerosol pirfenidone in healthy adult sheep.

METHODS

Pirfenidone concentrations were evaluated in plasma, lung-derived lymph and epithelial lining fluid (ELF) with data subjected to non-compartmental pharmacokinetic analysis.

RESULTS

Compartmental pharmacokinetic evaluation indicated that a 49 mg lung-deposited dose delivered an ELF Cmax of 62 ± 23 mg/L, and plasma Cmax of 3.1 ± 1.7 mg/L. Further analysis revealed that plasma pirfenidone reached Tmax faster and at higher concentrations than in lymph. These results suggested inhaled pirfenidone was cleared from the alveolar interstitium via blood faster than the drug could equilibrate between the lung interstitial fluid and lung lymphatics. However, the data also suggested that a 'reservoir' of pirfenidone feeds into lung lymph at later time points (after it has largely been cleared from plasma), prolonging lung lymphatic exposure.

CONCLUSIONS

This study indicates inhaled pirfenidone efficiently deposits in ELF and is cleared from the lungs by initial absorption into plasma, followed by later equilibrium with lung interstitial and lymph fluid.

Airway Macrophage and Dendritic Cell Subsets in the Resting Human Lung

Dendritic cells (DCs) and macrophages (MΦs) are antigen-presenting phagocytic cells found in many peripheral tissues of the human body, including the blood, lymph nodes, skin, and lung. They are vital to maintaining steady-state respiration in the human lung based on their ability to clear airways while also directing tolerogenic or inflammatory responses based on specific stimuli. Over the past three decades, studies have determined that there are multiple subsets of these two general cell types that exist in the airways and interstitium. Identifying these numerous subsets has proven challenging, especially with the unique microenvironments present in the lung. Cells found in the vasculature are not the same subsets found in the skin or the lung, as demonstrated by surface marker expression. By transcriptional profiling, these subsets show similarities but also major differences. Primary human lung cells and/ or tissues are difficult to acquire, particularly in a healthy condition. Additionally, surface marker screening and transcriptional profiling are continually identifying new DC and MΦ subsets. While the overall field is moving forward, we emphasize that more attention needs to focus on replicating the steady-state microenvironment of the lung to reveal the physiological functions of these subsets.

Correlative 3D Imaging and Microfluidic Modelling of Human Pulmonary Lymphatics using Immunohistochemistry and High-resolution μCT

Lung lymphatics maintain fluid homoeostasis by providing a drainage system that returns fluid, cells and metabolites to the circulatory system. The 3D structure of the human pulmonary lymphatic network is essential to lung function, but it is poorly characterised. Image-based 3D mathematical modelling of pulmonary lymphatic microfluidics has been limited by the lack of accurate and representative image geometries. This is due to the microstructural similarity of the lymphatics to the blood vessel network, the lack of lymphatic-specific biomarkers, the technical limitations associated with image resolution in 3D, and sectioning artefacts present in 2D techniques. We present a method that combines lymphatic specific (D240 antibody) immunohistochemistry (IHC), optimised high-resolution X-ray microfocus computed tomography (μCT) and finite-element mathematical modelling to assess the function of human peripheral lung tissue. The initial results identify lymphatic heterogeneity within and between lung tissue. Lymphatic vessel volume fraction and fractal dimension significantly decreases away from the lung pleural surface (p < 0.001, n = 25 and p < 0.01, n = 20, respectively). Microfluidic modelling successfully shows that in lung tissue the fluid derived from the blood vessels drains through the interstitium into the lymphatic vessel network and this drainage is different in the subpleural space compared to the intralobular space. When comparing lung tissue from health and disease, human pulmonary lymphatics were significantly different across five morphometric measures used in this study (p ≤ 0.0001). This proof of principle study establishes a new engineering technology and workflow for further studies of pulmonary lymphatics and demonstrates for the first time the combination of correlative μCT and IHC to enable 3D mathematical modelling of human lung microfluidics at micrometre resolution.

Pulmonary lymphatic vessel morphology: a review

Our understanding of lymphatic vessels has been advanced by the recent identification of relatively specific lymphatic endothelium markers, including Prox-1, VEGFR3, podoplanin and LYVE-1. The use of lymphatic markers has led to the observation that, contrary to previous assumptions, human lymphatic vessels extend deep inside the pulmonary lobule, either in association with bronchioles, intralobular arterioles or small pulmonary veins. Pulmonary lymphatic vessels may thus be classified into pleural, interlobular (in interlobular septa) and intralobular. Intralobular lymphatic vessels may be further subdivided in: bronchovascular (associated with a bronchovascular bundle), perivascular (associated with a blood vessel), peribronchiolar (associated with a bronchiole), and interalveolar (in interalveolar septa). Most of the intralobular lymphatic vessels are in close contact with a blood vessel, either alone or within a bronchovascular bundle. A minority is associated with a bronchiole, and small lymphatics are occasionally present even in interalveolar septa, seemingly independent of blood vessels or bronchioles. The lymphatics of the interlobular septa often contain valves, are usually associated with the pulmonary veins, and connect with the pleural lymphatics. The large lymphatics associated with bronchovascular bundles have similar characteristics to pleural and interlobular lymphatics and may be considered conducting vessels. The numerous small perivascular lymphatics and the few peribronchiolar ones that are found inside the lobule are probably the absorbing compartment of the lung responsible for maintaining the alveolar interstitium relatively dry in order to provide a minimal thickness of the air-blood barrier and thus optimize gas diffusion. These lymphatic populations could be differentially involved in the pathogenesis of diseases preferentially involving distinct lung compartments.

Effect of miR‑146a‑5p on tumor growth in NSCLC using chick chorioallantoic membrane assay and bioinformatics investigation

Our previous study demonstrated that the expression of miR-146a-5p was downregulated in non-small cell lung cancer (NSCLC) tissue, which affected the progression and prognosis of patients with NSCLC. Thus, the present study was conducted to investigate the functional mechanism of miR-146a-5p in tumorigenesis and angiogenesis in NSCLC. Following the construction of a H460 NSCLC cell line in which miR-146a-5p was overexpressed via lentivirus transduction, the NSCLC chick embryo chorioallantoic membrane (CAM) model was established by transplanting miR-146a-5p-overexpressing NSCLC cells into the CAM. Then, the size of the neoplasms within the CAM was measured, the vessel ratio was calculated, and the cellular morphology, metastasis and inflammation of tumor cell was observed using hematoxylin and eosin staining. The target genes of miR-146a-5p were predicted by 12 online software programs; these genes were then subjected to Gene Ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway annotations using the Database for Annotation, Visualization and Integrated Discovery 6.7 as well as constructed into a protein interaction network using protein-protein interaction from Search Tool for the Retrieval of Interacting Genes/Proteins. The xenograft tumor size and angiogenesis conditions of the miR-146a-5p-overexpressing group (volume 6.340±0.066 mm³, vessel ratio 9.326±0.083) was obviously restricted (P<0.001) when compared with the low expression group (volume 30.13±0.06 mm³, vessel ratio 16.94±0.11). In addition, marked necrosis along with inflammatory cell infiltration was observed with the HE-stained slices from the miR-146a-5p low expression group. Regarding the results of the target gene prediction, cancer and toll-like receptor signaling were the two most significant pathways represented among the target genes, while JUN, EGFR and RAC1 were the most relevant proteins among the selected potential targets of miR-146a-5p. In a CAM xenograft tumor model, overexpression of miR-146a-5p inhibited the tumorigenesis and angiogenesis of an NSCLC cell line. miR-146a-5p may act as a tumor suppressor gene in NSCLC and have moderate prognostic value in lung cancer.

Lymphatic Changes in Respiratory Diseases: More than Just Remodeling of the Lung?

Advances in our ability to identify lymphatic endothelial cells and differentiate them from blood endothelial cells have led to important progress in the study of lymphatic biology. Over the past decade, preclinical and clinical studies have shown that there are changes to the lymphatic vasculature in nearly all lung diseases. Efforts to understand the contribution of lymphatics and their growth factors to disease initiation, progression, and resolution have led to seminal findings establishing critical roles for lymphatics in lung biology spanning from the first breath after birth to asthma, tuberculosis, and lung transplantation. However, in other diseases, it remains unclear if lymphatics are part of the overall lung remodeling process or real contributors to disease pathogenesis. The goal of this Translational Review is to highlight some of the advances in our understanding of the role(s) of lymphatics in lung disease and shed light on the critical needs and unanswered questions that might lead to novel translational applications.

Airway eosinophil migration into lymph nodes in mice depends on leukotriene C4

BACKGROUND

We previously demonstrated in mice that airway eosinophils traffic from the airway lumen into lung-draining paratracheal lymph nodes. However, mechanisms whereby eosinophils traverse from the lungs and home to paratracheal lymph nodes remain unclear. We investigated roles of cysteinyl leukotrienes in mediating eosinophil trafficking from lungs to paratracheal lymph nodes.

METHODS

The expression of CCR7 was determined by flow cytometry. Transwell assays were used to test chemotactic responses of leukotriene C₄ synthase-deficient and control airway eosinophils to the chemokine CCL19 ex vivo. Eosinophils from the spleens of IL-5 transgenic mice, fluorescently labeled ex vivo, were intratracheally injected into ovalbumin-sensitized and ovalbumin aerosol-challenged leukotriene C₄ synthase-deficient and control mice. Eosinophils were identified by microscopy and flow cytometry in the lungs and paratracheal lymph nodes.

RESULTS

Mouse eosinophils expressed CCR7, the receptor for CCL19, and responded chemotactically to CCL19. Leukotriene C₄ synthase-deficient eosinophils exhibited impaired chemotaxis to CCL19 that was restored by exogenous leukotriene C₄ . The migration of intratracheally injected eosinophils into paratracheal lymph nodes from distal alveolar lung was diminished in leukotriene C₄ synthase-deficient mice compared with wild-type mice, with increased retention of eosinophils in the lungs of leukotriene C₄ synthase-deficient mice. Exogenous administration of leukotriene C₄ restored trafficking of eosinophils to paratracheal lymph nodes in leukotriene C₄ synthase-deficient mice.

CONCLUSIONS

Our findings that cysteinyl leukotrienes are involved in regulating airway and lung eosinophil migration into paratracheal lymph nodes identify previously unrecognized roles for the cysteinyl leukotrienes in regulating the pulmonary trafficking of eosinophils in experimental allergic asthma.

Exploiting lymphatic vessels for immunomodulation: Rationale, opportunities, and challenges

Lymphatic vessels are the primary route of communication from peripheral tissues to the immune system; as such, they represent an important component of local immunity. In addition to their transport functions, new immunomodulatory roles for lymphatic vessels and lymphatic endothelial cells have come to light in recent years, demonstrating that lymphatic vessels help shape immune responses in a variety of ways: promoting tolerance to self-antigens, archiving antigen for later presentation, dampening effector immune responses, and resolving inflammation, among others. In addition to these new biological insights, the growing field of immunoengineering has begun to explore therapeutic approaches to utilize or exploit the lymphatic system for immunotherapy.

Bacillus anthracis spore movement does not require a carrier cell and is not affected by lethal toxin in human lung models

The lung is the entry site for Bacillus anthracis in inhalation anthrax, the most deadly form of the disease. Spores escape from the alveolus to regional lymph nodes, germinate and enter the circulatory system to cause disease. The roles of carrier cells and the effects of B. anthracis toxins in this process are unclear. We used a human lung organ culture model to measure spore uptake by antigen presenting cells (APC) and alveolar epithelial cells (AEC), spore partitioning between these cells, and the effects of B. anthracis lethal toxin and protective antigen. We repeated the study in a human A549 alveolar epithelial cell model. Most spores remained unassociated with cells, but the majority of cell-associated spores were in AEC, not in APC. Spore movement was not dependent on internalization, although the location of internalized spores changed in both cell types. Spores also internalized in a non-uniform pattern. Toxins affected neither transit of the spores nor the partitioning of spores into AEC and APC. Our results support a model of spore escape from the alveolus that involves spore clustering with transient passage through intact AEC. However, subsequent transport of spores by APC from the lung to the lymph nodes may occur.

Development of Lymphatic Capillary Network Along the Alveolar Walls of Autopsied Human Lungs with Pneumonia

BACKGROUND

Limited information is available regarding the lymphatic vasculature during pneumonia.

OBJECTIVE

To characterize lymphatic vasculatures in autopsied cadavers with pneumonia.

METHODS

Paraffin-embedded lung tissues obtained from 20 autopsied cadavers with complicated pneumonia and 10 control cadavers without pneumonia were used for immunohistochemical analyses using primary antibodies against podoplanin, vascular endothelial growth factor receptor-3 (VEGFR-3), CD34, vascular endothelial growth factor (VEGF)-C, VEGF-D, CD73, and CD163.

RESULTS

There was no difference in the vascular density of podoplanin⁺ usual lymphatics between the individuals with and without pneumonia. In half of the cadavers with pneumonia, however, a network of podoplanin⁺ cells lying together in a side-by-side bead-like arrangement appeared along the alveolar septa; however, this was absent in the control cadavers. The podoplanin⁺ cells in the network were characterized by a weaker expression of podoplanin, relative to usual lymphatics, and the occasional presence of ductal structures. Although podoplanin⁺ cells were not coexpressed with VEGFR-3, a part of the network was connected to CD73⁺ afferent lymphatics. The network showed an intertwined relationship with CD34⁺ capillaries, suggesting that the network represents lymphatic capillaries. The number of CD163⁺ macrophages was significantly increased in individuals with the network than those without the network, while a significant decrease in neutrophils was observed. VEGF-C expressed in CD163⁺ macrophages and type II epithelial cells was observed in the cadavers with the network.

CONCLUSION

The development of lymphatic capillary networks along the alveolar septa rather than the usual lymphangiogenesis was noted in autopsied individuals with pneumonia.

Lymphangiogenesis and Lesion Heterogeneity in Interstitial Lung Diseases

The lymphatic system has several physiological roles, including fluid homeostasis and the activation of adaptive immunity by fluid drainage and cell transport. Lymphangiogenesis occurs in adult tissues during various pathologic conditions. In addition, lymphangiogenesis is closely linked to capillary angiogenesis, and the balanced interrelationship between capillary angiogenesis and lymphangiogenesis is essential for maintaining homeostasis in tissues. Recently, an increasing body of information regarding the biology of lymphatic endothelial cells has allowed us to immunohistochemically characterize lymphangiogenesis in several lung diseases. Particular interest has been given to the interstitial lung diseases. Idiopathic interstitial pneumonias (IIPs) are characterized by heterogeneity in pathologic changes and lesions, as typified by idiopathic pulmonary fibrosis/usual interstitial pneumonia. In IIPs, lymphangiogenesis is likely to have different types of localized functions within each disorder, corresponding to the heterogeneity of lesions in terms of inflammation and fibrosis. These functions include inhibitory absorption of interstitial fluid and small molecules and maturation of fibrosis by excessive interstitial fluid drainage, caused by an unbalanced relationship between capillary angiogenesis and lymphangiogenesis and trafficking of antigen-presenting cells and induction of fibrogenesis via CCL21 and CCR7 signals. Better understanding for regional functions of lymphangiogenesis might provide new treatment strategies tailored to lesion heterogeneity in these complicated diseases.

Isolation and Characterization of Human Lung Lymphatic Endothelial Cells

Characterization of lymphatic endothelial cells from the respiratory system may be crucial to investigate the role of the lymphatic system in the normal and diseased lung. We describe a simple and inexpensive method to harvest, isolate, and expand lymphatic endothelial cells from the human lung (HL-LECs). Fifty-five samples of healthy lung selected from patients undergoing lobectomy were studied. A two-step purification tool, based on paramagnetic sorting with monoclonal antibodies to CD31 and Podoplanin, was employed to select a pure population of HL-LECs. The purity of HL-LECs was assessed by morphologic criteria, immunocytochemistry, flow cytometry, and functional assays. Interestingly, these cells retain in vitro several receptor tyrosine kinases (RTKs) implicated in cell survival and proliferation. HL-LECs represent a clinically relevant cellular substrate to study lymphatic biology, lymphoangiogenesis, interaction with microbial agents, wound healing, and anticancer therapy.

Pulmonary fibrosis in sarcoidosis. Clinical features and outcomes

Sarcoidosis is a systemic inflammatory disease with a predilection for the respiratory system. Although most patients enter remission and have good long-term outcomes, up to 20% develop fibrotic lung disease, whereby granulomatous inflammation evolves to pulmonary fibrosis. There are several radiographic patterns of pulmonary fibrosis in sarcoidosis; bronchial distortion is common, and other patterns, including honeycombing, are variably observed. The development of pulmonary fibrosis is associated with significant morbidity and can be fatal. Dyspnea, cough, and hypoxemia are frequent clinical manifestations. Pulmonary function testing often demonstrates restriction from parenchymal involvement, although airflow obstruction from airway-centric fibrosis is also recognized. Complications of fibrotic pulmonary sarcoidosis include pulmonary hypertension from capillary obliteration and chronic aspergillus disease, with hemoptysis a common and potentially life-threatening manifestation. Immunosuppression is not always indicated in end-stage sarcoidosis. Lung transplantation should be considered for patients with severe fibrotic pulmonary sarcoidosis, as mortality is high in these patients.

[Lymphatic extension and lymphangiogenesis in non-small cell lung cancer]

Lymph node metastasis is a major adverse prognostic factor of malignant tumors, including non-small cell lung carcinoma (NSCLC). However the characterization of tumor associated lymphatic vessels and lymphangiogenic mediators in NSCLC are recent and their prognostic role is debated. Lymphatic vascular invasion (LVI) appears like a robust adverse prognostic factor when reported in NSCLC. This parameter should be better standardized and could be of use in adjuvant therapy indications. Moreover, anti-lymphangiogenesis therapies are currently under investigation and may become part of the anti-cancer strategy.

Altered pulmonary lymphatic development in infants with chronic lung disease

Pulmonary lymphatic development in chronic lung disease (CLD) has not been investigated, and anatomy of lymphatics in human infant lungs is not well defined. Hypothesis. Pulmonary lymphatic hypoplasia is present in CLD. Method. Autopsy lung tissues of eighteen subjects gestational ages 22 to 40 weeks with and without history of respiratory morbidity were stained with monoclonal antipodoplanin and reviewed under light microscopy. Percentage of parenchyma podoplanin stained at the acinar level was determined using computerized image analysis; 9 CLD and 4 control subjects gestational ages 27 to 36 weeks were suitable for the analysis. Results. Distinct, lymphatic-specific staining with respect to other vascular structures was appreciated in all gestations. Infants with and without respiratory morbidity had comparable lymphatic distribution which extended to the alveolar ductal level. Podoplanin staining per parenchyma was increased and statistically significant in the CLD group versus controls at the alveolar ductal level (0.06% ± 0.02% versus 0.04% ± 0.01%, 95% CI −0.04% to −0.002%, P < 0.03). Conclusion. Contrary to our hypothesis, the findings show that there is an increase in alveolar lymphatics in CLD. It is suggested that the findings, by expanding current knowledge of CLD pathology, may offer insight into the development of more effective therapies to tackle CLD.

[Lymphangioma and lymphangiectasia]

Primary thoracic lymphatic diseases are both infrequent and probably under diagnosed. The two major forms are lymphangiomas and lymphangiectasias. Lymphangiomas are focal proliferation of well-differentiated lymphatic vessels. Childhood lymphangiomas may follow embryologic disorders. Adult lymphangiomas are more likely secondary to lymphatic obstruction. When associated with typical CT and MRI features, their surgical resection is not mandatory, whereas in case of diagnostic difficulties or related complications, surgical resection is the rule. Lymphangiectasias are congenital or acquired pathologic lymphatic dilatation from pleura and interlobular septa without any proliferation. These diseases can be limited to one pulmonary lobe, or can involve the whole lymphatic network. In case of communication between the lymphangiectasias and the thoracic duct, symptoms may include chyloptysis, chylothorax, and chylopericardium. Lymphangio MRI allows visualisation of the lymphangiectasis and thoracic duct. Surgical treatment may be required in case of resistance to medical treatment.

Pulmonary metastatic nodules of uterine low-grade endometrial stromal sarcoma: histopathological and immunohistochemical analysis of 10 cases

AIMS

To identify histopathological and immunohistochemical findings that aid diagnosis of metastatic endometrial stromal sarcoma (ESS) in small biopsy specimens of the lung.

METHODS AND RESULTS

We reviewed the histology of 46 lung nodules from 10 cases of pulmonary metastatic ESS. Biopsy sections were analysed by immunohistochemistry to highlight blood and lymphatic vasculature, and for expression of CD10 and oestrogen receptor (ER). Various histological changes were identified that could mislead in making a diagnosis on small biopsy samples: haemangiopericytomatous blood vessels (39%), absence of characteristic spiral arteriole-like vasculature (26%), intratumoral cysts formed by dilatation of airways (22%) or intratumoral myxoid change (11%), prominent interstitial collagen deposits (48%), foam cell infiltration (4%) and smooth muscle differentiation (2%). Peribronchial/peribronchiolar distribution of tumour cells with juxtaepithelial growth was a frequent feature, observed in 59% of nodules. In two very small nodules the lesion was barely recognizable histologically; tumour cells were detected only by expression of ER and CD10.

CONCLUSIONS

Combined staining for ER and CD10 can be helpful in avoiding an erroneous diagnosis. As lymphatics are not normally present in the juxtaepithelial bronchial/bronchiolar wall, juxtaepithelial tumour growth beneath the bronchial epithelium in early metastatic lesions indicates a haematogenous metastastic route through the bronchial artery.

Increased number and altered phenotype of lymphatic vessels in peripheral lung compartments of patients with COPD

BACKGROUND

De novo lymphatic vessel formation has recently been observed in lungs of patients with moderate chronic obstructive pulmonary disease (COPD). However, the distribution of lymphatic vessel changes among the anatomical compartments of diseased lungs is unknown. Furthermore, information regarding the nature of lymphatic vessel alterations across different stages of COPD is missing. This study performs a detailed morphometric characterization of lymphatic vessels in major peripheral lung compartments of patients with different severities of COPD and investigates the lymphatic expression of molecules involved in immune cell trafficking.

METHODS

Peripheral lung resection samples obtained from patients with mild (GOLD stage I), moderate-severe (GOLD stage II-III), and very severe (GOLD stage IV) COPD were investigated for podoplanin-immunopositive lymphatic vessels in distinct peripheral lung compartments: bronchioles, pulmonary blood vessels and alveolar walls. Control subjects with normal lung function were divided into never smokers and smokers. Lymphatics were analysed by multiple morphological parameters, as well as for their expression of CCL21 and the chemokine scavenger receptor D6.

RESULTS

The number of lymphatics increased by 133% in the alveolar parenchyma in patients with advanced COPD compared with never-smoking controls (p < 0.05). In patchy fibrotic lesions the number of alveolar lymphatics increased 20-fold from non-fibrotic parenchyma in the same COPD patients. The absolute number of lymphatics per bronchiole and artery was increased in advanced COPD, but numbers were not different after normalization to tissue area. Increased numbers of CCL21- and D6-positive lymphatics were observed in the alveolar parenchyma in advanced COPD compared with controls (p < 0.01). Lymphatic vessels also displayed increased mean levels of immunoreactivity for CCL21 in the wall of bronchioles (p < 0.01) and bronchiole-associated arteries (p < 0.05), as well as the alveolar parenchyma (p < 0.001) in patients with advanced COPD compared with never-smoking controls. A similar increase in lymphatic D6 immunoreactivity was observed in bronchioles (p < 0.05) and alveolar parenchyma (p < 0.01).

CONCLUSIONS

This study shows that severe stages of COPD is associated with increased numbers of alveolar lymphatic vessels and a change in lymphatic vessel phenotype in major peripheral lung compartments. This novel histopathological feature is suggested to have important implications for distal lung immune cell traffic in advanced COPD.

[Lymphatics in non-tumoral pulmonary diseases. Review]

Whereas lymphatics in pulmonary non-tumoral diseases have been less studied than blood microcirculation, they clearly play a significant role. This review is a short update on lymphatics in various non-tumoral pulmonary diseases, from asthma to interstitial pneumonitis, excluding lymphangioleiomyomatosis. A lymphatic remodelling has been evidenced in asthma as well as in acute or chronic (UIP as NSIP) interstitial lung diseases. Such a remodelling can be explained as a side effect of local changes in fluidics but could also be an active player in the fibrosing process. Moreover the association of juxta-alveloar lymphatics and granulomas provides new insights in the emergence of these lesions in pulmonary sarcoidosis.

Morphometry analysis of lymphatics in pulmonary adenocarcinomas with a lepidic growth pattern

Lymph vessels play an important role in tumor progression. Pulmonary adenocarcinomas, accounting for half of non-small-cell lung carcinomas, compose a spectrum of histological types, exclusively or without a lepidic growth pattern (LGP) along preserved interalveolar septa. In that context, this study was designed to investigate the lymphatic vascular pattern associated with LGP and the concomitant invasive component of pulmonary adenocarcinomas. Using the D2-40 monoclonal antibody as a marker of lymphatic endothelial cells, the lymphatic vessel density (LVD) and vessel-area fraction (LVAF) were morphometrically analyzed in four adenocarcinomas in situ (AIS) and the LGP of eight invasive adenocarcinomas (LPIA), and compared with their invasive pattern (IPIA). LVD in AIS (2.1 ± 0.7 mm(-2)) and LPIA (2.4 ± 1 mm(-2)) were significantly lower than that in IPIA (14.9 ± 13.6 mm(-2)) (p=0.001). Moreover, the lymphatic vascular pattern in LGP was similar to that of normal lung, with isolated small lymphatic vessels within the interalveolar septa. Our results showing the scarcity of lymphatics in LGP suggest an absence of septal lymphangiogenesis associated with the LGP pattern in lung adenocarcinomas, which could explain, at least partially, the better prognosis observed in tumors with exclusive or predominant lepidic spread compared with other subtypes.

[Anatomy, micro-anatomy and physiology of the lymphatics of the lungs and chest wall]

The thoracic lymphatic vessels are pulsating channels which drain actively the fluid of lung parenchyma interstitium and pleural cavities. Their unidirectional valves that avoid reflux of contents, direct the current of fluid to the connection of thoracic duct to subclavian vein or to the thoracic duct itself by these pulsations. The ascending parietal and visceral currents have anastomoses between them. The parietal currents (internal thoracic anteriorly, external axillaries in lateral and paravertebral in posterior) drain the lymph of thoracic wall. Pleural cavities and the visceral currents, drain that of lungs and mediastinal organs. The thoracic duct goes upward in the posterior mediastinum and usually connects to the venous confluent of the left subclavian vein. It receives a part of thoracic lymph and also drains the lymph of trunk and inferior limbs. About a half or two thirds of thoracic duct lymph is originated from liver and intestines. The intestines have the lymph of digestion with the fatty elements, i.e., the chyle.

An important role of blood and lymphatic vessels in inflammation and allergy

Angiogenesis and lymphangiogenesis, the growth of new vessels from preexisting ones, have received increasing interest due to their role in tumor growth and metastatic spread. However, vascular remodeling, associated with vascular hyperpermeability, is also a key feature of many chronic inflammatory diseases including asthma, atopic dermatitis, psoriasis, and rheumatoid arthritis. The major drivers of angiogenesis and lymphangiogenesis are vascular endothelial growth factor- (VEGF-)A and VEGF-C, activating specific VEGF receptors on the lymphatic and blood vascular endothelium. Recent experimental studies found potent anti-inflammatory responses after targeted inhibition of activated blood vessels in models of chronic inflammatory diseases. Importantly, our recent results indicate that specific activation of lymphatic vessels reduces both acute and chronic skin inflammation. Thus, antiangiogenic and prolymphangiogenic therapies might represent a new approach to treat chronic inflammatory disorders, including those due to chronic allergic inflammation.

Lymphatics in lymphangioleiomyomatosis and idiopathic pulmonary fibrosis

The primary function of the lymphatic system is absorbing and transporting macromolecules and immune cells to the general circulation, thereby regulating fluid, nutrient absorption and immune cell trafficking. Lymphangiogenesis plays an important role in tissue inflammation and tumour cell dissemination. Lymphatic involvement is seen in lymphangioleiomyomatosis (LAM) and idiopathic pulmonary fibrosis (IPF). LAM, a disease primarily affecting females, involves the lung (cystic destruction), kidney (angiomyolipoma) and axial lymphatics (adenopathy and lymphangioleiomyoma). LAM occurs sporadically or in association with tuberous sclerosis complex (TSC). Cystic lung destruction results from proliferation of LAM cells, which are abnormal smooth muscle-like cells with mutations in the TSC1 or TSC2 gene. Lymphatic abnormalities arise from infiltration of LAM cells into the lymphatic wall, leading to damage or obstruction of lymphatic vessels. Benign appearing LAM cells possess metastatic properties and are found in the blood and other body fluids. IPF is a progressive lung disease resulting from fibroblast proliferation and collagen deposition. Lymphangiogenesis is associated with pulmonary destruction and disease severity. A macrophage subset isolated from IPF bronchoalveolar lavage fluid (BALF) express lymphatic endothelial cell markers in vitro, in contrast to the same macrophage subset from normal BALF. Herein, we review lymphatic involvement in LAM and IPF.

Differential mouse pulmonary dose and time course responses to titanium dioxide nanospheres and nanobelts

Three anatase titanium dioxide (TiO(2)) nanoparticles (NPs) were prepared; nanospheres (NSs), short nanobelts (NB1), and long nanobelts (NB2). These NPs were used to investigate the effect of NP shape and length on lung toxicity. Mice were exposed (0-30 µg per mouse) by pharyngeal aspiration and pulmonary toxicity was assessed over a 112-day time course. Whole lung lavage data indicated that NB1- and NB2-exposed mice, but not NS-exposed mice, had significant dose- and time-dependent pulmonary inflammation and damage. Histopathological analyses at 112 days postexposure determined no interstitial fibrosis in any NS-exposed mice, an increased incidence in 30 µg NB1-exposed mice, and significant interstitial fibrosis in 30 µg NB2-exposed mice. At 112 days postexposure, lung burden of NS was decreased by 96.4% and NB2 by 80.5% from initial deposition levels. At 112 days postexposure, enhanced dark field microscopy determined that alveolar macro- phages were the dominant deposition site, but a fraction of NB1 and NB2 was observed in the alveolar interstitial spaces. For the 30 µg exposure groups at 112 days postexposure, confocal micro- scopy and immunofluorescent staining demonstrated that retained NB2 but not NS were present in the interstitium subjacent to the terminal bronchiole near the normal location of the smallest lymphatic capillaries in the lung. These lymphatic capillaries play a critical role in particle clearance, and the accumulation of NB2, but not NS, suggests possible impaired lymphatic clearance by the high aspect ratio particles. In summary, our data indicate that TiO(2) NP shape alters pulmonary responses, with severity of responses being ranked as NS < NB1 < NB2.

[Primitive thoracic lymphatic disease in adults]

Primary thoracic lymphatic diseases are both infrequent and probably under diagnosed. Current classification distinguishes lymphangioma (solitary tumor), lymphangiectasies (dilatation), lymphangiomatosis (proliferation) and lymphatic dysplasia syndrome (dysplasia). Classifications' efforts and radiologic progress may lead to an improvement in the management of these patients.

Morphometric analysis of intralobular, interlobular and pleural lymphatics in normal human lung

In spite of their presumed relevance in maintaining interalveolar septal fluid homeostasis, the knowledge of the anatomy of human lung lymphatics is still incomplete. The recent discovery of reliable markers specific for lymphatic endothelium has led to the observation that, contrary to previous assumptions, human lymphatic vessels extend deep inside the pulmonary lobule in association with bronchioles, intralobular arterioles or small pulmonary veins. The aim of this study was to provide a morphometric characterization of lymphatic vessels in the periphery of the human lung. Human lung sections were immunolabelled with the lymphatic marker D2-40, followed by blood vessel staining with von Willebrand Factor. Lymphatic vessels were classified into: intralobular (including those associated with bronchovascular bundles, perivascular, peribronchiolar and interalveolar), pleural (in the connective tissue of the visceral pleura), and interlobular (in interlobular septa). The percentage area occupied by the lymphatic lumen was much greater in the interlobular septa and in the subpleural space than in the lobule. Most of the intralobular lymphatic vessels were in close contact with a blood vessel, either alone or within a bronchovascular bundle, whereas 7% were associated with a bronchiole and < 1% were not connected to blood vessels or bronchioles (interalveolar). Intralobular lymphatic size progressively decreased from bronchovascular through to peribronchiolar, perivascular and interalveolar lymphatics. Lymphatics associated with bronchovascular bundles had similar morphometric characteristics to pleural and interlobular lymphatics. Shape factors were similar across lymphatic populations, except that peribronchiolar lymphatics had a marginally increased roundness and circularity, suggesting a more regular shape due to increased filling, and interlobular lymphatics had greater elongation, due to a greater proportion of conducting lymphatics cut longitudinally. Unsupervised cluster analysis confirmed a marked heterogeneity of lymphatic vessels both within and between groups, with a cluster of smaller vessels specifically represented in perivascular and interalveolar lymphatics within the alveolar interstitium. Our data indicate that intralobular lymphatics are a heterogeneous population, including vessels surrounding the bronchovascular bundle analogous to the conducting vessels present in the pleural and interlobular septa, many small perivascular lymphatics responsible for maintaining fluid balance in the alveolar interstitium, and a minority of intermediate lymphatics draining the peripheral airways. These lymphatic populations could be differentially involved in the pathogenesis of diseases preferentially involving distinct lung compartments.

Lymphangiogenesis in COPD: another link in the pathogenesis of the disease

BACKGROUND

New lymphatic vessels are associated with tissue injury and repair. Recent studies have shown increased lymphatic follicles formation in the lungs of COPD patients. We hypothesized that lymphatic vascular remodeling could be part of COPD pathogenesis.

AIM

To investigate the lymphangiogenetic process in COPD we measured the lymphatic microvessel density (LMVD), the lymphatic invasion (L.I), and their correlation with clinical and laboratory parameters.

METHODS

Lung tissue from 20 COPD patients and 20 non-COPD smokers was immunohistochemically stained for D2-40 (lymphatic endothelial cell marker), and LYVE-1 (lymphatic endothelial hyaluronan receptor 1). Both groups had similar age and smoking history.

RESULTS

D2-40 and LYVE-1 were expressed in all specimens. Lymphatic invasion was presented only in COPD specimens. Lymphatic microvessel density (LMVD) as revealed by D2-40 and LYVE-1 markers was statistically significantly higher in COPD patients when compared with non-COPD smokers. Both markers (D2-40, LYVE-1) were correlated with FEV1 (% pred) (R(2) = 0.415, R(2) = 0.605, respectively).

CONCLUSIONS

We report for the first time high lymphatic microvessel density and lymphatic invasion in COPD patients, related to the degree of airway obstruction. Our findings could provide novel insights in the pathogenesis of the disease.

A novel method for isolating individual cellular components from the adult human distal lung

A variety of lung diseases, such as pulmonary emphysema and idiopathic pulmonary fibrosis, develop in the lung alveoli. Multiple cell types are localized in the alveoli, including epithelial, mesenchymal, and endothelial cells. These resident cells participate in the pathogenesis of lung disease in various ways. To elaborate clearly on the mechanisms of these pathologic processes, cell type-specific analyses of lung disease are required. However, no method exists for individually isolating the different types of cells found in the alveoli. We report on the development of a FACS-based method for the direct isolation of individual cell types from the adult human distal lung. We obtained human lung tissue from lung resections, and prepared single-cell suspension. After depleting CD45-positive cells, a combination of antibodies against epithelial cell adhesion molecule (EpCAM), T1α, and vascular endothelial (VE)-cadherin as used to delineate alveolar cell types. Alveolar Type II cells were highly purified in the EpCAM(hi)/T1α(-) subset, whereas the EpCAM(+)/T1α(-/low) subset contained a mixed epithelial population consisting of alveolar Type I and bronchiolar epithelial cells. The EpCAM(-)/T1α(-) subset included both microvascular endothelial and mesenchymal cells, and these were separated by immunoreactivity to VE-cadherin. Lymphatic endothelial cells existed in the EpCAM(-)/T1α(hi) subset. Isolated cells were viable, and further cell culture studies could be performed. These results suggest that this novel method enables the isolation of different cellular components from normal and diseased lungs, and is capable of elucidating phenotypes specific to certain alveolar cell types indicative of lung disease.

Lymphatics in idiopathic pulmonary fibrosis: new insights into an old disease

The lymphatic vasculature plays a key role in tissue homeostasis and immune surveillance. There is mounting evidence of a role for the lymphatic circulation and for newly formed lymphatic vessels in the pathogenesis of lung disease. Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, debilitating lung disease. In IPF, the lung parenchyma undergoes extensive remodeling. This review focuses on the current knowledge and understanding of the pathogenesis of IPF, and recent evidence of the involvement of lymphangiogenesis in lung injury and repair and the molecular and cellular pathways leading to the development of lymphatic vasculature.