Expression of cys–cys chemokine ligand 21 on human gingival lymphatic vessels

Porphyromonas gingivalis regulates atherosclerosis through an immune pathway

Atherosclerosis (AS) is a chronic inflammatory disease, involving a pathological process of endothelial dysfunction, lipid deposition, plaque rupture, and arterial occlusion, and is one of the leading causes of death in the world population. The progression of AS is closely associated with several inflammatory diseases, among which periodontitis has been shown to increase the risk of AS. Porphyromonas gingivalis (P. gingivalis), presenting in large numbers in subgingival plaque biofilms, is the “dominant flora” in periodontitis, and its multiple virulence factors are important in stimulating host immunity. Therefore, it is significant to elucidate the potential mechanism and association between P. gingivalis and AS to prevent and treat AS. By summarizing the existing studies, we found that P. gingivalis promotes the progression of AS through multiple immune pathways. P. gingivalis can escape host immune clearance and, in various forms, circulate with blood and lymph and colonize arterial vessel walls, directly inducing local inflammation in blood vessels. It also induces the production of systemic inflammatory mediators and autoimmune antibodies, disrupts the serum lipid profile, and thus promotes the progression of AS. In this paper, we summarize the recent evidence (including clinical studies and animal studies) on the correlation between P. gingivalis and AS, and describe the specific immune mechanisms by which P. gingivalis promotes AS progression from three aspects (immune escape, blood circulation, and lymphatic circulation), providing new insights into the prevention and treatment of AS by suppressing periodontal pathogenic bacteria.

CCL21/CCR7 axis regulates demyelination and vascular cognitive impairment in a mouse model for chronic cerebral hypoperfusion

OBJECTIVES

White matter lesions (WML) are usually accompanied by cognitive decline, which consist of axonal loss and demyelination. CC chemokine ligand 21 (CCL21) and its receptor C-C chemokine receptor 7 (CCR7) belong to the chemokine family, which are involved in many diseases. However, their function in the central nervous system (CNS) is still unexplored. This study aimed to explore the role of CCL21/CCR7 axis in the pathological process of chronic ischemia-induced WML.

METHODS

Bilateral common carotid artery stenosis (BCAS) was employed in C57BL/6 mice as the in vivo WML model. Microarray analysis was performed to detect the overall molecular changes induced in the endothelial cells by BCAS. Q-PCR, Western blotting, and immunofluorescence staining were performed to evaluate expression levels of the related molecules. The mice were injected with LV-CCL21-GFP virus in the corpus callosum to overexpress CCL21. WML degree was determined via MRI, and cognitive ability was assessed by Y-maze and novel object recognition tests. Myelin sheath integrity was evaluated via immunofluorescence staining.

RESULTS

CCL21 was significantly downregulated in endothelial cells after BCAS and CCL21 overexpression alleviated BCAS-induced cognitive deficits and demyelination. Furthermore, CCR7 was found to be mainly expressed in oligodendrocytes (OLs) after exposed to hypoxia and CCR7 silencing blocked the protective effects induced by CCL21 overexpression. Conclusions CCL21/CCR7 axis may play a key role in demyelination induced by BCAS. This might provide a novel therapeutic target for WML.

Tumor lymphangiogenesis promotes T cell infiltration and potentiates immunotherapy in melanoma

In melanoma, vascular endothelial growth factor-C (VEGF-C) expression and consequent lymphangiogenesis correlate with metastasis and poor prognosis. VEGF-C also promotes tumor immunosuppression, suggesting that lymphangiogenesis inhibitors may be clinically useful in combination with immunotherapy. We addressed this concept in mouse melanoma models with VEGF receptor-3 (VEGFR-3)-blocking antibodies and unexpectedly found that VEGF-C signaling enhanced rather than suppressed the response to immunotherapy. We further found that this effect was mediated by VEGF-C-induced CCL21 and tumor infiltration of naïve T cells before immunotherapy because CCR7 blockade reversed the potentiating effects of VEGF-C. In human metastatic melanoma, gene expression of VEGF-C strongly correlated with CCL21 and T cell inflammation, and serum VEGF-C concentrations associated with both T cell activation and expansion after peptide vaccination and clinical response to checkpoint blockade. We propose that VEGF-C potentiates immunotherapy by attracting naïve T cells, which are locally activated upon immunotherapy-induced tumor cell killing, and that serum VEGF-C may serve as a predictive biomarker for immunotherapy response.

Role of Hyperplasia of Gingival Lymphatics in Periodontal Inflammation

Lymphatic vessels are important for maintenance of tissue fluid homeostasis and afferent antigen transport. In chronic inflammation, lymphangiogenesis takes place and is characterized by lymphatic endothelial cell proliferation and lymphatic hyperplasia. Vascular endothelial growth factor C (VEGFC) is the main known lymphangiogenic growth factor, and its expression is increased in periodontitis, a common chronic infectious disease that results in tissue destruction and alveolar bone loss. The role of lymphangiogenesis during development of periodontitis is unknown. Here, we test if transgenic overexpression of epithelial VEGFC in a murine model is followed by hyperplasia of lymphatic vessels in oral mucosa and if the lymphatic drainage capacity is altered. We also test if lymphatic hyperplasia protects against periodontal disease development. Transgenic keratin 14 (K14)-VEGFC mice had significant hyperplasia of lymphatics in oral mucosa, including gingiva, without changes in blood vessel vasculature. The basal lymph flow was normal but slightly lower than in wild-type mice when oral mucosa was challenged with lipopolysaccharide from Porphyromonas gingivalis. Under normal conditions, K14-VEGFC mice exhibited an increased number of neutrophils in gingiva, demonstrated enhanced phagocyte recruitment in the cervical lymph nodes, and had more alveolar bone when compared with their wild-type littermates. After induction of periodontitis, no strain differences were observed in the periodontal tissues with respect to granulocyte recruitment, bone resorption, angiogenesis, cytokines, and bone-related protein expressions or in draining lymph node immune cell proportions and vascularization. We conclude that overexpression of VEGFC results in hyperplastic lymphatics, which do not enhance lymphatic drainage capacity but facilitate phagocyte transport to draining lymph nodes. Hyperplasia of lymphatics does not protect against development of ligature-induced periodontitis.

Anti-Inflammatory Cytokines in Peri-Implant Soft Tissues: A Preliminary Study on Humans Using CDNA Microarray Technology

The mucosa around implants and the gingiva around teeth respond to plaque formation with the development of an inflammatory lesion which has similar magnitude and histological features. Different cell types in inflamed and healthy periodontal and peri-implant tissues are capable of producing a variety of important pro-inflammatory and anti-inflammatory cytokines and growth factors which mediate the host response. The aim of this study is to compare the expression levels of anti-inflammatory cytokines detectable in the peri-implant soft tissue of two single-implant crowns supported either by zirconia or titanium abutments. Two frozen samples of peri-implant soft tissue of two single-implant crowns supported either by zirconia or titanium abutments were treated to obtain mRNA. The mRNA extracted from these specimens was converted in cDNA and analyzed with “SuperArray GEArray Q Series Human Inflammatory Cytokine/Receptor Gene Array kit”, planned for studying 96 genes involved in inflammatory response. Data showed that gene expression levels of anti-inflammatory cytokines were higher in specimens sampled from the zirconia abutment compared with those from the titanium abutment. It was considered important to detect the mRNA levels of the anti-inflammatory mediators in healthy peri-implant tissues to verify the biological tolerability of zirconia compared with titanium abutments. The difference detected in cytokine expression could be due to the intrinsic biological tolerability of zirconia ceramics or to a lesser bacterial accumulation.

Lymphangiogenesis and Lymphatic Function in Periodontal Disease

Lymphatic vessels return extravasated fluid, proteins, and cells back into the circulation and are important in immune cell trafficking. In the gingiva, lymphatic vessels are located in the lamina propria and travel over the external surface of the alveolar bone. The gingival lymphatics are important for fluid drainage, since lack of lymphatics has been shown to increase interstitial fluid pressure and fluid volume. Maintenance of gingival lymphatic vessels requires continuous signaling by the growth factors VEGF-C and -D via their receptor VEGFR-3. The growth factors are expressed in the gingival epithelium and also in immune cells in the lamina propria. VEGF-C seems to be crucial for lymphangiogenesis induced during periodontal disease development. The lymphatic vessels protect against periodontitis in mice, probably by clearing bacteria and bacterial products and by promoting humoral immune responses. Down-regulation of CCL21, a ligand important for dendritic cell migration, has been demonstrated in lymphatics from patients with periodontitis. High enzymatic activity in the gingiva of these patients may also contribute to impaired lymphatic function, due to the loss of structural components in the interstitium influencing lymphatic function. So far, knowledge is limited in this field because of the dearth of studies on the role of lymphatic vessels in periodontal disease.

Gingival lymphatic drainage protects against Porphyromonas gingivalis-induced bone loss in mice

Periodontitis is characterized by tissue destruction and bone loss mainly due to inflammatory responses after bacterial challenge of the gingiva. Gingiva is supplied with lymphatics that drain interstitial fluid and transport immune cells to the lymph nodes for antigen presentation; yet, the role of lymphatics in periodontal disease development is unknown. To investigate the lymphatic function after periodontal infection, we used K14-VEGF receptor 3-Ig (K14) mice that lack lymphatics in gingiva. Mice were orally infected with human Porphyromonas gingivalis and observed for 42 days. The infected K14 mice developed significantly more bone loss than the wild-type mice, and were associated with an increased number of macrophages and major histocompatibility complex class II antigen-presenting cells in the bone resorptional areas. The infected transgenic mice expressed a significant higher periodontal level of several proinflammatory cytokines, whereas the plasma level of P. gingivalis IgG was significantly lower than in the wild-type mice. No differences were found in immune cell distribution in draining lymph nodes between the strains. Our results show that a strong periodontal inflammatory response and a weakened systemic humoral B-cell response took place in K14 mice after infection. We conclude that gingival lymphatics protect against P. gingivalis-induced periodontitis, and we speculate that they are critical in the protection by clearance of infection and by promotion of humoral immune responses.

Lymphatics: at the interface of immunity, tolerance, and tumor metastasis

The lymphatic system has long been accepted as a passive escape route for metastasizing tumor cells. The classic view that lymphatics solely regulate fluid balance, lipid metabolism, and immune cell trafficking to the LN is now being challenged. Research in the field is entering a new phase with increasing evidence suggesting that lymphatics play an active role modulating inflammation, autoimmune disease, and the anti-tumor immune response. Evidence exists to suggest that the lymphatics and chemokines guide LN bi-functionally, driving immunity vs. tolerance according to demand. At sites of chronic inflammation, autoimmunity, and tumors, however, the same chemokines and aberrant lymphangiogenesis foster disease progression. These caveats point to the existence of a complex, finely balanced relationship between lymphatics and the immune system in health and disease. This review discusses emerging concepts in the fields of immunology, tumor biology, and lymphatic physiology, identifying critical, overlapping functions of lymphatics, the LN and lymphoid factors in tipping the balance of immunity vs. tolerance in favor of a growing tumor.

A critical role for lymphatic endothelial heparan sulfate in lymph node metastasis

BACKGROUND

Lymph node metastasis constitutes a key event in tumor progression. The molecular control of this process is poorly understood. Heparan sulfate is a linear polysaccharide consisting of unique sulfate-modified disaccharide repeats that allow the glycan to bind a variety of proteins, including chemokines. While some chemokines may drive lymphatic trafficking of tumor cells, the functional and genetic importance of heparan sulfate as a possible mediator of chemokine actions in lymphatic metastasis has not been reported.

RESULTS

We applied a loss-of-function genetic approach employing lymphatic endothelial conditional mutations in heparan sulfate biosynthesis to study the effects on tumor-lymphatic trafficking and lymph node metastasis. Lymphatic endothelial deficiency in N-deacetylase/N-sulfotransferase-1 (Ndst1), a key enzyme involved in sulfating nascent heparan sulfate chains, resulted in altered lymph node metastasis in tumor-bearing gene targeted mice. This occurred in mice harboring either a pan-endothelial Ndst1 mutation or an inducible lymphatic-endothelial specific mutation in Ndst1. In addition to a marked reduction in tumor metastases to the regional lymph nodes in mutant mice, specific immuno-localization of CCL21, a heparin-binding chemokine known to regulate leukocyte and possibly tumor-cell traffic, showed a marked reduction in its ability to associate with tumor cells in mutant lymph nodes. In vitro modified chemotaxis studies targeting heparan sulfate biosynthesis in lymphatic endothelial cells revealed that heparan sulfate secreted by lymphatic endothelium is required for CCL21-dependent directional migration of murine as well as human lung carcinoma cells toward the targeted lymphatic endothelium. Lymphatic heparan sulfate was also required for binding of CCL21 to its receptor CCR7 on tumor cells as well as the activation of migration signaling pathways in tumor cells exposed to lymphatic conditioned medium. Finally, lymphatic cell-surface heparan sulfate facilitated receptor-dependent binding and concentration of CCL21 on the lymphatic endothelium, thereby serving as a mechanism to generate lymphatic chemokine gradients.

CONCLUSIONS

This work demonstrates the genetic importance of host lymphatic heparan sulfate in mediating chemokine dependent tumor-cell traffic in the lymphatic microenvironment. The impact on chemokine dependent lymphatic metastasis may guide novel therapeutic strategies.

Simian immunodeficiency virus infection alters chemokine networks in lung tissues of cynomolgus macaques: association with Pneumocystis carinii infection

Infection by HIV-1 frequently leads to pulmonary complications, including alterations to local immune environments. To better understand these alterations, we have examined in detail the patterns and levels of expression of chemokine, cytokine, and chemokine receptor mRNAs in lung tissues from 16 uninfected or simian immunodeficiency virus (SIV)/DeltaB670 infected cynomolgus macaques at different stages of infection. Among the most up-regulated immune genes were interferon (IFN)-gamma, IFN-gamma-inducible CXCR3 ligands, and CCR5 ligands, as well as the cognate chemokine receptors. These changes were greatest in animals with clear Pneumocystis carinii coinfection. Immunohistochemistry and in situ hybridization revealed monocytes/macrophages to be the predominant type of cell infiltrating into lung tissues and serving as the major cellular source of chemokines. To explore the causes of chemokine alterations, we treated macaque lung cells with IFN-gamma, lipopolysaccharide, Poly(I:C), and P. carinii in vitro, and results revealed that these stimuli can induce the expression of CXCR3 ligand and/or CCR5 ligand mRNAs. Taken together, these studies provide a comprehensive definition of the chemokine networks available to modulate cellular recruitment to lung tissues during SIV infection and implicate both cytokines (IFN-gamma) and pathogens (SIV and P. carinii) as contributors to increased expression of pro-inflammatory chemokines.

Afferent and efferent interfaces of lymph nodes are distinguished by expression of lymphatic endothelial markers and chemokines

BACKGROUND

Lymph nodes (LNs) are important sites of connection between the sampled peripheral tissues, the many cells of the immune system, and the blood. The organization of the interface between the afferent and efferent lymphatic vasculature and LN parenchyma is incompletely understood, and obtaining a better understanding of these tissue microenvironments will contribute to an improved understanding of overall lymphatic function.

METHODS AND RESULTS

We used histologic approaches to define the distributions of cells expressing lymphatic endothelial cell (LEC) markers in LNs from healthy, simian immunodeficiency virus (SIV) infected, or Mycobacterium tuberculosis infected cynomolgus macaques. Cells at the afferent and efferent interfaces of LNs from all animals showed differential expression of LEC markers, with podoplanin, Prox-1, and VEGFR3 expressed in both microenvironments, but with LYVE-1 expressed only at the efferent interface. The chemokine CCL20 was uniquely expressed at the afferent interface by cells co-expressing podoplanin, and this expression was increased during SIV or M. tuberculosis infection. In contrast, only a small proportion of cells expressing the CCR7 ligand CCL21 co-expressed podoplanin. Treatment of model LECs with the TLR3 ligand poly(I:C) or gamma-irradiated M. tuberculosis increased production of CCL20 without altering CCL21 or LEC marker expression.

CONCLUSIONS

This study provides a comprehensive mapping of the organization of the lymphatic endothelial network entering and exiting LNs in health and in chronic infectious diseases in a nonhuman primate model. The differences we have defined between the afferent and efferent interfaces of LNs could inform the future design of vaccines and immunotherapies.

Dendritic-cell trafficking to lymph nodes through lymphatic vessels

Antigen-presenting dendritic cells often acquire foreign antigens in peripheral tissues such as the skin. Optimal encounter with naive T cells for the presentation of these antigens requires that the dendritic cells migrate to draining lymph nodes through lymphatic vessels. In this article, we review important aspects of what is known about dendritic-cell trafficking into and through lymphatic vessels to lymph nodes. We present these findings in the context of information about lymphatic-vessel biology. Gaining a better understanding of the crosstalk between dendritic cells and lymphatic vessels during the migration of dendritic cells to lymph nodes is essential for future advances in manipulating dendritic-cell migration as a means to fine-tune immune responses in clinical settings.