TCR-transgenic

mHfeWT mice deleted mHFE-reactive T cells in the thymus, but a fraction of reprogrammed cells were able to escape deletion. In contrast, TCR-transgenic mice deprived of mHFE molecules (mHfe KO mice) or expressing a C282Y mutated mHFE molecule – the most frequent mutation associated with human hereditary hemochromatosis – positively selected mHFE-reactive CD8+T lymphocytes and were Omipalisib mw not tolerant toward mHFE. By engrafting these mice with DBA/2 WT (mHFE+) skin, it was established, as suspected on the basis of similar engraftments performed on DBA/2 mHfeKO mice, that mHFE behaves as an autonomous skin-associated histocompatibility antigen, even for mHFE-C282Y mutated mice. By contrast, infusion SP600125 of DBA/2 mHFE+ mice with naïve mHFE-reactive transgenic CD8+T lymphocytes did not induce GVHD. Thus, tolerance toward HFE in mHfeWT mice can be acquired at either

thymic or peripheral levels but is disrupted in mice reproducing human familial hemochromatosis. HFE, an MHC class Ib molecule, controls iron metabolism; patients who are homozygous for a C282Y mutation that disrupts the disulfide bridge of the HFE heavy chain third domain and destabilizes the molecule, suffer from hereditary hemochromatosis [[1]]. Animal models of human hemochromatosis have been derived. Mice carrying the homozygous mouse HFE (mHFE) C282Y mutation exhibit the same iron overload as hemochromatosis patients [[2]]. Crystallographic analysis of the human HFE molecule has revealed that the groove delimited by the first and second domains of the heavy chain (where MHC class Ia molecules bind and present peptides to CD8+ T lymphocytes) is small and empty. Otherwise, the general structures of the human HFE and MHC class Ia molecules are very much alike, HFE sharing a 37% aa homology with HLA-A2 [3]. Despite the fact that HFE is deprived of antigen presenting function, we have shown that HFE could interact with CD8+ TCR T lymphocytes autonomously.

Whereas DBA/2 WT mice are tolerant toward mHFE, DBA/2 mHfe KO mice immunized with syngeneic mHFE-expressing P815 cells develop CD8+ TCR CTL responses with direct recognition of mHFE [4]. These data raise the possibility that mHFE could be a histocompatibility antigen autonomously, Y-27632 2HCl not only for mHfe KO mice but also for mice with the HFE C282Y mutation. To answer this question and to ascertain the mechanisms through which tolerance toward mHFE is acquired, DBA/2 mice that expressed a transgenic TCR that directly recognizes mHFE were created in either a mHfe WT, mHfe KO or mHfe-C282Y knock-in/mHfe KO heterozygous (mHfe-C282Y mutated) context. Whereas the TCR-transgenic CD8+ T lymphocytes are positively selected in both mHfe KO and mHfe-C282Y mutated mice, in mHfe WT mice, tolerance toward HFE is mainly acquired in the thymus by clonal deletion with, however, a fraction of cells escaping deletion by downregulating their TCR.