Sex steroids and the immune system

Immune responsiveness, susceptibility to infections, and autoimmune disorders exhibit sexual dimorphism. Women have higher immune reactivity, resulting in better protection against infections but a predisposition to autoimmune diseases. Evidence suggests that sex steroids mediate the sexual dimorphism in immune response. Estrogens induce thymic atrophy and alter the proportion of thymic cells, promoting an increase in the CD4(+):CD8(+) ratio. In the periphery, they enhance helper and inducer T-cell activity and production of antibodies. Androgens suppress most aspects of the immune system. They cause involution of the thymus and bursa of Fabricius, decrease cellular cytotoxicity and humoral immunity enhance suppressor T-cell activity, and, in animal models, ameliorate many autoimmune diseases.