The living skin-equivalent as a structural and immunological model in skin grafting

The living skin equivalent is a tissue formed when self-assembled collagen fibrils are contracted by fibroblasts. The rate and extent of volume contraction is proportional to the number of cells incorporated into the lattice. The fibroblasts are biochemically active in the lattice, synthesizing collagen and adding it to the matrix. This compacted lattice provides a substrate allowing attachment of keratinocytes and the formation of a multilayered keratinized epidermis with a basement lamella. When a skin equivalent grafted to a recipient animal is wounded, it is capable of wound contraction and repair. Because of the simplified character of the skin equivalent it may offer a useful model for studying wound healing. During the initial healing of the grafted skin equivalent, fibroblasts from the skin equivalent move freely into the surrounding tissue. Karyotyping of fibroblasts grown from skin surrounding the skin equivalent graft shows that fibroblasts from the graft migrate at least 6-9 mm from the graft edge. At 3-6 mm from the graft edge about 50% of the fibroblasts present are of donor origin. Fibroblasts also migrate from allogenic skin grafts before these grafts are rejected. At 3-6 mm from the scar left by the rejected graft 36% of the fibroblasts are of donor origin 2 months after grafting. The skin equivalent model provides a well-defined system for studying transplantation reactions. Results obtained on persistence of allografted fibroblasts support our theory that in the rat, the fibroblast is antigenically neutral.