Three-Dimensional Morphology of Follicular Dendritic Cells.

Abstract

Three-dimensional morphology of follicular dendritic cells (FDC) in vivo was studied with fluorescent microscopy and electron microscopy.FDC are specialized cells found within primary and secondary lymphoid follicles of lymphoid tissues. They retain antigen-antibody complexes on their surface and may play the leading role in the induction of immunological memory and the maintenance of long-term immunity. The author observed their unique distribution with the aids of their characteristics to retain immune complexes and new type of fluorescent microscope, confocal scanning laser microscope. Detailed structure of cytoplasmic processes was described by ultrastructural observation of serial ultrathin sections.Twelve days after human serum and red blood cells were injected to the Sprague-Dawley (SD) rats intravenously or peritoneally, FDC in the spleen were detected by surface human IgG with FITC-conjugated antibody using confocal scanning laser microscope. FDC had long cytoplasmic processes and formed complex labyrinth-like structures. FDC-clusters were not observed. S-100 protein was also a useful marker to detect FDC of the rat.Ultrastructural study on human tonsils with follicular hyperplasia showed that the nucleus was irregularly shaped, with well-defined nucleolus and prominent fibrous lamina. The cytoplasm had rough-surfaced endoplasmic reticulum, mitochondria, Golgi apparatus, polysomes, and bundle of microfilaments along the cell membrane. Extracellular dense materials were common findings. Observation of serial sections showed that the processes of FDC were ruffled dendritic processes with extensive branching and anastomoses. Lymphocytes also came in active contact with FDC.Author also made an observation on the S-100-positive cells in the rat lung, and found that reticular cells in the lymphoid follicles of bronchus-associated lymphoid tissue (BALT) have similar features to FDC ultrastructurally, although their cytoplasmic processes were not developed as those in the spleen. These dendritic cells may also play an important role to local defense of respiratory tract.