The immune system “protects” us from infections. An immunodeficiency is a defect in your immune system. Immunodeficiency increases one’s risk of developing recurrent and severe infections. The symptoms of an immunodeficiency vary depending on the part of your immune system that is affected; the most common symptoms include recurrent infections, prolonged infections that do not respond readily to antibiotics, unexplained fatigue, and a heightened vulnerability to certain autoimmune diseases.