Lymph node sinus. Light micrograph of a section through a lymph node, a filter that keeps the immune system in check. The subcapsular sinus (white) beneath the fibrous outer capsule of the node (blue, top) can be seen. Tissue fluid (lymph) drains into the sinuses, where white blood cells called macrophages (pink) remove and digest cellular debris, bacteria and other pathogens from the fluid. Azan stain. Magnification: x300 when printed 10cm wide.