A dose of worms, please

A prolonged bout of intestinal parasites seems to slow the decline of patients with multiple sclerosis, according to a study released today. The results suggest that immune-modulating molecules from parasites could be developed into drugs to ease autoimmune diseases, and that by conquering parasite infections, modern medicine may have inadvertently increased our vulnerability to these illnesses. Autoimmune diseases such as multiple sclerosis (MS) occur far more often in developed countries than in developing countries. And parasitic infections, which have been beaten down in the United States, are still common in South America and elsewhere in the developing world, says neuroimmunologist Jorge Correale of the Raúl Carrea Institute for Neurological Research in Buenos Aires, Argentina. What’s more, studies have shown that infecting mice with parasites eased symptoms of an MS-like syndrome.

To see if the parasite-autoimmune link held up in humans, Correale and his colleague Maurício Farez identified 12 MS patients with high levels of parasite-fighting white blood cells called eosinophils and then confirmed parasite infections by examining stool samples under the microscope. They tracked those patients and equal numbers of uninfected MS patients and healthy people for 4 and a half years. In MS, the immune system attacks the insulating myelin sheath of nerves, disrupting the transmission of messages. Infected patients as a group suffered just three instances of new or worsening symptoms, compared with 56 in the uninfected patients. As measured by a standard neurological test, the degree of disability increased in 11 of the 12 uninfected patients, but in only two of the 12 infected individuals.

Next, the team measured white blood cells and immune-signaling chemicals called cytokines from each patient to understand how the invaders changed the immune system. Parasite infections induced much higher levels of three types of immune cells called regulatory T cells, the researchers report in January 2007 issue of Annals of Neurology. They propose that while fighting the parasite infection, these three types of cells also happen to dial down a different arm of the immune system that attacks myelin to cause multiple sclerosis. By finding the immune-signaling molecules responsible, it may one day be possible to identify parasite molecules that deactivate the immune system arm that causes autoimmune attacks, Correale says. “It’s a provocative study, and it would be interesting to do this in a larger number of individuals,” says immunologist David Hafler of Harvard Medical School. If the results hold up, he says, it would underscore the emerging consensus that “an idle immune system is probably not good.”

February 6, 2007

Original web page at ScienceNow