| Abstract | The negative selection of immature T cells in the thymus cannot eliminate every self-reactive T cells that have a potential to cause autoimmune diseases. To prevent autoimmune diseases, regulatory T cells suppress the activity of self-reactive T cells, but they also interrupt normal immune reactions against foreign antigens. We discuss the advantage of having regulatory T cells by considering the ability of coping with foreign antigens and the harm of autoimmunity. We modeled the process of negative selection and the differentiation of T cells as follows, immature T cells reactive to abundant self antigens are completely eliminated, those reactive to rare self antigen will become regulatory T cells, and those that fail to interact with the antigens to which they are reactive will become conventional T cells. In this model, some self-reactive T cells can escape the negative selection during the limited training period and become to conventional T cells. Analysis suggests that producing regulatory T cells can be beneficial if the body is composed of many compartments and regulatory T cells suppress the immune reactions only within the same compartment (localized suppression). This result indicates that regulatory T cells should stop circulating once they are activated or suppress other T cells only on the same antigen presenting cells. |
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