Controlling autoimmunity--Lessons from the study of red blood cells as model antigens.

The characterization of human and animal red blood cell (RBC) autoantigens in autoimmune hemolytic anemia (AIHA) has provided an opportunity study the control of specific autoimmune responses of unequivocal pathogenic relevance. The results reveal that censorship of the autoimmune helper T (Th) cell repertoire by deletion and anergy is very incomplete in healthy individuals, even for widely distributed, abundant self-antigens on RBC. There is strong evidence that autoaggression by surviving Th cells is normally held in check by other mechanisms, including failure to display the epitopes that they recognize, and active immunoregulation. AIHA is one of the first human autoimmune diseases in which regulatory T (Tr) cells that are specific for the major autoantigens have been identified. These Tr cells recognize the dominant naturally processed epitopes, and recent studies suggest that disease develops when other determinants, to which such tolerance is less secure, and which are normally inefficiently presented, are displayed at higher levels. Together, the results raise the possibility that therapy for diseases such as AIHA could be based on switching the balance of the response back towards regulation, in particular by the administration of the dominant peptides recognized by specific Tr cells.