Biological Effects of Trogocytosis on CD4+ T Lymphocytes

Douglas Grant Osborne, The University of Montana

Abstract

Antigen recognition by CD4+ T cells leads to large-scale spatial and temporal molecular redistributions, forming the immunological synapse. We have previously shown that upon dissociation, T cells capture large membrane fragments from antigen-presenting cells directly from the immunological synapse. The mechanism and biological significance of this process, termed trogocytosis, is still unclear. In this thesis I examined the impact that trogocytosis has on the individual T cell after capturing molecules from the antigen presenting cell. I employed murine fibroblast cell lines expressing an I-Ek molecule loaded with a covalently attached antigenic peptide (moth cytochrome C 88-103) and with or without a GFP-tagged cytoplasmic tail as antigen presenting cells for T cells from a peptide-specific TCR transgenic mouse. Using a combination of high-resolution microscopy and flow cytometry, I showed that the trogocytosed material is retained on the surface of the T cell and is associated with sustained signaling after removal of the antigen presenting cells. The intercellular trogocytosis correlates with alterations in and is associated with sustained survival of the trogocytosis-positive (trog+) cells in vitro. I also showed that sustained signaling in trog+ T cells occurs at the trogocytosed spot and is initiated by the trogocytosed material. I conclude, that after trogocytosis, trog+ T cells present antigen and induce activation of antigen-specific naïve T cells. The findings from this thesis will help to elucidate the role of trogocytosis on CD4+ T cells.