title: Role of endogenous peptide in human alloreactive cytotoxic T cell responses.
abstract: The T x B hybrid 174 x CEM.T2 (T2) has been shown to be defective in the processing of proteins for presentation by MHC class I molecules. It continues, however, to express significant quantities of HLA-A2.1, suggesting that this class I molecule is expressed either in a largely peptide-free form or in association with a small subset of peptides. In this paper T2 was used in conjunction with limiting dilution analysis to provide a direct estimate of the fraction of alloreactive cytotoxic T lymphocytes (CTLs) that were dependent upon the presence of peptides for their recognition of HLA-A2.1. Alloreactive cytotoxic T cell lines generated by stimulation with HLA-A2.1 expressing peripheral blood lymphocytes recognized T2 poorly. Split-well analysis of 240 clonal limiting dilution cultures demonstrated that this reflected the existence of two subpopulations. An average 85% of HLA-A2.1 specific CTLs recognized HLA-A2.1 on normal cells but not on T2. The remainder recognized HLA-A2.1 on both T2 and normal targets. CTL lines with the latter specificity could be generated by using T2 as a stimulator cell. Using target cells that either expressed a lower density of HLA-A2.1 or that expressed HLA-A2 molecules that had been mutated to affect CD8 binding, no significant differences in avidity between T2-reactive and T2-unreactive CTLs were seen. Thus the failure of the majority of alloreactive CTLs to recognize T2 is not a consequence of the lower level of HLA-A2.1 surface expression on this cell, but is instead due to the absence of appropriate epitopes.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Microbiology, University of Virginia, Charlottesville 22908.
authors.forename: S
authors.initials: S
authors.lastname: Man
authors.forename: R D
authors.initials: RD
authors.lastname: Salter
authors.forename: V H
authors.initials: VH
authors.lastname: Engelhard
mesh_terms: D001402:B-Lymphocytes / Q000276:immunology; D002460:Cell Line; D000939:Epitopes; D015789:HLA-A2 Antigen; D006801:Humans; D006822:Hybrid Cells / Q000276:immunology; D010455:Peptides / Q000276:immunology*; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D000939:Epitopes; D015789:HLA-A2 Antigen; D010455:Peptides