Modeling immune behavior for experimentalists.

This article outlines the requirements for useful models of biologic systems. Such models should fulfill three conditions: (i) suit the bottom-up data of the living system, not merely adhere to top-down logic; (ii) abet experimentation by stimulating new ideas for novel experiments; and (iii) engage the mind of the experimentalist with understandable, visual representations. Seven characteristics of a useful model are discussed.