Research may explain why females are more prone to autoimmune diseases & how to prevent them. www.ncbi.nlm.nih.gov/pubmed/2332839 Sex differences in the gut microbiome drive hormone-dependent regulation of autoimmunity. Markle JG, Frank DN, Mortin-Toth S, Robertson CE, Feazel LM, Rolle-Kampczyk U, von Bergen M, McCoy KD, Macpherson AJ, Danska JS. Source Program in Genetics and Genome Biology, Hospital for Sick Children Research Institute, Toronto, Ontario, Canada. Abstract Microbial exposures and sex hormones exert potent effects on autoimmune diseases, many of which are more prevalent in women. We demonstrate that early-life microbial exposures determine sex hormone levels and modify progression to autoimmunity in the nonobese diabetic (NOD) mouse model of type 1 diabetes (T1D). Colonization by commensal microbes elevated serum testosterone and protected NOD males from T1D. Transfer of gut microbiota from adult males to immature females altered the recipient's microbiota, resulting in elevated testosterone and metabolomic changes, reduced islet inflammation and autoantibody production, and robust T1D protection. These effects were dependent on androgen receptor activity. Thus, the commensal microbial community alters sex hormone levels and regulates autoimmune disease fate in individuals with high genetic risk. Comment in "Welcome to the Microgenderome," Science, 1 March 2013, p. 1044. "Male puberty (in mice) leads to changes in the gut microbiota that reinforce testosterone production, which is protective against the development of T and B cell functions linked to autoimmune disease. In mice, the protective properties of the male-associated microbiota can be transferred to younger females and confer testosterone-mediated protection from autopimmune disease upon the recipients."