Date of Award
Doctor of Philosophy (PhD)
Interactions between the ab T cell receptor (TCR) and peptide-bound MHC molecules (pMHC) are highly specific and sensitive despite low affinities. The basis of TCR ligand specificity and its functional manifestations during protective immune responses are incompletely understood. To study this, we have generated two TCR transgenic mice called LLO56 and LLO118, which bear CD4+ T cells that recognize the same dominant epitope from the virulence factor Listeriolysin O (LLO) of Listeria monocytogenes. These TCRs were cloned from Listeria-infected B6 mice, and thus represent two solutions to recognizing the same pathogen-derived pMHC. LLO118 T cells expanded better than LLO56 during primary responses to Listeria, due to LLO56 cells' greater propensity to undergo cell death. Both TCRs utilize an overall similar constellation of contacts with the LLO peptide, but differ dramatically in their contacts with peptide residues flanking the MHC binding groove. Nevertheless, LLO56 and LLO118 bind cognate pMHC with identical affinities. Unexpectedly, LLO56 T cells showed greater IL-2 responses in vitro than LLO118. This was true even when cells were stimulated nonspecifically downstream of the TCR, suggesting intrinsic differences in their responses to stimulation. LLO56's stronger IL-2 responses were associated with greater TCRz phosphorylation at baseline and ERK phosphorylation upon activation. Interestingly, the strength of these responses, in both the transgenic and polyclonal CD4+ and CD8+ T cells, tracked with the expression of CD5, which reflects TCR reactivity to self-pMHC. Consistently, LLO56 and LLO118 T cells acquired their respective sensitivities, basal signaling and propensities for cell death during positive selection, paralleling the strength of signal received from selecting self-pMHC. Notably, withdrawal of self-pMHC reduced LLO56 and LLO118 IL-2 and pERK responses, and compromised the LLO56 response to Listeria. We conclude that thymic education is a crucial inflection point about which the functional properties of CD4+ T cells are determined, ultimately impacting their performance in antipathogen responses.
Chair and Committee
Paul M Allen
Brian T Edelson, Ted H Hansen, Kenneth M Murphy, Andrey S Shaw, Emil R Unanue
Persaud, Stephen Phillip, "Functional Consequences of CD4+ T Cell Receptor Ligation in the Immune Response to Listeria monocytogenes" (2015). Arts & Sciences Electronic Theses and Dissertations. 429.