LANGERHANS CELLS IN EQUINE CUTANEOUS PAPILLOMAS AND NORMAL SKIN

Langerhans' cells (LC) were investigated immunohistochemically and electronmicroscopically in normal equine epidermis and 133 equine cutaneous papillomas experimentally induced in five 2-year-old Thoroughbred horses. Class 11 major histocompatibility complex antigen-positive dendritic LC were found in the normal epidermis and ultrastructurally had the characteristic Birbeck's granules. In the developing phase of the papillomas, LC were significantly decreased in number and size, indicative of a hypofunctional state. In the regressing phase of the papillomas, LC were markedly increased in number, especially at the epidermis-dermis junction. LC with long dendrites were rich in cytoplasm with well-developed cytoplasmic organelles, including Golgi apparatus, lysosomes, Birbeck's granules, and multivesicular bodies. These LC were hyper-functional. An infiltration of many T lymphocytes was also observed at the epidermis-dermis junction.