Deep splenic lymphatics, studied in five marmots, entwine major arteries of white pulp. Lymphatics vary in prominence from spleen to spleen and within a spleen.
These lymphatics constitute efferent channels likely draining splenic fluid flowing within the spleen counter-current to blood.
The endothelium is irregular, thin and imperforate, beset with vacuoles and containing filaments. Its hyaloplasm is light or dark. Flap-like inter-endothelial cell junctions without membranous specializations are typical. Endothelial cells richly interdigitate with one another resulting in extensive, closely-spaced intercellular junctions. Long endothelial processes extend into subjacent connective tissue.
The lymphatics lie in an extracellular ground substance, continuous with that surrounding arteries and with the fibrous reticulum of white pulp. Filaments, about 100 Å in width, lie in the ground substance close upon the basal endothelial surface. The filaments appear to attach to the endothelium and run out into surrounding collagenous fibers. The collagen is abundant, occurring in thick layers around lymphatics and extending, with the ground substance, into the white pulp.
Macrophages, replete with phagosomes, surround lymphatic vessels and extend processes toward them, penetrating the peri-lymphatic connective tissue. Erythrocytes lie outside these vessels and within their lumen. Sheets of plasma cells may surround the lymphatics. Lymphocytes, in large number, are present around the lymphatics, cross their wall between endothelial cells, and lie in their lumen.