In this review several examples of so-called non-linear network interaction in the immune system are critically discussed. Non-linear immune network circuits are typically observed in immune responses that switch or alter the initial target of immune attack. Such interactions are based on idioypic or paratopic crossreactivities and produce often un-expected immune responses. The understanding of these network circuits can be exploited to design novel vaccines and immunotherapies. in AIDS, cancer and autoimmune diseases.