The Piv-Otal Class II Transactivator Promoter Regulates Major Histocompatibility Complex Class II Expression in the Thymus

Recognition of antigen by CD4⁺ T cells requires presentation of short peptide fragments in the context of heterodimeric MHC class II molecules 1,2. Antigen presentation by MHC class II molecules is pivotal to the induction of adaptive immune responses, peripheral tolerance, and central tolerance, as well as being required for CD4⁺ T cell survival 1,2,3. Constitutive expression of MHC class II molecules is restricted to APCs: B cells, dendritic cells and macrophages; and cortical thymic epithelial cells (cTECs), where MHC class II molecules mediate positive selection of CD4⁺ T cells 4. The expression of MHC class II on APCs can be further upregulated in response to inflammatory mediators such as IFN-γ and LPS. These stimuli are also able to induce MHC class II expression on other cell...