While viruses are not thought to cause autoimmune diseases like multiple sclerosis (MS), it's believed they might accelerate the diseases' development in people predisposed to them. That's the conclusion of a study that used mice to answer that question.1
The Viral Role
Doctors led by Matthias von Herrath in the department of Developmental Immunology at the La Jolla Institute for Allergy and Immunology in California tested mice who were genetically susceptible to developing type I diabetes to determine if exposing them to a virus might augment the disease process.
The study suggested that while certain viruses cannot specifically cause diabetes or other autoimmune diseases, they can help boost their development much more rapidly.
The investigators theorize that in the events that lead up to rapid autoimmune disease development, the immune system attacks and kills the virus, but a secondary viral infection that subsequently occurs is directly responsible for the acceleration. This secondary infection somehow causes the immune system to launch a second attack, but on a more widespread basis, von Herrath and his team suggest.
The scientists found that infecting the mice with a certain virus caused type I diabetes to occur in the animals. Each of the rodents were prone to developing diabetes to begin with. "A major implication is that the infectious history of a patient is of growing importance in defining agents that potentially can induce autoimmunity or push a preexisting autoimmune condition toward clinical disease," they wrote.
Theoretically, lowering a person's odds of developing autoimmune disease in this way might lay in a therapy that potentially drives back the heightened immune reaction that initiates the process, they wrote.
An Attack Gone Awry
Normally, the body's immune system launches an attack against a foreign substance like a virus. When it goes amiss, however, and launches an attack against the body's own tissue, it is described as an autoimmune disease.
Multiple sclerosis is thought to be such as a disease. The immune system, for unknown reasons, initiates an attack against the body's own tissue. One key target is myelin, a protective sheath that covers nerve cells in the brain and spinal cord. When scarring and inflammation of myelin occur, nerve cells are unable to communicate with each other. This leads to varying degrees of neurological impairment depending on the location and extent of the scarring.
Other theories have pointed toward viruses as one potential cause of MS. If that's the case, the disease may be caused by a persistent viral infection, or conversely, by a transient viral infection that constantly activates the immune system.2
Environmental studies indicating where MS exists and where it is absent suggest that there is a triggering factor.3
It's estimated that the disease affects about 400,000 people in the United States alone. Each week, it's believed about 200 Americans are newly diagnosed.4
1. Christen U, Edelman KH, McGaven DB et al. A viral epitope that mimics a self antigen can accelerate but not initiate autoimmune diseases. J Clin Invest 2004 Nov;114(9):1290-8.
2. Multiple Sclerosis Foundation. What is Multiple Sclerosis? What Causes Multiple Sclerosis? Available at: http://www.msfacts.org/info/info_faq.html. Accessed November 12, 2004.
3. Casetta I, Granieri E. Prognosis of multiple sclerosis: environmental factors. Neurol Sci 2000;21(4 Suppl 2):S839-42.
4. National Multiple Sclerosis Society. Who Gets MS? Available at: http://www.nationalmssociety.org/Who%20gets%20MS.asp. Accessed November 12, 2004.
John Martin is a long-time health journalist and an editor for Priority Healthcare. His credits include coverage of health news for the website of Fox Television's The Health Network, and articles for the New York Post and other consumer and trade publications.
