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A major process of rediscovery has taken place in the field of Cellular Immunology over the past 12 years—subsets of T lymphocytes exist that are specifically dedicated to regulation or as it should be more appropriately termed suppression of all aspects of immune responses. It was only after Prof. Sakaguchi identified the CD25 antigen in 1995 as a marker for a major population of T cells that had suppressor functions both in vitro and in vivo that the resurgence in the regulatory T cell area could begin. The regulatory T cells field has grown dramatically over the past decade. It is now impossible to read a journal that does not contain numerous papers whose titles deal with regulatory T cells. More importantly, it is also difficult to submit a new research grant proposal in any area of immunologic research that does not include a section on analysis on the contribution of regulatory T cells to the subject matter under study. Regulatory T cells can be best thought of today as'teenagers'ready to take on all the challenges of complex immune responses. In ten years, the field will certainly be more mature, and manipulation of regulatory T cell function by cellular biotherapy, antibodies and small molecules will be routine function of the clinical immunologist. - From Preface by Prof. Ethan Shevach, National Institute of Health, USA It has been for long debated whether suppressor/regulatory T cells did actually even exist. Today, this question is no longer accurate and the subject of regulatory T cells is the object of a constantly growing interest in immunologists and clinicians. There is no doubt that the history of Tregs will make a new big leap ahead. - From Chapter One by Prof. Shimon Sakaguchi, Kyoto University, Japan

Superantigens constitute a growing family of bacterial and viral proteins that share the capacity of inducing massive activation of the immune system. This volume contains contributions from leaders in the field of classical T cell superantigens and sheds light on relevant B cell superantigens at the molecular and biochemical levels. Moreover, articles in this publication deal with the emerging, intriguing possibility that immunoglobulin superantigens can activate primary effector cells of allergic disorders both in vitro and in vivo, thus acting as superallergens. A detailed account is also given of the biochemical, immunological and clinical characteristics of several endogenous, viral and bacterial superallergens, which are probably relevant in a variety of human diseases. This is the first volume to put together basic and clinical aspects of the classical T cell superantigens, B cell superantigens and superallergens. It will therefore be indispensable reading to basic and clinical immunologists, microbiologists, virologists and specialists in allergic and immune disorders.

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.

It has been said that the development of vaccines against a variety of infectious diseases is among the greatest triumphs of immunology. Indeed, several pathogens have lost their horror through the availability of effective vaccination measures. Unfortunately, this does not hold true for the pathogens dealt within this volume. Malaria, schistosomiasis, leishmaniasis, leprosy, and tuberculosis together are prevalent in more than 100 countries, and over 400 million persons suffer from these diseases. It is becoming increasingly clear that the failure to control these infections in a satisfactory way is directly related to the complexity oftheir interactions with the immune system. These agents have lived with their hosts for long enough to give both-host and parasite-ample opportunity to develop a highly sophisticated interrelationship. The central role of T lymphocytes both in acquired resistance to and pathogenesis of these microbes is well appreciated. In the beginning it may have been thought that acq uired resistance against infectious agents is nothing but another aspect of the immune response, studied with soluble and particulate antigens. This simple concept has gradually changed, and it has become clear that the viability not only of the immune cells but also of the'antigens'adds another dimension to the game. Several achievements in cellular immunology and molecular biology have now made it possible to better understand at least some mechanisms in this intricate interplay.