The rapid progress in clinical and experimental immunological research, in addition to the radical change in immunological concepts in recent years, has been accompanied by similar developments in the technical vocabulary, and, as a consequence, frequent widespread confusion. The fourth edition of The Dictionary of Immunology will satisfy the needs of any biologist, clinician or biochemist who requires easy reference to current immunological usage. This well-established work has been completely revised and updated to include key terms arising from new discoveries in the fast-developing fields of molecular and cellular immunology. The Dictionary of Immunology contains brief descriptions of the most commonly used immunological techniques, as well as definitions, useful in clinical immunology, of immunodeficiency states and autoimmune diseases. Clear illustrations and tables have been added to complement the text, and extensive cross-referencing is used to inform an integrated view. The Dictionary will serve equally as a handy reference, a companion to other reference texts, or a spelling and fact checker for students, research scientists and those engaged in ancillary activities such as science journalists, and the curious lay reader.