Autoreactivity and self-tolerance in an invertebrate

Abstract

One hallmark of the vertebrate immune system is self-tolerance; those mechanisms deployed against foreign tissues are not directed against autologous tissues¹. Defects in self-tolerance, such as those leading to autoimmunity, have provided important insights into the mechanisms of discrimination between self and non-self. Although many invertebrates display a capacity to discriminate foreign tissues, it is not established that these systems represent ‘simpler’ homologues of vertebrate immune recognition^1–5. In particular, there is a lack of evidence that any invertebrate possesses active mechanisms of self-tolerance. During a hydroid breeding programme, we found several individuals possessing a striking defect. These individuals were autoreactive, using their rejection system to actively destroy their own tissues. Here we characterize this ‘autoimmune’ phenomenon, which we believe to be the first described in an invertebrate.