Demonstration of the intralobular lymphatics in the guinea pig pancreas by an enzyme-histochemical method

Exploration of peripancreatic lymphatic pathways in a live porcine model

Pancreatic cancer is associated with a poor prognosis, mainly due to lymph node invasion and lymph node recurrence after surgical resection, even after extended lymphadenectomy. The peripancreatic lymphatic system is highly complex and the specific lymphatic drainage of each part of the pancreas has not been established. The aim of this study was to determine the lymphatic drainage pathways specific to each part of the pancreas on live pigs using Patent Blue. The pancreases of 14 live pigs were injected in different parts of the gland. The technique was efficient and reproducible. The diffusion patterns were similar for each location and were reported. Our results in pigs allowed us to define specific nodal relay stations and lymphatic drainage for each part of the pancreas and confirm that independent anatomical-surgical pancreatic segments can be described. It is interesting to note that lymphatic drainage for the upper part of the proximal part of pancreas (duodenal lobe) occurred on the left side of the portal vein. This suggests that lymph node resection during cephalic duodenopancreatectomy in humans should be extended to the left side of the mesenteric vein, and probably to the right side of the superior mesenteric artery, as recently suggested. These results could help surgeons perform safe anatomical-segmental pancreatic resections with accurate lymphadenectomies and improve survival in patients with pancreatic cancer. Based on these results we will perform an innovative prospective study. Patent Blue will be injected into different parts of the gland in patients operated for pancreatic resection, and lymphatic diffusion of the dye will be recorded in relation to their origin from the theoretical pancreatic segments (ClinicalTrials.gov Identifier: NCT03597230).

Lymphatic Vessel Network Structure and Physiology

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

Histochemical analysis of lymphatic endothelial cells in the pancreas of non-obese diabetic mice

We studied the relationship between insulitic development and function-structural changes of pancreatic lymphatics in non-obese diabetic (NOD) mice using combined 5'-nucleotidase (5'-Nase) enzyme histochemical and secondary lymphoid tissue chemokine (SLC/CCL21) immunohistochemical methods. Interlobular lymphatic vessels were positive for 5'-Nase throughout the pancreas, and dependent on both blood vessels and pancreatic ducts. Intralobular initial lymphatics were rare and occasionally ran in the neighbourhood of islets. During the non-insulitic stage, the 5'-Nase-reactive product was evenly distributed on the surface of lymphatic endothelial cells (LECs) with weak expression of CCL21. The activity of 5'-Nase on lymphatic vessels became slightly reduced as insulitis developed. The increasing blood glucose values appeared to be consistent with an increasing CCL21 expression by the endothelial lining, especially on the surface of LECs adjacent to the infiltrated islets and tissues. Lymphocytes and dendritic cells (DCs) were frequently located in the connective tissue, surrounding the lymphatic wall with deposition of 5'-Nase precipitates. As the infiltration became severe, lymphocytes and DCs accumulated within lymphatic vessels and expressed high levels of CCL21. The most significant finding was that many DCs adhered to lymphatic vessels, transmigrating via the thin and indented endothelial walls. The activity of 5'-Nase was increased on the adhesion surface between DCs (or lymphocytes) and LECs. The latter were characterized by open intercellular junctions and obvious cytoplasmic protrusions. These results suggest that LECs closely interact with DCs and lymphocytes, and play a key role in the migration of DCs and lymphocytes via lymphatic vessels during the pathological processes of insulitis in NOD mice.

Histochemical analysis of lymphatic endothelial cells in lymphostasis

The ultrastructure of endothelial cells of intestinal lymphatics and the thoracic duct (TD) and the relation to lymphostasis were examined in rats and monkeys. Localization of 5'-nucleotidase (5'-Nase) and endothelial nitric oxide synthase (eNOS) was studied. In normal lymphatic endothelial cells, 5'-Nase reaction product was evenly deposited on the cell surface in vivo and on cultured TD endothelial cells (TDECs), whereas eNOS was evenly distributed throughout the nucleus and cytoplasm. TDECs had a long filamentous process extending towards the subendothelial extracellular matrix but became flat and regular within 30-40 minutes after gastric perfusion with olive oil. According to their electron-density, two types of cells were found in the TD endothelial layer. The cells with low electron-density exhibited stronger 5'-Nase activity. Valves were bicuspid formations and the valvular endothelial surface of the convex side showed weaker 5'-Nase activity than the concave side. During TD blockage-induced lymphostasis in rats, the 5'-Nase product was almost not discernible in the TDECs within 2 weeks. Larger vesicles were found in the endothelial cytoplasm of the ligated TD. Their number decreased after 6-12 weeks. The small intestinal lymphatics in the mucosa and submucosa were dilated, with numerous open intercellular junctions. The endothelial lining appeared to have reduced activities for 5'-Nase and eNOS in 9 of 11 experimental animals. The results indicated that the inability of the open intercellular junctions, normally working as one-way endothelial flap valves, may be a key morphological feature after TD blockage. Reduced eNOS and 5'-Nase may functionally influence contractile activity and transport capability of the lymphatic vessels in the lymphostasis.

Pancreatic lymphatic system in rodents

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

Vascular endothelial growth factor-C-mediated lymphangiogenesis promotes tumour metastasis

Metastasis is a frequent and lethal complication of cancer. Vascular endothelial growth factor-C (VEGF-C) is a recently described lymphangiogenic factor. Increased expression of VEGF-C in primary tumours correlates with dissemination of tumour cells to regional lymph nodes. However, a direct role for VEGF-C in tumour lymphangiogenesis and subsequent metastasis has yet to be demonstrated. Here we report the establishment of transgenic mice in which VEGF-C expression, driven by the rat insulin promoter (Rip), is targeted to beta-cells of the endocrine pancreas. In contrast to wild-type mice, which lack peri-insular lymphatics, RipVEGF-C transgenics develop an extensive network of lymphatics around the islets of Langerhans. These mice were crossed with Rip1Tag2 mice, which develop pancreatic beta-cell tumours that are neither lymphangiogenic nor metastatic. Double-transgenic mice formed tumours surrounded by well developed lymphatics, which frequently contained tumour cell masses of beta-cell origin. These mice frequently developed pancreatic lymph node metastases. Our findings demonstrate that VEGF-C-induced lymphangiogenesis mediates tumour cell dissemination and the formation of lymph node metastases.

Intrinsic interrelation of lymphatic endothelia with nerve elements in the monkey urinary bladder

Histochemical staining techniques for 5'-nucleotidase (5'-Nase) and acetylcholinesterase (AChE) were undertaken to localize the lymphatic network and nerve plexus in the monkey urinary bladder. Abundant 5'-Nase-positive lymphatic networks were characterized by increased number of valve-like structures and decreased calibre of blind-ends from the subepithelium to the subserosa. AChE-positive nerve fibers were visible throughout the vesical walls as fine plexuses, the densest being the neuromuscular plexus among the detrusor muscle cells or in each muscle bundle. AChE-positive nerve fibers or terminals were more frequently discernible around blood vessels than around lymphatics, and showed more intimate association with the lymphatics in the muscularis than those in the subepithelium. The nerve terminals in the subepithelium were frequently separated from attenuated lymphatic endothelium by the long processes of fibroblasts or some connective tissue cells. An ultrastructural observation revealed that unmyelinated nerve fibers with numerous neurofilaments and neurotubules run in close apposition to the lymphatic endothelium. Noteworthily, fewer terminal varicosities containing numerous small agranular vesicles (30-50 nm) and mitochondria, partially or completely bare of their Schwann cell covering in the vicinity of the lymphatic endothelium, were found in the subendothelium of initial lymphatics than in collecting ones. These terminals were occasionally identified at a distance of 120-350 nm from the subendothelial aspect of valve-originating roots, although no direct innervation of the vascular muscle cells could be found. A loose fibro-elastic connective tissue was usually interlaced between glial cell covering and lymphatic endothelium. The intrinsic interrelation of the lymphatic wall with the nerve plexus implies that the twisted subendothelial nerve terminals might be involved in intramural lymph drainage of the bladder.