Effects of UV irradiation on skin and nonskin-associated herpes simplex virus infections in rats

Herpes simplex virus (HSV) normally causes vescular lesions on mucocutancou s surfaces but can also cause encephalitis, The virus can reactivate from t he latent state in neurons to form recrudescent lesions. One common stimulu s for reactivation Is exposure to sunlight. In the present study, the effec ts of irradiating rats with suberythemal ultraviolet (UV) before or after i nfecting them epidermally with HSV was investigated. Preexposure to UV impa ired NSV-specific cellular immune responses, as indicated by delayed type h ypersensitivity (DTH) and in vitro lymphoproliferation assays, However, the number and severity of the skin lesions were not altered. In contrast, exp osure after infection did not affect cellular immunity but resulted in a la rge Increase in the severity and number of lesions. In a second series of e xperiments, the effects of preirradiating with UV on HSV infection was exam ined using a route of inoculation which was not skin-associated, namely int ranasal, allowing direct noninvasive access to the nervous system. It was f ound that suppressed DTH resulted, together with an increase in the inciden ce and severity of neurological symptoms and an increased viral load in the brain. Therefore, unlike the situation In the skin, irradiation of rats be fore intranasal inoculation led to a suppressed immune response to HSV whic h correlated with increased viral load and symptoms. These results indicate that the effects of UV may he dependent on whether the animal is exposed b efore or after the infection, and whether the infection is skin-associated or systemic.