The Limits of the Self: Immunology and Biological Identity

by Thomas Pradeu, Elizabeth Vitanza (Translator)

What counts as an individual in the living world? What does it mean for a living thing to remain the same through time, while constantly changing? These questions are the province of immunology, one of the most dynamic fields in biology. Immunology answers these questions with its theory of "self" and "nonself" which has dominated the field since the 1940s. Thomas Pradeu argues that this theory is inadequate, because immune responses to self constituents and immune tolerance of foreign entities are the rule, not the exception. Instead Pradeu advances an alternative theory, the continuity theory, which offers a new way to answer the question of what triggers an immune response. It also echoes the recent realization that all organisms, and not only higher vertebrates, have an immune system.
Pradeu's main thesis is that the self-nonself theory should be abandoned, but that immunology still proves to be decisive for delineating the boundaries of the organism. Articulating an evolutionary and an immunological perspective, he offers an original conception of the organism. Tolerance of the fetus by the mother and of countless bacteria on the body's surfaces proves that every organism is heterogeneous, that is, made of entities of different origins. In other words, every organism appears as a chimera , a mixed living thing-the cohesiveness of which is ensured by the constant action of its immune system.
The Limits of the Self , will be essential reading for anyone interested in the definition of biological individuality and the understanding of the immune system. Key words : immune system, self, non-self, tolerance, identity, individuality, theoretical immunology, continuity-discontinuity theory, philosophy of immunology, philosophy of biology. 

Genres: Philosophy, Biology, Nonfiction

320 pages, Hardcover

First published February 16, 2010

Reviews

[bejo]

Read this book after my immunology course. Enjoyed the continuity theory as an alternative to the self-non self theory we learned, really nuanced the picture of the immune system for me. Definitely need immunological background to understand the details. Ending of book where Pradeu puts forth a physiological theory of biological individuation was where the philosophy of biology was heaviest, which I do not have very much exposure to compared to general phil sci, so probably did not appreciate as much as someone who does. Overall, an even handed approach to immunology and biological individuation that paid respect to its intellectual predecessors without being beholden to their ideas.

[Tomás Narvaja]

There is a clear reason why Pradeu won the Lakatos Award. While densely informative and perhaps difficult for a reader unfamiliar with immunity, Pradeu effectively demonstrates how immunology can contribute to a biological understanding of identity, not in terms of uniqueness (as the self-nonself theory suggests), but in terms of individuality.

In the first chapter Pradeu discusses the question of what makes the identity of a living entity and how immunology has made the study of biological identity its own domain. He claims the question of identity is (at least) two question: 1) what makes the uniqueness of a living being different from other living beings including those of its own species and 2) what makes its individuality – what counts as one living being, what is the unit. He also pointed out that it was in 1949, that Australian virologist, Frank Macfarlane Burnet, suggested based on transplantation experiments to conceive of immunity in terms of self and nonself where recognition of the self/nonself by the immune system makes the question of biological identity one to which immunology can respond.

Pradeu demonstrates a wide variety of claims in his book quite effectively. 1) immunological self-nonself theory is inadequate for a satisfying conception of biological identity 2) continuity theory permits elaboration of a satisfying conception of biological identity 3) immunology brings precise and decisive elements to bear on one particular meaning of the term, “identity,” that of diachronic individuality 4) immunological conception of identity applies to all organisms, showing its usefulness in dealing with the question of biological identity 5) immunology leads to precise answer of what counts as an organism – the organism is not an endogenous reality, but a heterogeneous reality made up of components of different origins 6) Immunology when combined with other fields, particularly evolutionary biology, shows the organism is most highly individuated biological entity.

Throughout his book, Pradeu clear defines the self-nonself theory, explains its history and contextualizes its popularity. He then provides a coherent, effective critique and points out various immunological phenomena, such as pregnancy, that self-nonself theory largely fails to understand. Pradeu proposes his alternative theory, the continuity theory. He claims that an immune response is not triggered by the non-self, but by a strong discontinuity in molecular patterns with which immune receptors interact. In the chapter that follows, Pradeu compares his theory to other popular theories in immunology, including Polly Matzinger's Danger Theory. At the end of his book, he returns to the question of what defines the organism and what immunology can say about the identity of an organism. He does all this while constantly referring to specific biochemical processes in the body as evidence of his claims.

Pradeu concludes that 1) immunology sheds light on one meaning of identity, understood as organism’s individuality (where immunology’s criterion of immunogenicity is itself a criterion of individuality) 2) Immunology does not bring new or decisive contributions to other definitions of identity, such as when understood as uniqueness or as description of individual characteristics. With regards to the question of individuality, Pradeu states that currently, evolutionary biology is the only field in biology successfully presenting a theory that unifies various types of independent facts under a single explanatory framework, can be tested empirically, and has been corroborated by data in various fields. Non-evolutionary fields like physiology and morphology could be useful for determining the biological individual if they were able to offer a theory, but there is none in same sense that evolutionary theory is a theory. It is exactly this lack of theory that Pradeu is trying to address and does so by providing a physiological theory, specifically an immunological one. He effectively demonstrates how the biochemical focus of immunology helps with precision when combined with evolutionary theory.

Overall, Pradeu makes a significant contribution to the philosophy of mechanistic biology (or physiology) and demonstrates how questions asking "how?" raise exciting philosophical problems and can provide valuable insight to though philosophers of biology focused on the question of "why?" such as in evolutionary biology. While he critiqued various theories' lack of precision, I do not recall any exact definition of what constitutes continuous interactions among immune receptors as defined by precise time intervals, what quantity of antigens is considered a "very small quantity" that does not provoke an immune response, what quantity is a "large quantity" that can paralyze the immune system, etc. Additionally, I hesitated to accept his critique of claims that immunology functions as language and his critiques of anthropomorphism, especially given his generalization of the capacity of immunity. If immunity is not unique to vertebrates, but is a capacity of all cells, I question why he would suggest language would be any different. I would like to see an expansion of Pradeu's work that takes into consideration the philosophical insights of Vicki Kirby and her question of "What If Culture Was Really Nature All Along?"

[George]

Really interesting read if you like immunology and the idea of what constitutes an individual. In this book, Pradeu introduces the concept of “continuity theory” which is a fuller explanation of immunological responses than the classic “self vs non-self” theory.

[Pete]

This book provides an excellent history of immunology and ends with a discussion of units of selection. Im not completely sure how original the discontinuity theory is but taking the authors word for it for the time being.