Characterizing antigen-specific CD4⁺ T cells using HLA-DR oligomers

Abstract

T cells are activated by the engagement of their surface T cell receptors (TCR) by antigenic peptide bound to major histocompatibility complex (MHC). The success or failure of this TCR to MHC-peptide interaction determines the specificity of T cell action, and thus plays a central role in proper immune function. In this thesis, soluble oligomers of MHC-peptide complex were used to investigate several aspects of the T cell immune response. Soluble fluorescent oligomers of human class II MHC were produced and used to detect CD4+ T cells of particular specificities. The critical parameters of this interaction were determined, and differing behaviors of various T cell clones were observed. The implications of these results are discussed, and MHC oligomers are suggested as powerful tools for the investigation T cell avidity modulation. Using a novel methodology for the analysis of the antigen-specific TCR repertoire which includes identification by MHC oligomers, T cells specific for a peptide derived from influenza were isolated, cloned and sequenced. This pool of sequences was observed to be extremely diverse in both VP usage and CDR3 sequence. These results are discussed with regard to the TCR repertoire, structural aspects of TCR/MHC-peptide interaction, and future studies of TCR repertoire analysis. Other studies investigating the triggering mechanism of TCR are summarized and implications of these results for various models of transmembrane activation are discussed. A novel mechanism is proposed involving the reorganization of a receptor oligomer from a specific inhibited state into an uninhibited state. Future directions of research based on the work presented in this thesis are suggested.