The mole theory: primary function of melanocytes and melanin may be antimicrobial defense and immunomodulation (not solar protection)

Physician: “No one has the foggiest notion why God gave us moles on our skin ... and that’s the honest truth.” Melanocytes are derived from melanoblasts that arise from the neural crest. Melanocyte numbers vary little between human populations, although they differ in size, number, and the structure of melanosomes. 1 In the human epidermis, they have a close association with keratinocytes via dendrites. Although well known for their role in skin pigmentation, this is probably not the only function of these cells. Indeed, melanocytes have numerous enzymes with capabilities in antimicrobial defense, as well as genetic, biochemical, and functional links to the immune system. 2 Melanin, endogenously produced by melanocytes, is able to interact with enzymes and modulate their behavior, is a powerful cation chelator, and can bind and neutralize oxidants, microbicidal peptides, and antimicrobial drugs. 3–6 A better appreciation of the biological effects of melanocytes may assist in all aspects of the evaluation, understanding, and treatment of diseases associated with this cell line, such as vitiligo and melanoma. There are definite flaws in the media dogma that melanin’s main role is in protection against ultraviolet light. To begin with, it fails to explain the increase in the prevalence of melanin and melanocytes in skin not normally exposed to the sun, such as the genitalia, 1 and other body tissues, such as the epithelium of the inner ear, uveal tract of the eye, brain tissue, and the peritoneum. 7 Moreover, many nocturnal animals, such as bats, are highly melanized on their exterior surface. In addition, African albinos, despite the absence of melanin’s sun protection, do not have an increased incidence of melanoma. 2