Autoantigens 

Autoimmune diseases are the result of specific immune responses directed

against structures of the self. The organism possesses powerful mechanisms to avoid immune auto-aggression. The acquired ability of the immune system to avoid responsiveness to self-antigens is defined as ‘tolerance’, and is obtained by the cooperative efforts of central and peripheral mechanisms, which allow a rapid and efficient removal of pathogens (e.g. viruses or bacteria) in the absence of self-recognition. 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.