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J. Exp. Med.,
Volume 189, Number 10, May 17, 1999 1531-1544
By




From the * Department of Pediatrics and the We have developed a unique in vivo system to determine the relationship between endogenous altered peptide ligands and the development of major histocompatibility complex class II-
restricted T cells. Our studies use the 3.L2 T cell receptor (TCR) transgenic mouse, in which
T cells are specific for Hb(64-76)/I-Ek and positively selected on I-Ek plus self-peptides. To this
endogenous peptide repertoire, we have individually added one of six well-characterized 3.L2
ligands. This transgenic approach expands rather than constrains the repertoire of self-peptides.
We find that a broad range of ligands produce negative selection of thymocytes in vivo. When
compared with the in vitro TCR-ligand binding kinetics, we find that these negatively selecting ligands all have a half-life of 2 s or greater. Additionally, one of two ligands examined with no
detectable binding to the 3.L2 TCR and no activity on mature 3.L2 T cells (Q72) enhances the
positive selection of transgenic thymocytes in vivo. Together, these data establish a kinetic threshold between negative and positive selection based on the longevity of TCR-ligand complexes.
Department of Pathology, Center for Immunology,
Washington University School of Medicine, St. Louis, Missouri 63110
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