Project Summary Activation of T cells is the mainstay of host defense against Mycobacterium tuberculosis (Mtb) infection and tuberculosis disease (TB). For decades, T cells were thought to recognize solely peptide antigens bound to polymorphic antigen presenting molecules encoded in the MHC locus. However, the discovery that human CD1 proteins present mycobacterial antigens to T cells provides fundamentally new perspectives on the role of T cells in host defense. First, the foundational studies for this R01 proposal showed that CD1 proteins present mycobacterial glycolipids, phospholipids and lipopeptides to and T cells. Thus, lipids must now be considered a diverse class of natural antigens for the human immune system. Second, whereas the MHC locus is the most polymorphic of the human genome, the non-polymorphic nature of CD1 genes creates a situation in which T cell responses are not restricted to an individual’s genotype. Such ‘donor-unrestricted T cells’ have simplified patterns of antigen recognition and T cell receptor usage that could be exploited for therapy. Building on substantial published and unpublished data, this human-focused renewal proposal seeks to test a general model of antigen recognition in which T cell receptors (TCRs) bind onto a roof structure in CD1, or shift away from the roof to contact bacterial antigen. Using recently validated human CD1a, CD1b and CD1c tetramers, we will discover new conserved TCRs that are equivalent to NKT TCRs in the CD1d system. We propose to determine the effector functions of newly discovered innate T cell types in humans, focusing on genes that define an innateness gradient and the known effector functions needed to protect the host against Mtb. Finally, we combine newly produced reagents, including tetramers, transfectants and monoclonal antibodies, to use the guinea pig as a tractable model for study of host T cell responses in the lung and over time. These studies contribute to an innovative view that the human T cell system recognizes and responds to lipid antigens.