Over the last two decades, it has been established that peptides are not the only antigens
recognized by T lymphocytes. Here, we review information on two T lymphocyte populations
that recognize nonpeptide antigens: invariant natural killer T cells (iNKT cells), which
respond to glycolipids, and mucosal associated invariant T cells (MAIT cells), which
recognize microbial metabolites. These two populations have a number of striking properties
that distinguish them from the majority of T cells. First, their cognate antigens are presented …