Histological and Immunohistochemical Studies on the Architecture of Lymph Nodes in Pig

Abstract

The general structures, intranodal lymph pathway and thymus (T)-dependent area of pig lymph nodes, known as the "Reverse type of lymph nodes", were histologically and immunohistochemically studied. The lymph nodes consisted of several lymphoid segments, "nodular unit" of various sizes. Each nodular unit possessed the "A-type hilus", at which afferent lymph vessels entered the nodes, and the "E-type hilus", which located between nodular units, and efferent lymph vessels left the node both at the E-type hilus and convex surfaces. The cortex-like tissues were located not only in the central area of the nodular units but also in the sub-capsular area around the A-type hilus. On the other hand, medulla-like tissues were distributed in the peripheral regions around the E-type hilus. These regional interrelations between the cortex-like tissues and the medulla-like tissues gave rise to various patterns (reverse or non-reverse) depending on the levels of sectioning for histological preparations. Large central cisternae (CC) and intra-trabecular lymph channels (ITLC) with lymphatic valves were found within the trabeculae, and the ITLC diverged subsequently into the peri-trabecular lymph sinuses (PTLS). Sub-capsular lymph sinuses (SCLS) were distinguished around the cortex-like tissues and were associated with PTLS. In the nodular units intranodal lymph flowed not only from the center to the periphery but also into the other two routes: by one route, it drained into the SCLS directly via the CC, and by the other, it drained into neighbouring nodular units through the internodular communicating routes of the SCLS. T-dependent area occupied almost all of the spacious cortex-like tissues except for the germinal centers. These areas closely faced the PTLS and SCLS.