The obvious question was why the immune system of the first mouse was not capable of recognizing the tumour. The answer, it emerged, was that UV radiation was able to compromise the immune system. And so the field of photoimmunology was born. Our immune systems should protect us from infection. Many humans have already experienced one result, developing cold sores after being exposed to sunlight.
Cold sores develop as a result of a reactivation of latent herpes simplex virus.
It is thought that suppression of the immune response allows the virus, which hides in the nerve serving the skin while latent, to replicate again. On a larger scale, this could lead to us developing severe or more prolonged infections. To subclinical or even latent infections becoming clinically apparent or productive. Or even to previously harmless, non-pathogenic organisms becoming pathogenic. Such fears have led to European Commission-funded studies involving experimental animal models of infection.