Lymphangiogenesis is induced by mycobacterial granulomas via vascular endothelial growth factor receptor-3 and supports systemic T-cell responses against mycobacterial antigen

Influenza Induces Lung Lymphangiogenesis Independent of YAP/TAZ Activity in Lymphatic Endothelial Cells

The lymphatic system consists of a vessel network lined by specialized lymphatic endothelial cells (LECs) that are responsible for tissue fluid homeostasis and immune cell trafficking. The mechanisms for organ-specific LEC responses to environmental cues are not well understood. We found robust lymphangiogenesis during influenza A virus infection in the adult mouse lung. We show that the number of LECs increases 2-fold at 7 days post-influenza infection (dpi) and 3-fold at 21 dpi, and that lymphangiogenesis is preceded by lymphatic dilation. We also show that the expanded lymphatic network enhances fluid drainage to mediastinal lymph nodes. Using EdU labeling, we found that a significantly higher number of pulmonary LECs are proliferating at 7 dpi compared to LECs in homeostatic conditions. Lineage tracing during influenza indicates that new pulmonary LECs are derived from preexisting LECs rather than non-LEC progenitors. Lastly, using a conditional LEC-specific YAP/TAZ knockout model, we established that lymphangiogenesis, fluid transport and the immune response to influenza are independent of YAP/TAZ activity in LECs. These findings were unexpected, as they indicate that YAP/TAZ signaling is not crucial for these processes.

Lymphatic vessel: origin, heterogeneity, biological functions, and therapeutic targets

Lymphatic vessels, comprising the secondary circulatory system in human body, play a multifaceted role in maintaining homeostasis among various tissues and organs. They are tasked with a serious of responsibilities, including the regulation of lymph absorption and transport, the orchestration of immune surveillance and responses. Lymphatic vessel development undergoes a series of sophisticated regulatory signaling pathways governing heterogeneous-origin cell populations stepwise to assemble into the highly specialized lymphatic vessel networks. Lymphangiogenesis, as defined by new lymphatic vessels sprouting from preexisting lymphatic vessels/embryonic veins, is the main developmental mechanism underlying the formation and expansion of lymphatic vessel networks in an embryo. However, abnormal lymphangiogenesis could be observed in many pathological conditions and has a close relationship with the development and progression of various diseases. Mechanistic studies have revealed a set of lymphangiogenic factors and cascades that may serve as the potential targets for regulating abnormal lymphangiogenesis, to further modulate the progression of diseases. Actually, an increasing number of clinical trials have demonstrated the promising interventions and showed the feasibility of currently available treatments for future clinical translation. Targeting lymphangiogenic promoters or inhibitors not only directly regulates abnormal lymphangiogenesis, but improves the efficacy of diverse treatments. In conclusion, we present a comprehensive overview of lymphatic vessel development and physiological functions, and describe the critical involvement of abnormal lymphangiogenesis in multiple diseases. Moreover, we summarize the targeting therapeutic values of abnormal lymphangiogenesis, providing novel perspectives for treatment strategy of multiple human diseases.

The Function of T Cell Immunity in Lymphedema: A Comprehensive Review

Lymphedema is a debilitating disease characterized by extremity edema, fibroadipose deposition, impaired lymphangiogenesis, and dysfunctional lymphatics, often with lymphatic injury secondary to the treatment of malignancies. Emerging evidence has shown that immune dysfunction regulated by T cells plays a pivotal role in development of lymphedema. Specifically, Th1, Th2, Treg, and Th17 cells have been identified as critical regulators of pathological changes in lymphedema. In this review, our aim is to provide an overview of the current understanding of the roles of CD4+ T cells, including Th1, Th2, Treg, and Th17 subsets, in the progression of lymphedema and to discuss associated therapies targeting T cell inflammation for management of lymphedema.

Early innate cell interactions with Mycobacterium tuberculosis in protection and pathology of tuberculosis

Tuberculosis (TB) remains a significant global health challenge, claiming the lives of up to 1.5 million individuals annually. TB is caused by the human pathogen Mycobacterium tuberculosis (Mtb), which primarily infects innate immune cells in the lungs. These immune cells play a critical role in the host defense against Mtb infection, influencing the inflammatory environment in the lungs, and facilitating the development of adaptive immunity. However, Mtb exploits and manipulates innate immune cells, using them as favorable niche for replication. Unfortunately, our understanding of the early interactions between Mtb and innate effector cells remains limited. This review underscores the interactions between Mtb and various innate immune cells, such as macrophages, dendritic cells, granulocytes, NK cells, innate lymphocytes-iNKT and ILCs. In addition, the contribution of alveolar epithelial cell and endothelial cells that constitutes the mucosal barrier in TB immunity will be discussed. Gaining insights into the early cellular basis of immune reactions to Mtb infection is crucial for our understanding of Mtb resistance and disease tolerance mechanisms. We argue that a better understanding of the early host-pathogen interactions could inform on future vaccination approaches and devise intervention strategies.

L-selectin-dependent and -independent homing of naïve lymphocytes through the lung draining lymph node support T cell response to pulmonary Mycobacterium tuberculosis infection

Recruiting large numbers of naïve lymphocytes to lymph nodes is critical for mounting an effective adaptive immune response. While most naïve lymphocytes utilize homing molecule L-selectin to enter lymph nodes, some circulating cells can traffic to the lung-draining mediastinal lymph node (mLN) through lymphatics via the intermediate organ, lung. However, whether this alternative trafficking mechanism operates in infection and contributes to T cell priming are unknown. We report that in pulmonary Mycobacterium tuberculosis-infected mice, homing of circulating lymphocytes to the mLN is significantly less efficient than to non-draining lymph node. CD62L blockade only partially reduced the homing of naïve T lymphocytes, consistent with L-selectin-independent routing of naïve lymphocytes to the site. We further demonstrated that lymphatic vessels in infected mLN expanded significantly and inhibiting lymphangiogenesis with a vascular endothelial growth factor receptor 3 kinase inhibitor reduced the recruitment of intravenously injected naïve lymphocytes to the mLN. Finally, mycobacterium-specific T cells entering via the L-selectin-independent route were readily activated in the mLN. Our study suggests that both L-selectin-dependent and -independent pathways contribute to naïve lymphocyte entry into mLN during M. tuberculosis infection and the latter pathway may represent an important mechanism for orchestrating host defence in the lungs.

The lymphatic vasculature in lung function and respiratory disease

The lymphatic vasculature maintains tissue homeostasis via fluid drainage in the form of lymph and immune surveillance due to migration of leukocytes through the lymphatics to the draining lymph nodes. Lymphatic endothelial cells (LECs) form the lymphatic vessels and lymph node sinuses and are key players in shaping immune responses and tolerance. In the healthy lung, the vast majority of lymphatic vessels are found along the bronchovascular structures, in the interlobular septa, and in the subpleural space. Previous studies in both mice and humans have shown that the lymphatics are necessary for lung function from the neonatal period through adulthood. Furthermore, changes in the lymphatic vasculature are observed in nearly all respiratory diseases in which they have been analyzed. Recent work has pointed to a causative role for lymphatic dysfunction in the initiation and progression of lung disease, indicating that these vessels may be active players in pathologic processes in the lung. However, the mechanisms by which defects in lung lymphatic function are pathogenic are understudied, leaving many unanswered questions. A more comprehensive understanding of the mechanistic role of morphological, functional, and molecular changes in the lung lymphatic endothelium in respiratory diseases is a promising area of research that is likely to lead to novel therapeutic targets. In this review, we will discuss our current knowledge of the structure and function of the lung lymphatics and the role of these vessels in lung homeostasis and respiratory disease.

Stimulated expression of ELR+ chemokines, VEGFA and TNF-AIP3 promote mycobacterial dissemination in extrapulmonary tuberculosis patients and Cavia porcellus model of tuberculosis

Pathogenic mycobacteria induce and accelerate blood vessel formation driven by extensive inflammation during granuloma formation, which is a central feature of mycobacterial pathogenesis. Tumor necrosis factor-alpha (TNF-α) enhances the expression of vascular endothelial growth factor (VEGF) and glutamic acid-leucine-arginine (ELR+) chemokines, which are potent inducers of vascularization. Most of the reported research work contends that VEGF growth factor induces neovascularization in human tuberculosis (TB) patients, but the evidence is inconclusive. Considerable ambiguity exists concerning the factors responsible for miliary tuberculosis. To identify such factors, we proposed an alternative explanation that could be found in miliary tuberculosis (MTB) cases. We performed a comparative analysis of angiogenic factors TNF-α, VEGF, and angiogenic ELR+ CXC and CC chemokine ligands in extrapulmonary tuberculosis (EPTB) and pulmonary tuberculosis (PTB) patients. To observe the relationship of these factors with the severity of bacterial burden, guinea pigs were infected with Mycobacterium tuberculosis (M.tb) and levels of the angiogenic factors were examined at different time intervals. Expression of these factors also exhibited a significant positive correlation with bacterial burden in other organs like the spleen, liver, and lymph nodes. We demonstrated statistical data on bacterial burden at different time points following the dissemination of infection in guinea pigs. In this study, we observed that there was a stimulated increase in the expression of ELR+ chemokines and VEGF in EPTB patients as compared to PTB patients. Following increased dissemination, the host immune response clears bacteria from the lungs during disease progression in guinea pigs.

Tuberculosis pathophysiology and anti-VEGF intervention

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A review of tuberculosis pathophysiology reveals only a few pharmaceutical targets.

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Current drugs focus on targeting the bacteria and its replication.

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One target revealed by analyzing tuberculosis pathophysiology is VEGF released by macrophages.

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One Anti-VEGF-A drug has shown promise in treating disseminated tuberculosis.

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We should clinically evaluate all Anti-VEGF and Anti-VEGFR drugs with current FDA approval for treating cancer for tuberculosis intervention.

The pathophysiological understanding of tuberculosis is growing, and with this growth comes the possibility of applying established pharmaceuticals in new ways. These new ways interlude with the many mechanisms by which the intracellular pathogen, Mycobacterium tuberculosis, thrives in its human host. This article will discuss those mechanisms in the context of the pathophysiological processes associated with tuberculosis. Tuberculosis is a disease that results in systemic lesions arising from bacterial-immune interactions. The pathophysiology of this disease proceeds as aerosolization, phagocytosis, phagolysosome blockage and replication, T- helper response, granuloma formation, clinical manifestations, and concluding with active disease and transmission. Herein are the brief details of each of these processes. The conclusion of this article will be current tuberculosis treatments and future promising pharmacological directions. Particularly using the anti-vascular endothelial growth factor treatments currently used in cancer therapy, which are rationally presented with support from case studies. The purpose of this article is thus to present the pathophysiology of tuberculosis to convince the reader of the logical theory behind why anti-VEGF intervention should be used in tuberculosis treatment.

Inhibition of infection-induced vascular permeability modulates host leukocyte recruitment to Mycobacterium marinum granulomas in zebrafish

Mycobacterial granuloma formation involves significant stromal remodeling including the growth of leaky, granuloma-associated vasculature. These permeable blood vessels aid mycobacterial growth, as antiangiogenic or vascular normalizing therapies are beneficial host-directed therapies in preclinical models of tuberculosis across host-mycobacterial pairings. Using the zebrafish-Mycobacterium marinum infection model, we demonstrate that vascular normalization by inhibition of vascular endothelial protein tyrosine phosphatase (VE-PTP) decreases granuloma hypoxia, the opposite effect of hypoxia-inducing antiangiogenic therapy. Inhibition of VE-PTP decreased neutrophil recruitment to granulomas in adult and larval zebrafish, and decreased the proportion of neutrophils that extravasated distal to granulomas. Furthermore, VE-PTP inhibition increased the accumulation of T cells at M. marinum granulomas. Our study provides evidence that, similar to the effect in solid tumors, vascular normalization during mycobacterial infection increases the T cell:neutrophil ratio in lesions which may be correlates of protective immunity.

Neuroinflammation-Driven Lymphangiogenesis in CNS Diseases

The central nervous system (CNS) undergoes immunosurveillance despite the lack of conventional antigen presenting cells and lymphatic vessels in the CNS parenchyma. Additionally, the CNS is bathed in a cerebrospinal fluid (CSF). CSF is continuously produced, and consequently must continuously clear to maintain fluid homeostasis despite the lack of conventional lymphatics. During neuroinflammation, there is often an accumulation of fluid, antigens, and immune cells to affected areas of the brain parenchyma. Failure to effectively drain these factors may result in edema, prolonged immune response, and adverse clinical outcome as observed in conditions including traumatic brain injury, ischemic and hypoxic brain injury, CNS infection, multiple sclerosis (MS), and brain cancer. Consequently, there has been renewed interest surrounding the expansion of lymphatic vessels adjacent to the CNS which are now thought to be central in regulating the drainage of fluid, cells, and waste out of the CNS. These lymphatic vessels, found at the cribriform plate, dorsal dural meninges, base of the brain, and around the spinal cord have each been implicated to have important roles in various CNS diseases. In this review, we discuss the contribution of meningeal lymphatics to these processes during both steady-state conditions and neuroinflammation, as well as discuss some of the many still unknown aspects regarding the role of meningeal lymphatics in neuroinflammation. Specifically, we focus on the observed phenomenon of lymphangiogenesis by a subset of meningeal lymphatics near the cribriform plate during neuroinflammation, and discuss their potential roles in immunosurveillance, fluid clearance, and access to the CSF and CNS compartments. We propose that manipulating CNS lymphatics may be a new therapeutic way to treat CNS infections, stroke, and autoimmunity.

Current concepts in granulomatous immune responses

Persistent irritants that are resistant to innate and cognate immunity induce granulomas. These macrophage-dominated lesions that partially isolate the healthy tissue from the irritant and the irritant induced inflammation. Particles, toxins, autoantigens and infectious agents can induce granulomas. The corresponding lesions can be protective for the host but they can also cause damage and such damage has been associated with the pathology of more than a hundred human diseases. Recently, multiple molecular mechanisms underlying how normal macrophages transform into granuloma-inducing macrophages have been discovered and new information has been gathered, indicating how these lesions are initiated, spread and regulated. In this review, differences between the innate and cognate granuloma pathways are discussed by summarizing how the dendritic cell - T cell axis changes granulomatous immunity. Granuloma lesions are highly dynamic and depend on continuous cell replacement. This feature provides new therapeutic approaches to treat granulomatous diseases.

VEGF-A from Granuloma Macrophages Regulates Granulomatous Inflammation by a Non-angiogenic Pathway during Mycobacterial Infection

Many autoimmune and infectious diseases are characterized by the formation of granulomas which are inflammatory lesions that consist of spatially organized immune cells. These sites protect the host and control pathogens like Mycobacterium tuberculosis (Mtb), but are highly inflammatory and cause pathology. Using bacille Calmette-Guerin (BCG) and Mtb infection in mice that induce sarcoid or caseating granulomas, we show that a subpopulation of granuloma macrophages produces vascular endothelial growth factor (VEGF-A), which recruits immune cells to the granuloma by a non-angiogenic pathway. Selective blockade of VEGF-A in myeloid cells, combined with granuloma transplantation, shows that granuloma VEGF-A regulates granulomatous inflammation. The severity of granuloma-related inflammation can be ameliorated by pharmaceutical or genetic inhibition of VEGF-A, which improves survival of mice infected with virulent Mtb without altering host protection. These data show that VEGF-A inhibitors could be used as a host-directed therapy against granulomatous diseases like tuberculosis and sarcoidosis, thereby expanding the value of already existing and approved anti-VEGF-A drugs.

Host-directed therapies targeting the tuberculosis granuloma stroma

Mycobacteria have co-evolved with their hosts resulting in pathogens adept at intracellular survival. Pathogenic mycobacteria actively manipulate infected macrophages to drive granuloma formation while subverting host cell processes to create a permissive niche. Granuloma residency confers phenotypic antimicrobial resistance by physically excluding or neutralising antibiotics. Host-directed therapies (HDTs) combat infection by restoring protective immunity and reducing immunopathology independent of pathogen antimicrobial resistance status. This review covers innovative research that has discovered ‘secondary’ symptoms of infection in the granuloma stroma are actually primary drivers of infection and that relieving these stromal pathologies with HDTs benefits the host. Advances in our understanding of the relationship between tuberculosis and the host vasculature, haemostatic system and extracellular matrix reorganisation are discussed. Preclinical and clinical use of HDTs against these stromal targets are summarised.

Granulomatous Inflammation in Tuberculosis and Sarcoidosis: Does the Lymphatic System Contribute to Disease?

A striking and unexplained feature of granulomatous inflammation is its anatomical association with the lymphatic system. Accumulating evidence suggests that lymphatic tracks and granulomas may alter the function of each other. The formation of new lymphatics, or lymphangiogenesis, is an adaptive response to tumor formation, infection, and wound healing. Granulomas also may induce lymphangiogenesis which, through a variety of mechanisms, could contribute to disease outcomes in tuberculosis and sarcoidosis. On the other hand, alterations in lymph node function and lymphatic draining may be primary events which attenuate the risk and severity of granulomatous inflammation. This review begins with an introduction of granulomatous inflammation and the lymphatic system. A role of the lymphatic system in tuberculosis and sarcoidosis is then hypothesized. With a focus on lymphangiogenesis in these diseases, and on the potential for this process to promote dissemination, parallels are established with the well-established role of lymphangiogenesis in tumor biology.

Tuberculous lymphadenitis is associated with altered levels of circulating angiogenic factors

BACKGROUND

Angiogenic factors are important in granuloma formation and serve as biomarkers in pulmonary tuberculosis (PTB). The relationship between these markers and tuberculous lymphadenitis (TBL) is not known.

OBJECTIVE AND DESIGN

To examine the association of vascular endothelial growth factor (VEGF) and angiopoietin (Ang) family molecules in TBL, we measured systemic levels of VEGF-A, C, D, R1 (VEGF-receptor 1), R2, R3, Ang-1, Ang-2 and TIE2 (tyrosine kinase with immunoglobulin-like and epidermal growth factor-like domains 2) levels in TBL, latent tuberculous infection (LTBI) and lymph node culture supernatants (VEGF-A, C and Ang-2) of the same TBL patients.

RESULTS

Circulating levels of VEGF-A and VEGF-C were significantly diminished, whereas VEGF-R2, R3, Ang-2 and TIE2 levels were significantly increased, in TBL. Likewise, VEGF-A, C and Ang-2 levels were significantly increased in lymph node supernatants compared with plasma in individuals with TBL. Receiver operating characteristic curve analysis showed that VEGF-C and VEGF-R2 markers clearly distinguished TBL from LTBI. Following treatment, VEGF-C and Ang-1 levels were significantly altered. No association was observed between angiogenic factors and culture grade or lymph node size, except for VEGF-A. VEGF-A was also significantly decreased in multiple lymph nodes compared with single lymph nodes.

CONCLUSIONS

Our data suggest that altered levels of circulating angiogenic factors in TBL might reflect underlying vasculo-endothelial dysfunction. Reversal of angiogenic markers after anti-tuberculosis treatment suggests that these angiogenic markers may serve as biomarkers of disease severity or response to treatment in TBL.

Revisiting hypoxia therapies for tuberculosis

The spectre of the coming post-antibiotic age demands novel therapies for infectious diseases. Tuberculosis (TB), caused by Mycobacterium tuberculosis, is the single deadliest infection throughout human history. M. tuberculosis has acquired antibiotic resistance at an alarming rate with some strains reported as being totally drug resistant. Host-directed therapies (HDTs) attempt to overcome the evolution of antibiotic resistance by targeting relatively immutable host processes. Here, I hypothesise the induction of hypoxia via anti-angiogenic therapy will be an efficacious HDT against TB. I argue that anti-angiogenic therapy is a modernisation of industrial revolution era sanatoria treatment for TB, and present a view of the TB granuloma as a 'bacterial tumour' that can be treated with anti-angiogenic therapies to reduce bacterial burden and spare host immunopathology. I suggest two complementary modes of action, induction of bacterial dormancy and activation of host hypoxia-induced factor (HIF)-mediated immunity, and define the experimental tools necessary to test this hypothesis.

Neuroinflammation-induced lymphangiogenesis near the cribriform plate contributes to drainage of CNS-derived antigens and immune cells

There are no conventional lymphatic vessels within the CNS parenchyma, although it has been hypothesized that lymphatics near the cribriform plate or dura maintain fluid homeostasis and immune surveillance during steady-state conditions. However, the role of these lymphatic vessels during neuroinflammation is not well understood. We report that lymphatic vessels near the cribriform plate undergo lymphangiogenesis in a VEGFC – VEGFR3 dependent manner during experimental autoimmune encephalomyelitis (EAE) and drain both CSF and cells that were once in the CNS parenchyma. Lymphangiogenesis also contributes to the drainage of CNS derived antigens that leads to antigen specific T cell proliferation in the draining lymph nodes during EAE. In contrast, meningeal lymphatics do not undergo lymphangiogenesis during EAE, suggesting heterogeneity in CNS lymphatics. We conclude that increased lymphangiogenesis near the cribriform plate can contribute to the management of neuroinflammation-induced fluid accumulation and immune surveillance.

Lymphangiogenesis occurs in the context of systemic inflammation and development but has not been reported for the lymphatics that surround the CNS. Here the authors show that in the context of experimental autoimmune encephatlitis, lymphangiogenesis occurs at the cribriform plate, but not the meninges, and contributes to immune cell and antigen drainage.

Cyclopropane Modification of Trehalose Dimycolate Drives Granuloma Angiogenesis and Mycobacterial Growth through Vegf Signaling

Mycobacterial infection leads to the formation of characteristic immune aggregates called granulomas, a process accompanied by dramatic remodeling of the host vasculature. As granuloma angiogenesis favors the infecting mycobacteria, it may be actively promoted by bacterial determinants during infection. Using Mycobacterium marinum-infected zebrafish as a model, we identify the enzyme proximal cyclopropane synthase of alpha-mycolates (PcaA) as an important bacterial determinant of granuloma-associated angiogenesis. cis-Cyclopropanation of mycobacterial mycolic acids by pcaA drives the activation of host Vegf signaling within granuloma macrophages. Cyclopropanation of the mycobacterial cell wall glycolipid trehalose dimycolate is both required and sufficient to induce robust host angiogenesis. Inducible genetic inhibition of angiogenesis and Vegf signaling during granuloma formation results in bacterial growth deficits. Together, these data reveal a mechanism by which PcaA-mediated cis-cyclopropanation of mycolic acids promotes bacterial growth and dissemination in vivo by eliciting granuloma vascularization and suggest potential approaches for host-directed therapies.

Endothelial lineage-specific interaction of Mycobacterium tuberculosis with the blood and lymphatic systems

Mycobacterium tuberculosis (Mtb) has plagued humanity for tens of thousands of years, yet still remains a threat to human health. Its pathology is largely associated with pulmonary tuberculosis with symptoms including fever, hemoptysis, and chest pain. Mtb, however, also manifests in other extrapulmonary organs, such as the pleura, bones, gastrointestinal tract, central nervous system, and lymph nodes. Compared to the knowledge of pulmonary tuberculosis, extrapulmonary pathologies of Mtb are quite understudied. Lymph node tuberculosis is one of the most common extrapulmonary manifestations of tuberculosis, and presents significant challenges in its diagnosis, management, and treatment due to its elusive etiologies and pathologies. The objective of this review is to overview the current understanding of the tropism and pathogenesis of Mtb in endothelial cells of the extrapulmonary tissues, particularly, in lymph nodes. Lymphatic endothelial cells (LECs) are derived from blood vascular endothelial cells (BECs) during development, and these two types of endothelial cells demonstrate substantial molecular, cellular and genetic similarities. Therefore, systemic comparison of the differential and common responses of BECs vs. LECs to Mtb invasion could provide new insights into its pathogenesis, and may promote new investigations into this deadly disease.

Angiopoietins as biomarkers of disease severity and bacterial burden in pulmonary tuberculosis

BACKGROUND

Circulating angiogenic factors of the vascular endothelial growth factor family are important biomarkers of disease severity in pulmonary tuberculosis (PTB). However, the role of angiopoietins, which are also involved in angiogenesis, in PTB is not known.

OBJECTIVE AND DESIGN

To examine the association of circulating angiopoietins with TB disease or latent tuberculous infection (LTBI), we examined the systemic levels of angiopoietin (Ang) 1, Ang 2 and Tie-2 receptor in individuals with PTB (n = 44), LTBI (n = 44) or no tuberculous infection (NTBI) (n = 44).

RESULTS

Circulating levels of Ang-1, Ang-2 and Tie-2 were significantly higher in PTB than in individuals with LTBI or NTBI. Moreover, Ang-1, Ang-2 and Tie-2 levels were significantly higher in PTB with bilateral disease. The levels of these factors also exhibited a significant positive relationship with bacterial burdens in PTB. Receiver operating characteristics curve analysis revealed Ang-2 as a marker distinguishing PTB from LTBI or NTBI. Finally, the circulating levels of Ang-1, Ang-2 and Tie-2 were significantly reduced following anti-tuberculosis chemotherapy.

CONCLUSIONS

Our data demonstrate that PTB is associated with elevated levels of circulating angiopoietins, possibly reflecting endothelial dysfunction. In addition, Ang-2 could prove useful as a biomarker to monitor disease severity, bacterial burden and therapeutic responses.

Imaging Lymphatics in Mouse Lungs

Lymphatic malformations and other conditions where lymphatic function is disturbed in the respiratory tract present diagnostic and therapeutic challenges. Advances in lymphatic development, growth regulation, function, and imaging have increased the understanding of lymphatics, but the airways and lungs have not received as much attentions as many other organs. The lung presents challenges for studies of lymphatics because of the complex, densely packed three-dimensional architecture of the airways and vasculature, and because it cannot readily be examined in its entirety. To address this problem, we developed methods for immunohistochemical examination of the lymphatics in mouse lungs, based on approaches we devised for lymphatic vessels and blood vessels in whole mounts of the mouse trachea. This report provides a practical guide for visualizing by fluorescence and confocal microscopy the lymphatics in mouse airways and lungs under normal conditions and in models of disease. Materials and methods are described for immunohistochemical staining of lymphatics in whole mounts of the mouse trachea and 200-μm sections of mouse lung. Also described are mouse models in which lymphatics proliferate in the lung, blocking antibodies for preventing lymphatic growth, methods for fixing mouse lungs by vascular perfusion, and techniques for staining, visualizing, and analyzing lymphatic endothelial cells and other cells in the lung. These methods provide the opportunity to learn as much about lymphatics in the lung as in other organs.

Anti-angiogenic and anti-lymphangiogenic role of praziquantel and artemether in experimental mansoniasis

Angiogenesis is one of the pillars of neoplasia. Lymphangiogenesis in context of granulomas is not yet understood. This study aimed to evaluate the role of praziquantel (PZQ) and artemether (ART) as anti-angiogenic and anti-lymphangiogenic drugs in Schistosoma mansoni induced experimental hepatic model through immunohistochemical and serological studies, this can be used as a potential novel prophylactic approach in hepatic malignancy prevention and possible management. Forty female CD-1 Swiss albino mice were used divided into 4 groups (10 mice each); control healthy, control infected untreated, PZQ-treated and ART-treated. Angiogenic and lymphangiogenic effect of the drugs assessed pathologically through counting of the newly formed capillaries and lymphatics that immunohistochemically expressed by vascular Endothelial Growth Factor (VEGF), CD34 and D2-40 in liver sections using Cell Image Analyzer and serologically by evaluation of serum level of Tumor Necrosis Factor-Alpha (TNF-α). Our results showed significant decrease in serum TNF-α in ART-treated group compared to control infected and PZQ treated groups. ART exhibited significant anti-angiogenic role on granulomas illustrated by remarkable milder intensity and significantly lower expression values of VEGF and CD34 immunostaining compared to PZQ and non-treated groups. Also, ART treated group exhibited negative D2-40 expression in the granulomas in contrast to the other groups, supporting the potent ART' anti-lymphangiogenic role that exceeded PZQ. In conclusion, ART showed not only anti-angiogenic effect but also prominent anti-lymphangiogenic effect on hepatic S. mansoni granulomas compared to PZQ. Our study supports the potential use of ART as a potential novel prophylactic approach in hepatic malignancy prevention and possible management.

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.

Lymphangiogenesis: fuel, smoke, or extinguisher of inflammation's fire?

Lymphangiogenesis is a recognized hallmark of inflammatory processes in tissues and organs as diverse as the skin, heart, bowel, and airways. In clinical and animal models wherein the signaling processes of lymphangiogenesis are manipulated, most studies demonstrate that an expanded lymphatic vasculature is necessary for the resolution of inflammation. The fundamental roles that lymphatics play in fluid clearance and immune cell trafficking from the periphery make these results seemingly obvious as a mechanism of alleviating locally inflamed environments: the lymphatics are simply providing a drain. Depending on the tissue site, lymphangiogenic mechanism, or induction timeframe, however, evidence shows that inflammation-associated lymphangiogenesis (IAL) may worsen the pathology. Recent studies have identified lymphatic endothelial cells themselves to be local regulators of immune cell activity and its consequential phenotypes - a more active role in inflammation regulation than previously thought. Indeed, results focusing on the immunocentric roles of peripheral lymphatic function have revealed that the basic drainage task of lymphatic vessels is a complex balance of locally processed and transported antigens as well as interstitial cytokine and immune cell signaling: an interplay that likely defines the function of IAL. This review will summarize the latest findings on how IAL impacts a series of disease states in various tissues in both preclinical models and clinical studies. This discussion will serve to highlight some emerging areas of lymphatic research in an attempt to answer the question relevant to an array of scientists and clinicians of whether IAL helps to fuel or extinguish inflammation. Impact statement Inflammatory progression is present in acute and chronic tissue pathologies throughout the body. Lymphatic vessels play physiological roles relevant to all medical fields as important regulators of fluid balance, immune cell trafficking, and immune identity. Lymphangiogenesis is often concurrent with inflammation and can potentially aide or worsen disease progression. How new lymphatic vessels impact inflammation and by which mechanism is an important consideration in current and future clinical therapies targeting inflammation and/or vasculogenesis. This review identifies, across a range of tissue-specific pathologies, the current understanding of inflammation-associated lymphangiogenesis in the progression or resolution of inflammation.

Tuberculosis-diabetes co-morbidity is characterized by heightened systemic levels of circulating angiogenic factors

BACKGROUND

Tuberculosis-diabetes co-morbidity (TB-DM) is characterized by increased inflammation with elevated circulating levels of inflammatory cytokines and other factors. Circulating angiogenic factors are intricately involved in the angiogenesis-inflammation nexus.

METHODS

To study the association of angiogenic factors with TB-DM, we examined the systemic levels of VEGF-A, VEGF-C, VEGF-D, VEGF-R1, VEGF-R2, VEGF-R3 in individuals with either TB-DM (n = 44) or TB alone (n = 44).

RESULTS

Circulating levels of VEGF-A, C, D, R1, R2 and R3 were significantly higher in TB-DM compared to TB individuals. Moreover, the levels of VEGF-A, C, R2 and/or R3 were significantly higher in TB-DM with bilateral or cavitary disease or with hemoptysis, suggesting an association with both disease severity and adverse clinical presentation. The levels of these factors also exhibited a significant positive relationship with bacterial burdens and HbA1c levels. In addition, VEGF-A, C and R2 levels were significantly higher (at 2 months of treatment) in culture positive compared to culture negative TB-DM individuals. Finally, the circulating levels of VEGF-A, C, D, R1, R2 and R3 were significantly reduced following successful chemotherapy at 6 months.

CONCLUSION

Our data demonstrate that TB-DM is associated with heightened levels of circulating angiogenic factors, possibly reflecting both dysregulated angiogenesis and exaggerated inflammation.

Mycobacterium tuberculosis exploits the formation of new blood vessels for its dissemination

The mechanisms by which the airborne pathogen Mycobacterium tuberculosis spreads within the lung and leaves its primary niche to colonize other organs, thus inducing extrapulmonary forms of tuberculosis (TB) in humans, remains poorly understood. Herein, we used a transcriptomic approach to investigate the host cell gene expression profile in M. tuberculosis-infected human macrophages (ΜΦ). We identified 33 genes, encoding proteins involved in angiogenesis, for which the expression was significantly modified during infection, and we show that the potent angiogenic factor VEGF is secreted by M. tuberculosis-infected ΜΦ, in an RD1-dependent manner. In vivo these factors promote the formation of blood vessels in murine models of the disease. Inhibiting angiogenesis, via VEGF inactivation, abolished mycobacterial spread from the infection site. In accordance with our in vitro and in vivo results, we show that the level of VEGF in TB patients is elevated and that endothelial progenitor cells are mobilized from the bone marrow. These results strongly strengthen the most recent data suggesting that mycobacteria take advantage of the formation of new blood vessels to disseminate.

Lymphatic endothelial cells are a replicative niche for Mycobacterium tuberculosis

In extrapulmonary tuberculosis, the most common site of infection is within the lymphatic system, and there is growing recognition that lymphatic endothelial cells (LECs) are involved in immune function. Here, we identified LECs, which line the lymphatic vessels, as a niche for Mycobacterium tuberculosis in the lymph nodes of patients with tuberculosis. In cultured primary human LECs (hLECs), we determined that M. tuberculosis replicates both in the cytosol and within autophagosomes, but the bacteria failed to replicate when the virulence locus RD1 was deleted. Activation by IFN-γ induced a cell-autonomous response in hLECs via autophagy and NO production that restricted M. tuberculosis growth. Thus, depending on the activation status of LECs, autophagy can both promote and restrict replication. Together, these findings reveal a previously unrecognized role for hLECs and autophagy in tuberculosis pathogenesis and suggest that hLECs are a potential niche for M. tuberculosis that allows establishment of persistent infection in lymph nodes.

Circulating Angiogenic Factors as Biomarkers of Disease Severity and Bacterial Burden in Pulmonary Tuberculosis

BACKGROUND

Angiogenesis and lymphangiogenesis are classical features of granuloma formation in pulmonary tuberculosis (PTB). In addition, the angiogenic factor--VEGF-A is a known biomarker for PTB.

AIMS/METHODOLOGY

To examine the association of circulating angiogenic factors with PTB, we examined the systemic levels of VEGF-A, VEGF-C, VEGF-D, VEGF-R1, VEGF-R2 and VEGF-R3in individuals with PTB, latent TB (LTB) or no TB infection (NTB).

RESULTS

Circulating levels of VEGF-A, VEGF-C andVEGF-R2 were significantly higher in PTB compared to LTB or NTB individuals. Moreover, the levels of VEGF-A, VEGF-C and VEGF-R2 were significantly higher in PTB with bilateral and/or cavitary disease. The levels of these factors also exhibited a significant positive relationship with bacterial burdens in PTB. ROC analysis revealed VEGF-A and VEGF-R2 as markers distinguishing PTB from LTB or NTB. Finally, the circulating levels of all the angiogenic factors examined were significantly reduced following successful chemotherapy.

CONCLUSION

Therefore, our data demonstrate that PTB is associated with elevated levels of circulating angiogenic factors, possibly reflecting vascular and endothelial dysfunction. In addition, some of these circulating angiogenic factors could prove useful as biomarkers to monitor disease severity, bacterial burden and therapeutic responses.