The immune system: your defensive partner and offensive foe.

Immune function and inflammation are normal physiologic processes essential to health and well-being. However, overactivity of any inflammatory or immune responses can result in tissue-damaging reactions that threaten the functional integrity of tissues and organs. This article reviews the normal defense responses of inflammation and immune function as well as selected conditions resulting from offensive or hyperactive inflammatory and immune responses. The selected conditions include those seen more often in the acute and critical-care setting, such as tissue-damaging inflammation, drug allergy, autoimmunity, and transplant rejection.