Immunogenicity signals 1,2,3 ... and 0.

The most critical property of the immune system is its ability to discriminate self from nonself. Failure to respond to nonself can lead to overwhelming infection, while failure in the ability not to respond to self, or self tolerance, leads to autoimmunity. A meeting held in Steamboat Springs focused on this issue under the title of 'Immunogenicity'. This brief summary focuses on one of the key issues considered at this conference - the signals involved in the induction of lymphocyte activation. In addition, an hypothesis of immune system function that appears to follow from these findings is described.