Molecular mimicry and the role of B lymphocytes in the processing of autoantigens

The immune system has evolved several mechanisms that provide lymphocytes w ith the intelligence to ignore self proteins while attacking foreign pathog enic agents. Notably, B and T lymphocytes that encounter self antigen at ei ther the inappropriate levels or affinity are usually instructed to perish or become anergized. However, the presence of autoimmune disease suggests t hat the induction of self tolerance is not foolproof. In fact, autoreactive cells are now found to be normal inhabitants of the B and T lymphocyte rep ertoire. This review examines how foreign peptides which resemble self prot eins can elicit autoimmunity that is amplified to many sites on a target au toantigen. In particular, B lymphocytes initiated by foreign molecular mimi cs can process and present self peptides in the shaping of autoimmune T cel l responses.