Self-reorganizations in a simple model of the immune system

We report results of studies carried out on a simple 2D shape space model of the immune system, where a network of clones is perturbed by long-lived molecules whose presence triggers the disappearance (avalanche) of existing clones. The resulting reorganizations of the system, which occur over many different time and length scales, enable it to respond efficiently to changing environments. The system's dynamics is very reminiscent of self-organized criticality, with a 1/*int; spectrum in the number of particles, but we observe a clear cutoff in the size of avalanches in the present model. We argue that such a cutoff is a desirable feature in the case of a biological system.