Women are far more likely than men to get autoimmune diseases, illnesses like lupus or rheumatoid arthritis that occur when the immune system mistakenly attacks their own bodies. That gender disparity has baffled scientists for decades but new research may finally explain why. Females have two X chromosomes and Stanford University researchers say how cells handle that extra X can be a red flag for the immune system, essentially an early risk factor. The findings, published Thursday in the journal Cell, could lead to better ways to detect autoimmunity.