Possible phagocytosis by keratinocytes: ultrastructural evidence from the study of human oral mucosa in organ culture.

Surgical samples of human oral mucosa undergo striking transformations within 24 hr, when maintained in organ culture, at 37”C, on fibrin foam mats, with 5 per cent CO2 in air as the atmosphere. These transformations include disorganization of the tonofibrillar apparatus, reduction or loss of desmosomes, and loss of the intercellular relationships characteristic of stratified squamous epithelium. Under these conditions, remnants of whole, nucleated cells or fragments of nuclei were observed in membrane-bound vacuoles within keratinocytes. The ingestion of cells or cell fragments by keratinocytes usually resulted in some damage to the cytoplasm immediately adjacent to the phagocytic vacuoles containing the cells or cell fragments. While instances of keratinocyte phagocytosis were rare in the system studied, they, nevertheless, contribute additional support to previous descriptions of keratinocyte phagocyte capability. It also appears, that, while being able to phagocytose and degrade both cells and extracellular products, keratinocytes do so at the partial expense of their own structural integrity.