Melanocytes are Melanin-producing neural-crest derived cells located in the stratum basale layer of the Epidermis. Melanin is a dark pigment primarily responsible for skin color. Once synthesized, melanin is contained in special organelles called melanosomes which can be transported to nearby Keratinocytes to induce pigmentation. Functionally, Melanin serves as protection against UV radiation. Melanocytes also play an important role in the immune systems.
Typically, between 1000 and 2000 melanocytes are found per square millimeter of skin or approximately 5% to 10% of the cells in the basal layer of the Epidermis. There are both basal and activated levels of melanogenesis. In general, lighter-skinned people have low basal levels of melanogenesis. Exposure to UV-B radiation causes increased melanogenesis. The purpose of melanogenesis is to protect the hypodermis, the layer under the skin, from damage by UV-B radiation. The color of Melanin is black, allowing it to absorb a majority of the UV-B light and block it from passing through the epidermis.
The difference in skin color between lightly and darkly pigmented individuals is not due to the number of Melanocytes in their skin, but to the Melanocytes' level of activity. This process is under hormonal control. Tyrosinase is required for melanocytes to produce melanin from the amino acid Tyrosine.
In addition to their role as UV radical scavengers, melanocytes are also part of the immune system, and are considered to be immune cells. Although the full role of Melanocytes in immune response is not fully understood, Melanocytes share many characteristics with dendritic cells: e.g. phagocytic capacity, presentation of antigens to T-cells and production and release of cytokines.