Functional evidence for the recognition of endogenous peptides by autoreactive T cell clones

Abstract

The fine specificity of two human T cell clones responding to autologous HLA-DR1 expressing antigen-presenting cells (APC) in the absence of nominal antigen has been investigated using Epstein-Barr virus-transformed B cells (BCL) of known DR β₁ domain sequence. it was found that responsiveness was markedly affected by changes in a limited number of residues in this domain. Substitution of the DRlβ sequence at one residue, position 74, even conservatively, was found to be particularly significant. Located on the β1, domain a-helix, this residue is predicted to point into the antigen-binding groove and is therefore unlikely to make contact with the T cell receptor. This finding suggests that these T cells are specific for a bound endogenous peptide within the autologous major histocompatibility (MHC) binding groove. The autospecific T cell clones also responded to murine L cell transfectants expressing DRα DR1β as well as to transfectants expressing the mouse/human hybrid MHC molecule I-Eα DR1β but not to the reciprocal combination DRα I-Eβ, thus confirming the importance of the β₁ domain to T cell recognition. In contrast to the autocytotoxicity observed with BCL, cytoiysis of the murine L cells expressing the HLA-DR1 molecule was slight and only found at high effector-target ratios. In addition, although fixation enhanced the recognition of BCL, capacity of the murine L cells bearing the HLA-DR1 molecule to stimulate T cell clone proliferation was markedly reduced by aldehyde fixation. When taken together, these results suggest that the endogenous peptides recognized by these autoreactive T cells are of human origin.