Introduction: knowledge is survival-the mission of the immune system and its stochastic simulations

In this introduction the timeliness and interest of dedicating an issue of Autoimmunity to mostly "discrete" models is motivated by highlighting number of circumstances, observations encounters, that all have favored the rise of a family of agent based simulations of the Immune System. Franco Celada was among the first experimentalists to accept the challenge of interdisciplinarity and create a computational Immune System. He thinks that discrete models are especially useful in handling hypotheses: initiating them, representing their consequences, and revealing their plusses and minuses. He is sure that "looking at" the immune machinery as a cognitive system is useful both to the intuitive understanding and the creative development of models.