Peptide-induced changes in class I heavy chains alter allorecognition.

Class I molecules of the MHC are intimately involved in the development and function of CD8+ T cells. Small peptides, derived from endogenous proteins, bind within the Ag binding groove created by the beta-pleated sheets and alpha-helices of the alpha 1 and alpha 2 domains of the class I molecule. This peptide-MHC complex has been shown to influence allorecognition by CD8+ T cells. However, the precise role of peptide in alloantigen recognition remains unclear. We have previously shown that conformational changes induced in the class I molecules can be identified as specific alterations in serologic epitopes. These results suggested that alloreactive T cells may detect structural changes in MHC based on the nature of the peptide binding to the class I protein. Here, we have shown that, in at least some instances, alloreactivity may not depend on the recognition of a precise self-peptide but on an epitope on the class I molecule influenced by the peptide. The nature of specific peptides expressed by class I-bearing cells may, therefore, have a dramatic effect on T cell development, self-tolerance, and alloreactivity.