Uptake, Intracellular Transport and Degradation of Exogenous Protein by Langerhans Cells An Electron Microscopic-Cytochemical Study Using Peroxidase as Tracer Substance

Abstract

The uptake, intracellular transport and degradation of exogenous proteins by Langerhans cells were investigated at the ultrastructural level using peroxidase as a tracer substance. The following observations were made: 1. Langerhans cells utilize mechanisms of endocytosis to engulf exogenous proteins. 2. Phagosomes derived from the cytomembrane transport the ingested material into the interior of the cell, usually into the vicinity of the Golgi system. 3. By the incorporation of acid phosphatase the phagosomes are transformed into phagolysosomes. Thus, the internalized protein becomes subject to degradation within the lysosomal system of Langerhans cells. 4. Keratinocytes engulf more protein per cell than do Langerhans cells. After injury Langerhans cells fail to perform a scavenger function by specifically clearing the epidermis of cellular fragments. Therefore, despite their capacity to engulf exogenous material and despite their structural identity with certain histiocytic cells, Langerhans cells should not be designated epidermal macrophages. 5. Langerhans cell granules attached to the cytomembrane are patent to the intercellular space and may be filled with extracellular tracer protein. However, the marker protein is invariably absent from intracytoplasmic Langerhans cell granules indicating that these organelles do not move from the cytomembrane into the interior of the cell. Langerhans cell granules do not participate in the uptake and intracellular transport of exogenous protein and, therefore, their endocytic function is questioned.