The majority of autoimmune diseases predominate in females. In searching for an explanation for this female excess, most attention has focused on hormonal changes--both exogenous changes (for example, oral contraceptive pill) and fluctuations in endogenous hormone levels particularly related to menstruation and pregnancy history. Other reasons include genetic differences, both direct (influence...

Microchimerism is defined as the presence of two genetically distinct cell populations in the same individual. It can arise from several causes including the bidirectional transfer of cells between mother and fetus during pregnancy, twin-to-twin transfer in utero, from organ transplantation, and blood transfusion. Recently, scientists have found male fetal cells from decades earlier imbedded in...