Intracellular collagen fibrils in cultured human skin.

During cultivation, the collagen fibrils of skin explants are broken down. The cells of the explants participate in this resorption. The ultrastructure of the intracellular degradation of collagen fibrils of cultured human skin has been examined. Intracellular collagen fibrils occur in fibroblasts, macrophages, smooth muscle cells and unidentifiable cells. Normal collagen fibrils are engulfed and appear within membrane-bounded tubes of the cytoplasm. Primary lysosomes fuse with the tubes. Degraded intracellular collagen fibrils are frequently present in secondary lysosomes and show decreasing diameters, filamentous splitting, loss of axial periodicity, variable stainability and cross-banded filamentous aggregates. The changes in the intracellular collagen fibrils are identical with those seen in the extracellular space. The present study demonstrates that various cell types in dermis are involved in collagen fibril degradation and that the lysosomes play an important part in the intracellular resorption.