Hoffmann, G.W., "A Theory of Regulation and Self-Nonself Discrimination in an Immune Network", European Journal of Immunology, 5, 638-647 (1975).

This is the first paper on what later became known as the symmetrical network theory. The symmetrical network theory is the version of network theory that has been developed most extensively, and which has the greatest scope. The paper includes a mathematical model to demonstrate switching from the virgin state to the suppressed state, and from the virgin state to the immune state. However, the mathematical model contains a large number of parameters relative to the number of phenomena being explained, and is less elegant than the ones developed in later papers.