In vertebrates, a special secondary lymphatic organ, the spleen, is responsible for immunological survey of the blood. This task necessitates an astonishing solution for directly confronting T- and B-lymphocytes and macrophages with blood-borne materials: In humans and rodents, the arterial and the venous side of the splenic microcirculation are completely separated by a gap. This gap is filled by connective tissue of the splenic cords. Thus, blood leaves the open ends of the arterial capillary network, freely traverses the cords and then enters the venous sinuses from the outside via functional slits in their walls. On its way across the cords, the blood flows along the cell membranes of fibroblasts and of a large population of highly active macrophages without any barrier formed by endothelial cells. In humans, in addition to the sinuses, there is a second spleen-specific type of microvessel, the sheathed capillaries, which feed the capillary network.
We used Enzo chromogens in light microscopic triple staining of serial sections to definitively demonstrate that the arterial and the venous side of the human splenic microvasculature lack any connections. This was possible by detecting open capillary ends and by visualizing their unique morphology in 3D models viewed in virtual reality. Our method also permitted defining sheathed capillaries as post-arteriolar vessels surrounded by sheaths consisting of special stromal sheath cells, macrophages and recirculating B-lymphocytes. The sheaths most likely represent the splenic entry compartment for all types of antigens and particulate substances from the blood, because they are irrigated by open side branches of their capillary. Using 3D models based on immunohistology in transmitted light we are able to settle the 170-year-long debate of open versus closed circulation in the human spleen and provide previously unseen insight into the tissue microanatomy of the spleen.

Main Target Audience: Anatomists, Physiologists; Histologists; Clinical Laboratories; Hospitals; - Researchers interested in the following topics: Anatomy, The cardiovascular system, Immunohistochemistry (IHC), Histology, blood circulation, Immunology, Pathology

Why should you attend?: Whether you are a scientist, a student, a lab technician, or a curious citizen, this webinar will provide fascinating new anatomic insight into the architecture of the spleen and highlight captivating, state-of-the art digital visualization of immunohistochemistry results, a method which forms the pillar of our anatomical understanding since over a century.

Presented by: Prof. Dr. Birte Steiniger
Professor emeritus and head of Department of Immunobiology
Institute of Anatomy and Cell Biology, Faculty of Medicine, University of Marburg

Prof. Dr. Oleg Lobachev
Professor for IT-Security and Artificial Intelligence
Leibniz University of Applied Sciences, Hannover

Topic: IHC, Immunology