Pulmonary lymphatics and their spatial relationship to venous sphincters

Adventitial Cuffs: Regional Hubs for Tissue Immunity

Inflammation must be effective, while limiting excessive tissue damage. To walk this line, immune functions are grossly compartmentalized by innate cells that act locally and adaptive cells that function systemically. But what about the myriad tissue-resident immune cells that are critical to this balancing act and lie on a spectrum of innate and adaptive immunity? We propose that mammalian perivascular adventitial 'cuffs' are conserved sites in multiple organs, enriched for these tissue-resident lymphocytes and dendritic cells, as well as lymphatics, nerves, and subsets of specialized stromal cells. Here, we argue that these boundary sites integrate diverse tissue signals to regulate the movement of immune cells and interstitial fluid, facilitate immune crosstalk, and ultimately act to coordinate regional tissue immunity.

Lymphatic Vessel Network Structure and Physiology

The lymphatic system is comprised of a network of vessels interrelated with lymphoid tissue, which has the holistic function to maintain the local physiologic environment for every cell in all tissues of the body. The lymphatic system maintains extracellular fluid homeostasis favorable for optimal tissue function, removing substances that arise due to metabolism or cell death, and optimizing immunity against bacteria, viruses, parasites, and other antigens. This article provides a comprehensive review of important findings over the past century along with recent advances in the understanding of the anatomy and physiology of lymphatic vessels, including tissue/organ specificity, development, mechanisms of lymph formation and transport, lymphangiogenesis, and the roles of lymphatics in disease. © 2019 American Physiological Society. Compr Physiol 9:207-299, 2019.

Disposition and safety of inhaled biodegradable nanomedicines: Opportunities and challenges

The inhaled delivery of nanomedicines can provide a novel, non-invasive therapeutic strategy for the more localised treatment of lung-resident diseases and potentially also enable the systemic delivery of therapeutics that are otherwise administered via injection alone. However, the clinical translation of inhalable nanomedicine is being hampered by our lack of understanding about their disposition and clearance from the lungs. This review provides a comprehensive overview of the biodegradable nanomaterials that are currently being explored as inhalable drug delivery systems and our current understanding of their disposition within, and clearance from the lungs. The safety of biodegradable nanomaterials in the lungs is discussed and latest updates are provided on the impact of inflammation on the pulmonary pharmacokinetics of inhaled nanomaterials. Overall, the review provides an in-depth and critical assessment of the lung clearance mechanisms for inhaled biodegradable nanomedicines and highlights the opportunities and challenges for their translation into the clinic.

Lymphatic fluctuation in the parenchymal remodeling stage of acute interstitial pneumonia, organizing pneumonia, nonspecific interstitial pneumonia and idiopathic pulmonary fibrosis

Because the superficial lymphatics in the lungs are distributed in the subpleural, interlobular and peribroncovascular interstitium, lymphatic impairment may occur in the lungs of patients with idiopathic interstitial pneumonias (IIPs) and increase their severity. We investigated the distribution of lymphatics in different remodeling stages of IIPs by immunohistochemistry using the D2-40 antibody. Pulmonary tissue was obtained from 69 patients with acute interstitial pneumonia/diffuse alveolar damage (AIP/DAD, N = 24), cryptogenic organizing pneumonia/organizing pneumonia (COP/OP, N = 6), nonspecific interstitial pneumonia (NSIP/NSIP, N = 20), and idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP, N = 19). D2-40+ lymphatic in the lesions was quantitatively determined and associated with remodeling stage score. We observed an increase in the D2-40+ percent from DAD (6.66 ± 1.11) to UIP (23.45 ± 5.24, P = 0.008) with the advanced process of remodeling stage of the lesions. Kaplan-Meier survival curves showed a better survival for patients with higher lymphatic D2-40+ expression than 9.3%. Lymphatic impairment occurs in the lungs of IIPs and its severity increases according to remodeling stage. The results suggest that disruption of the superficial lymphatics may impair alveolar clearance, delay organ repair and cause severe disease progress mainly in patients with AIP/DAD. Therefore, lymphatic distribution may serve as a surrogate marker for the identification of patients at greatest risk for death due to IIPs.

Toward managing chronic rejection after lung transplant: the fate and effects of inhaled cyclosporine in a complex environment

The fate and effects of inhaled cyclosporine A (CsA) are considered after deposition on the lung surface. Special emphasis is given to a post-lung transplant environment and to the potential effects of the drug on the various cell types it is expected to encounter. The known stability, metabolism, pharmacokinetics and pharmacodynamics of the drug have been reviewed and discussed in the context of the lung microenvironment. Arguments support the contention that the immuno-inhibitory and anti-inflammatory effects of CsA are not restricted to T-cells. It is likely that pharmacologically effective concentrations of CsA can be sustained in the lungs but due to the complexity of uptake and action, the elucidation of effective posology must ultimately rely on clinical evidence.

Lung lymphatic anatomy and correlates

The pulmonary lymphatics do much more than keep the lung dry. They defend the lungs from airborne particles and microbes and allow a local influx of liquid to clear and clean inflamed or damaged tissue. Lymphatic morphology, especially the three-dimensional structure, is best demonstrated by casting the lymphatics, corroding the tissue, and viewing the casts by scanning electron microscopy. With this technique, different lymphatic forms exist. On the pleural surface prelymphatics are simply tissue planes that connect with lymphatic channels. Reservoir lymphatics are another form of initial lymphatics that have blind-ending pouches. They empty into conduit lymphatics. Lymphatics around blood vessels and airways are generally tubular and saccular. In the last decade, lymphatic markers have been discovered that allow the study of lymphatic development in health and disease. Modulators of these pathways could be potential therapeutics for diverse pulmonary problems such as cancer and lung transplantation. The size of the lymphatic system expands manifold in response to an excess fluid load, cancer, or inflammation. Immune cells move through the lymphatics, mature, and become activated there. The lymphatics enable the immune defense system by allowing a sequestered place and close proximity for antigen presentation and lymphocyte maturation.

Organization and developmental aspects of lymphatic vessels

The lymphatic system plays important roles in maintaining tissue fluid homeostasis, immune surveillance of the body, and the taking up dietary fat and fat-soluble vitamins A, D, E and K. The lymphatic system is involved in many pathological conditions, including lymphedema, inflammatory diseases, and tumor dissemination. A clear understanding of the organization of the lymphatic vessels in normal conditions would be critically important to develop new treatments for diseases involving the lymphatic vascular system. Therefore, the present paper reviews the organization of the lymphatic vascular system of a variety of organs, including the thyroid gland, lung and pleura, small intestine, cecum and colon in the rat, the diaphragm in the rat, monkey, and human, Peyer's patches and the appendix in the rabbit, and human tonsils. Methods employed include scanning electron microscopy of lymphatic corrosion casts and tissues with or without treatment of alkali maceration technique, transmission electron microscopy of intact tissues, confocal microscopy in conjunction with immunohistochemistry to some lymphatic-specific markers (i.e., LYVE-1 and VEGFR-3), and light microscopy in conjunction with enzyme-histochemistry to 5'-nucleotidase. Some developmental aspects of the lymphatic vessels and lymphedema are also discussed.

Angiogenesis: The Major Abnormality of the Keratin-14 IL-4 Transgenic Mouse Model of Atopic Dermatitis

OBJECTIVE

Angiogenesis plays an important role in psoriasis, but its role in atopic dermatitis is unknown. The authors examined the dermal microvasculature of an IL-4 transgenic mouse model of atopic dermatitis to determine whether angiogenesis was present.

METHODS

Transmission and scanning electron microscopy and confocal microscopy studies were performed.

RESULTS

Transmission electron microscopy showed sprouting, transcapillary pillars of intussusception, thickened endothelial cells with large nuclei, and increased interendothelial junctional cleft number and length. Compared to nontransgenic littermates, there was a significant increase in the lengths and numbers of the interendothelial junctional clefts, along with a decrease in the length ratios of tight junction to interendothelial junctional clefts in both the early and late disease stages. In the early and late skin lesions, scanning electron microscopy of vascular corrosion casts showed disorganization of the capillary network hierarchy with increased density of capillary sprouts. Confocal microscopy of the animals with early and late skin lesions showed significant reduction in tight junction protein claudin-5.

CONCLUSIONS

Angiogenesis is the major pathologic feature in this model of atopic dermatitis. The chronic skin inflammation is intertwined with and may cause the angiogenesis, but the angiogenesis itself is likely to be important in this disease process.

Pulmonary lymphatics and edema accumulation after brief lung injury

In a past study of hyperoxia-induced lung injury, the extensive lymphatic filling could have resulted from lymphatic proliferation or simple lymphatic recruitment. This study sought to determine whether brief lung injury could produce similar changes, to show which lymphatic compartments fill with edema, and to compare their three-dimensional structure. Tracheostomized rats were ventilated at high tidal volume (12-16 ml) or low tidal volume (3-5 ml) or allowed to breathe spontaneously for 25 min. Light microscopy showed more perivascular, interlobular septal, and alveolar edema in the animals ventilated at high tidal volume (P < 0.0001). Scanning electron microscopy of lymphatic casts showed extensive filling of the perivascular lymphatics in the group ventilated at high tidal volume (P < 0.01), but lymphatic filling was greater in the nonventilated group than in the group that was ventilated at low tidal volume (P < 0.01). The three-dimensional structures of the cast interlobular and perivascular lymphatics were similar. There was little filling and no difference in pleural lymphatic casts among the three groups. More edema accumulated in the surrounding lymphatics of larger blood vessels than smaller blood vessels. Brief high-tidal-volume lung injury caused pulmonary edema similar to that caused by chronic hyperoxic lung injury, except it was largely restricted to perivascular and septal lymphatics and prelymphatic spaces.

Pancreatic lymphatic system in rodents

The lymphatic network of the pancreas has been little investigated and recent studies have provided contrasting data. This research is aimed to supply the morphologic basis to outline the involvement of the lymphatic system in pancreatic pathology. Guinea pigs, rats, and mice were anesthetized with ether and sacrificed with the same anesthetic. Pieces of pancreas were processed for transmission electron microscopy. Semithin sections were observed by light microscopy and, after positive identification by transmission electron microscopy, lymphatics were followed with long series of consecutive sections to define their distribution. Lymphatics were detected in the pancreas of all the animals both in the inter and the intralobular sites. Closer relations with the exocrine parenchyma (ducts and acini) were observed in guinea pig pancreas. Remarkably, interesting relationships between lymphatics and endocrine tissue were observed in all the animals. Overall, however, the lymphatic network of rat pancreas was less develop and preferentially associated with blood vessels. The distribution of the pancreatic lymphatic network appears consistent with an active role in pancreatic pathology.

Combined vascular-bronchoalveolar casting using formalin-fixed canine lungs and a low viscosity silicone rubber

BACKGROUND

Previous work using unfixed or fixed tissues has shown that casts can be made that demonstrate the three-dimensional structure of tissues such as the bronchoalveolar tree or the vasculature. In this report, a new method for creating a vascular-bronchoalveolar cast is described.

METHOD

Canine lungs were taken from storage in formalin. Silastic 734 RTV (room temperature vulcanizing) with added red or blue pigments was injected into the pulmonary arteries and veins, respectively, using compressed air. This was followed by filling the airway with clear (translucent) Silastic 734 RTV. The lung tissue was then corroded with potassium hydroxide.

RESULTS

Vascular-bronchoalveolar casts were recovered giving fine detail as shown using stereo light microscopy or scanning electron microscopy.

CONCLUSIONS

This method may be useful for not only microvascular anatomy studies of lungs, but also for studying the microvasculature of other normal and diseased tissues.