Figure 1: Thymic selection and generation of the various CD4++ T lymphocyte subsets: negative selection, nTreg selection and positive selection of thymocytes in the medulla as the outcome of high affinity, intermediate affinity, and low affinity interaction of TCR on immature thymocytes and MHC II plus peptide on medullary APCs. The differentiation into Th1/Th2/Th17 etc cells, takes place in the periphery. Tregs may also be selected in the periphery under the influence of factors such as TGFβ and IL-2, and are then called iTregs [40-43].