Histochemical investigations of different types of collagen

During histochemical studies of connective tissue in the early 1960's, striking differences were observed between basement membranes and collagen fibers. A third histochemically distinct collagen was identified in premature infants. At that time, these findings could not be correlated with chemical data. However, during the last decade chemists described several types of collagen. Correlation of chemical, histochemical and immunofluorescence data indicated that the tendon-type collagen seen in coarse collagen fibers, e.g. in skin and adventitia of adults, contains type I collagen. The distribution of embryonic-type or pseudo-elastic collagen was similar to that of type III collagen; the major exception was reticulum fibers. Since antibodies and dyes are bound at different sites, it seems possible that fibers with the immunofluorescence characteristics of type III collagen may differ in their binding sites for other reagents. The trypsin-lresistant protein of basement membranes corresponded to type IV collagens. The collagen formed in glomerulosclerosis was histochemically indistinguishable from tendon-type, i.e. type I, collagen. A review or early literature since 1850 showed that histologists repeatedly described distinct chemical and histochemical differences between various collagens. These long ignored findings can easily be fitted into the framework of current collagen chemistry.