ABSTRACT
Our understanding of immunity in general and autoimmunity in particular has been derived almost exclusively from the study of young adult subjects. A fundamental observation concerning the operation of the immune system is that exposure of healthy young humans or experimental animals to molecules foreign to the host stimulates a specific immune response to the nominal antigen, although no immune response is normally made to the large number of molecules of the host. Ehrlich called this fundamental law of the immune system “horror autotoxicus” (1). When autoimmune reactions develop in young individuals, as the reader of this volume knows, autoimmune disease usually follows. In contrast, during aging, autoimmune reactions develop but rarely cause autoimmune diseases. In this chapter, the nature and significance of ageassociated autoimmunity will be considered.
