Geometry of the lymph node. (A) A cleared popliteal lymph node was stained for B cells (CD35/21, green), blood endothelial cells (CD31, red), and lymphatic endothelial cells (LYVE-1, blue), and was imaged using confocal microscopy. Lymph enters the node (arrow) through afferent lymphatic vessel(s) (Af). It then moves to subcapsular sinus (SCS), which can then go to either B cell follicles (BF) and T cell cortex (TC) through central path, or directly to medullary sinuses (MS) through peripheral path. Lymph will leave the node (arrow head) through efferent vessel(s) (Ef), although some lymph fluid will be absorbed by blood vessels (BV). Scale bar is 200 μm. (B) Z-stack confocal images were acquired for blood vessel geometry reconstruction. (C) Blood vessels (CD31+ cells) of the node are segmented using a threshold/paint technique. The surface area and the total volume of the node are extracted from the images and are used to calculate surface area density of the blood vessels. The B cell follicles are segmented to demonstrate the relative location of the major blood vessels to them. Scale bar is 200 μm. A color version of this figure is available in the online article at www.liebertpub.com/lrb.