Browsing by Author "Dr. Wayne Tompkins, Committee Chair"

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Cellular and Molecular Mechanisms Involved with Feline CD8+ T Cell Mediated Anti-FIV Activity
(2006-03-02) Hewitt, Tracy P.; Dr. Wayne Tompkins, Committee Chair
A population of activated CD8+ T cells that express the B7.1 (CD80) and B7.2 (CD86) costimulatory molecules and their ligand CTLA4 exist in the blood of asymptomatic FIV-infected cats. As evidence of CD8+ T cell mediated anti-FIV activity, coculture of CD8+ depleted-PBMC with FCD4E cells resulted in a significant increase in FIV p24 levels as compared to total PBMC cocultures. This anti-FIV activity was not overridden by the addition of either rhIL-2 or ConA. All cats were infected either intravenously or vaginally. There was no correlation between the route of infection and the presence of CD8+ T cell-mediated antiviral activity. Nonsuppressor cats had a higher number of viral RNA molecules per milliliter of plasma than the suppressor cats. PBMC from suppressor cats had a higher percentage of CD8+ CD25+ cells as compared to nonsuppressor cats. Both CD8+ CD25+ and CD8+ CD25- subsets inhibited FIV replication. CD8+ cells from suppressor cats also had an increased in the frequency of B7.1+ CD8+ cells with a low expression of the CD8β chain, suggesting that the CD8+ anti-FIV cells express the activation phenotype, CD8+ βlo B7.1+. Depletion of B7.1+ cells from PBMC of suppressor cats resulted in increased viral replication similar to depletion of CD8+ cells. CD8+B7.1+ and CD8+B7.1- subsets cocultured with infected CD4+ T cells revealed that the antiviral activity reside primarily in CD8+ B7.1+ subset. The presence of CD8+ antiviral cells lead to a decrease in the number of FIV RNA molecules per 106 CD4+ T cells in suppressor cats with no appreciable difference in the expression of IL-2 mRNA levels from either group of cats. The results of this study showed a strong correlation between the presence of CD8+ T cell anti-FIV activity, a reduction in viremia, low expression of the CD8β chain and expression of B7.1 costimulatory molecule on CD8+ T cells in suppressor cats suggesting that CD8+ βlo B7.1+ antiviral cells may play a major role in controlling FIV replication in vivo.
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
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).
Role of CD4+CD25+ and CD4+CD25- T Cells in Feline Immunodeficiency Virus Infection.
(2005-01-30) Joshi, Anjali; Dr. Wayne Tompkins, Committee Chair
Treatment of HIV infected individuals with HAART reduces the levels of plasma viral loads to below the limit of detection by standard clinical assays. HAART however, does not result in virus eradication as a small but detectable virus reservoir persists in all individuals receiving therapy. Studies attempting to identify reservoirs of HIV-1 latency have documented that the virus persists as both a latent and productive infection in subsets of CD4+ T cells. However, reports regarding establishment of a stable HIV-1 infection in quiescent T cells in vitro remain controversial. In the present study, we investigated the susceptibility of naive (CD4+CD25-) and activated (CD4+CD25+) feline T cells to FIV infection, their ability to replicate the virus and potentially act as a reservoir for virus persistence in infected animals. While both CD4+CD25+ and CD4+CD25- cells are susceptible to FIV infection in vitro and in vivo, only CD4+CD25+ cells produce infectious virions in the absence of a strong mitogenic stimulus like ConA. In contrast to CD4+CD25- cells, CD4+CD25+ cells display the key characteristics of Treg cells in that they remain unresponsive to mitogenic stimulation, and are relatively resistant to apoptosis. Mechanisms regulating infection of these cells revealed that CD4+CD25- cells are less susceptible to FIV infection, both at the level at viral entry and cellular transcriptional activity. The ability of CD4+CD25+ cells to replicate FIV efficiently in the presence of IL-2 but remain anergic and unresponsive to apoptotic signaling suggests that these cells may provide a reservoir of productive FIV infection. CD4+CD25- cells, on the contrary, seem to establish as latent viral reservoirs capable of being reactivated after stimulation.
The Role of the B7 Co-stimulation Pathway in Feline Immunodeficiency Virus (FIV) and Human Immunodeficiency Virus (HIV)Associated T cell depletion
(2003-03-09) Bull, Marta Eileen; Dr. Mary Tompkins, Committee Member; Dr. Wayne Tompkins, Committee Chair; Dr. Fred Fuller, Committee Member; Dr. Holly Jordan, Committee Member; Dr. Gregg Dean, Committee Member
Feline immunodeficiency virus (FIV) in the domestic cat provides a good animal model for dissecting the immunopathology associated with HIV infected individuals, as the immune dysfunction in the cat replicates the immune deterioration in humans. Lentiviruses characteristically cause a gradual loss in T-helper cells numbers and functions. A variety of mechanisms have been proposed to account for lentivirus-induced T cell depletion although none of these mechanisms alone account for all the T cell changes. The B7/cytotoxic T lymphocyte antigen four (CTLA4) signaling pathway is a major signaling pathway in the initiation and termination of T cell immune responses. The B7 receptors are normally expressed on the surface of antigen presenting cells (APC), while CD28 and CTLA4 are differentially expressed on the surface of T cells. Recent studies show that chronic stimulation in vitro or in vivo results in an unusual increase in the percent of T cells that express the B7 and CTLA4 molecules. These chronically activated T cells also up-regulate major histocompatibility complex class II molecules (MHC II) and are capable of inducing anergy and apoptosis of other activated T cells. In this study we found that individuals with a HIV or FIV infections had increased expression of B7 and CTLA4 on T cells in peripheral blood and lymph nodes (LN). These B7+CTLA4+ T cells were associated with an increased frequency of spontaneous apoptosis. Analysis of MHCII receptor expression on PBMC from HIV infected patients revealed a significant increase in MHCII+ expression on B7+ or CTLA4+ T cells. TUNEL analysis of B7+MHCII+ or CTLA4+MHCII+ compared to B7+MHCIIneg or CTLA4+MHCIIneg T cells revealed that the increased frequency of T cell apoptosis could almost exclusively be attributed to B7+MHCII+ and CTLA4+MHCII+ T cells, similar to our observations in the cat From these data we hypothesize that T: T interactions between CD4+ and CD8+ B7+CTLA4+MHCII+ T cells within the LN results in IL2 inhibition rendering them susceptible to cytokine deprived apoptosis.