Avian lymph node: Light and electron microscopic study

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Abstract
We have observed by light and transmission electron microscopy lymphoid accumulations (LA) in the chicken located along the posterior tibial‐popliteal and lower femoral veins. Three types of LA were characterized: (1) LA on the wall of the lymphatic, (2) LA with germinal center, and (3) well‐developed LA possessing germinal centers and an intricate lymphatic sinus system. The latter will be termed a lymph node and is perhaps the structure responding to foot‐pad injection of antigen and/or phytohemagglutinin (PHA). After the injection of PHA into the foot‐pad, the lymph node enlarged and revealed the intermingling of two distinct groups of cells consisting of either small lymphocytes or medium lymphocytes and lymphoblasts. Because our earlier immunological paper proved the presence of T and B cells in the node, the two histologically distinct groups of cells appearing after PHA injection could reflect compartmentalization of T and B cells in the avian lymph node. Lymphoid and adipose tissues are in the same compartment. After PHA or antigen injection into the foot pad, the lymphoid tissue proliferates and the amount of the adipose tissue rapidly decreases. This suggests that lymphoid and adipose tissue form a special complex which is separated from the surrounding tissue by delicate connective tissue capsule. The relationship of the lymphoid and adipose tissue is comparable with that of myeloid and adipose tissue in the bone marrow. The majority of the sinuses shows smooth endothelial lining while others contain “hairy” macrophages attached to the endothelium. The germinal centers are located at the periphery of the node, but a few occur inside. The cellular content of the germinal centers is not unusual except for the presence of plasma cells.