The art of the probable: System control in the adaptive immune system

The immune system provides very effective hose defense against infectious a gents. Although many details are known about the cells and molecules involv ed, a broader "systems engineering" view of this complex system is just beg inning to emerge. Here the argument is put forward that stochastic events, potent amplification mechanisms, feedback controls, and heterogeneity arisi ng from spatially dispersed cell interactions give rise to many of the gros s properties of the immune system. A better appreciation of these underlyin g features will not only add to our basic understanding of how immunity dev elops or goes awry, but also illuminate new directions far manipulating the system in prophylactic and therapeutic settings.