Analysis of the Antigen-Specificity of T Follicular Helper Cells Generated from the Endogenous CD4 T cell Repertoire

Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Microbiology and Immunology, 2013.CD4 T cells are a key subset of leukocytes that help orchestrate adaptive immunity. Several lineages comprise the CD4 T cell compartment, each with unique abilities to coordinate immune responses. Our investigations have focused on one particular lineage of CD4 T cells that are specially programmed to support the B cell immune response, T follicular helper (Tfh) cells. Upon immunological challenge, Tfh cells help B cells to initiate and maintain germinal center reactions within B cell follicles of the lymph node. The result of the germinal center reaction is the generation of memory B cells and long-lived antibody secreting plasma cells that produce class-switched, highaffinity antibodies. Titers of high-affinity antibodies are the most common indication of human vaccine efficacy. Therefore, understanding the processes and cells that contribute to their generation are of great importance to human health. To generate Tfh cells, naïve CD4 T cells undergo an initial differentiation step through antigen-specific interactions with dendritic cells (DC) that poise CD4 T cells for secondary interactions with B cells. These secondary antigen-specific interactions with B cells are required for CD4 T cells to fully initiate and maintain the Tfh program. Since DC and B cells are known to differ in the way they acquire, process and present antigen, we were intrigued by the possibility that these distinct types of antigen presenting cells would present different repertoires of peptide-MHC class II complexes that would be reflected in their immunodominance hierarchy. Herein, we develop methods to purify Tfh cells from mouse and human tissues and blood. Using several different methods, we have evaluated the distribution of the hierarchy of antigen-specific responses of Tfh and conventional T cells generated from the endogenous CD4 T repertoire of the host. In our mouse model of protein immunization, peptide-specific immunodominance hierarchies were similar between Tfh and conventional CD4 T cells. Our studies of Tfh cells isolated from human peripheral blood have focused on clinically relevant influenza A protein-specific responses. This evaluation revealed enrichment of hemagglutinin (H1) specific cells within the CD4+CD45RACXCR5+ compartment, while nuclear protein specific cells were found to be enriched within the CD4+CD45RA-CXCR5- population