Title page for ETD etd-05092001-104901

Type of Document Master's Thesis
Author Martins, Ryan Stephen
Author's Email Address rmartins@vt.edu
URN etd-05092001-104901
Title Tumor-Bearing Host Macrophage Dysfunction: Role of CD40/CD40L Interactions
Degree Master of Science
Department Biology
Advisory Committee
Advisor Name Title
Elgert, Klaus D. Committee Chair
  • tumors
  • macrophages
  • immunosuppression
Date of Defense 2001-05-01
Availability unrestricted
A functional immune system is a potential barrier to tumor growth and progression. Cancer is caused, in part, by the loss of immune surveillance leading to the inability of the immune system to destroy the cancer cells. Macrophages (Mfs) are essential cellular components of the immune system; they influence immune responses in diverse and fundamental ways. As a consequence, Mfs present targets for tumors to evade, thereby enhancing tumor survival and growth. An interaction between CD40 on Mfs and CD40L on T cells is required for cell-mediated inflammatory responses. The CD40/CD40L interaction is bi-directional; suppressed expression of either protein by the tumor will prevent activation of both Mfs and T cells. We showed that tumor growth suppresses T-cell CD40L expression. Decreased CD40L expression disrupted Mf activation pathways, leading to impaired production of immunostimulatory cytokines, interleukin (IL)-12 and IL-18 by tumor-bearing host (TBH) Mfs. Disruption of CD40L expression, via dysregulation of IL-12 and IL-18 production, impeded T-cell interferon (IFN)-g production, which in turn exacerbated Mf dysfunction. We showed that IFN-g induced interferon consensus sequence binding protein (ICSBP) expression is impaired in TBH Mfs due to tumor cell-derived TGF-b and, to a lesser extent, IL-10. ICSBP induces CD40L, IL-12, and IL-18 expression. Disruption of the CD40/CD40L interaction via lowered CD40L expression generates an immunosuppressive loop that may be a strategy for tumor survival and growth. This was demonstrated by impaired cytotoxicity; via impaired tumor necrosis factor (TNF)-a and nitric oxide (NO) production by TBH Mfs against Meth-KDE tumor cells. Collectively, these studies show that multiple antitumor mechanisms could be enhanced by restoration of CD40L expression.
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