LONDON - Scientists studying the autoimmmune disease lupus have found that blood platelets are key in its development and say their findings in the lab suggest blood-thinning drugs may offer a new way to treat patients.

The researchers found that lupus patients have an excess of platelets -- a type of blood cell that clump together to form clots -- and, after tests on mice, suggested that treating them with a drug like Sanofi-Aventis' and Bristol-Myers Squibb's Plavix could prevent flare-ups of the disease.

"These observations open a possible therapeutic avenue for human inflammatory autoimmune diseases -- the long-term utilization of antiplatelet therapy," the scientists wrote in the Science Translational Medicine Journal on Wednesday.

Patrick Blanco of the Centre Hospitalier Universitaire in Bordeaux, France, said his team hopes to start clinical trials soon on human lupus patients, but it could be many years yet before such a treatment is approved.

Lupus is a chronic disease where the body's own immune system attacks healthy tissue, causing inflammation, pain and damage in organs, particularly the kidneys. Its cause is largely unknown although researchers say there are several genetic, hormonal and environmental factors that can drive it.

According to the Lupus Foundation of America, as many as five million people around the world have a form of lupus, including 1.5 million in the United States.

There is no cure for lupus, although its symptoms can be managed to some extent with a range of different drugs. Raging infections and kidney failure are the most common causes of death in people with the disease.

Wiping out platelets

Current standard lupus treatments include steroids and some chemotherapy-like medications -- but almost all of these options can have toxic side effects.

Being able to treat lupus with a drug like Plavix, known generically as clopidogrel and commonly used to treat heart disease and stroke, could markedly improve quality of life for lupus patients, the French researchers said.

Plavix is the world's second-biggest drug, with sales last year of more than $9.5 billion. It is already off patent in parts of Europe and will lose US patent protection in 2012.

For this study, Blanco and colleagues collected blood platelets from patients experiencing lupus flare-ups. They found these platelets had an abundance of CD154 -- a protein normally activated for clotting -- and that they triggered production of interferons, causing inflammation in both human and mouse cells.

Using mice with lupus, they found that if they wiped out platelets by injecting an antibody to destroy them, the inflammation of the kidneys -- an organ often affected by lupus -- was significantly decreased.

"Because wiping out platelets is not possible in humans, we decided to test the lupus mice with clopidogrel, which has been used for many years in humans -- and found that this also significantly reduced the development of the lupus disease," Blanco said in a telephone interview.

As well as experiencing less kidney damage, the clopidogrel-treated mice also lived for an extra three months.

British drugmaker GlaxoSmithKline and US biotech firm Human Genome Sciences Inc are seeking approval for their keenly awaited lupus drug, Benlysta.

If approved it would be the first new drug for the disease in 50 years. Analysts expect it to be a blockbuster with annual sales of $2.2 billion by 2014.