Dose-dependent T cell tolerance to an immunodominant self peptide

We have previously described a model of tolerance to self peptides in a mouse transgenic (Tg) line producing secreted hen egg-white lysozyme (HEL). The HEL cDNA was placed under the control of a ubiquitous promoter expressed early in embryogenesis, so that HEL should be present in Tg mice throughout the development of the immune system. Since individual HEL Tg mice express different amounts of serum HEL, we were previously able to show that H-2d mice with HEL blood level > 10 ng/ml are tolerant to HEL and to the immunodominant (ID) peptide 108-116. However, autoreactive T lymphocytes recognizing the HEL subdominant (SD) peptides 74-96 and 1-18 still persist and the SD-specific response disappear at higher blood HEL concentrations. In the present work, we have studied HEL Tg H-2d mice with HEL serum levels < 10 ng/ml (HEL-low Tg animals). We find that 50% of Tg animals with HEL blood concentration < 2 ng/ml are responsive to HEL in T cell proliferation assays, although these responses are lower than those seen in non-Tg control mice. The HEL-specific T lymphocytes react only with 15-mer overlapping peptides encompassing the single H-2d ID region of HEL (residues 102-122); whereas the 9-mer minimal ID peptide 108-116, which strongly triggers non-Tg T cells, is unable to stimulate auto-reactive T cells in vitro from HEL-low Tg mice. Altogether, our results suggest that T lymphocytes specific for the minimal ID peptide are deleted or inactivated, while T cell clones of lower affinity and reacting with epitopes on longer peptides persist. Thus, the high affinity ID peptide-specific T cell clones can be negatively selected even in the presence of low amounts of HEL.