A HISTOLOGICAL AND ULTRASTRUCTURAL COMPARATIVE-STUDY OF RETRACTED ANDTENSE COLLAGEN LATTICES

Collagen gel cultures containing human fibroblasts have been observed to undergo a rapid contraction process. If contraction is prevented, t he lattice becomes tensed and very thin, reproducing skin tension in v ivo. We have used light microscopy and transmission electron microscop y (TEM) to study the architectural organization of the tissue, the sta te of differentiation of fibroblasts and morphology of fibres in freel y-retracted and tense lattices. A striking feature of both lattices wa s the encapsulation process by fibroblasts and generation of mechanica l retracting forces inducing cell locomotion and orientation. In freel y-retracted lattices, the cells looked like fibrocytes; they compacted mature collagen fibrils in bundles around them. The mechanical inhibi tion of retraction caused the fibroblasts to become spindle-shaped, a decrease in the lattice density in collagen fibrils, a peripheral laye r of microfilaments and the production of fibronexus junction characte ristic of myofibroblasts. Both fibroblasts and collagen fibrils became aligned in the same plane along the axis of the tensile force. After 3 months of culture, mature collagen had almost disappeared and was re placed by loosely arranged tropocollagen-like microfibrils. Meanwhile the cells retained ultrastructural features, consistent with a good me tabolic activity. These observations show that freely-retracted and te nse lattices are different in architecture, cell type and metabolic ac tivity.