Viral meningitis is cured in mice by blocking the action of an anti-inflammatory immune molecule. The technique may one day lead to cures in humans for hepatitis C and other chronic viral infections, including meningitis and HIV.
Researchers have studied viral infections in mice and discovered that in chronic infections – where a virus lingers in the body – the rodents’ natural anti-inflammatory response effectively prevents its immune system from attacking the virus.
Matthias von Herrath and colleagues at the La Jolla Institute for Allergy and Immunology in California, US, studied an acute and chronic meningitis infection in mice, called lymphocytic choriomeningitis virus (LCMV). They discovered that mice with chronic infections had high levels of the inflammatory-damping chemical interleukin-10 (IL-10).
When they gave mice with chronic LCMV a drug that blocks the inflammatory-calming action of IL-10, the inflammatory immune response was re-activated. Within a week the mice were healthier. In two weeks, they had cleared the virus completely.
Strong response
When a virus first invades, the body attacks it with an all-purpose immune response. But to prevent an immune over-response that destroys too much of the host’s own tissue, a complex network of damping-down feedbacks keep it in check. Viruses exploit these to slip past innate defences.
Von Herrath’s team discovered that the chronic form of LCMV induces such a strong response from one type of inflammatory immune cell that those immune cells damp down their own production. As a result, the IL-10, which normally balances these inflammatory immune cells, starts to build up in the blood, preventing the rodents’ broader immune system from attacking the virus.
Many chronic viral infections in humans also elicit high levels of IL-10, including cytomegalovirus, HIV, and hepatitis C. The latter infects 180 million people worldwide – 3% of the total population – and causes liver cirrhosis and cancer. Blocking IL-10 might allow such people to clear these viruses, the researchers hope.
Blood tests
”We are very excited about this,” von Herrath told New Scientist. There is always a risk that turning inflammation back on might lead to excessive immune reactions, especially auto-immunity, where the body attacks itself, he cautions. So they plan to first study the blood of infected people to see if the antibody that blocks IL-10 will alter the balance of immune cells.
Then perhaps it will be possible to treat people, perhaps alongside other anti-viral treatments, such as vaccines. The US pharmaceutical firm Schering-Plough, which owns the antibody, is already testing it in humans against cancer, another disease where IL-10 may be damping more immunity than is good for us.
Von Herrath thinks IL-10 may have evolved as a protective mechanism: allowing us to live for a few decades with a chronic infection, rather than being killed by a very strong autoimmune response.
