Lack of testosterone -- male sex hormones -- could be the reason why women are more prone to autoimmune diseases such as multiple sclerosis (MS), celiac disease, lupus, and rheumatoid arthritis, finds a study.

In autoimmune diseases, the immune system creates antibodies that attack the body's own tissue. Men are generally more protected than women, who only have one tenth as much testosterone, the researchers said. Testosterone was found to be the key which reduces the number of B cells -- a type of lymphocyte that releases harmful antibodies.

"It's very important to understand what causes these diseases to be so much more common among women," said Asa Tivesten, Professor at the University of Gothenburg's Sahlgrenska Academy in Sweden. "In this way, we can eventually provide better treatment for the diseases," Tivesten added, in a paper published in Nature Communications. After numerous experiments on mice and studies of blood samples from 128 men, the researchers found a protein named BAFF, which makes the B cells more viable.

"We have concluded that testosterone suppresses BAFF. If you eliminate testosterone, you get more BAFF and thereby more B cells in the spleen because they survive to a greater extent," Tivesten said. The results correlate well with a previous study showing that genetic variations in BAFF can be linked to the risk of diseases such as lupus.