Immune system
In some organisms, the immune system has its own problems within itself, called disorders. These result in other diseases, including autoimmune diseases, inflammatory diseases and possibly even cancer. Immunodeficiency diseases occur when the immune system is less active than normal. Immunodeficiency can either be the result of a genetic (inherited) disease, or an infection, such as the acquired immune deficiency syndrome (AIDS), that is caused by the retrovirus HIV, or other causes.