As a further trigger of autoimmunity, it has been speculated that increased cell turnover or, more specifically, increased cell apoptosis may lead to exposure of otherwise rarely exposed antigens and induction of immune response to self. Enhanced apoptosis has been implicated in several autoimmune diseases, including Hashimoto's thyreoiditis [177] . This hypothesis would also provide an appealing explanation for the tissue specificity of most autoimmune reactions despite the often ubiquitous expression of the targeted autoantigen.