Possible impact of the mode of peptide delivery on the mechanisms of T cell tolerance. The nature of peptide delivery may influence the mechanism(s) of tolerance that are evoked. High dose peptide or peptides that lead to strong, transient TCR stimulation may favour deletion of allergen-reactive T cells. Persistence of peptide may favour adaptive tolerance and thus anergy/unresponsiveness of allergen-reactive T cells. Adaptive tolerance may, however, be reversed when peptide no longer persists. Regulatory mechanisms may be favoured by multi-dose regimens and/or low dose applications.