Immune deficiency disorders result from defects that occur in immune mechanisms. The defects arise in the components of the immune system, such as the white blood cells involved in immune responses (T and B lymphocytes and scavenger cells) and the complement proteins, for a number of reasons. Some deficiencies are hereditary and result from genetic mutations that are passed from parent to child. Others are caused by developmental defects that occur in the womb. In some cases immune deficiencies result from damage inflicted by infectious agents. In others drugs used to treat certain conditions, or even the diseases themselves, can depress the immune system. Poor nutrition also can undermine the immune system. Limited contact with natural environmental factors, particularly with microorganisms found in bio diverse settings, also has been associated with increased risk of allergies, autoimmune disorders, and chronic inflammatory diseases.
