Identification of specific T lymphocytes against to an IFNg inducible lysosomal thiol reductase (GILT)-dependent, class II MHC-associated epitope in GILT−/− mice

Abstract

Abstract IFNγ inducible lysosomal thiol reductase (GILT) is the only thiol reductase localized in lysosomes and late endosomes, with its optimal activity at acidic pH. GILT is constitutively expressed in professional APC, further upregulated by IFNγ, and participates in Ag processing by catalyzing disulfide (S-S) bond reduction in proteins thus facilitating unfolding of native S-S bond containing Ag for further processing. It was reported that GILT−/− mice mounted significantly reduced T cell proliferative responses to S-S bond-containing protein Ags in vitro, but responded normally to a non-S-S bond containing protein. In addition, GILT−/− APC showed a selective deficiency in presenting some cysteine-containing epitopes within a model protein Ag, hen egg white lysozyme. Using HPLC-MS/MS, we first identified one group of unique GILT-dependent, class II MHC-associated peptides from B6 mice, but not from GILT−/− mice. Binding of these GILT dependent, class II MHC-associated peptides to I-Ab proteins was confirmed in vitro. Furthermore, T cells specific to one of the unique GILT-dependent peptides, BP7, was detected in GILT−/− mice, but not found in B6 mice. BP7 peptide specific T cell hybridoma clones were established as well. Taken together, our results indicate that GILT−/− mice have a deficiency in generation of certain T cell epitopes due to loss of GILT activity. Missing of GILT dependent epitopes might lead to survival of the T cells specific to these GILT-dependent epitopes (escaping from the negative selection) in thymus of GILT−/− mice. We are in progress of cloning the BP7 specific TCRs from T cell hybridoma clones. The potential role of the BP7 specific T lymphocytes in autoimmunity will be examined in BP7 specific T cell retrogenic mice.