A group from Tunisia has reported a significantly increased prevalence of HHV-6 U94/REP “latency” antibodies among their cohort of multiple sclerosis patients. Previous studies have shown that there is little difference between generalized antibodies to the whole virus amongst patients and controls since nearly all controls carry HHV-6. However, several studies have shown a difference between patients and controls when examining either IgM (Soldan 1997) or HHV-6 early antigen antibodies (Ablashi 2000).
The authors speculate that in MS there is an impairment of cellular immune response that may lead to the reactivation of HHV-6 latent infection. HHV-6 U94/REP antibodies were discovered in 51.5% of 60 patients with MS compared to 28.6% of 63 healthy controls. Mean titer values were also significantly elevated in MS patients compared to controls (1:242 vs. 1:110; p=.0005).
The HHV-6 U94/REP protein is associated with the latency phase of HHV-6, and previous reports suggest that MS patients may experience variations in U94 production as a result of frequent switches between latency and active HHV-6 replication (Caselli 2002). Among patients who could be analyzed during both relapsing and remitting phases, the group found anti-U94/REP IgG values significantly increased during the relapse phase in particular (p=.007). Further studies will be conducted to analyze the etiological relationship between HHV-6 activity and particular phases of MS disease progression among individual patients.
This reactivation is low-level and may fall below the level of detection in PCR DNA testing. HHV-6 DNA in peripheral blood was found in 5.8% of patients and 1.9% of controls. MS patients had a higher viral load compared to controls when detected (708 copies/mL vs. 85 copies/mL). Most of the recent studies of DNA in MS patients have been conducted on plasma or serum, not whole blood. Several studies by a group in Spain have found HHV-6A in the serum of MS patients during relapse but not during remission. HHV-6B is more likely to be found in whole blood than in serum; all of the positive patients were determined to be HHV-6B.
The authors also suggest that HHV-6 may be infecting cells other than the lymphocytes circulating in the peripheral blood of patients with MS, such as olidogdendrocytes.
For more information, read the full paper published in the Journal of Neurovirology, and visit the HHV-6 Foundation’s webpage on HHV-6 & multiple sclerosis.