Scientists at Imperial College London have discovered a protein that triggers rheumatoid arthritis.
They have found a protein called IRF5 that acts as a switch, telling immune system cells, called macrophages, to promote or stop inflammation, reports the Daily Express.
Rheumatoid arthritis is an incurable immune system disease where joints are swollen by inflammation.
The body uses inflammation as a defense against infection and tissue damage, but too much is harmful.
Blocking the production of IRF5 could help in a range of diseases including RA, lupus and even MS.
"This is really exciting," said senior researcher Irina Udalova.