Dermal collagen distribution. A histochemical and ultrastructural study.

Normal skin biopsy specimens obtained from 5 representative species of mammals, including man, were studied by the silver impregnation technique for reticulin fibers, by the histochemical Picrosirius-polarization method which is specific for collagen, and by transmission electron microscopy. The finely woven meshwork of argyrophilic reticulin fibers present in the adventitial dermis showed characteristics which are typical of collagen type III, when studied by aid of the Picrosirius-polarization method and by electron microscopy. On the other hand, the coarse collagen fibers of the deeper layers displayed ultrastructural and histochemical aspects which are characteristic of collagen type I. The foregoing observations support previous biochemical and immunohistologic findings, strongly suggesting that collagen type III is found mainly in the upper dermis while collagen type I predominates in the deeper layers.