Infrequent detection of human herpesvirus 6 DNA in peripheral blood mononuclear cells from multiple sclerosis patients

Several studies have suggested an association between human herpesvirus 6 (HHV-6) infection and multiple sclerosis. As HHV-6 is predominantly a T- cell tropic virus, we examined the frequency of detection of HHV-6 genome in peripheral blood mononuclear cells from relapsing-remitting (n = 32) and chronic progressive (n = 14) patients and from healthy (n = 17) and neurological (n = 7) controls. Two sensitive polymerase chain reaction assays were used to target different regions within the HHV-6 genome. Depending on the polymerase chain reaction assay used, the detection of HHV-6 genome ranged from 11.7 to 23.5% (controls), 3.1 to 23.0% (relapsing-remitting), and 14.2 to 28.5% (chronic progressive). Although these observations do not exclude a pathogenic role for HHV-6 in multiple sclerosis, they indicate a lack of correlation between HHV-6 infection of peripheral blood mononuclear cells and the development of multiple sclerosis.