Site-dependent differences and common features of lymph node architecture, with special reference to the distribution...

Although human lymph node architecture varies by site, the intranodal distribution of interdigitating dendritic cells (DCs) remains poorly understood. To address this, we compared the morphology of submandibular, paratracheal, mesenteric, and inguinal nodes obtained from 24 donated cadavers. Immunoreactivity was evaluated by comparing these cadaveric nodes with surgically resected lymph nodes obtained from five old-aged patients with nonmetastatic cancer. Despite the limited number of dendritic cell-specific ICAM-3-grabbing nonintegrin (DC-SIGN)-positive cells (candidate DCs) in cadaveric specimens, these tissues were deemed suitable for analysis. The submandibular and paratracheal nodes exhibited a belt-like cortex, with paracortical lymph sinus extending from the subcapsular sinus and surrounding the follicle. In contrast, the mesenteric and inguinal nodes contained multiple island-like cortices separated by thick paracortical lymph sinuses. Endothelial cells lining all lymph sinuses showed reactivity for smooth muscle actin and DC-SIGN. Macrophages and candidate DCs were abundant in the paratracheal and mesenteric node sinuses but scarce in the submandibular and inguinal nodes. Notably, the medullary sinus in the submandibular and inguinal nodes was filled with fibrous tissue, and the surrounding paracortical sinuses formed a "sea" around the island-like cortices, often resulting in loss of nodal polarization. Although the proportional area occupied by candidate DCs per nodal section was almost the same at the four sites, the overlap between DCs and macrophage clusters was small in paratracheal and inguinal nodes. The amount of afferent lymph and the retention of efferent lymph might determine the site-dependent architecture. Therefore, in aged nodes, DCs were preferentially localized in the paracortical sinus.