| During thymic development, NKT cells diverge from the pathways of conventional CD4 and CD8 T cells at the CD4+CD8+ double-positive (DP) stage. This corresponds to the stage at which their semi-invariant Valpha14 TCR interacts with the MHC I-like molecule, CD1d, complexed with the self-glycolipid iGb3.; In this project, I hypothesized that the conditions of TCR stimulation of NKT precursors must differ from those of conventional T cells. Using transgenic approaches to redirect CD1d expression in different cell types, I demonstrated that cortical DP thymocytes, rather than thymic epithelial cells, were both necessary and sufficient for NKT cell development. Additional interactions with CD1d expressed on other cell types were not essential, but they influenced subtle aspects of the terminal differentiation and reactivity of NKT cells.; Using a modified Valpha14 TCR transgenic system, I demonstrated the agonist nature of the CD1d/iGb3 ligand, another unusual feature distinguishing NKT cell development from MHC/peptide-restricted conventional T cell development. Further, these Valpha14 transgenic cells allowed for a dissection of the contribution of the Vbeta repertoire associated with the canonical Valpha14 TCR a chain. The results indicated a clear hierarchy of affinity with Vbeta7 > Vbeta8 > Vbeta2.; Collectively, these results identify two distinct features of NKT cell selection, the agonistic nature of Valpha14 TCR signals and the homotypic nature of thymocyte interactions (DP-DP), which may both contribute to the unusual signaling events leading to the NKT developmental pathway. |
