UPTAKE, INTRACELLULAR TRANSPORT, AND DEGRADATION OF EXOGENOUS PROTEIN BY KERATINOCYTES - AN ELECTRON MICROSCOPIC-CYTOCHEMICAL STUDY USING PEROXIDASE AS MARKER SUBSTANCE

This paper details investigations on the uptake, intracellular transport, and degradation of exogenous proteins by epidermal cells utilizing peroxidase as an electron microscopic tracer substance. The following observations were made: 1. Immediately after injection into the skin the tracer protein permeates the epidermis filling the intercellular spaces. 2. Two hours after injection the keratinocytes start to engulf the exogenous protein utilizing endocytic mechanisms. Peroxidase is incorporated into micropinocytotic vesicles and into large phagosomes which, subsequently, are transferred into central portions of the cells. Fusions of phagosomes result in the formation of large paranuclear cavities containing the engulfed tracer protein. Finally, peroxidase is also found within multivesicular bodies. Protein uptake may exceed the holding capacities of the cells and may lead to cytolysis. 3. During the process described above increasing quantities of acid phosphatase can be demonstrated within the phagosomes which contain the internalized protein. Obviously, the phagosomes are transformed into phagolysosomes in which the resorbed protein becomes subject to degradation mechanisms. 4. It is concluded that epidermal cells are capable of heterophagy. Therefore, apart from their ability to synthesize proteins they also possess considerable resorptive capacities. Keratinocytes possess an efficient lysosomal system which secures the degradation of the phagocytosed material. © 1969 Springer-Verlag.