An immune deficiency disease occurs when one or more cells within the immune system do not operate properly, or the system is absent altogether. Some immune deficiency diseases are relatively common, while others are extremely rare.
Primary Immune Deficiency
A primary immune deficiency occurs when the abnormalities of the immune system develop from an inborn defect in the cells. Affected cells include T-cells, B-cells, phagocytic cells or the complement system.
Most primary immune deficiencies are inherited diseases; examples include X-linked agammaglobulinemia (XLA) and severe combined immunodeficiency (SCID), and this appears to run in families. Other primary immune deficiencies, such as common variable immunodeficiency (CVID), appear less obviously inherited, but the causes of the defects are unknown and genetic factors cannot be ruled out.
Secondary Immune Deficiency
Secondary immune deficiencies occur when damage is caused by an environmental factor. Radiation, chemotherapy, burns and infections contribute to the many causes of secondary immune deficiencies. Acquired Immune Deficiency Syndrome (AIDS) is a secondary immune deficiency caused by the Human Immunodeficiency Virus (HIV). In leukemia and multiple myeloma, cancerous immune cells crowd out the normal stem cells of the bone marrow. These abnormal cells reduce the number of B cells and lead to hypogammaglobulinemia, another type of secondary immune deficiency.