Hormones affect function of immune cells and consequently immune system activities. For example, estrogen influences the production of regulatory factors produced by immune cells and tissues
As immune cell functions are dependent on these regulatory factors, estrogen levels alter the functioning of immune system to a certain extent. Onset of some autoimmune diseases may coincide with pregnancy or menopause.
For example, autoimmune thyroiditis (Hashimoto’s and Grave’s) and rheumatoid arthritis generally improve during pregnancy (pregnancy is associated primarily with elevated progesterone and to a lesser extent estrogen), but tend to return post partum.
In addition, the typical age of onset varies among autoimmune diseases. For example, SLE (systemic lupus erythmatosis) onset commonly occurs after puberty and during the reproductive years, while rheumatoid arthritis onset tends to occur later with a peak around the age of menopause and declining estrogen levels.