ReviewThe immunology and inflammatory responses of human melanocytes in infectious diseases

- Skin is a major portal of entry for pathogens such as alphaviruses and bacteria.
- Melanogenesis and barrier function (including from UV) could be affected.
- Pathogens and melanocyte cell debris (danger signals) could drive local inflammation.
- Melanocytes express many innate immune molecules and receptors to contain infection.
- Melanocytes, keratinocytes and immune cells will also orchestrate resolution of injuries.

SummaryMelanin is a canonical and major defense molecule in invertebrates but its role in mammalian immunity remains unexplored. In contrast, several recent studies have highlighted the emerging innate immune activities of human melanin-producing cells which can sense and respond to bacterial and viral infections. Indeed, the skin is a major portal of entry for pathogens such as arboviruses (Chikungunya, Dengue) and bacteria (mycobacterium leprae, Leptospira spirochetes). Melanocytes of the epidermis could contribute to the phagocytosis of these invading pathogens and to present antigens to competent immune cells. Melanocytes are known to produce key cytokines such as IL-1β, IL6 and TNF-α as well as chemokines. These molecules will subsequently alert macrophages, neutrophils, fibroblasts and keratinocytes through unique crosstalk mechanisms. The infection and the inflammatory responses will control melanocyte's immune and metabolic functions and could contribute to skin manifestations (rash, hyper or de-pigmentation, epidermolysis and psoriasis-like lesions). This review will address the potential role of melanocytes in immunity, inflammation and infection of the skin in health and diseases.