Evolution of Multispecificity in an Immune Network

Divergence in antigen response of the immune network is discussed, based on shape-space modelling. The present model extends the shapespace model by introducing the evolution of specificity of idiotypes. When the amount of external antigen increases, stability of the immune network changes and the network responds to the antigen. It is shown that specific and non-specific responses emerge as a function of antigen levels. A specific response is observed with a fixed point attractor, and a nonspecific response is observed with a long-lived chaotic transient state of the lymphocyte population dynamics. The network topology also changes between these two states. The relevance of such a long-lived transient state is discussed with respect to immune function.