Browsing by Author "Dr. Frederick Fuller, Committee Member"

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    Feline Lentivirus enhanced CD4+CD25+ T regulatory conversion of CD4+CD25- T cells to phenotypic and functional T reg cells via the TGF-b/TGF-bR signaling pathway
    (2007-08-10) Petty, Christopher Samuel; Dr. Frederick Fuller, Committee Member; Dr. Linda Martin, Committee Member; Dr. Gregg Dean, Committee Member; Dr. Wayne Tompkins, Committee Chair
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    Molecular Characterization of T Regulatory Cells in FIV-infection
    (2006-04-24) Emani, Sirisha; Dr. Mary Tompkins, Committee Member; Dr. Barbara Sherry, Committee Member; Dr. Wayne Tompkins, Committee Chair; Dr. Frederick Fuller, Committee Member
    Naturally occurring CD4+CD25+ T regulatory cells (Treg) play important roles in maintaining immunologic self-tolerance in addition to controlling the magnitude of anti-microbial immune responses. However, the capacity of these CD4+CD25+ Treg cells to control immune responses both in vivo and in vitro is not well established. CD4+CD25+ Treg cell-mediated suppression can control autoimmune diseases; transplantation tolerance and graft verses host disease and, in contrast hinder tumor immunity and immunity to infectious agents. As Treg cells have been reported to be involved in several diseases, this study focused on molecular characteristics that enables them to maintain anergy and also resistance to programmed cell death along with the effect of FIV-infection on regulation of the above phenotypic characteristics. Our results show that feline CD4+CD25+ Treg cells are phenotypically and functionally anergic as indicated by elevated levels of the cyclin dependent kinase inhibitors, CdkI's, (p21cip1,p16ink4, and p27kip1) , and resistance to mitogen-induced proliferation compared to their counter parts CD4+CD25- T cells. Importantly, CdkI's are constitutively over-expressed only in FIV-infected cats. As expected Treg cells from FIV-infected cats that over-expressed CdkI's expressed low levels of the cyclins (mainly cyclins D) and phosphorylated retinoblastoma protein (pRb) that are responsible for cell cycle progression. We investigated the role of TGFβ signaling and found that TGFβ1 plus ConA stimulation was able to convert CD4+CD25- T cells to CD4+CD25+ T cells with functional and phenotypic characteristics including upregulation of CdkI's and bcl-2. The differential expression of CdkI's and bcl-2 between the two CD4+ T cell subsets may be linked to TGFβ-Smad pathway. Consistent with upregulation of CdkI's and bcl-2, we found that although natural and TGFβ1 converted CD4+CD25+ Treg cells are anergic, they are more resistant to activation induced cell death compared to CD4+CD25- T cells functionally which correlated with increased bcl-2 to bax ratio in Treg cells. Thus, the molecular characterization of this unique population of Treg cells may be essential for understanding their role and function for developing effective therapeutics and vaccination especially against chronic infections such as Acquired Immune Deficiency Syndrome (AIDS).