Why women get autoimmune diseases

Autoimmune diseases strike women three times more than men.

"Women - particularly African-American, Hispanic-American, and Native-American women - have a higher risk for some autoimmune diseases." MedlinePlus

Possible explanations are put forward in three different areas:
(1) hormone theory: Does estrogen production puts women at greater risk for getting an autoimmune disease?
(2) environmental factors: Does exposure to different toxins, e.g. in cleaning products, put women at greater risk?
(3) genetic influences: Is it our differences in DNA with mens?

What theory are you thinking it might be?
So do you know or suspect any other reasons why or maybe you have a theory??