ABSTRACT
Many studies in photoimmunology have used ultraviolet (UV) sources contaminated with UVC and these need to be treated with caution, as their relevance to human biology or health is unclear. Immune responses can be divided into two arms, cellular and humoral, which are responsible for immune recognition and destruction of the invading pathogen or skin cancer. First evidence that UV radiation influences the immune system was the observation that UV radiation inhibits the immunologic rejection of transplanted tumors. UV suppression of memory immunity probably explains why UV radiation can be an effective therapy for chronic autoimmune disorders, such as psoriasis. Higher UV doses also affect immune reactions induced at a distant, non-UV-exposed site. Even before delving into molecular or cellular mechanisms, UV has a complex suppressive effect on the immune system. It is able to suppress not only the activation of primary immunity at UV-irradiated and -unirradiated skin sites, but also the reactivation of memory immunity.
