Filters old / damaged red blood cells

Traversed by thin walled venous sinusoids lined by littoral cells, a type of endothelial cell which also stains with histiocytic markers and has a discontinuous wall, allowing passing of red blood cells between sinus and cords

Sinuses are separated by splenic cords (cords of Billroth) containing a labyrinth of splenic macrophages, which filter red blood cells and ingest old (normal lifespan is 120 days), damaged (seen in hereditary spherocytosis, sickle cell anemia) or antibody coated red blood cells

Also remove Heinz bodies or other red blood cell inclusions (peripheral blood has Howell-Jolly bodies if no functional spleen is present)

Forms sheaths of lymphoid cells around arteries (periarteriolar lymphatic sheath), composed of T cells and lymphoid follicles (B cells) with surrounding mantle zone (proliferating B cells) and outer marginal zone (memory B cells)

Traps antigens for processing

In young infants, immature marginal zone may contribute to increased susceptibility to bacterial infections or sudden infant death syndrome (Hum Pathol 2004;35:113)