What is immune deficiency and what are the classic symptoms?

Severe infections. The immune system main role is to protect our body from infections, and also from tumors. When there is a deficiency, infections come often and are more severe. The symptoms are from the infections. If there is no infection, there are no symptoms. Some immune defciencies are of regulation, in those cases, parts of our body is harmed by our own immunity, this is called autoimmunity, as in lupus.