Do autoantigens define autoimmunity or vice versa?

The basic function of the adaptive immune system is to distinguish self from foreign. The failure of self tolerance can result in autoimmunity, which comes in many forms but still targets a limited selection of the total available autologous determinants. This selectivity must reflect the underlying mechanisms of the autoimmune reaction, as well as the particular features of the autoantigens that are targeted. Here I discuss the overall paradigm of autoimmunity, and what kinds of mechanisms might play a role. It is likely that multiple different pathways are critical in various diseases, and even in a single condition.