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“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

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6. The Animal Self : Molecular Recognition....................

Chapter 6 Molecular Recognition

Molecular markings delineate bodily self.

Overview: In a most subtle and intricate manner, the animal body zealously
guards itself against intrusion by other “selves,” using a mechanism known
as immunity. Different aspects of immunity define self in various degrees of
stringency. In innate immunity, self is defined categorically in a phylogenetic
sense — for example, animals against microbes. In adaptive (acquired) immu-
nity, the distinction is further refined so that antibodies against one species of
pathogen are different from those against others — for example, diphtheria
versus tuberculosis. However, the most stringent definition of molecular self
appears in the recognition of MHC (major histocompatibility complex) protein
by T lymphocytes, for here immunity recognizes differences not only among
species, but also among individuals of the same species, including siblings. The
animal body is defined by its immunological self, which is based on recogni-
tion of the detailed structure of body proteins. The rejection of organs when
transplanted from one person to another is a prime example of “self” versus
“non-self” discrimination.

6.1 Drama in a Glasgow Hospital

In 1943 a lady was admitted to the Glasgow Royal Infirmary for an exten-
sive burn, involving the right side of her back and part of her right arm.
For this she underwent skin transplantation for the burnt area. One part
was replaced with her own skin taken from a normal site, and another
was transplanted with skin from her brother. Both skin grafts survived
initially. But, surprisingly, by the fifteenth day, whereas the transplant