Perifollicular, perisinusal and trabecular myofibroblasts in the human fetal spleen

Electron microscopic studies of the human fetal spleen were performed on 22 embryos and fetuses from 31 days to 32 weeks of age. In the course of splenic development myofibroblasts were frequently observed in the perifollicular and perisinusal regions and within the trabeculae. The perifollicular cells were flattened and markedly elongated in shape and had distinct bundles of microfilaments in their cytoplasm. The perisinusal cells under the sinal basement membrane had microfilaments found in particular beneath the plasmalemma. They were attached to each other and constituted a cellular network throughout the splenic cords. The trabecular myofibroblasts, embedded among the abundant collagen fibers, had elongated and often indented nuclei. The cytoplasm contained well developed Golgi apparatus, abundant rough surfaced ER cisternae and massive bundles of myofilaments. These cells showed cell-to-cell and cell-to-stroma connections and were assumed to play a role in the excretion of lymphocytes from the follicles and in pumping blood from the sinuses by their contraction.