ABSTRACT
The immune system has evolved to ensure constant surveillance of “nonself” structures. Both T and B lymphocytes have cell-surface receptors that are able to recognize structures not normally presented or expressed by the organism. Once that recognition takes place, a complex series of events is triggered, leading to the proliferation and differentiation of immune competent cells and to the development of immunological memory. These events will be directly or indirectly responsible for the elimination of the organism, cells, or molecules presenting nonself structures. Considerable effort has been applied to the study of in vitro and animal models, allowing a detailed insight into the steps involved in the generation of an immune response.
