From a germ of an idea to the noble art ofself-defence

This is the first book in a series about the philosophy underlying contemporary biology. Alfred Tauber's elegantly conceived thesis is that the self as a metaphor has achieved its status in immunology not because it is a precise scientific term, but because it resonates with our understanding of core identity. In an analogous manner to the debates provoked by the Cartesian proof of existence, the immunological self offers a conceptual framework that has served to orientate the major avenues of immunological research. Tauber posits that the metaphor projects immunology into a broader culture where it may help us to discover more about ourselves. And beyond this he is concerned that cultural assumptions might covertly infiltrate science.

The book traces the history of the discipline of immunology from its roots in the study of infectious diseases at the end of the 19th century. The early chapters set the scene with the great debate between the cellularists, led by Elie Metchnikoff (who believed in the primacy of phagocytes) and the humoralists exemplified by Paul Ehrlich (who viewed soluble factors as the tools of the immune response). As the biology became clearer and it became obvious there was truth in both arguments, the debate shifted to trying to deal with the nature of the immune system itself; what was being defended and how was identity of the defender established.

The concept of immunological self is generally attributed to Sir Frank Macfarlane Burnet, who with Frank Fenner in 1949 published the hypothesis that the immune system works because of its ability to discriminate self from non-self. Tauber shows how the imagery is consonant with the post-second world war search for identity and meaning. Burnet had toyed with the idea of self/non-self discrimination as early as 1937 but the zeitgeist was not auspicious for the development of the theory. Referring to an amoeba digesting another microorganism, he wrote in Biological Aspects of Infectious Diseases (1940) that "the fact that the one is digested, the other not, demands that in some way or other the living substance of the amoeba can distinguish between the chemical structure characteristics of 'self' and any sufficiently different chemical structure which is recognized as 'not self'."

The immune self concept evolved into the clonal selection theory, which is now so widely held that Jan Klein says in his textbook that it is no longer a theory but a fact and one of the foundations on which immunology stands. Clonal selection is simply the notion that the selectable element in the immune system is the immunocompetent cell and that specificity resides in clonally distributed receptors, only a few of which will be able to respond to a particular antigen. When immune system meets antigen, those cells that bear receptors with the best fit are amplified by clonal proliferation. Conversely, tolerance or the lack of reactivity against self (what Paul Ehrlich called horror autotoxicus) results from the elimination of self-reactive lymphocytes. Tauber shows how the metaphor of self and the aggrandisement of the body as a "nation" can have profound effects on social mores. Infectious organisms are perceived as immoral baddies in populist military imagery of the body at war. The fact that HIV infects the immune system is irrationally regarded with horror as an attack on the core of self so that the person with Aids is diminished as a victim or case.

The meaning of self is the subject of deep philosophical discourse. Tauber draws from a rich background to delineate a continuum, the poles of which he defines as "punctual" and "elusive". The punctual self is the everyday extended individual confident of his/her own embodiment; the elusive self inhabits the vexed arena of the metaphysical and is illustrated here as the ability to recognise the significance of the question What is the self? Somewhere between the poles is the cognitive self, the reflective self that is hard-wired but adaptable, that recognises the essence of things very much like the archetypes of Platonic forms. Tauber weaves these meanings of self into extant theories of immune function to show how the interdependence of these superficially disparate disciplines moves our thinking from metaphor to theory to metaphor to theory and so on.

Richard Lake is lecturer in immunology, St Mary's Hospital Medical School, London.