Increased lymphoproliferative response to human herpesvirus type 6A variant in multiple sclerosis patients

Several reports have suggested an association of human herpesvirus 6 (HHV-6) and multiple sclerosis (MS) based on immunohistochemical demonstration of HHV-6 antigens in inflammatory lesions, detection of increased HHV-6 specific serum antibody titers, and amplification of HHV-6 DNA from sera and cerebrospinal fluid of MS patients but not in controls. Characterization of the cellular immune response of MS patients to HHV-6 may further clarify the role of HHV-6 in MS and provide insight into the pathogenesis of this immune-mediated disease. We have compared lymphoproliferative responses to HHV-6A (U1102)-, HHV-6B (Z29)-, and HHV-7 (H7SB)-infected cell lysates in healthy controls and patients with MS. Most healthy controls (71%) proliferated to HHV-6B lysate, and fewer (33%) responded to the HHV-6A lysate. In contrast, 67% of MS patients had a lymphoproliferative response to HHV-6A, which is a significant increase in comparison with healthy controls. A similar frequency of lymphoproliferative response (78%) to HHV-6B was demonstrated in MS patients. Lymphoproliferation to HHV-7 lysate was demonstrated in 23% of healthy controls and 28% of MS patients. These results indicate that the lymphoproliferative response to the HHV-6A variant, which was recently reported to have greater neurotropism, is increased in MS patients.