Microanatomy of the blood vasculature of lymph node follicles in the dog.

We studied the anatomical features of the arterial vasculature of the lymphoid follicles (LF) of tracheobronchial lymph nodes in the dog. The microvascular organization of the lymph node was visualized after systemic perfusion of the canine arterial system with gelatinated colloidal carbon. We found that LF contained a substantial number of blood capillaries forming a vascular network with a density comparable to that of neighboring domains of the node. The density of the vascular supply was greater in the secondary than in the primary LF. The geometric arrangement of LF capillaries was also different in the two types of LF. These findings are in contrast with the current view that the LF is a vascular-poor domain of the lymph node. We also document the plasticity of the LF blood microvasculature that appears to proliferate in conjunction with lymphoblast turnover and immune reactivity characteristic of secondary LF.