MHC Molecules in Thymic Development and Selection of the T Cell Repertoire

The hallmark of the immune system is its ability to discriminate between self and non-self (foreign) products. The T cell is the prime player in this respect during the cellular immune response. The thymus provides both the environment and the support for T cells to be “educated” in self-nonself recognition. The thymus has been aptly called the “black box” because of the complexity of its role in this process. Indeed, much light has been cast upon the arcane processes of the thymus that lead to the elimination of self-reactive T cells and yet, at same time, enable it to maintain an optimum set of immune-responsive cells that can react with the whole universe of foreign antigens that assail the body during an entire lifetime.