| This dissertation presents the discovery of the expression of the novel molecules, I-TAC, B7-H1 and GL50, by EC, which further characterizes endothelial cells (EC) as dynamic players in the immune response.; To understand how EC can be involved in immune responses, we began by identifying molecules EC express during their interactions with immune cells, in particular T cells. In the second chapter, we devised a subtractive hybridization screen that would identify molecules involved in EC activation of T cells. This led to the discovery that EC express the chemokine, I-TAC. The function of EC expressed I-TAC was addressed using adhesion assays, which showed that I-TAC attracts T cells, and activates T cell integrins to allow them to firmly adhere to EC monolayers, illustrating the ability of EC to express molecules required for T cell recruitment.; We further analyzed EC interactions with T cells by studying the ability of EC to activate T cells. Antigen presenting cells (APC) are the only cells capable of providing both signals needed to activate a T cell. APC express MHC molecules which present antigens to T cells thus providing the primary, antigen-dependent, signal. They also express costimulatory molecules needed to provide the second, antigen-independent, signal called costimulation. In chapter 3, we provide evidence for EC acting as antigen presenting cells (APC). Using superantigens (SAg) as the primary stimulus, we developed an in vitro model mimicking more physiological T cell stimulation conditions than is possible using the polyclonal stimulators PHA and anti-CD3 antibody. SAg are polyclonal activators of T cells that crosslink MHC class II molecules to specific Vβ regions of the T cell receptor (TCR). Thus, this system is dependent on the expression of MHC class II molecules on the EC and the correct Vβ regions of the TCR on the T cell. Using this system we studied, at the single cell level, the ability of EC to costimulate T cells to translocate NFAT to the nucleus, to express the activation marker CD69, and to synthesize the cytokines IL-2 and IFN-γ.; In order to act as APC, EC must express costimulatory molecules. Although EC do not express the conventional B7 costimulatory molecules which costimulate T cells through the CD28 pathway, they do express CD58 (LFA-3) which costimulates T cells through the CD2 pathway. (Abstract shortened by UMI.)... |
