The clinical relevance of immunosuppression by UV irradiation.

Ultraviolet light has been shown to modify the immune system. Photo immunosuppression occurs already when the skin is exposed to low doses of UVB. The physiological role of this suppression may be to prevent the occurrence of an inflammatory reaction after UVB exposure which could damage the sun-exposed skin. The pathogenic consequences of UVB radiation can be observed in the exacerbation of infectious diseases and the development of skin cancer. Especially for immunocompromised patients the additional role of photo immunosuppression is of great clinical importance. Renal transplant recipients have a highly increased risk for the development of squamous cell carcinomas and the great majority of these tumours are present on sun-exposed skin. In many of the skin lesions DNA of human papilloma virus (HPV) is present, suggesting that UVB light affects the local immune response and renders the skin unable to reject (pre)malignant HPV. The pathogenic consequences of photo immunosuppression in other patient groups and in the general population have still to be determined.