The effect of endogenous altered peptide ligands on peripheral T-cell responses

Numerous studies have shown that a T cell can productively interact through its TCR with less-than-optimal ligands resulting in partial T-cell activation. These ligands, that we called 'altered peptide ligands' (APLs) can act as partial agonists, antagonists or weak agonists for the T cells. Here we discuss the self-antigen system that we used to provide evidence that endogenous APLs exist in vivo and affect T-cell development. We also report the ability of endogenous APLs to induce partial T-cell activation of peripheral T cells, and describe in which circumstances this could occur in vivo.