Mesothelial Cells Covering the Surface of Primo Vascular System Tissue

Bundle structures inside the deep cervical lymphatic vessels of mice

The lymphatic system plays a crucial role in immune function and the removal of cellular waste. Recent studies have highlighted the presence of primo vessels (PVs) inside lymphatic vessels, distinct from conventional lymphatic tissues, yet their structural and functional characteristics remain poorly understood, particularly PVs inside deep cervical lymphatic vessels (dcLVs) connected to the meningeal lymphatics. We used a combination of Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Alcian Blue (AB) and H&E staining techniques to identify and characterize PVs inside the dcLVs of mice. PVs were identified inside the dcLVs, revealing distinct bundle structures composed of 3 to 5 primo subvessels (sub-PV), with diameters of 5.4 ± 2.4 μm. AFM analyses confirmed the presence of nm-sized pores on the sub-PVs, which may facilitate the absorption and retention of nanoparticles. Rod-shaped nuclei were also observed, further distinguishing PVs from other vascular structures. Our study provides new insights into the structural characteristics of PVs inside dcLVs, suggesting their potential role in targeted drug delivery. However, further research is required to explore the functional implications of these structures, especially their therapeutic applications and roles in various lymphatic regions, including the meningeal lymphatics.

Characterization of the primo vascular system in rabbit vagina

The primo vascular system (PVS) is observed in different parts of the body under different physiological and disease conditions. Previously, the PVS was not observed in the vagina. The vaginal samples of this study were collected from the female genitalia of healthy New Zealand white rabbits from the animal house, Faculty of Medicine, Assiut University. The vaginal samples were fixed in Bouin's solution. The sections were stained with hematoxylin and eosin and Crossmon's trichrome. Additionally, the sections were immunohistochemically stained with neuron-specific enolase (NSE) and vascular endothelial growth factor (VEGF). A primo node was observed on the lymph vessel of the vagina and has several characteristics that resemble those of the previously discovered primo nodes. The primo node in this study was surrounded by mesothelial cells that provide positive immunoreactivity to NSE and VEGF. Sinuses of different sizes, floating cells, telocyte-like cell, and primo microcells were observed as the main constituents of the primo node. Additionally, migratory cells were detected, which passed from the primo node to the enclosing lymph vessel.

Primo Bundles Identified by Microcomputed Tomography in Primo Vascular Tissue on the Surface of Rat Abdominal Organs

BACKGROUND

The primo vascular system (PVS) is a novel network composed of primo nodes (PNs) and primo vessels (PVs). Currently, its anatomy is not fully understood.

OBJECTIVES

The aim of this study was to elucidate the three-dimensional PN-PV structure.

METHODS

Organ-surface PVS tissue was isolated from healthy and anemic rats. The tissues were analyzed by X-ray microcomputed tomography (CT), hematoxylin and eosin staining, and scanning electron microscopy.

RESULTS

From CT images, we identified one or more bundles in a PV. In the PN, the bundles were enlarged and existed in isolation and/or in anastomosis. The transverse CT images revealed four areas of distinct intensities: zero, low, intermediate, and high. The first two were considered to be the sinuses and the subvessels of the PVS and were identified in the hematoxylin and eosin-stained PN sections. The enlargement of the PN from anemic rats was associated with an increase in the intermediate-intensity area. The high-intensity area demarcated the bundle and was overlapped with the mesothelial cells. In scanning electron microscopy, the PV bundles branched out, tapering down to a single bundle at some distance from the PN. Each bundle was composed of several subvessels (∼5 μm). Clustered round microcells (1-25 μm), scattered flat oval cells (∼15 μm), and amorphous extracellular matrix were observed on the surface of the PVS tissue.

CONCLUSIONS

The results newly showed that the primo bundle is a structural unit of both PVs and PNs. A bundle was demarcated by high CT intensity and mesothelial cells and consisted of multiple subvessels. The PN bundles contained also sinuses.