Recognition of Self or Nonself? Theoretical Implications and an Empirical Test

Abstract

There are two ways that a historecognition system could distinguish self from nonself: by detecting the presence or absence of attributes that define self, or by detecting the presence or absence of nonself attributes. In the vertebrate immune system detection of nonself antigens appears to be the primary mechanism by which self and nonself are distinguished. The mechanisms that distinguish self from nonself in invertebrate historecognition systems are presently unknown, as are their phylogenetic relationships to the vertebrate immune system. However, some 25 years ago, Burnet (1971) proposed that invertebrate historecognition systems may utilize self-recognition to distinguish self from nonself. His reasoning was based on the genetics of histocompatibility in tunicates and hydroids. In these invertebrate systems, partial sharing of compatibility alleles is sufficient for histocompatibility.