LEP and rheumatoid arthritis: Another indication for the important role of leptin in autoimmunity is the sexual dimorphism of serum leptin levels; indeed women display serum leptin levels two to three times higher than those observed in age- and BMI-matched men, and moreover, they are more prone to develop autoimmune diseases such as multiple sclerosis (MS), RA, or systemic lupus erythematosus, thus suggesting that leptin could favor the predisposition of females to this kind of disorders (122, 123).