JC polyomavirus is a ubiquitous human virus that establishes persistent infection in renal and lymphoid tissues and, in the setting of severe immunosuppression, can reactivate and cause progressive multifocal leukoencephalopathy by destroying oligodendrocytes in the central nervous system.
Explanation
JC polyomavirus (JCPyV) is a member of the Polyomaviridae family with a circular double‑stranded DNA genome of about 5 kb. Primary infection typically occurs in childhood and is asymptomatic; the virus then remains latent in the kidney, bone marrow and lymphoid organs. The genome encodes regulatory proteins, notably large T and small t antigens, and structural proteins VP1, VP2 and VP3. Virus entry into susceptible cells involves binding to sialic acid‑containing receptors, such as the 5‑HT2A serotonin receptor on glial cells. In immunocompetent hosts, cell‑mediated immunity keeps viral replication in check. Profound immunosuppression, as seen in advanced HIV infection, hematologic malignancies or therapy with monoclonal antibodies like natalizumab or rituximab, allows viral reactivation and dissemination to the central nervous system. There JCPyV infects oligodendrocytes and astrocytes, leading to cell lysis, demyelination and the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). Viral variants with rearranged regulatory regions are associated with neurovirulence. Diagnosis relies on detecting JCPyV DNA in cerebrospinal fluid by PCR and characteristic lesions on MRI. No specific antivirals exist; the main treatment is to restore immune function by stopping immunosuppressive therapy or initiating antiretroviral therapy.
Clinical relevance and examples
PML was first described in patients with chronic lymphocytic leukemia but became more common during the AIDS pandemic. Individuals with untreated HIV may develop rapidly progressive neurologic deficits, and detection of JCPyV in CSF confirms the diagnosis. Cases of PML have been reported in patients with multiple sclerosis receiving natalizumab, prompting risk stratification and monitoring for JCPyV seropositivity before therapy. Serological surveys show that 50–90 % of adults have antibodies to JCPyV, and viruria is common in healthy individuals without disease. Rarely, JCPyV has been implicated in nephropathy in transplant recipients and in colorectal tumors, but its oncogenic role remains unclear. The virus provides a model for studying latency, reactivation and host control of polyomaviruses.
JC polyomavirus infection illustrates the delicate balance between viral persistence and host immunity. Awareness of its reactivation in immunosuppressed patients enables early diagnosis and intervention to reduce morbidity and mortality.
Related Terms: Progressive multifocal leukoencephalopathy, Polyomavirus, Oligodendrocyte, Immunosuppression, VP1