[Mechanisms and classification of immunological diseases]

Immunological diseases comprise a clinically heterogenous group of disorders that result either from defects in one or more compartmens of the immune system or from aberrant, excessive or uncontrolled immune reactions. Immunodeficiency disaeses are caused by congenital or acquired defects in lymphocytes, phagocytes or other mediators of specific or natural immunity. The second group of immunological diseases result from the failure to control physiological immune response against foreign antigens or to maintain self-tolerance. The two principal factors that determine the clinical and pathological manifestation of such diseases are 1. the type of immune response that leads to tissue injury, and 2. the nature and location of antigen that initiates or is a target of this response. The most frequently used classification of immunological diseases is based on the principal pathogenic mechanism responsible for cell and tissue injury. Immunological diseases can also be subdivided based on the source of antigen against which the immune responses are directed. Mechanisms implicated in the pathogenic immune response to foreign and self antigens are discussed.