Date of Award

December 2013

Degree Type

Thesis

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Douglas A. Steeber

Committee Members

Julie A. Oliver, Jeri A. Lyons

Keywords

CCR7, L-Selectin, T Cell Apoptosis, T Cell Proliferation

Abstract

Lymphocytes require antigenic encounter to activate and proliferate, eventually clearing the source of antigenic challenge. The peripheral lymph nodes (PLN) are the primary sites of antigenic encounter and thus the ability of lymphocytes to migrate to this tissue is a requirement for mounting effective immune responses. The process of lymphocyte migration to the PLN is known as the "adhesion cascade". Specifically, lymphocytes are captured from the blood through the adhesion molecule, L-selectin, followed by CC chemokine receptor 7 (CCR7)-mediated integrin activation, which ultimately results in cell transmigration into the PLN. Because the PLN is the site where antigenic encounter is most likely, we hypothesized that migration may induce pro-proliferative signaling, mediated by L-selectin and conducted through CCR7. To study the potential "priming" effects of adhesion to antigen-mediated lymphocyte proliferation, spleen and PLN lymphocytes were subjected to in vitro transmigration and proliferation assays. Subsequently, multi-color flow cytometry analysis was used to examine treatment effects on the T cell population. Results showed that lymphocyte proliferation was significantly increased when L-selectin and CCR7 were activated simultaneously, compared to CCR7 activation alone.

Specifically, bulk tissue populations, as well as the CD4+ and CD8+ T cell subsets showed enhanced proliferation from both spleen and PLN sources at early and late time points. Additionally, to discern whether this enhanced proliferation may be a by-product of decreased apoptosis, an apoptosis assay was also performed at the same time points. Interestingly, L-selectin engagement resulted in protection from apoptosis for all T cell populations 72 hour following activation. However, this protective effect was not observed at the 36 hour time point. Taken together, these results suggest a role for L-selectin in enhancing T cell proliferation, at least in part, through an anti-apoptotic effect. This research will add to a better understanding of the regulation of lymphocyte proliferation and increase our knowledge of L-selectin signaling function.

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