Immunohistochemical study on leukocyte adhesion molecules expressed on lymphatic endothelium

Anti-angiogenic agents - overcoming tumour endothelial cell anergy and improving immunotherapy outcomes

Immune checkpoint inhibitors have revolutionized medical oncology, although currently only a subset of patients has a response to such treatment. A compelling body of evidence indicates that anti-angiogenic therapy has the capacity to ameliorate antitumour immunity owing to the inhibition of various immunosuppressive features of angiogenesis. Hence, combinations of anti-angiogenic agents and immunotherapy are currently being tested in >90 clinical trials and 5 such combinations have been approved by the FDA in the past few years. In this Perspective, we describe how the angiogenesis-induced endothelial immune cell barrier hampers antitumour immunity and the role of endothelial cell anergy as the vascular counterpart of immune checkpoints. We review the antitumour immunity-promoting effects of anti-angiogenic agents and provide an update on the current clinical successes achieved when these agents are combined with immune checkpoint inhibitors. Finally, we propose that anti-angiogenic agents are immunotherapies - and vice versa - and discuss future research priorities.

Gastrointestinal lymphatics in health and disease

Lymphatics perform essential transport and immune regulatory functions to maintain homeostasis in the gastrointestinal (GI) system. Although blood and lymphatic vessels function as parallel and integrated systems, our understanding of lymphatic structure, regulation and functioning lags far behind that of the blood vascular system. This chapter reviews lymphatic flow, differences in lymphangiogenic and hemangiogenic factors, lymphatic fate determinants and structural features, and examines how altered molecular signaling influences lymphatic function in organs of the GI system. Innate errors in lymphatic development frequently disturb GI functioning and physiology. Expansion of lymphatics, a prominent feature of GI inflammation, may also play an important role in tissue restitution following injury. Destruction or dysregulation of lymphatics, following injury, surgery or chronic inflammation also exacerbates GI disease activity. Understanding the physiological roles played by GI lymphatics is essential to elucidating their underlying contributions to forms of congenital and acquired forms of GI pathology, and will provide novel approaches for therapy.

Induction of ICAM-1 and VCAM-1 on the mouse lingual lymphatic endothelium with TNF-alpha

This study investigated the TNF-α-induced ICAM-1 and VCAM-1 expression on mouse lingual lymphatic vessels. All podoplanin-positive lymphatic vessels expressed PECAM-1. In the lamina propria mucosae of TNF-α-treated tongue, almost all initial lymphatics expressed ICAM-1. There were initial lymphatics with the VCAM-1 expression and also the vessels without the expression. In the tunica muscularis of TNF-α-treated tongue, collecting lymphatic vessels expressed ICAM-1, but rarely expressed VCAM-1 whereas blood vessels simultaneously expressed ICAM-1 and VCAM-1. The ICAM-1-positive rate increased with TNF-α to 75% from 10% on initial lymphatics, and to 40% from 0% on collecting lymphatic vessels while it increased to 90% from 45% on blood vessels. The VCAM-1-positive rate increased with TNF-α to 30% from 0% on initial lymphatics, and to 5% from 0% on collecting lymphatic vessels while it increased to 75% from 5% on blood vessels. These findings suggest that the lingual lymphatic endothelium has the ability to express ICAM-1, and VCAM-1 to a lesser extent than the ICAM-1 induction with TNF-α, and that the ICAM-1 and VCAM-1 induction predominantly occurs in the initial lymphatics compared with collecting lymphatic vessels.

Inflammation, lymphatic function, and dendritic cell migration

The lymphatic system is not only essential for maintenance of normal fluid balance, but also for proper immunologic function by providing an extensive network of vessels, important for cell trafficking and antigen delivery, as well as an exclusive environment, the lymph node (LN), where antigen-presenting cells (APCs) and lymphocytes can encounter and interact. Among APCs, dendritic cells (DCs) have a remarkable capacity to traffic from peripheral tissues to the draining LN, which is critical for execution of their functions. To reach the LN, DCs must migrate towards and enter lymphatic vessels. Here, the authors review what is known about the factors that drive this process. They touch particularly on the topic of how DC migration is affected by inflammation and discuss this in the context of lymphatic function. Traditionally, inflammatory mediators are regarded to support DC migration to LNs because they induce molecules on DCs known to guide them to lymphatics. The authors recently showed that inflammatory signals present in a strong vaccine adjuvant induce swelling in LNs accompanied by lymphangiogenesis in the draining LN and radius of peripheral tissue. These increased lymphatics, at least for several days, lead to a more robust migration of DCs. However, the density of lymphatic vessels can become overly extended and/or their function impaired as observed during lymphedema and various chronic inflammatory reactions. Diseases characterized by chronic inflammation often present with impaired DC migration and adaptive immunity. Gaining a better understanding of how lymphatic vessel function may impact adaptive immunity by, for example, altering DC migration will benefit clinical research aiming to manipulate immune responses and manage chronic inflammatory diseases.

Molecular markers (PECAM-1, ICAM-3, HLA-DR) determine prognosis in primary non-Hodgkin's gastric lymphoma patients

AIM

To investigate the prognostic significance of PECAM-1, ICAM-3 and HLA-DR antigens in patients with primary non-Hodgkin's gastric lymphoma.

METHODS

We immunohistochemically studied PECAM-1, ICAM-3 and HLA-DR antigen expression in 36 B-cell MALT-type primary gastric lymphoma patients. Ten non-malignant and ten healthy gastric tissue specimens were used as controls. Clinicopathological and survival data were correlated with the staining results.

RESULTS

HLA-DR antigen expression was detected in 33 gastric lymphoma patients (91.7%) and 6 non-malignant patients (54.5%). PECAM-1 stained tumor cells of 10 patients (27.8%), endothelial cells of 9 patients (25%) and inflammatory infiltrate of 4 patients (40%) with benign gastric disease. ICAM-3 expression was observed on the tumor cells of 17 patients (47.2%), while 5 non-malignant patients (50%) were stained positive as well. None of the healthy controls was stained for any of the genes studied. In the multivariate analysis, HLA-DR antigen and PECAM-1 were proved to be statistically significant independent prognostic factors associated with a favourable and an unfavourable prognosis respectively (P=0.009 and P=0.003). In the univariate analysis, PECAM-1(+)/ICAM-3(-) and HLA-DR(-)/ICAM-3(-) patients exhibited a significantly decreased overall survival compared to those with the exactly opposite gene expression patterns (P=0.0041 and P=0.0091, respectively). Those patients who were HLA-DR(+)/ICAM-3(+)/PECAM-1(-) (n=8) had a significantly higher survival rate compared to the rest of the group (n=24) (P=0.0289).

CONCLUSION

PECAM-1, ICAM-3 and HLA-DR are representative markers of tumor expansion potential and host immune surveillance respectively. Their combined use may help us to identify high-risk patients who could benefit from more aggressive therapeutic protocols.

Isolation and Characterization of A Novel Mouse Lymphatic Endothelial Cell Line: SV-LEC

BACKGROUND

The lymphatic system regulates interstitial fluid and protein balance and modulates immune responses by regulating leukocyte and antigen traffic to lymph nodes. The present article describes a stable mouse lymphatic endothelial cell line from mesenteric adventitial tissue (SV-LEC) which is distinct from blood aortic (AEC) and venous (VEC) endothelial cells, based on expression of several lymphatic markers (e.g., Prox-1, LYVE-1, Flt-4). SV-LEC also expresses MAdCAM-1 in response to TNF-alpha, an effect seen in VEC, but not AEC.

METHODS AND RESULTS

Lymphatic endothelial cells (SV-LEC) were isolated from mesenteric adventitia from mice expressing temperature-sensitive SV40 large T ('Immortomouse', H-2K(b)tsA58) selected with hypoxia culture in D-valine-substituted MEM supplemented with VEGFC in a low oxygen atmosphere (0% O2, 5% CO2, and 95% N2) with 5 mM thioglycolate. Expression of lymphatic-specific markers (Flt-4, LYVE-1, Prox-1) and the tight junction proteins (ZO-1) were examined by RT-PCR, immunoblotting, and fluorescent microscopy. MAdCAM-1 (a high endothelial venular marker) expression was also examined in response to TNF-alpha IL-1beta and IFN-gamma.

RESULTS

Message for Flt-4 and LYVE-1 was detected on SV-LEC. Immunoblotting for LYVE-1 and Prox-1 showed strong expression on SV-LEC and VEC, but not AEC. Occludin expression was seen in all cell types, junctional ZO-1 was detected at SV-LEC and VEC junctions, not AEC.

CONCLUSION

SV-LEC expresses several lymphatic endothelial markers, some of which are shared with VEC, but not AEC, and may represent a useful system for modeling lymphatic function in vitro.

Transendothelial transport and migration in vessels of the apparatus lymphaticus periphericus absorbens (ALPA)

The vessel of the apparatus lymphaticus periphericus absorbens (ALPA) represents the sector with high absorption capacity of the canalization of the lymphatic vascular system. It plays a basic role in preserving tissue homeostasis and in directing interstitial capillary filtrate back to the bloodstream. ALPA lymphatic endothelium differs from the endothelia of conduction and flowing vessels (precollectors, prelymph nodal and postlymph nodal collectors, main trunks), since it presents a discontinuous basement membrane, which is often absent, and lacks pores and fenestrations. The mesenchymal origin of the ALPA lymphatic vessel, morphological and ultrastructural aspects, intrinsic contractile properties, the presence of valves, innervation, and specific lymphatic markers that reliably distinguish it from blood capillaries are studied. Furthermore, its role in lymph formation through different mechanisms (hydrostatic pressure and colloidal osmotic-reticular mechanisms, vesicular pathway, and intraendothelial channel) is investigated. We have studied morphological and biomolecular mechanisms that control the transendothelial migration, from the extracellular interstitial matrix into the lumen of the lymphatic vessel, of cells involved in immune response and resistance (lymphocyte recirculation, etc.) and in the tumoral metastatic process via the lymphatic system. Finally, future research prospects, clinical implications, and therapeutic strategies are considered.

Desmoplakin and Plakoglobin - Specific Markers of Lymphatic Vessels in the Skin?

Monoclonal antibodies against Desmoplakin and Plakoglobin were tested for their suitability as specific markers of lymphatic vessels. The tissue samples were taken from horse skin in an attempt to establish the horse as a model for human lymphatic diseases. To obtain a clear, positive identification of blood and lymphatic vessels, immunohistochemical staining with antibodies against vascular endothelial growth factor receptor 3 (VEGFR-3) and platelet endothelial adhesion molecule (PECAM-1, CD31), was compared with Desmoplakin and Plakoglobin. Because anti-VEGFR-3 is specific for lymphatic vessels in the skin while anti-CD31 stains blood and lymphatic vessels as well, it can be concluded that VEGFR-3(-)/CD31(+) vessels are blood vessels and VEGFR-3(+)/CD31(+) vessels are lymphatic vessels. It was documented on serial sections that Plakoglobin stains both blood and lymphatic vessels. However, Desmoplakin did not stain several positively identified lymphatic vessels. Therefore, Desmoplakin and Plakoglobin antibodies are not specific markers of lymphatic vessels in the skin and the staining pattern is tissues and species dependent.

Expression of VEGFR-3 and 5?-Nase in regenerating lymphatic vessels of the cutaneous wound healing

The vascular endothelial growth factor-C (VEGF-C), a specific lymphangiogenic growth factor, raises new questions and perspectives in studying lymphatic development and regeneration. Wound healing skins in mice were processed for 5'-nucleotidase (5'-Nase) and VEGFR-3 (the receptor of VEGF-C) histochemical staining to distinguish lymphatics from blood capillaries and to analyze lymphangiogenesis. In the wounds of 3-5 days after injury, anti-VEGFR-3 immunopositive signals unevenly appeared in 5'-Nase-positive lymphatic vessels in the subcutaneous tissue. A few small circular and irregular lymphatic-like structures with VEGFR-3 expression scattered in the dermal and subcutaneous tissues. Between days 7 and 15 of the wounds, numerous accumulated vasculatures were stained for 5'-Nase and PECAM-1, extending irregularly along the wound edge. Von Willebrand factor was expressed in the endothelial cells of blood vessels and lymphatics in the subcutaneous tissue. Ultrastructural changes of lymphatic vessels developed at different stages, from lymphatic-like structures to newly formed lymphatic vessels with an extremely thin and indented wall. Endothelial cells of the lymphatic vessel were eventually featured by typical intercellular junctions, which deposited with reaction products of VEGFR-3 and 5'-Nase-cerium but lacked VEGF-C expression. The present findings indicate that VEGF-C-induced lymphangiogenesis occurs from the subcutaneous to the dermis along the wound healing edge, especially in the dermal-subcutaneous transitional area, favorable to growth of regenerating lymphatic vessels.

Markers for the lymphatic endothelium: in search of the holy grail?

The ability to discriminate reliably at the histological level between blood and lymphatic microcapillaries would greatly assist the study of a number of biological and pathological questions and may also be of clinical utility. A structure-function comparison of these types of microcapillary suggests that differences which could function as markers to allow discrimination between blood and lymphatic endothelium should exist. Indeed, to date a variety of such markers have been proposed, including basement membrane components, constituents of junctional complexes such as desmoplakin and enzymes such as 5'-nucleotidase. Additionally, a variety of cell surface molecules are thought to be differentially expressed, including PAL-E, VEGFR-3, podoplanin, and LYVE-1. Several of the lymphatic markers proposed in the literature require further characterization to demonstrate fully their lymphatic specificity and some have proven not to be reliable. The relative merits and drawbacks of each of the proposed markers is discussed.

Immunoelectron microscopic study of PECAM-1 expression on lymphatic endothelium of the human tongue

The expression of platelet-endothelial cell adhesion molecule-1 (PECAM-1) on lymphatic and blood vessels of the human tongue was examined with fluorescence and transmission electron microscopy (TEM). The study used anti-desmoplakins antiserum for light microscopic identification of the lymphatic vessels, plus a pre-embedding immunogold electron microscopic technique for TEM observations. Before making TEM observations, cryostat serial sections were immunostained with anti-desmoplakins or anti-PECAM-1 and then embedded. Semithin sections from each cryostat section were photographed under a light microscope and compared in order to identify the lymphatic vessels expressing PECAM-1. In fluorescence microscopy, PECAM-1 expression on lymphatic vessels was weaker than that on blood vessels. TEM observations showed that PECAM-1 expression on the blood vessels was observed only on the luminal surface of the endothelium. In lymphatic vessels, PECAM-1 expression was found both on the luminal and abluminal surfaces of the endothelium. The density of the PECAM-1 reaction products was lower in lymphatic vessels than in blood vessels. The density of PECAM-1 reaction products on the luminal surface of lymphatic vessels was higher than on the abluminal surfaces. The results suggest that blood vessels are more active than lymphatic vessels in leukocyte migration. The expression of PECAM-1 on the abluminal surface of lymphatic endothelium may allow leukocytes to adhere to the endothelium and interact in their migration from tissue into lymphatic vessels.

The beta-chemokine receptor D6 is expressed by lymphatic endothelium and a subset of vascular tumors

The lymphatic vessels (lymphatics) play an important role in channeling fluid and leukocytes from the tissues to the secondary lymphoid organs. In addition to driving leukocyte egress from blood, chemokines have been suggested to contribute to leukocyte recirculation via the lymphatics. Previously, we have demonstrated that binding sites for several pro-inflammatory beta-chemokines are found on the endothelial cells (ECs) of lymphatics in human dermis. Here, using the MIP-1alpha isoform MIP-1alphaP, we have extended these studies to further support the contention that the in situ chemokine binding to afferent lymphatics exhibits specificity akin to that observed in vitro with the promiscuous beta-chemokine receptor D6. We have generated monoclonal antibodies to human D6 and showed D6 immunoreactivity on the ECs lining afferent lymphatics, confirmed as such by staining serial skin sections with antibodies against podoplanin, a known lymphatic EC marker. In parallel, in situ hybridization on skin with antisense D6 probes demonstrated the expression of D6 mRNA by lymphatic ECs. D6-immunoreactive lymphatics were also abundant in mucosa and submucosa of small and large intestine and appendix, but not observed in several other organs tested. In lymph nodes, D6 immunoreactivity was present on the afferent lymphatics and also in subcapsular and medullary sinuses. Tonsilar lymphatic sinuses were also D6-positive. Peripheral blood cells and the ECs of blood vessels and high endothelial venules were consistently nonreactive with anti-D6 antibodies. Additionally, we have demonstrated that D6 immunoreactivity is detectable in some malignant vascular tumors suggesting they may be derived from, or phenotypically similar to, lymphatic ECs. This is the first demonstration of chemokine receptor expression by lymphatic ECs, and suggests that D6 may influence the chemokine-driven recirculation of leukocytes through the lymphatics and modify the putative chemokine effects on the development and growth of vascular tumors.