Epithelial cells expressing aberrant MHC class II determinants can present antigen to cloned human T cells

Abstract

The first step in the induction of immune responses, whether humoral or cell mediated, requires the interaction between antigen-presenting cells and T lymphocytes restricted at the major histo-compatibility complex (MHC)^1,2. These cells invariably express MHC class II molecules (HLA-D region in man and Ia in mouse) which are recognized by T cells of the helper/inducer subset in association with antigen fragments^3,4. Interestingly, in certain pathological conditions^5–8, for example in autoimmune diseases such as thyroiditis⁵ and diabetic insulitis⁶, class II molecules may be expressed on epithelial cells that normally do not express them. We speculated that these cells may be able to present their surface autoantigens to T cells, and that this process may be crucial to the induction and maintenance of autoimmunity⁹. A critical test of this hypothesis would be to determine whether epithelial cells bearing MHC class II molecules (class II⁺ cells) can present antigen to T cells. We report here that class II⁺thyroid follicular epithelial cells (thyrocytes) can indeed present viral peptide antigens to cloned human T cells.