The immune system is made up of lymphoid tissue that includes the bone marrow, tonsils and lymph nodes. These organs help to protect the body from harmful substances such as bacteria, virus, toxins and cancer cells. Immunodeficiency disorders may affect any part of the immune system and may be inherited or acquired later in life. The most common type of primary immunodeficiency is when the body does not produce enough or normally functioning antibodies, which are specialized proteins that destroy harmful substances. In addition, other causes such as chemotherapy, infections or severe burns may cause a secondary immunodeficiency. The typical symptoms of immunodeficiency are recurrent infections such as: sinusitis, pneumonia, ear, skin and gastrointestinal infections. Immunologists evaluate your ability to fight infections, devise a plan for you to prevent exposures and treat some forms of immunodeficiency with therapies such as replacement immunoglobulin.