A comparison between the expected probability of encountering autoreactive T-lymphocytes in the peripheral blood vs that in peripheral lymphoid organs would be helpful. (This might have implications in predicting the probability of autoimmune reactions which might occur following HSCT vs those that occur after solid organ transplants)
The thymus serves as the central organ of immunologic self-non-self discrimination. Thymocytes undergo both positive and negative selection resulting in T cells with a broad range of reactivity to foreign antigens but a lack of reactivity to self-antigens. The thymus is also the source of a subset of regulatory T cells that inhibit autoreactivity of T cell clones that may escape negative selection. As a result of these functions, the thymus has been shown to be essential for the induction of tolerance in many rodent and large animal models.
Functional tolerance consists of two coordinated processes: 1) deletion of autoreactive lymphocytes during maturation in the central lymphoid organs before such cells reach maturity, and 2) functional suppression in the periphery of autoreactive lymphocytes that have escaped elimination. These two processes are referred to as central and peripheral tolerance.
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