What Are Primary Immunodeficiency Diseases? Primary immunodeficiency diseases are caused by intrinsic defects in the cells of the immune system and are often caused by inherited genetic defects. This is in contrast to secondary immunodeficiency diseases such as acquired immunodeficiency syndrome caused by infection with human immunodeficiency virus. The hallmark of primary immunodeficiency diseases is increased susceptibility to infection, but they can cause other problems as well. These diseases are grouped according to what part of the immune system is affected. B lymphocytes and plasma cells producing proteins called antibodies Antibody Deficiencies Antibodies are proteins made by white blood cells called B lymphocytes and plasma cells. The function of antibodies is to recognize and mark bacteria, viruses, and other foreign invaders tant for T cell growth. Patients are diagnosed within the first year of life with frequent and severe infections often caused by organisms that do not affect people with healthy immune systems. Complement Deficiencies The complement system consists of a group of proteins that attach to antibody-coated foreign invaders like bacteria and viruses. Complement proteins kill antibody-coated bacteria and viruses These proteins work together to disable and kill invading pathogens. People deficient in one or another of these proteins have a diminished ability to kill invaders, resulting in increased infections. Such people may also develop antibodies that react against the body's own cells and tissues, resulting in autoimmune diseases with immune-mediated damage to the body. The most common of these deficiencies is: C2 Deficiency-an inherited defect in the gene for the complement protein called C2. This defect can cause an autoimmune disease such as systemic lupus erythematosus or can result in severe infections such as meningitis. The illnesses usually appear in childhood or in early adulthood. Phagocytic Cell Deficiencies Phagocytes include white blood cells called neutrophils and macrophages that engulf and kill antibody-coated foreign invaders. Phagocytes can be defective either in their ability to kill pathogens or in their ability to move to the site of an infection. In either case, the defect results in increased infections. The most severe form of phagocytic cell deficiency is: Phagocytic cells ingest antibody- and/or complement-coated bacteria and kill them Chronic Granulomatous Disease-inherited deficiencies of molecules needed by neutrophils to kill certain infectious organisms. These illnesses usually appear early in childhood but may appear as late as adolescence. People with chronic granulomatous disease develop frequent and severe infections of the skin, lungs, and bones and develop localized, swollen collections of inflamed tissue called granulomas. Back | Contents | Next Publications | NIAID Home | Search Last updated December 9, 1999 (hrs)