Researchers have known for years that smoking can increase the likelihood of developing rheumatoid arthritis (RA). A recent study now suggests why: tobacco usage makes it more likely that a rare genetic condition will trigger the body's immune system to literally attack itself. The findings were reported in the January 2006 issue of Arthritis & Rheumatism.
The researchers analyzed blood samples from >1200 participants, 930 with early symptoms of RA and 383 without. They found that a combination of smoking and a genetic trait often came together to cause RA. Smokers who had 2 copies of a gene known as HLA-DR shared epitope were 21 times more likely to develop RA than nonsmokers without the gene. The researchers found that smoking causes an immune reaction in the lungs of people with the gene, and this reaction then occurs in the joints, causing inflammation as the body tries to fight off what it believes is an invader. This reaction involves citrulline- modified protein, which is rare in healthy people but common in approximately two thirds of RA patients.
The investigators stated that this finding gives them more insight into causes of RA and how it is likely to develop. It offers the promise of developing more specific treatment therapies as research continues.