Researchers have knownfor years that smoking canincrease the likelihood ofdeveloping rheumatoid arthritis(RA). A recent study nowsuggests why: tobacco usagemakes it more likely that a raregenetic condition will triggerthe body's immune system toliterally attack itself. The findingswere reported in theJanuary 2006 issue of Arthritis& Rheumatism.
The researchers analyzedblood samples from >1200participants, 930 with earlysymptoms of RA and 383 without.They found that a combinationof smoking and a genetictrait often came together tocause RA. Smokers who had 2copies of a gene known asHLA-DR shared epitope were21 times more likely to developRA than nonsmokers withoutthe gene. The researchersfound that smoking causes animmune reaction in the lungsof people with the gene, andthis reaction then occurs inthe joints, causing inflammationas the body tries to fightoff what it believes is an invader.This reaction involves citrulline-modified protein, whichis rare in healthy people butcommon in approximatelytwo thirds of RA patients.
The investigators statedthat this finding gives themmore insight into causes ofRA and how it is likely todevelop. It offers the promiseof developing more specifictreatment therapies as researchcontinues.