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In 1960 Sir Frank Macfarlane Burnet received the Noble Prize in Physiology and Medicine. He titled his Nobel Lecture “Immunological Recognition of Self” emphasizing the central argument of immunological tolerance in “How does the vertebrate organism recognize self from nonself in this the immunological sense—and how did the capacity evolve.” The concept of self is linked to the concept of biological self identity. All organisms, from bacteria to higher animals, possess recognition systems to defend themselves from nonself. Even in the context of the limited number of metazoan phyla that have been studied in detail, we can now describe many of the alternative mechanism of immune recognition that have emerged at varying points in phylogeny. Two different arms—the innate and adaptive immune system—have emerged at different moments in evolution, and they are conceptually different. The ultimate goals of immune biology include reconstructing the molecular networks underlying immune processes.

Immunological memory has fascinated microbiologists and immunologists for decades as one of the new frontiers to conquer to better understand the response to pathogens, cancer and vaccination. Over the past decade, attention has turned to the intrinsic properties of the memory T cells themselves, as it has become clear that the eradication of both infected cells and tumors requires T cells. This book is an attempt to capture the wave of discoveries associated with these recent studies. Its chapters represent a wide collection of topics related to memory T cells by laboratories that have invested their skills and knowledge to understand the biology and the principles upon which memory T cells are generated, maintained and expanded upon re-encounter with antigen. Ultimately, these studies are all aimed at a better understanding of the function of memory T cells in protection against disease.

The ability to remember an antigenic encounter for several decades, even for a life time, is one of the fundamental properties of the immune system. This phenomenon known as'immunological memory', is the foundation upon which the concept if vaccination rests. Therefore, understanding the mechanisms by which immunological memory is regulated is of paramount importance. Recent advances in immunology, particularly in the field of innate immunity, suggest that the innate immune system plays fundamental roles in influencing immunological memory. Indeed, emerging evidence suggests that events that occur early, within hours if not minutes of pathogen or vaccine entry profoundly shape the quantity, quality and duration of immunological memory. The present volume assembles a collection of essays from leading experts that span the entire spectrum research from understanding the molecular mechanisms of innate immune recognition, to dendritic cell function, to the generation and maintenance of antigen-specific B and T-cell responses.

Although immunologists know rather a lot about the manif­ estation of immunological memory, an understanding of the mechanism of memory at cellular and biochemical levels eludes us. Indeed, as we shall see, it is not even clear which of the several models used to explain the working of memory approximates to the truth. It is in order to report on approaches to this problem and on recent experimental advances in the field of memory cells that this volume has been put together. In the past 4-5 years cell surface molecules that may enable us to define memory Band T cells have been identified. It may now be possible to ask how memory cells are generated and to define what signals are required during or after antigenic encounter for a cell to enter the memory cell pool rather than to terminally differentiate into an effector cell. The transition from virgin cell to memory cell is clearly accompanied by several biochemical changes. For B cells, isotype switching and somatic mutations (leading to affinity maturation) are well-defined phenomena, although the molecular mechanisms remain mys­ terious. Both have received attention in many excellent reviews of late and so are not considered in detail in this book. Neither switching nor somatic mutation is a feature of peripheral T-cell maturation; biochemical differences between virgin and mem­ ory T cells may only relate to differing activation requirements and possibly changes in the expression of accessory molecules.