February 4, 2003
Baylor College of Medicine scientist Dr. Maria V. Tejada-Simon and colleagues have reported findings on a possible role for human herpesvirus 6 (HHV-6) in the immune attack in multiple sclerosis. This study, reported in the February 2003 issue of Annals of Neurology, was partly funded by a National MS Society research grant to Ying C. Q. Zang, MD, PhD.
Researchers have long suspected that a virus triggers the immune attack in MS. One candidate is HHV-6. However, over 90 percent of the population has been exposed to or infected by HHV-6. It has not been possible to separate a simple association of this virus with MS from a more critical, causal role.
The Baylor group undertook their study to determine whether HHV-6 might play a role in activating immune “T cells” that react to myelin basic protein (MBP), a major component of the nerve fiber-insulating myelin damaged by the immune attack in MS. They speculated that immune responses to HHV-6 might also trigger immune responses to look-alike myelin components, through a process called “molecular mimicry,” a concept that is widely discussed in theories of infectious triggers in autoimmune diseases.
The team determined that there were, in fact, some matching protein segments in HHV6 and in MBP. They then designed synthetic proteins comprising these matching segments and examined T-cell immune responses to the segments in 12 people with MS and 11 volunteers without MS. The results showed that more than half of the T cells that respond to MBP also could respond to HHV-6. T cells from people with MS were activated by both the MBP segment and the HHV-6 segment significantly more frequently than those from the non-MS controls.
This study indicates an association between the immune response to a myelin protein and the virus HHV-6. However, it remains unclear whether an initial exposure to HHV-6 generates a response that is “cross-reactive” with MBP – meaning that it results in the T cells attacking myelin; or, if the T cells’ reaction to MBP results in a greater immune response to HHV-6.
Research efforts continue: Society-funded grantees are tackling the
relation between MS and infectious agents from many angles, exploring how
may alter the immune system in MS; examining the role of gender
differences in an MS-like disease induced by a virus; and testing antibiotics
that target a bacterium in people with relapsing-remitting MS.
© 2003 The National Multiple Sclerosis Society