Robert L. Olson

PENETRATION OF EPIDERMIS BY ULTRAVIOLET RAYS.

Abstract— The u.v. transmission characteristics of various epidermal specimens prepared by various methods were measured by a recording spectrophotometer and integrating spheres. Although suction or stretch and heat produced the most satisfactory specimens, transmission data obtained from all specimens were similar and generally resembled that reported by previous investigators. The important contribution of forward scattering to total transmitted light was demonstrated. Significant numbers of u.v. photons have been shown to penetrate to the dermis and papillary capillaries. Erythema was produced in vivo by monochromatic light filtered through epidermal specimens after exposure of skin to the quantity of u.v. anticipated by these data.

Epidermal Apoptosis: Cell Deletion by Phagocytosis

Apoptosis is a process found in many tissues by which devitalized cells are eliminated in an orderly manner. In skin, apoptosis occurs following sunburn, in Bowens disease and in basal cell carcinoma. Scattered cells are observed in which the cytoplasm has become condensed and dyskeratotic. These dyskeratotic cells are phagocytized, either in toto or in fragments by surrounding keratinocytes. This process involves the condensation, fragmentation, phagocytosis and digestion of individually degenerated cells. The mass of a tissue is thus related to the balance between cell formation (mitosis) and cell destruction (apoptosis). In epidermal and other surface tissues, the rate of exfoliation must also be considered.

THE ROLE OF EPIDERMAL LYSOSOMES IN MELANIN PHYSIOLOGY

SUMMARY.— Melanosomes are formed within melanocytes and transferred via dendrites to keratinocytes. In caucasoids, most melanosomes are aggregated in membrane‐bound organelles (melanosome complexes). These aggregates have phagocytic capacity, stain positively with aryl sulphatase and acid phosphatase, contain melanosomes apparently undergoing degradation, and are lysosomes. In addition to melanosome complexes, individual melanosomes, both in melanocytes and keratinocytes, also exhibit lysosomal properties of phagocytosis and hydrolytic enzyme activity. In contrast, negro melanosomes are mostly singly dispersed and are rarely aggregated in complexes. Melanosome dispersal contributes to the darker colour and superior sunlight protection of negro skin. Degradation by lysosomal enzymes explains the limitation of melanin principally to the basal layer.

Ultraviolet-Induced Individual Cell Keratinization

Characteristic cells have been demonstrated as being individually dispersed throughout the superficial epidermis 24 h after being exposed to ultraviolet light. These „sunburn cells” with cosinophilic cytoplasm and pyknotic nuclei observed by light microscopy are also observed to be dyskeratotic by using electron microscopy.

Ultrastructure of human epidermis following chronic sun exposure.

—The epidermis of 6 patients with actinic degeneration was studied by electron microscopy. In comparison with nonexposed skin of the buttock, sections from exposed areas revealed abnormalities of 3 epidermal cellular functions. Epidermal cells were characterized by focal areas of dej^eneration involving groups of adjacent cells. Degenerative changes resembling dyskeratosis were present in cytoplasm of basal as well as spinous cells. Secondly, cellular cohesion was disturbed. Desmosomes varied from few to greatly increased in quantity, and exhibited variable degrees of maturity and distribution. The third disturbance was in epidermal pigment distribution. Melanin concentration varied from none to excessive, and melanosome complexes were often abnormally large. These clones of epidermal aberrations, visible by electron microscopy when no light microscopic or clinical abnormalities are present, suggest that epidermal alterations induced by u.v. light may parallel or even precede dermal damage.