Endogenous TNFα orchestrates the trafficking of neutrophils into and within lymphatic vessels during acute inflammation

Relative Values of Hematological Indices for Prognosis of Heart Failure: A Mini-Review

Owing to the augmented perception of heart failure (HF) pathophysiology, management of the affected patients has been improved dramatically; as with the identification of the inflammatory background of HF, new avenues of HF prognosis research have been opened up. In this regard, relative values of hematologic indices were demonstrated by a growing body of evidence to successfully predict HF outcomes. Cost-effectiveness, accessibility, and easy obtainability of these relative values make them a precious option for the determination of HF prognosis; particularly in low-income developing countries. In this short review, we aimed to present the current literature on the predictability of these hematologic parameters for HF outcomes.

LECs regulate neutrophil clearance through IL-17RC/CMTM4/NF-κB axis at sites of inflammation or infection

The lymphatic system plays a vital role in the regulation of tissue fluid balance and the immune response to inflammation or infection. The effects of lymphatic endothelial cells (LECs) on the regulation of neutrophil migration have not been well-studied. In three murine models: imiquimod-induced skin inflammation, Staphylococcus aureus-induced skin infection, and ligature-induced periodontitis, we show that numerous neutrophils migrate from inflamed or infected tissues to the draining lymph nodes via lymphatic vessels. Moreover, inflamed or infected tissues express a high level of interleukin (IL)-17A and tumor necrosis factor (TNF)-α, simultaneously with a significant increase in the release of neutrophil attractors, including CXCL1, CXCL2, CXCL3, and CXCL5. Importantly, in vitro stimulation of LECs with IL-17A plus TNF-α synergistically promoted these chemokine secretions. Mechanistically, tetra-transmembrane protein CMTM4 directly binds to IL-17RC in LECs. IL-17A plus TNF-α stimulates CXC chemokine secretion by promoting nuclear factor-kappa B signaling. In contrast, knockdown of CMTM4 abrogates IL-17A plus TNF-α activated nuclear factor-kappa B signaling pathways. Lastly, the local administration of adeno-associated virus for CMTM4 in Prox1-CreERT2 mice, mediating LEC-specific overexpression of CMTM4, promotes the drainage of neutrophils by LECs and alleviates immune pathological responses. Thus, our findings reveal the vital role of LECs-mediated neutrophil attraction and clearance at sites of inflammation or infection.

Chronological Management of Adjuvant Effect for Optimized mRNA Vaccine Inspired by Natural Virus Infection

The efficacy and safety of mRNA vaccines both rely on a fine-tuning of specific humoral and cellular immune responses. Instead of adjustments in vaccine component, we proposed a concept of chronological management of adjuvant effect to modulate the adaptive immune potency and preference inspired by natural virus infection. By simulating type I interferon expression dynamics during viral infection, three vaccine strategies employing distinct exposure sequences of adjuvant and mRNA have been developed, namely Precede, Coincide, and Follow. Follow, the strategy of adjuvant administration following mRNA, effectively suppressed tumor progression, which was attributed to enhanced mRNA translation, augmented p-MHC I expression, and elevated CD8+ T cell response. Meanwhile, Follow exhibited improved biosafety, characterized by reduced incidences of cardiac and liver toxicity, owing to its alteration to the vaccination microenvironment between successive injections. Our strategy highlights the importance of fine-tuning adjuvant effect dynamics in optimizing mRNA vaccines for clinical application.

Different cellular and molecular responses of Bovine milk phagocytes to persistent and transient strains of Streptococcus uberis causing mastitis

Streptococcus uberis is frequently isolated from milk collected from dairy cows with mastitis. According to the host's immunity, bacterial virulence, and their interaction, infection with some strains can induce persistent subclinical inflammation, while infection with others induces severe inflammation and transient mastitis. This study compared the inflammatory response of milk-isolated white blood cells (mWBCs) to persistent and transient S. uberis strains. Quarter milk samples were collected aseptically for bacterial culture from all lactating cows once a week over a 10-week period. A transient and noncapsular strain with a 1-week intramammary infection duration was selected from this herd, while a persistent and capsular S. uberis strain with an intramammary infection longer than 2 months from our previous study was selected based on an identical pulse field gel electrophoresis pattern during the IMI episode. Cellular and molecular responses of mWBCs were tested, and the data were analyzed using repeated analysis of variance. The results showed a higher response in migration, reactive oxygen species generation, and bacterial killing when cells were stimulated with transient S. uberis. In contrast, the persistent strain led to increased neutrophil extracellular trap release. This study also highlighted several important molecular aspects of mWBCs. Gene expression analyses by real-time RT-PCR revealed a significant elevation in the expression of Toll-like receptors (TLR-1, TLR-2, TLR-6) and proinflammatory cytokines (tumor necrosis factor-alpha or TNF-α) with the transient strain. Additionally, Streptococcus uberis capsule formation might contribute to the capability of these strains to induce different immune responses. Altogether, these results focus on the immune function of activated mWBCs which demonstrate that a transient strain can elicit a stronger local immune response and, subsequently, lead to rapid recovery from mastitis.

Increased contractile activity and dilation of popliteal lymphatic vessels in the TNF-α-overexpressing TNFΔARE/+ arthritic mouse

AIMS

TNF-α acute treatment has been found to disrupt lymphatic drainage in the setting of arthritis through the NF-kB-iNOS- signaling pathway. We examined whether popliteal lymphatic vessels (pLVs) contractile activity was altered in 12- and 24- week-old females of an arthritic mouse model overexpressing TNF-α (TNFΔARE/+).

MAIN METHODS

pLVs were prepared for intravital imaging to measure lymph flow speed, and ex vivo functional responses to a stepwise increase in transmural pressure in the absence or presence of the non-selective NOS inhibitor (L-NNA) or the selective iNOS inhibitor (1400W) were compared between TNFΔARE/+ and WT mice. Total eNOS (t-eNOS) and eNOS phosphorylated at ser1177 (p-eNOS) were evaluated by western blotting.

KEY FINDINGS

In vivo imaging revealed a significantly increase in lymph flow speed in TNFΔARE/+ mice in comparison to WT at both ages. Pressure myography showed an increase in contraction frequency, diameters and fractional pump flow at both ages, whereas amplitude and ejection fraction were significantly decreased in older TNFΔARE/+ mice. Additionally, contraction frequency was increased in the presence of 1400W, and systolic diameter was abolished with L-NNA in TNFΔARE/+ mice compared to WT. Significant increases in p-eNOS expression and neutrophil recruitment (MPO activity) were observed in TNFΔARE/+ mice compared to WT.

SIGNIFICANCE

Our data reveal functional changes in pLVs, especially in advanced stage of arthritis. These alterations may be related to eNOS and iNOS response, which can affect drainage of the inflammatory content from the joints.

The lymphatic endothelium-derived follistatin: activin A axis regulates neutrophil motility in response to Pseudomonas aeruginosa

The lymphatic system plays an active role during infection, however the role of lymphatic-neutrophil interactions in host-defense responses is not well understood. During infection with pathogens such as Pseudomonas aeruginosa, Staphylococcus aureus and Yersinia pestis, neutrophils traffic from sites of infection through the lymphatic vasculature, to draining lymph nodes to interact with resident lymphocytes. This process is poorly understood, in part, due to the lack of in vitro models of the lymphatic system. Here we use a 3D microscale lymphatic vessel model to examine neutrophil-lymphatic cell interactions during host defense responses to pathogens. In previous work, we have shown that follistatin is secreted at high concentrations by lymphatic endothelial cells during inflammation. Follistatin inhibits activin A, a member of the TGF-β superfamily, and, together, these molecules form a signaling pathway that plays a role in regulating both innate and adaptive immune responses. Although follistatin and activin A are constitutively produced in the pituitary, gonads and skin, their major source in the serum and their effects on neutrophils are poorly understood. Here we report a microfluidic model that includes both blood and lymphatic endothelial vessels, and neutrophils to investigate neutrophil-lymphatic trafficking during infection with P. aeruginosa. We found that lymphatic endothelial cells produce secreted factors that increase neutrophil migration toward P. aeruginosa, and are a significant source of both follistatin and activin A during Pseudomonas infection. We determined that follistatin produced by lymphatic endothelial cells inhibits activin A, resulting in increased neutrophil migration. These data suggest that the follistatin:activin A ratio influences neutrophil trafficking during infection with higher ratios increasing neutrophil migration.

Lymphatic coagulation and neutrophil extracellular traps in lung-draining lymph nodes of COVID-19 decedents

Clinical manifestations of severe COVID-19 include coagulopathies that are exacerbated by the formation of neutrophil extracellular traps (NETs). Here, we report that pulmonary lymphatic vessels, which traffic neutrophils and other immune cells to the lung-draining lymph node (LDLN), can also be blocked by fibrin clots in severe COVID-19. Immunostained tissue sections from COVID-19 decedents revealed widespread lymphatic clotting not only in the lung but also in the LDLN, where the extent of clotting correlated with the presence of abnormal, regressed, or missing germinal centers (GCs). It strongly correlated with the presence of intralymphatic NETs. In mice, tumor necrosis factor α induced intralymphatic fibrin clots; this could be inhibited by DNase I, which degrades NETs. In vitro, TNF-α induced lymphatic endothelial cell upregulation of ICAM-1 and CXCL8, among other neutrophil-recruiting factors, as well as thrombomodulin downregulation; in decedents, lymphatic clotting in LDLNs. In a separate cohort of hospitalized patients, serum levels of Myeloperoxidase-DNA (MPO-DNA, a NET marker) inversely correlated with antiviral antibody titers, but D-dimer levels, indicative of blood thrombosis, did not correlate with either. Patients with high MPO-DNA but low D-dimer levels generated poor antiviral antibody titers. This study introduces lymphatic coagulation in lungs and LDLNs as a clinical manifestation of severe COVID-19 and suggests the involvement of NETosis of lymphatic-trafficking neutrophils. It further suggests that lymphatic clotting may correlate with impaired formation or maintenance of GCs necessary for robust antiviral antibody responses, although further studies are needed to determine whether and how lymphatic coagulation affects adaptive immune responses.

Trafficking and retention of protein antigens across systems and immune cell types

In response to infection or vaccination, the immune system initially responds non-specifically to the foreign insult (innate) and then develops a specific response to the foreign antigen (adaptive). The programming of the immune response is shaped by the dispersal and delivery of antigens. The antigen size, innate immune activation and location of the insult all determine how antigens are handled. In this review we outline which specific cell types are required for antigen trafficking, which processes require active compared to passive transport, the ability of specific cell types to retain antigens and the viruses (human immunodeficiency virus, influenza and Sendai virus, vesicular stomatitis virus, vaccinia virus) and pattern recognition receptor activation that can initiate antigen retention. Both where the protein antigen is localized and how long it remains are critically important in shaping protective immune responses. Therefore, understanding antigen trafficking and retention is necessary to understand the type and magnitude of the immune response and essential for the development of novel vaccine and therapeutic targets.

Onset of Pyoderma Gangrenosum in Patients on Biologic Therapies: A Systematic Review

OBJECTIVE

To summarize clinical outcomes of paradoxical pyoderma gangrenosum (PG) onset in patients on biologic therapy.

METHODS

The authors conducted MEDLINE and EMBASE searches using PRISMA guidelines to include 57 patients (23 reports).

RESULTS

Of the included patients, 71.9% (n = 41/57) noted PG onset after initiating rituximab, 21.1% (n = 12/57) noted tumor necrosis factor α (TNF-α) inhibitors, 5.3% (n = 3/57) reported interleukin 17A inhibitors, and 1.8% (n = 1/57) reported cytotoxic T-lymphocyte-associated protein 4 antibodies. The majority of patients (94.3%) discontinued biologic use. The most common medications used to resolve rituximab-associated PG were intravenous immunoglobulins, oral corticosteroids, and antibiotics, with an average resolution time of 3.3 months. Complete resolution of PG in TNF-α-associated cases occurred within an average of 2.2 months after switching to another TNF-α inhibitor (n = 1), an interleukin 12/23 inhibitor (n = 2), or treatment with systemic corticosteroids and cyclosporine (n = 3), systemic corticosteroids alone (n = 1), or cyclosporine alone (n = 1).

CONCLUSIONS

Further investigations are warranted to determine whether PG onset is associated with underlying comorbidities, the use of biologic agents, or a synergistic effect. Nevertheless, PG may develop in patients on rituximab or TNF-α inhibitors, suggesting the need to monitor and treat such adverse effects.

CCR7-guided neutrophil redirection to skin-draining lymph nodes regulates cutaneous inflammation and infection

Neutrophils are the first nonresident effector immune cells that migrate to a site of infection or inflammation; however, improper control of neutrophil responses can cause considerable tissue damage. Here, we found that neutrophil responses in inflamed or infected skin were regulated by CCR7-dependent migration and phagocytosis of neutrophils in draining lymph nodes (dLNs). In mouse models of Toll-like receptor-induced skin inflammation and cutaneous Staphylococcus aureus infection, neutrophils migrated from the skin to the dLNs via lymphatic vessels in a CCR7-mediated manner. In the dLNs, these neutrophils were phagocytosed by lymph node-resident type 1 and type 2 conventional dendritic cells. CCR7 up-regulation on neutrophils was a conserved mechanism across different tissues and was induced by a broad range of microbial stimuli. In the context of cutaneous immune responses, disruption of CCR7 interactions by selective CCR7 deficiency of neutrophils resulted in increased antistaphylococcal immunity and aggravated skin inflammation. Thus, neutrophil homing to and clearance in skin-dLNs affects cutaneous immunity versus pathology.

Photochemically-Mediated Inflammation and Cross-Presentation of Mycobacterium bovis BCG Proteins Stimulates Strong CD4 and CD8 T-Cell Responses in Mice

Conventional vaccines are very efficient in the prevention of bacterial infections caused by extracellular pathogens due to effective stimulation of pathogen-specific antibodies. In contrast, considering that intracellular surveillance by antibodies is not possible, they are typically less effective in preventing or treating infections caused by intracellular pathogens such as Mycobacterium tuberculosis. The objective of the current study was to use so-called photochemical internalization (PCI) to deliver a live bacterial vaccine to the cytosol of antigen-presenting cells (APCs) for the purpose of stimulating major histocompatibility complex (MHC) I-restricted CD8 T-cell responses. For this purpose, Mycobacterium bovis BCG (BCG) was combined with the photosensitiser tetraphenyl chlorine disulfonate (TPCS2a) and injected intradermally into mice. TPCS2a was then activated by illumination of the injection site with light of defined energy. Antigen-specific CD4 and CD8 T-cell responses were monitored in blood, spleen, and lymph nodes at different time points thereafter using flow cytometry, ELISA and ELISPOT. Finally, APCs were infected and PCI-treated in vitro for analysis of their activation of T cells in vitro or in vivo after autologous vaccination of mice. Combination of BCG with PCI induced stronger BCG-specific CD4 and CD8 T-cell responses than treatment with BCG only or with BCG and TPCS2a without light. The overall T-cell responses were multifunctional as characterized by the production of IFN-γ, TNF-α, IL-2 and IL-17. Importantly, PCI induced cross-presentation of BCG proteins for stimulation of antigen-specific CD8 T-cells that were particularly producing IFN-γ and TNF-α. PCI further facilitated antigen presentation by causing up-regulation of MHC and co-stimulatory proteins on the surface of APCs as well as their production of TNF-α and IL-1β in vivo. Furthermore, PCI-based vaccination also caused local inflammation at the site of vaccination, showing strong infiltration of immune cells, which could contribute to the stimulation of antigen-specific immune responses. This study is the first to demonstrate that a live microbial vaccine can be combined with a photochemical compound and light for cross presentation of antigens to CD8 T cells. Moreover, the results revealed that PCI treatment strongly improved the immunogenicity of M. bovis BCG.

ADAM17, A Key Player of Cardiac Inflammation and Fibrosis in Heart Failure Development During Chronic Catecholamine Stress

Heart failure development is characterized by persistent inflammation and progressive fibrosis owing to chronic catecholamine stress. In a chronic stress state, elevated catecholamines result in the overstimulation of beta-adrenergic receptors (βARs), specifically β2-AR coupling with Gαi protein. Gαi signaling increases the activation of receptor-stimulated p38 mitogen-activated-protein-kinases (p38 MAPKs) and extracellular signal-regulated kinases (ERKs). Phosphorylation by these kinases is a common way to positively regulate the catalytic activity of A Disintegrin and Metalloprotease 17 (ADAM17), a metalloprotease that has grown much attention in recent years and has emerged as a chief regulatory hub in inflammation, fibrosis, and immunity due to its vital proteolytic activity. ADAM17 cleaves and activates proinflammatory cytokines and fibrotic factors that enhance cardiac dysfunction via inflammation and fibrosis. However, there is limited information on the cardiovascular aspect of ADAM17, especially in heart failure. Hence, this concise review provides a comprehensive insight into the structure of ADAM17, how it is activated and regulated during chronic catecholamine stress in heart failure development. This review highlights the inflammatory and fibrotic roles of ADAM17’s substrates; Tumor Necrosis Factor α (TNFα), soluble interleukin-6 receptor (sIL-6R), and amphiregulin (AREG). Finally, how ADAM17-induced chronic inflammation and progressive fibrosis aggravate cardiac dysfunction is discussed.

Meningeal Lymphatics: An Immune Gateway for the Central Nervous System

The recent (re)discovery of the meningeal lymphatic system has opened new theories as to how immune cells traffic and interact with the central nervous system (CNS). While evidence is accumulating on the contribution of the meningeal lymphatic system in both homeostatic and disease conditions, a lot remains unknown about the mechanisms that allow for interaction between the meningeal lymphatic system and immune cells. In this review, we synthesize the knowledge about the lymphatic immune interaction in the CNS and highlight the important questions that remain to be answered.

Imaging innate immunity

Innate immunity is the first line of defense against infectious intruders and also plays a major role in the development of sterile inflammation. Direct microscopic imaging of the involved immune cells, especially neutrophil granulocytes, monocytes, and macrophages, has been performed since more than 150 years, and we still obtain novel insights on a frequent basis. Initially, intravital microscopy was limited to small-sized animal species, which were often invertebrates. In this review, we will discuss recent results on the biology of neutrophils and macrophages that have been obtained using confocal and two-photon microscopy of individual cells or subcellular structures as well as light-sheet microscopy of entire organs. This includes the role of these cells in infection defense and sterile inflammation in mammalian disease models relevant for human patients. We discuss their protective but also disease-enhancing activities during tumor growth and ischemia-reperfusion damage of the heart and brain. Finally, we provide two visions, one experimental and one applied, how our knowledge on the function of innate immune cells might be further enhanced and also be used in novel ways for disease diagnostics in the future.

Imaging leukocyte migration through afferent lymphatics

Afferent lymphatics mediate the transport of antigen and leukocytes, especially of dendritic cells (DCs) and T cells, from peripheral tissues to draining lymph nodes (dLNs). As such they play important roles in the induction and regulation of adaptive immunity. Over the past 15 years, great advances in our understanding of leukocyte trafficking through afferent lymphatics have been made through time‐lapse imaging studies performed in tissue explants and in vivo, allowing to visualize this process with cellular resolution. Intravital imaging has revealed that intralymphatic leukocytes continue to actively migrate once they have entered into lymphatic capillaries, as a consequence of the low flow conditions present in this compartment. In fact, leukocytes spend considerable time migrating, patrolling and interacting with the lymphatic endothelium or with other intralymphatic leukocytes within lymphatic capillaries. Cells typically only start to detach once they arrive in downstream‐located collecting vessels, where vessel contractions contribute to enhanced lymph flow. In this review, we will introduce the biology of afferent lymphatic vessels and report on the presumed significance of DC and T cell migration via this route. We will specifically highlight how time‐lapse imaging has contributed to the current model of lymphatic trafficking and the emerging notion that ‐ besides transport – lymphatic capillaries exert additional roles in immune modulation.

Neutrophils in secondary lymphoid organs

Neutrophils are traditionally considered short‐lived, circulating innate immune cells that are rapidly recruited to sites of inflammation in response to infectious and inflammatory stimuli. Neutrophils efficiently internalize, kill or entrap pathogens, but their effector molecules may cause collateral tissue damage. More recently, it has been appreciated that neutrophils can also influence adaptive immunity. Lymph nodes (LNs) are immune cell‐rich secondary lymphoid organs that provide an ideal platform for cellular interaction and the integration of immunological information collected from local tissues. A variety of peripheral stimuli promote neutrophil migration to draining LNs via blood or lymphatics, utilizing differing molecular cues depending on the site of entry. Within LNs, neutrophils interact with other innate and adaptive cells. Crosstalk with subcapsular sinus macrophages contributes to the control of pathogen spread beyond the LN. Neutrophils can influence antigen presentation indirectly by interacting with DCs or directly by expressing major histocompatibility complex (MHC) and costimulatory molecules for antigen presentation. Interactions between neutrophils and adaptive lymphocytes can alter B‐cell antibody responses. Studies have shown conflicting results on whether neutrophils exert stimulatory or inhibitory effects on other LN immune cells, with stimulus‐specific and temporal differences in the outcome of these interactions. Furthermore, neutrophils have also been shown to traffick to LNs in homeostasis, with a potential role in immune surveillance, antigen capture and in shaping early adaptive responses in LNs. Understanding the mechanisms underpinning the effects of neutrophils on LN immune cells and adaptive immunity could facilitate the development of neutrophil‐targeted therapies in inflammatory diseases.

Neutrophil Interactions with the Lymphatic System

The lymphatic system is a complex network of lymphatic vessels and lymph nodes designed to balance fluid homeostasis and facilitate host immune defence. Neutrophils are rapidly recruited to sites of inflammation to provide the first line of protection against microbial infections. The traditional view of neutrophils as short-lived cells, whose role is restricted to providing sterilizing immunity at sites of infection, is rapidly evolving to include additional functions at the interface between the innate and adaptive immune systems. Neutrophils travel via the lymphatics from the site of inflammation to transport antigens to lymph nodes. They can also enter lymph nodes from the blood by crossing high endothelial venules. Neutrophil functions in draining lymph nodes include pathogen control and modulation of adaptive immunity. Another facet of neutrophil interactions with the lymphatic system is their ability to promote lymphangiogenesis in draining lymph nodes and inflamed tissues. In this review, we discuss the significance of neutrophil migration to secondary lymphoid organs and within the lymphatic vasculature and highlight emerging evidence of the neutrophils’ role in lymphangiogenesis.

Structure and Immune Function of Afferent Lymphatics and Their Mechanistic Contribution to Dendritic Cell and T Cell Trafficking

Afferent lymphatic vessels (LVs) mediate the transport of antigen and leukocytes to draining lymph nodes (dLNs), thereby serving as immunologic communication highways between peripheral tissues and LNs. The main cell types migrating via this route are antigen-presenting dendritic cells (DCs) and antigen-experienced T cells. While DC migration is important for maintenance of tolerance and for induction of protective immunity, T cell migration through afferent LVs contributes to immune surveillance. In recent years, great progress has been made in elucidating the mechanisms of lymphatic migration. Specifically, time-lapse imaging has revealed that, upon entry into capillaries, both DCs and T cells are not simply flushed away with the lymph flow, but actively crawl and patrol and even interact with each other in this compartment. Detachment and passive transport to the dLN only takes place once the cells have reached the downstream, contracting collecting vessel segments. In this review, we describe how the anatomy of the lymphatic network supports leukocyte trafficking and provide updated knowledge regarding the cellular and molecular mechanisms responsible for lymphatic migration of DCs and T cells. In addition, we discuss the relevance of DC and T cell migration through afferent LVs and its presumed implications on immunity.

Afferent Lymphatic Transport and Peripheral Tissue Immunity

Lymphatic vessels provide an anatomical framework for immune surveillance and adaptive immune responses. Although appreciated as the route for Ag and dendritic cell transport, peripheral lymphatic vessels are often not considered active players in immune surveillance. Lymphatic vessels, however, integrate contextual cues that directly regulate transport, including changes in intrinsic pumping and capillary remodeling, and express a dynamic repertoire of inflammatory chemokines and adhesion molecules that facilitates leukocyte egress out of inflamed tissue. These mechanisms together contribute to the course of peripheral tissue immunity. In this review, we focus on context-dependent mechanisms that regulate fluid and cellular transport out of peripheral nonlymphoid tissues to provide a framework for understanding the effects of afferent lymphatic transport on immune surveillance, peripheral tissue inflammation, and adaptive immunity.

In Sickness and in Health: The Immunological Roles of the Lymphatic System

The lymphatic system plays crucial roles in immunity far beyond those of simply providing conduits for leukocytes and antigens in lymph fluid. Endothelial cells within this vasculature are distinct and highly specialized to perform roles based upon their location. Afferent lymphatic capillaries have unique intercellular junctions for efficient uptake of fluid and macromolecules, while expressing chemotactic and adhesion molecules that permit selective trafficking of specific immune cell subsets. Moreover, in response to events within peripheral tissue such as inflammation or infection, soluble factors from lymphatic endothelial cells exert “remote control” to modulate leukocyte migration across high endothelial venules from the blood to lymph nodes draining the tissue. These immune hubs are highly organized and perfectly arrayed to survey antigens from peripheral tissue while optimizing encounters between antigen-presenting cells and cognate lymphocytes. Furthermore, subsets of lymphatic endothelial cells exhibit differences in gene expression relating to specific functions and locality within the lymph node, facilitating both innate and acquired immune responses through antigen presentation, lymph node remodeling and regulation of leukocyte entry and exit. This review details the immune cell subsets in afferent and efferent lymph, and explores the mechanisms by which endothelial cells of the lymphatic system regulate such trafficking, for immune surveillance and tolerance during steady-state conditions, and in response to infection, acute and chronic inflammation, and subsequent resolution.

Dendritic cell entry to lymphatic capillaries is orchestrated by CD44 and the hyaluronan glycocalyx

CD44 anchors the hyaluronan glycocalyx on migrating dendritic cells to permit docking to the endothelial receptor LYVE-1, thus orchestrating lymphatic trafficking through modulating glycocalyx density.

DCs play a vital role in immunity by conveying antigens from peripheral tissues to draining lymph nodes, through afferent lymphatic vessels. Critical to the process is initial docking to the lymphatic endothelial receptor LYVE-1 via its ligand hyaluronan on the DC surface. How this relatively weak binding polymer is configured for specific adhesion to LYVE-1, however, is unknown. Here, we show that hyaluronan is anchored and spatially organized into a 400–500 nm dense glycocalyx by the leukocyte receptor CD44. Using gene knockout and by modulating CD44-hyaluronan interactions with monoclonal antibodies in vitro and in a mouse model of oxazolone-induced skin inflammation, we demonstrate that CD44 is required for DC adhesion and transmigration across lymphatic endothelium. In addition, we present evidence that CD44 can dynamically control the density of the hyaluronan glycocalyx, regulating the efficiency of DC trafficking to lymph nodes. Our findings define a previously unrecognized role for CD44 in lymphatic trafficking and highlight the importance of the CD44:HA:LYVE-1 axis in its regulation.

Shape and Function of Interstitial Chemokine CCL21 Gradients Are Independent of Heparan Sulfates Produced by Lymphatic Endothelium

Gradients of chemokines and growth factors guide migrating cells and morphogenetic processes. Migration of antigen-presenting dendritic cells from the interstitium into the lymphatic system is dependent on chemokine CCL21, which is secreted by endothelial cells of the lymphatic capillary, binds heparan sulfates and forms gradients decaying into the interstitium. Despite the importance of CCL21 gradients, and chemokine gradients in general, the mechanisms of gradient formation are unclear. Studies on fibroblast growth factors have shown that limited diffusion is crucial for gradient formation. Here, we used the mouse dermis as a model tissue to address the necessity of CCL21 anchoring to lymphatic capillary heparan sulfates in the formation of interstitial CCL21 gradients. Surprisingly, the absence of lymphatic endothelial heparan sulfates resulted only in a modest decrease of CCL21 levels at the lymphatic capillaries and did neither affect interstitial CCL21 gradient shape nor dendritic cell migration toward lymphatic capillaries. Thus, heparan sulfates at the level of the lymphatic endothelium are dispensable for the formation of a functional CCL21 gradient.

The neutrophil antimicrobial peptide cathelicidin promotes Th17 differentiation

The host defence peptide cathelicidin (LL-37 in humans, mCRAMP in mice) is released from neutrophils by de-granulation, NETosis and necrotic death; it has potent anti-pathogen activity as well as being a broad immunomodulator. Here we report that cathelicidin is a powerful Th17 potentiator which enhances aryl hydrocarbon receptor (AHR) and RORγt expression, in a TGF-β1-dependent manner. In the presence of TGF-β1, cathelicidin enhanced SMAD2/3 and STAT3 phosphorylation, and profoundly suppressed IL-2 and T-bet, directing T cells away from Th1 and into a Th17 phenotype. Strikingly, Th17, but not Th1, cells were protected from apoptosis by cathelicidin. We show that cathelicidin is released by neutrophils in mouse lymph nodes and that cathelicidin-deficient mice display suppressed Th17 responses during inflammation, but not at steady state. We propose that the neutrophil cathelicidin is required for maximal Th17 differentiation, and that this is one method by which early neutrophilia directs subsequent adaptive immune responses.

The Gut-Lung Axis in Systemic Inflammation. Role of Mesenteric Lymph as a Conduit

Emerging evidence shows that after injury or infection, the mesenteric lymph acts as a conduit for gut-derived toxic factors to enter the blood circulation, causing systemic inflammation and acute lung injury. Neither the cellular and molecular identity of lymph factors nor their mechanisms of action have been well understood and thus have become a timely topic of investigation. This review will first provide a summary of background knowledge on gut barrier and mesenteric lymphatics, followed by a discussion focusing on the current understanding of potential injurious factors in the lymph and their mechanistic contributions to lung injury. We also examine lymph factors with antiinflammatory properties as well as the bidirectional nature of the gut-lung axis in inflammation.

Dysregulation of leukocyte trafficking in ageing: Causal factors and possible corrective therapies

Ageing is a universal biological phenomenon that is accompanied by the development of chronic, low-grade inflammation and remodelling of the immune system resulting in compromised immune function. In this review, we explore how the trafficking of innate and adaptive immune cells under homeostatic and inflammatory conditions is dysregulated in ageing. We particularly highlight the age-related changes in the expression of adhesion molecules and chemokine receptor/ligands, and the accumulation of senescent cells that drive modulated leukocyte trafficking. These age-related changes to leukocyte trafficking are multifactorial and specific to leukocyte subset, tissue, type of vascular bed, and inflammatory status. However, dysregulated leukocyte trafficking ultimately affects immune responses in older adults. We therefore go on to discuss approved drugs, including anti-integrins, anti-chemokines and statins, as well as novel therapeutics that may be used to target dysregulated leukocyte trafficking in ageing, improve immune responses and delay the onset of age-related diseases.

Identifying in vivo inflammation using magnetic nanoparticle spectra

We are developing magnetic nanoparticle (NP) methods to characterize inflammation and infection in vivo. Peritoneal infection in C57BL/6 mice was used as a biological model. An intraperitoneal NP injection was followed by measurement of magnetic nanoparticle spectroscopy of Brownian rotation (MSB) spectra taken over time. MSB measures the magnetization of NPs in a low frequency alternating magnetic field. Two groups of three mice were studied; each group had two infected mice and one control with no infection. The raw MSB signal was compared with two derived metrics: the NP relaxation time and number of NPs present in the sensitive volume of the receive coil. A four compartment dynamic model was used to relate those physical properties to the relevant biological processes including phagocytic activity and migration. The relaxation time increased over time for all of the mice as the NPs were absorbed. The NP number decreased over time as the NPs were cleared from the sensitive volume of the receive coil. The composite p-values for all three rate constants were significant: raw signal, 0.0002, relaxation, <10^-16 and local NP clearance, <10^-16. However, not all the individual mice had significant changes: Only half the infected mice had significantly different rate constants for raw signal reduction. All infected mice had significantly smaller relaxation time constants. All but one of the infected mice had significantly lower rate constants for local clearance. Relaxation is affected by both phagocytic activity, edema and temperature changes and it should be possible to better isolate those effects to more completely characterize inflammation using more advanced MSB methods. The MSB NP signal can be used to identify inflammation in vivo because it has the unique ability to monitor phagocytic absorption through relaxation measurements.

Targeting of Formyl Peptide Receptor 2 for in vivo imaging of acute vascular inflammation

Inflammatory conditions are associated with a variety of diseases and can significantly contribute to their pathophysiology. Neutrophils are recognised as key players in driving vascular inflammation and promoting inflammation resolution. As a result, neutrophils, and specifically their surface formyl peptide receptors (FPRs), are attractive targets for non-invasive visualization of inflammatory disease states and studying mechanistic details of the process.

Methods: A small-molecule Formyl Peptide Receptor 2 (FPR2/ALX)-targeted compound was combined with two rhodamine-derived fluorescent tags to form firstly, a targeted probe (Rho-pip-C1) and secondly a targeted, pH-responsive probe (Rho-NH-C1) for in vivo applications. We tested internalization, toxicity and functional interactions with neutrophils in vitro for both compounds, as well as the fluorescence switching response of Rho-NH-C1 to neutrophil activation. Finally, in vivo imaging (fluorescent intravital microscopy [IVM]) and therapeutic efficacy studies were performed in an inflammatory mouse model.

Results: In vitro studies showed that the compounds bound to human neutrophils via FPR2/ALX without causing internalization at relevant concentrations. Additionally, the compounds did not cause toxicity or affect neutrophil functional responses (e.g. chemotaxis or transmigration). In vivo studies using IVM showed Rho-pip-C1 bound to activated neutrophils in a model of vascular inflammation. The pH-sensitive (“switchable”) version termed Rho-NH-C1 validated these findings, showing fluorescent activity only in inflammatory conditions.

Conclusions: These results indicate a viable design of fluorescent probes that have the ability to detect inflammatory events by targeting activated neutrophils.

Potential Protective Effects of the Water-Soluble Chinese Propolis on Hypertension Induced by High-Salt Intake

High‐salt (HS) intake is closely associated with the ignition and progression of hypertension. The mechanisms might be involved in endothelial dysfunction, nitric oxide deficiency, oxidative stress, and proinflammatory cytokines. Propolis is widely used as a natural antioxidant and is a well‐known functional food for its biological activities, which includes anti‐inflammation, antimicrobial, and liver detoxification. In this study, we successfully replicated a HS diet‐induced hypertensive rat model. We found that in the long‐term HS diet group, the myocardial function of the rats was altered and led to a significant decrease (around 49%) in heart function. However, doses of Chinese water‐soluble propolis (WSP) were found directly proportional (11%, 60%, 91%, respectively) to the myocardial function improvement in hypertensive rats. The results from the blood circulation test and hematoxylin‐eosin stains showed that propolis had protective effects on myocardial functions and blood vessels in hypertensive rats. Also, based on the results of western blot and polymerase chain reaction, WSP effectively regulated Nox2 and Nox4 levels and was responsible for a decrease in reactive oxygen species synthesis. Our findings demonstrate that Chinese WSP has a significant effect on the blood pressure of hypertensive rats and their cardiovascular functions that improved significantly. The improvement in the cardiovascular functions might be related to the process of anti‐oxidation, anti‐inflammation, and the improvements of the endothelial function in hypertensive rats.

Characterization of the Dynamic Behavior of Neutrophils Following Influenza Vaccination

Neutrophils are amongst the first cells to respond to inflammation and infection. Although they play a key role in limiting the dissemination of pathogens, the study of their dynamic behavior in immune organs remains elusive. In this work, we characterized in vivo the dynamic behavior of neutrophils in the mouse popliteal lymph node (PLN) after influenza vaccination with UV-inactivated virus. To achieve this, we used an image-based systems biology approach to detect the motility patterns of neutrophils and to associate them to distinct actions. We described a prominent and rapid recruitment of neutrophils to the PLN following vaccination, which was dependent on the secretion of the chemokine CXCL1 and the alarmin molecule IL-1α. In addition, we observed that the initial recruitment occurred mainly via high endothelial venules located in the paracortical and interfollicular regions of the PLN. The analysis of the spatial-temporal patterns of neutrophil migration demonstrated that, in the initial stage, the majority of neutrophils displayed a patrolling behavior, followed by the formation of swarms in the subcapsular sinus of the PLN, which were associated with macrophages in this compartment. Finally, we observed using multiple imaging techniques, that neutrophils phagocytize and transport influenza virus particles. These processes might have important implications in the capacity of these cells to present viral antigens.

Heparanase-Dependent Remodeling of Initial Lymphatic Glycocalyx Regulates Tissue-Fluid Drainage During Acute Inflammation in vivo

The glycocalyx is a dense layer of carbohydrate chains involved in numerous and fundamental biological processes, such as cellular and tissue homeostasis, inflammation and disease development. Composed of membrane-bound glycoproteins, sulfated proteoglycans and glycosaminoglycan side-chains, this structure is particularly essential for blood vascular barrier functions and leukocyte diapedesis. Interestingly, whilst the glycocalyx of blood vascular endothelium has been extensively studied, little is known about the composition and function of this glycan layer present on tissue-associated lymphatic vessels (LVs). Here, we applied confocal microscopy to characterize the composition of endothelial glycocalyx of initial lymphatic capillaries in murine cremaster muscles during homeostatic and inflamed conditions using an anti-heparan sulfate (HS) antibody and a panel of lectins recognizing different glycan moieties of the glycocalyx. Our data show the presence of HS, α-D-galactosyl moieties, α2,3-linked sialic acids and, to a lesser extent, N-Acetylglucosamine moieties. A similar expression profile was also observed for LVs of mouse and human skins. Interestingly, inflammation of mouse cremaster tissues or ear skin as induced by TNF-stimulation induced a rapid (within 16 h) remodeling of the LV glycocalyx, as observed by reduced expression of HS and galactosyl moieties, whilst levels of α2,3-linked sialic acids remains unchanged. Furthermore, whilst this response was associated with neutrophil recruitment from the blood circulation and their migration into tissue-associated LVs, specific neutrophil depletion did not impact LV glycocalyx remodeling. Mechanistically, treatment with a non-anticoagulant heparanase inhibitor suppressed LV HS degradation without impacting neutrophil migration into LVs. Interestingly however, inhibition of glycocalyx degradation reduced the capacity of initial LVs to drain interstitial fluid during acute inflammation. Collectively, our data suggest that rapid remodeling of endothelial glycocalyx of tissue-associated LVs supports drainage of fluid and macromolecules but has no role in regulating neutrophil trafficking out of inflamed tissues via initial LVs.

Phenotypically distinct neutrophils patrol uninfected human and mouse lymph nodes

Neutrophils play a key role in innate immunity. As the dominant circulating phagocyte, they are rapidly recruited from the bloodstream to sites of infection or injury to internalize and destroy microbes. More recently, neutrophils have been identified in uninfected organs, challenging the classical view of their function. Here we show that neutrophils were present in lymph nodes (LNs) in homeostasis. Using flow cytometry and confocal imaging, we identified neutrophils within LNs in naive, unchallenged mice, including LNs draining the skin, lungs, and gastrointestinal tract. Neutrophils were enriched within specific anatomical regions, in the interfollicular zone, a site of T cell activation. Intravital two-photon microscopy demonstrated that LN neutrophils were motile, trafficked into LNs from both blood and tissues via high endothelial venules and afferent lymphatics, respectively, and formed interactions with dendritic cells in LNs. Murine and human LN neutrophils had a distinct phenotype compared with circulating neutrophils, with higher major histocompatibility complex II (MHCII) expression, suggesting a potential role in CD4 T cell activation. Upon ex vivo stimulation with IgG immune complex (IC), neutrophils up-regulated expression of MHCII and costimulatory molecules and increased T cell activation. In vivo, neutrophils were capable of delivering circulating IC to LNs, suggesting a broader functional remit. Overall, our data challenge the perception that neutrophil patrol is limited to the circulation in homeostasis, adding LNs to their routine surveillance territory.

Lymphatic Migration of Immune Cells

Lymphatic vessels collect interstitial fluid that has extravasated from blood vessels and return it to the circulatory system. Another important function of the lymphatic network is to facilitate immune cell migration and antigen transport from the periphery to draining lymph nodes. This migration plays a crucial role in immune surveillance, initiation of immune responses and tolerance. Here we discuss the significance and mechanisms of lymphatic migration of innate and adaptive immune cells in homeostasis, inflammation and cancer.

Amelioration of PM2.5-induced lung toxicity in rats by nutritional supplementation with fish oil and Vitamin E

BACKGROUND

Exposure to fine particulate matter (PM_2.5) has been associated with respiratory morbidity and mortality. Identification of interventional measures that are efficacious against PM_2.5-induced toxicity may provide public health benefits. This study examined the inhibitory effects of nutritional supplementation with fish oil as a source of omega-3 fatty acids and vitamin E (Vit E) on PM_2.5-induced lung toxicity in rats.

METHOD

Sixty four male Sprague Dawley rats were gavaged with phosphate buffered saline (PBS), corn oil (5 ml/kg), fish oil (150 mg/kg), or Vit E (75 mg/kg), respectively, once a day for 21 consecutive days prior to intratracheal instillation of PM_2.5 (10 mg/kg) every other day for a total of 3 times. Serum and bronchoalveolar lavage fluids (BALFs) were collected 24 h after the last instillation of PM_2.5. Levels of total proteins (TP), lactate dehydrogenase (LDH), superoxide dismutase (SOD), 8-epi-prostaglandin F2α (8-epi-PGF2α), interleukin-1β (IL-1β), C-reactive protein (CRP), IL-6, and tumor necrosis factor-ɑ (TNF-ɑ) were analyzed for markers of cell injury and inflammation. Additionally, histological alterations of lung tissues were examined by hematoxylin-eosin staining.

RESULT

Exposure to PM_2.5 resulted in lung toxicity, represented as increased levels of total proteins, LDH, 8-epi-PGF2α, IL-1β and TNF-α, and increased infiltration of inflammatory cells, and decreased SOD in the BALFs, and systemic inflammation, as evinced by increased levels of CRP and IL-6 in serum. Strikingly, supplementation with fish oil but not Vit E significantly ameliorated PM_2.5-induced lung toxicity and systemic inflammation.

CONCLUSION

PM_2.5 exposure induces oxidative stress, lung injury and inflammation, which is ameliorated significantly by fish oil and partially by Vit E.

Neutrophil trafficking to lymphoid tissues: physiological and pathological implications

Recent advances have provided evidence for the involvement of neutrophils in both innate and adaptive immunity, robustly challenging the old dogma that neutrophils are short-lived prototypical innate immune cells solely involved in acute responses to microbes and exerting collateral tissue damage. There is now ample evidence showing that neutrophils can migrate into different compartments of the lymphoid system where they contribute to the orchestration of the activation and/or suppression of lymphocyte effector functions in homeostasis and during chronic inflammation, such as autoimmune disorders and cancer. In support of this notion, neutrophils can generate a wide range of cytokines and other mediators capable of regulating the survival, proliferation and functions of both T and B cells. In addition, neutrophils can directly engage with lymphocytes and promote antigen presentation. Furthermore, there is emerging evidence of the existence of distinct and diverse neutrophil phenotypes with immunomodulatory functions that characterise different pathological conditions, including chronic and autoimmune inflammatory conditions. The aim of this review is to discuss the mechanisms implicated in neutrophil trafficking into the lymphoid system and to provide an overview of the immuno-regulatory functions of neutrophils in health and disease in the context of adaptive immunity. Copyright © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Leucocyte Trafficking via the Lymphatic Vasculature- Mechanisms and Consequences

The lymphatics fulfill a vital physiological function as the conduits through which leucocytes traffic between the tissues and draining lymph nodes for the initiation and modulation of immune responses. However, until recently many of the molecular mechanisms controlling such migration have been unclear. As a result of careful research, it is now apparent that the process is regulated at multiple stages from initial leucocyte entry and intraluminal crawling in peripheral tissue lymphatics, through to leucocyte exit in draining lymph nodes where the migrating cells either participate in immune responses or return to the circulation via efferent lymph. Furthermore, it is increasingly evident that most if not all leucocyte populations migrate in lymph and that such migration is not only important for immune modulation, but also for the timely repair and resolution of tissue inflammation. In this article, I review the latest research findings in these areas, arising from new insights into the distinctive ultrastructure of lymphatic capillaries and lymph node sinuses. Accordingly, I highlight the emerging importance of the leucocyte glycocalyx and its novel interactions with the endothelial receptor LYVE-1, the intricacies of endothelial chemokine secretion and sequestration that direct leucocyte trafficking and the significance of the process for normal immune function and pathology.

Distinct neutrophil counts and functions in newly diagnosed type 1 diabetes, latent autoimmune diabetes in adults, and type 2 diabetes

BACKGROUND

Recent discoveries from animal models demonstrated that neutrophils can induce type 1 diabetes (T1D) through infiltrating into the islets. However, the evidence of their actions in T1D patients is relatively rare, and the change trend of neutrophil numbers and functions in different subtypes of diabetes has not been investigated.

METHODS

Patients with newly diagnosed T1D (n = 189), latent autoimmune diabetes in adults (LADA) (n = 86), T2D (n = 235), and healthy controls (n = 709) were enrolled. Circulating neutrophil counts were measured, and their correlations with clinical parameters were analysed. Neutrophils were isolated by density gradient centrifugation and magnetic bead cell sorting method. Neutrophil migration rate and chemokine levels in the blood were explored by trans-well and ELISA, respectively. Neutrophil phagocytosis rate, adhesion molecules and chemokine receptors expression were investigated by flow cytometry.

RESULTS

Compared with controls, neutrophil counts decreased in T1D patients but increased in T2D patients, with no change in LADA patients. The numbers showed a gradual increase trend from T1D, LADA to T2D. In autoimmune diabetes, neutrophil counts were associated with the number and titre of positive autoantibodies against β-cell antigens. No difference was found in neutrophil phagocytosis rate, but neutrophil migration in T1D patients was impaired and associated with CD62L expression, which was related closely to the titre of autoantibody.

CONCLUSIONS

Neutrophil numbers and migration abilities displayed distinct levels in different types of diabetes. In T1D, CD62L seems to play an important role in the migration of neutrophils and β-cell autoimmunity.

Neutrophil Vaccination Dynamics and Their Capacity To Mediate B Cell Help in Rhesus Macaques

Neutrophils are the most abundant leukocyte and play a critical role in the initial response to an Ag. Recently, their ability to contribute to adaptive immunity has been highlighted. We evaluated the ability of neutrophils from blood to contribute to the adaptive immune response in a preclinical rhesus macaque SIV vaccine trial. Replication-competent adenovirus-SIV recombinants induced neutrophil activation, B cell help markers, and enhanced ability to generate reactive oxygen species. Boosting with SIV vaccines (adjuvant together with ALVAC or DNA plus envelope protein) elicited significant neutrophil responses. Serum cytokine and chemokine levels induced correlated with the frequency of neutrophil subsets expressing IL-21, myeloperoxidase, and CD64. Post-SIV infection, neutrophils exhibited dysfunction, both phenotypically and functionally. B cells from protected and infected macaques cocultured with autologous polymorphonuclear cells, consisting primarily of neutrophils, were activated, underwent class switching, and produced Abs. This B cell help was not aided by addition of IL-10 and was largely contact dependent. Numerous genes associated with inflammation, Ab production, and chemotaxis were upregulated in the cocultured B cells. We conclude that immune stimulation by vaccination or antigenic exposure imparts a greater ability of neutrophils to contribute to the adaptive immune response. Harnessing this granulocytic response has the potential to improve vaccine efficacy.

Cellular traffic through afferent lymphatic vessels

The lymphatic system has long been known to serve as a highway for migrating leukocytes from peripheral tissue to draining lymph nodes (dLNs) and back to circulation, thereby contributing to the induction of adaptive immunity and immunesurveillance. Lymphatic vessels (LVs) present in peripheral tissues upstream of a first dLN are generally referred to as afferent LVs. In contrast to migration through blood vessels (BVs), the detailed molecular and cellular requirements of cellular traffic through afferent LVs have only recently started to be unraveled. Progress in our ability to track the migration of lymph-borne cell populations, in combination with cutting-edge imaging technologies, nowadays allows the investigation and visualization of lymphatic migration of endogenous leukocytes, both at the population and at the single-cell level. These studies have revealed that leukocyte trafficking through afferent LVs generally follows a step-wise migration pattern, relying on the active interplay of numerous molecules. In this review, we will summarize and discuss current knowledge of cellular traffic through afferent LVs. We will first outline how the structure of the afferent LV network supports leukocyte migration and highlight important molecules involved in the migration of dendritic cells (DCs), T cells and neutrophils, i.e. the most prominent cell types trafficking through afferent LVs. Additionally, we will describe how tumor cells hijack the lymphatic system for their dissemination to draining LNs. Finally, we will summarize and discuss our current understanding of the functional significance as well as the therapeutic implications of cell traffic through afferent LVs.

Visceral Adipose Tissue Immune Homeostasis Is Regulated by the Crosstalk between Adipocytes and Dendritic Cell Subsets

Visceral adipose tissue (VAT) has multiple roles in orchestrating whole-body energy homeostasis. In addition, VAT is now considered an immune site harboring an array of innate and adaptive immune cells with a direct role in immune surveillance and host defense. We report that conventional dendritic cells (cDCs) in VAT acquire a tolerogenic phenotype through upregulation of pathways involved in adipocyte differentiation. While activation of the Wnt/β-catenin pathway in cDC1 DCs induces IL-10 production, upregulation of the PPARγ pathway in cDC2 DCs directly suppresses their activation. Combined, they promote an anti-inflammatory milieu in vivo delaying the onset of obesity-induced chronic inflammation and insulin resistance. Under long-term over-nutrition, changes in adipocyte biology curtail β-catenin and PPARγ activation, contributing to VAT inflammation.

Neutrophil-lymphatic interactions during acute and chronic disease

The lymphatic system aids in osmoregulation through tissue fluid transport, but is also designed to support communication between cells of the innate and adaptive immune systems. During inflammation, changes within the lymphatics can result in an altered response to infection. Neutrophils have been described as one key cell type that facilitates antigen capture and presentation within the lymphatic system, enabling an effective adaptive immune response. Disruption of neutrophil recruitment during inflammation, due to alterations in lymphatics, is a growing area of study due to their key role in infection resolution. In this review, we discuss the currently known methods by which neutrophils are recruited to the lymphatic system and what subsequent effects they have on resident and recruited cells within the lymph vessels and nodes. We also discuss the changes in neutrophil activation and recruitment during chronic inflammatory diseases and their relationship to lymphatic dysfunction.

Organ-specific lymphatic vasculature: From development to pathophysiology

Recent discoveries of novel functions and diverse origins of lymphatic vessels have drastically changed our view of lymphatic vasculature. Traditionally regarded as passive conduits for fluid and immune cells, lymphatic vessels now emerge as active, tissue-specific players in major physiological and pathophysiological processes. Lymphatic vessels show remarkable plasticity and heterogeneity, reflecting their functional specialization to control the tissue microenvironment. Moreover, alternative developmental origins of lymphatic endothelial cells in some organs may contribute to the diversity of their functions in adult tissues. This review aims to summarize the most recent findings of organotypic differentiation of lymphatic endothelial cells in terms of their distinct (patho)physiological functions in skin, lymph nodes, small intestine, brain, and eye. We discuss recent advances in our understanding of the heterogeneity of lymphatic vessels with respect to the organ-specific functional and molecular specialization of lymphatic endothelium, such as the hybrid blood-lymphatic identity of Schlemm's canal, functions of intestinal lymphatics in dietary fat uptake, and discovery of meningeal lymphatic vasculature and perivascular brain lymphatic endothelial cells.