The JC virus is a human polyomavirus. The JC virus can respond in immunocompromised patients and is in those conditions with Progressive Multi-focal Leukoencephalopathy, PML. In sporadic cases, the JC virus also corresponds to an interstitial nephritis. PML is a development in the central design that can cause irreversible brain damage, the condition is caused by reactivation of the JC virus. Reactivation mainly occurs in infected with cellular immunodeficiency. The most unusual symptoms of PML are behavioral changes, cognitive disorders, motor disorders.

The JC virus can be detected by means of the JC Virus PCR kit, for this purpose collection material from plasma, urine or whole blood is used. In this PCR kit, detection is performed for T-Ag encoding the small tumor antigen. This antigen interacts with Agnoprotein and thus plays a role in the process of cell transformation and in viral replication. By measuring the expression of T-Ag, the presence of the JC virus can be detected.