Hydrangea, a flowering plant used for centuries in Chinese medicine, may revolutionise the treatment for auto-immune diseases like multiple sclerosis, it was claimed yesterday.

A drug derived from the plant's root has been found to block the development of cells recently shown to play a key role in the disorders.

Scientists hope the compound, called halofuginone, can be used to tackle conditions such as MS, rheumatoid arthritis, Type 1 diabetes, inflammatory bowel disease and psoriasis.

Auto-immune diseases are caused by inflammatory attacks by the body's own immune system.

A major challenge is finding ways to treat them that do not weaken the immune system.

Existing treatments that regulate immune function are expensive and mostly have to be injected. While they hold back inflammation, they do not prevent it happening.

In severe cases, immuno-suppressive drugs have to be given that can leave patients at risk of life-threatening infections.

Halofuginone appears to target inflammation at source by preventing the development of a class of "T-cell" immune cells known as Th17 cells. Crucially, it does not seem to affect other kinds of T-cell vital to the body's defences.

The white blood cells were only identified in 2006 and have been implicated in a wide range of auto-immune diseases. They are genetically different from other T-cells and generate signalling molecules which trigger inflammation.

Th17 cells normally develop from a more immature type of T-cell. But laboratory tests in the US showed this process was prevented when cultures of the immature cells were exposed to halofuginone.

Mice with a multiple sclerosis-like disease marked by Th17 infiltration into the central nervous system were far less severely affected when given low doses of the plant compound.

Further work showed that halofuginone activates a biochemical pathway called the "amino acid starvation response" (AAR), which normally kicks in when amino acids - the building blocks of proteins - are in short supply.

Inflammation causes cells to proliferate, using up a lot of protein material. AAR acts as a brake on this process, and is triggered more easily in the presence of halofuginone.

Senior investigator Dr Anjana Rao, from the Children's Hospital, Boston, Massachusetts, said: "Remarkably, halofuginone evokes the AAR in all cells but selectively inhibits T-cell inflammatory responses. Halofuginone may herald a revolution in the treatment of certain types of auto-immune/inflammatory diseases."

The research was published in the journal Science.

Hydrangea root has traditionally been used to relieve inflammation and cleanse the joints, and to improve urinary function. An ancient Chinese remedy, it is also a traditional medicine of north American Cherokee Indians.

Leaf extract of hydrangea is also said to have anti-malarial properties.