The Cellular Architecture of the Primo Vascular System.

The primo vascular system (PVS) is of great interest to scientists in the last few years. The PVS plays a role in stem cell migration, immune function, erythropoiesis, tissue regeneration, and cancer metastasis. Discovered by Bong Han Kim in 1960, the PVS was described as a new, independent system that is distributed in the body of different animals. Since then, several cells have been discovered as important constituents of the PVS. Endothelial cells are hallmarks for the identification of the PVS, as they line the sinuses of the primo vessels and are characterized by their arrangement of rod-shaped nuclei in a parallel, broken-line fashion along the primo vessels. Immune cells as mast cells, eosinophils, neutrophils, and lymphocytes are also hallmarks for the identification of the PVS. One of the most interesting cells in the PVS are p-microcells. Primo nodes are a stem cell niche due to their p-microcells content, which express stem cell biomarkers CD133 and Oct 4. Mature erythrocytes and hematopoietic stem cells have also been observed in the PVS. Hematopoietic stem cells were observed in the PVS. Hematopoietic Stem Cells are the source of the cellular component of blood. Additionally, adrenaline and noradrenaline-producing cells, mesothelial cells, and smooth-muscle-like cells have also been described in the PVS.