Biochemical Composition of the Epidermal-dermal Junction and Other Basement Membrane

The epidermo-dermal junction ultrastructurally appears to be high organized, presenting 4 layers: (1) the basal cell plasma membrane, a trilaminar layer with special attachment structures (hemidesmosomes); (2) lamina lucida (rara) an electron-lucent zone with 'anchoring' filaments (vide infra); (3) basal lamina (densa) electron-dense and relatively thick (30-50 nm) and (4) the subbasal fibrous area, composed of 3 different fibrils: (a) 'anchoring fibrils' meshing with the lamina densa upwards and forming and interlocking (a) meshwork with the adjacent anchoring fibrils downwards; (b) dermal microfibril bundles starting from the basal lamina and passing deep in the dermis. The dermal part of these, are in connection with the elastic fibers and ultrastructurally they are identical and; (c) collagen fibers, randomly oriented without connection with the basal lamina. The biochemical composition comprises collagenous and noncollagenous substances: collagens can be divided into 3 groups designated as type IV collagen, type V(AB collagen) and 7S collagen. The non-collagenous materials as yet identified are: bullous pemphigoid antigen (reactive with the bullous pemphigoid antibodies), laminin, heparan-sulfate containing proteoglycan and amyloid P-component (a normal plasma constituent). Functional aspects of basement membrane components: (1) support of a caffolding function assumed by the collagens; (2) attachment of cells of different embryonic origin (fibronectin, PB antigen and laminin); (3)regulation of the permeability (heparan-sulfate proteoglycan and other glycosaminoglycans); and (4) a role in development and morphogenesis (laminin) and type IV collagen). This paper must be read in extenso by those interested in the microstructure and functions of the skin. (I. Capusan - Cluj