Gender and risk of autoimmune diseases: possible role of estrogenic compounds

Abstract

A striking common feature of many autoimmune diseases in humans and experimental animals, despite differences in pathology, is that females are highly susceptible to autoimmune conditions compared to males. In several animal models, estrogens promote, whereas androgens abrogate, B-cell-mediated autoimmune diseases. To understand mechanisms by which estrogens regulate autoimmunity, it is first necessary to decipher estrogen effects on the normal immune system. Estrogen treatment of nonautoimmune mice diminished lymphocyte numbers in both developmental and mature lymphoid organs. Estrogen dysregulated T- and B-cell balance by inducing selective T-cell hypoactivity and B-cell hyperactivity. Even though estrogen did not alter the relative percentages of splenic T-cell subsets, splenic lymphocytes had a reduced proliferative response to T-cell stimulants and were refractory to rescue from activation-induced apoptosis compared to cells from placebo-treated mice. In contrast, estrogen induced B-cell hyperactivity (promoted autoantibodies to double-stranded DNA and phospholipids, increased numbers of plasma cells, and increased autoantibody yield per B cell). Note that treatment of normal mice with estrogen can alter T- and B-cell regulation and overcome B-cell tolerance to result in autoimmunity in normal individuals. Could environmental estrogens promote some human autoimmune disorders? Is there a link between environmental estrogens and autoimmune disorders, especially since these disorders are reported possibly more frequently? These provocative questions warrant investigation. Our findings on immunomodulatory effects may serve as a benchmark to examine whether endocrine-disrupting chemicals will have similar immunologic effects.