Immunodeficiency. Immunodeficiency diseases cause the immune system to malfunction completely or partially. Secondary immunodeficiencies are caused by environmental causes such as HIV/AIDS or starvation, whereas primary immunodeficiencies are caused by genetic abnormalities. The two main types of immunodeficiency are CD4+ T-cell lymphocytopenia and B-cell lymphocytopenia. Primary immunodeficiencies affect many parts of the immune system and can be categorized into three groups: cellular, molecular, and functional defects. These disorders can be inherited, acquired after birth, or result from use of cancer chemotherapy drugs.