Ultrastructural study of germinal center macrophages in peripheral lymphoid organs of the rat.

The ultrastructural study of macrophages of germinal centers in the secondary lymphoid follicles of the rat spleen and mesenteric lymph nodes was performed. It was demonstrated that besides macrophages containing necrotic lymphocytes and plasma cells in various stages of degradation (which are already well described in the literature) the germinal centers are also populated with macrophages displaying specific ultrastructural features which enable their precise identification. These cells contain numerous vacuolar inclusions of different size, filled with electron lucent, flocculent material. The dense bodies and membrane profiles are also present in varying amount within the vacuolar content. The dense bodies contain polysaccharides which are detected by the thiocarbohydrazide-silver proteinate method. Very rarely, these cells contain the phagocytosed cellular debris, which is readily distinguished from the cytoplasmic inclusions.