Human T cells use CD1 and MR1 to recognize lipids and small molecules

For decades immunologists thought that T cells solely recognize peptides bound to Major Histocompatibility Complex (MHC) proteins. Therefore, nearly all medical technology that seeks to measure and manipulate human T cells during immunization, infection, allergy and autoimmune diseases relies on peptide antigens. Newer insights into αβ and γδ T cell activation by CD1 or MR1 proteins greatly expand the biochemical range of T cell antigens to include lipids and non-peptidic small molecules. Moving beyond in vitro studies, the recent development of human CD1a, CD1b, CD1c and MR1 tetramers allows direct and specific enumeration of lipid-reactive and small molecule-reactive T cells, providing a new approach to study of T cell-mediated diseases.