ABSTRACT
The flexible nature of the adaptive immune system and its capacity to identify and respond to foreign matter is of immense importance for the survival of any higher organism. For this purpose, an intricate network of cell populations participates in the identification of foreign molecules. The recognition of a molecular structure as foreign will result in activation of cellular (T cell) and humoral (B cell) responses against such a potentially dangerous component. The nature and level of these responses will depend upon the genetic makeup of the individual and intrinsic features of the antigen that induces the immune reaction. A key feature of the ability to respond correctly to foreign matter resides in the dual way through which the immune system interact with potential antigens. This involves (i) the recognition of intact antigen by antibodies, and (ii) the recognition of processed antigen in complex with histocompatibility antigens by T cell receptors.
