[Myofibroblasts in connective tissue of the human amnion]

Connective tissue of the human amnion at 14, 19, 21 and 33 weeks of gestation and at full term was examined by electron microscopy. Myofibroblasts which have not been described in the amnion so far were identified in addition to fibroblasts and macrophages (Hofbauer cells). Myofibroblasts display the following morphological characteristics: 1. The nuclei have multiple indentations and deep folds. 2. Numerous bundls of filaments (5 nm and 10 nm in diameter) are present within the cytoplasm. The bundles of 5 nm-filaments contain dense bodies. 3. Frequently they are connected to each other by desmosomes or by gap junctions. 4. The plasma membrane shows many hemidesmosome-like zones of thickening. 5. The cell surface is partly covered by basement membrane. Since these cells possess the ability of contraction, we suggest that they may contribute to the protection of the amniontic membrane from overdistension.