90% of Human Immunodeficiency Virus (HIV) infections are acquired across the genital or gastrointestinal mucosa, and infection leads to profound depletion of CD4+ lymphocytes. Antiretroviral therapy can restore blood CD4+ T cells. However, immune dysfunction and defects in mucosal antimicrobial defence persist. Some CD4+ T-subsets, particularly antimicrobial Th17 cells, show enhanced susceptibility to HIV infection and are also preferentially depleted in the course of HIV infection; the latter may allow microbial translocation into the bloodstream. Genital infections have been shown to have direct mucosal immune effects and to increase susceptibility to HIV; however, the effect of systemic infections, such as Malaria (which is holo-endemic in some HIV prevalent regions) is unknown. Understanding the relationship between HIV, highly susceptible immune cells, immune activation and malaria infection on mucosal tissues has been the main focus of my thesis. In HIV-infected individuals, I explored whether HIV antiretroviral therapy restores gut Th17 populations and improves gut antimicrobial defences. Therapy restored gut Th17 populations in some, but not all individuals, but antimicrobial defence remained impaired. I then piloted a novel mucosal-optimized PCR assay to measure cervical immune gene responses, as standard mucosal assays are inadequate. I succeeded in measuring mitogen-induced, but not HIV-specific, cervical immune responses in HIV-infected individuals. Next, using this PCR platform I examined mitogen-induced cervical immune responses in individuals demonstrating reduced susceptibility to HIV, and found that they had reduced production of both Th17-associated and pro-inflammatory cytokines from cervical cells. Finally, in a murine model I found that malaria caused genital and gastrointestinal mucosal immune activation, and increased both the expression of mucosal HIV susceptibility immune markers, and mucosal T cell immune activation. In summary, insufficient gastrointestinal Th17 cells restoration does not underlie persistent mucosal immune activation and microbial translocation in HIV-infected people on therapy. A reduced frequency of highly susceptible Th17 cells in the cervix of HIV-exposed but uninfected individuals was identified as a correlate of reduced HIV susceptibility. Malaria, a common systemic infection in HIV-endemic countries, may enhance susceptibility to HIV through increasing putative immune markers of HIV susceptibility and immune activation in potential mucosal sites of HIV exposure.

Endoglin is an auxiliary receptor for ligands of TGF-β receptor superfamily, present in endothelial cells and the placental syncytiotrophoblast. The expression of placental membrane endoglin (mEng) is further increased during preeclampsia, a pregnancy-specific hypertensive syndrome. We hypothesize that the soluble form of endoglin (sEng) released from the placenta leads to endothelial dysfunction and hypertension by disrupting normal BMP-9 signaling. We show that cell surface mEng inhibits TGF-β1, BMP-2, and BMP-7 induced Smad1,5,8 phosphorylation while potentiating BMP-9 induced signaling. sEng has been shown to be elevated in the sera of preeclamptic women and is postulated to interfere with endothelial cell function. We show that sEng binds to BMP-9 with a 2 nM affinity and can compete for its binding to endothelial cells, inhibiting downstream Smad1,5,8 phosphorylation. Our results suggest that sEng is contributing to endothelial dysfunction by dysregulating BMP-9 signaling.

Endoglin is an auxiliary receptor for ligands of TGF-β receptor superfamily, present in endothelial cells and the placental syncytiotrophoblast. The expression of placental membrane endoglin (mEng) is further increased during preeclampsia, a pregnancy-specific hypertensive syndrome. We hypothesize that the soluble form of endoglin (sEng) released from the placenta leads to endothelial dysfunction and hypertension by disrupting normal BMP-9 signaling. We show that cell surface mEng inhibits TGF-β1, BMP-2, and BMP-7 induced Smad1,5,8 phosphorylation while potentiating BMP-9 induced signaling. sEng has been shown to be elevated in the sera of preeclamptic women and is postulated to interfere with endothelial cell function. We show that sEng binds to BMP-9 with a 2 nM affinity and can compete for its binding to endothelial cells, inhibiting downstream Smad1,5,8 phosphorylation. Our results suggest that sEng is contributing to endothelial dysfunction by dysregulating BMP-9 signaling.

NK cells are innate lymphocytes that are crucial for host immunity during infections. Discrimination between healthy and infected cells is facilitated through a sum of inhibitory and stimulatory signals. Host cells can modulate the expression of NK ligands in response to infection, transformation, and stress, while viruses can exploit these mechanisms to prevent the killing of the infected cells. This thesis focuses on the interaction between the NK receptor, NKR-P1B, and its ligand, Clr-b. First, we used a reporter cell-based protocol to establish hybridomas producing monoclonal antibodies against a putative viral immunoevasin, RCTL. We express CD3ζ-fusion proteins on the reporter cells, which we then use to immunize and screen hybridoma specificities. Our results demonstrate a rapid, efficient, and high-throughput method of monoclonal antibody screening, and provide the framework for our work on cytomegalovirus evasion of the NKR-P1B:Clr-b system. Next, we show that RCMV infection results in a notable downregulation of rClr-b at the protein and transcript levels. Conversely, RCTL is upregulated during infection, and binds to the same NK-inhibitory receptor as Clr-b, NKR-P1B. In the absence of RCTL, RCMV-mediated Clr-b loss leads to increased NK-killing of infected targets and an NK-dependent reduction of viral titers in vivo. Notably, NKR-P1B is highly polymorphic, and certain rat NKR-P1B alleles have lost binding to the viral RCTL but not to the host Clr-b molecule, suggesting co-evolution between the host and the virus. In the next chapter, we address some of the mechanisms responsible for CMV-mediated Clr-b downregulation, and show that Clr-b downregulation also occurs to mice in response to MCMV infection. Moreover, early gene expression (host or viral) appears to be required for Clr-b downregulation. Interestingly, engagement of any one conventional pattern recognition receptor is insufficient to mimic MCMV-mediated Clr-b downregulation. Similarly, fibroblasts lacking various intermediates for the interferon or inflammasome pathways still downregulate mClr-b, with the exception of the DNA sensor, Zbp-1. Lastly, a recently identified autocatalytic motif conserved in the rat and mouse Clr-b transcripts, the hammerhead ribozyme, appears to be involved in Clr-b regulation. Taken together, our results explore a novel and important role for NKR-P1B:Clr-b interactions in viral immunity.

B lymphopoiesis is regulated by cytokines, chemokines and cell surface proteins that initiate signal transduction pathways necessary for maturation to proceed. Many of these factors are expressed by cells in the surrounding bone marrow (BM) microenvironment, which also form the niches that support development. Interleukin-7 (IL-7) is an essential cytokine for progenitor B cells and is important in providing survival, proliferation and maturation signals. By growing BM B cells for extended periods of time in vitro with IL-7 it is possible to select for cells that possess the ability to grow indefinitely, and these cultures can be used to generate cell lines. Data presented herein describe the generation and characterization of IL-7-dependent B cell lines as well as their utility in investigating aspects of B cell development. As B cells mature they lose responsiveness to IL-7, yet retain IL-7 receptor expression. I demonstrate that a B cell’s ability to respond to IL-7 is controlled by the expression of suppressor of cytokine signaling (SOCS) proteins, which are regulated by a variety of signaling pathways including those initiated by IL-7. Development of progenitor B cells to mature immunoglobulin secreting B cells is mediated in part by surface proteins present on stromal cells as well as on B cells themselves. Heparan sulfate and CD19 play important roles in regulating this transition and I provide data that demonstrates how their ability to regulate Erk activation downstream of the pre-B cell receptor (pre-BCR) alters the proliferation and maturation of developing B cells.

Prostate cancer is a leading cause of cancer deaths in North American men. Current treatments are often not curative, particularly in cases of advanced metastatic disease. Immunotherapy is a promising approach to treating cancer as it harnesses the immune system’s ability to mount potent responses against tumor-associated antigens (TAAs). Dendritic cells (DCs) play a central role in mediating antigen-specific immunity and have been recently used with some success in clinical trials. The difficulties associated with obtaining sufficient quantities of DCs from cancer patients provided the rationale for developing low-dose DC-based immunotherapy approaches in my thesis project. DCs were genetically engineered using a lentiviral vector (LV) to express erbB2tr, a kinase-deficient version of erbB2. The human form of erbB2, HER2/neu, is overexpressed in 20% of primary prostate tumors and 80% of their metastases, making this TAA an attractive target. Using this LV system, efficient transgene delivery into DCs was achieved without compromising DC function or phenotype. Administering low prime and boost doses (2x10^5 or 2x10^3) of LV-transduced DCs to mice yielded potent and long-term anti-tumor responses against murine prostate tumors engineered to overexpress erbB2tr. The 2x10^5 DC dose yielded complete tumor protection and was associated with humoral and cellular responses. The 2x10^3 dose also offered complete protection in some mice, suggesting that we had reached a lower threshold DC dose. This novel finding prompted us to determine if co-transducing DCs with an additional LV carrying the cDNA for an immunomodulatory factor could augment the efficacy of our low-dose strategy. We chose to test both the DC survival-enhancing RANKL protein and DC function-enhancing IL-12 in combination with erbB2tr. Although DCs co-transduced with the LV/RANKL and LV/erbB2tr did not appear to offer enhanced anti-tumor benefits in a prophylactic setting, co-transduction with LV/IL-12 and LV/erbB2tr did. The incorporation of IL-12 into the low-dose immunization strategy led to robust long-term tumor protection and relatively high levels of Th1 immunity. This is the first demonstration of the efficacy of low-dose DC-mediated immunotherapy using lentiviral vectors as gene transfer tools. These studies establish a platform for DC-mediated therapies that can be realistically translated to the clinic.

Progressive obesity and its associated metabolic syndromes represent a globally growing challenge, yet mechanistic understanding and current therapeutics are unsatisfactory. We discovered that CD4+ T-lymphocytes, resident in visceral adipose tissue (VAT), control insulin-resistance in diet-induced obese (DIO) mice and likely humans. DIO VAT-associated T cells display biased TCR-Valpha/betarepertoires suggesting antigen-specific expansion. CD4+ T-lymphocyte control of glucose homeostasis is compromised in DIO when VAT accumulates pathogenic IFNgamma-secreting Th1 cells, overwhelming static numbers of Th2 (CD4+GATA-3+) and regulatory Foxp3+ T cells. CD4+ T cell transfer into DIO, lymphocyte-free RAGnull mice reversed weight gain and insulin resistance predominately through Th2 cells. Brief systemic treatment with anti-CD3 antibody or its F(ab’)2 fragment, restores the Th1/Foxp3+ balance and reverses insulin resistance for months, despite continuing high-fat diet. CD4+ T cells impact the progression of obesity-associated metabolic abnormalities and can be manipulated by immunotherapy.

NK cells are innate lymphocytes that are crucial for host immunity during infections. Discrimination between healthy and infected cells is facilitated through a sum of inhibitory and stimulatory signals. Host cells can modulate the expression of NK ligands in response to infection, transformation, and stress, while viruses can exploit these mechanisms to prevent the killing of the infected cells. This thesis focuses on the interaction between the NK receptor, NKR-P1B, and its ligand, Clr-b. First, we used a reporter cell-based protocol to establish hybridomas producing monoclonal antibodies against a putative viral immunoevasin, RCTL. We express CD3ζ-fusion proteins on the reporter cells, which we then use to immunize and screen hybridoma specificities. Our results demonstrate a rapid, efficient, and high-throughput method of monoclonal antibody screening, and provide the framework for our work on cytomegalovirus evasion of the NKR-P1B:Clr-b system. Next, we show that RCMV infection results in a notable downregulation of rClr-b at the protein and transcript levels. Conversely, RCTL is upregulated during infection, and binds to the same NK-inhibitory receptor as Clr-b, NKR-P1B. In the absence of RCTL, RCMV-mediated Clr-b loss leads to increased NK-killing of infected targets and an NK-dependent reduction of viral titers in vivo. Notably, NKR-P1B is highly polymorphic, and certain rat NKR-P1B alleles have lost binding to the viral RCTL but not to the host Clr-b molecule, suggesting co-evolution between the host and the virus. In the next chapter, we address some of the mechanisms responsible for CMV-mediated Clr-b downregulation, and show that Clr-b downregulation also occurs to mice in response to MCMV infection. Moreover, early gene expression (host or viral) appears to be required for Clr-b downregulation. Interestingly, engagement of any one conventional pattern recognition receptor is insufficient to mimic MCMV-mediated Clr-b downregulation. Similarly, fibroblasts lacking various intermediates for the interferon or inflammasome pathways still downregulate mClr-b, with the exception of the DNA sensor, Zbp-1. Lastly, a recently identified autocatalytic motif conserved in the rat and mouse Clr-b transcripts, the hammerhead ribozyme, appears to be involved in Clr-b regulation. Taken together, our results explore a novel and important role for NKR-P1B:Clr-b interactions in viral immunity.

About 10% of the world population suffers from chronic virus infections such as infections with hepatitis B virus, hepatitis C virus, and human immunodeficiency virus. Chronic virus infection is associated with the loss of functional cytotoxic T cells. Recent studies uncovered several mechanisms that play a central role in T cell exhaustion and thus development of chronic infections. The role of the innate immune system in the development of chronic virus infections remains unclear. Here we show that type I interferons trigger not only inhibition of virus replication but also immunoregulatory functions. The antiviral effects of type I interferons in the liver were dependent on the presence of macrophages. Macrophage depletion led to excessive virus replication and the development of chronic infection. Moreover, specific deletion of the type I interferon receptor on macrophages led to a decreased innate immune response. The regulatory functions of type I interferons were carried out by natural killer cells. Activated natural killer cells inhibited the virus specific cytotoxic T cell response and therefore delayed virus control. Depletion of natural killer cells prevented development of chronic infections and immunopathology. Moreover, type I interferons acted directly on the cytotoxic T cell response. Treatment with interferon 3 lead to increased T cell function. This resulted in induction of autoimmune diabetes in transgenic mice. In conclusion, the nature of the innate immune response triggers the development of chronic virus infection. These results uncover new mechanisms that might provide the foundation for new therapeutic approaches for patients with chronic infections.

Systemic lupus erythematosus (SLE) is an autoimmune disorder that is characterized by the production of antibodies directed against self-antigens, such as nuclear components. Genetic analyses of lupus patients have consistently demonstrated a complex genetic basis for disease susceptibility that involves multiple genes. Identifying genes and pathways that promote disease genesis has been aided by murine studies. In particular, congenic mouse studies that examine the role of chromosomal intervals from inbred lupus-prone mouse strains on a non-autoimmune background have been useful in dissecting the genetic contribution of novel susceptibility loci in lupus pathogenesis. In this thesis, the role of New Zealand Black (NZB) chromosomes 4 and 13 are examined in non-lupus prone C57BL/6 (B6) congenic mouse strains, denoted B6.NZBc4 and B6.NZBc13, respectively. Although repeatedly mapped to contain disease augmenting alleles,NZBc4 alone was not sufficient to initiate disease, despite an expansion of NKT and B1a cells–both with controversial pathogenic roles in lupus. Instead, by crossing the B6.NZBc4 mouse with another congenic mouse strain that develops fatal lupus autoimmunity, NZBc4 was unexpectedly found to contain a suppressor locus; disease suppression was mediated by a shift away from pathogenic immunoglobulin isotypes and associated with changes in the NKT and B1a cell compartments. In contrast to the NZBc4 locus, the NZBc13 locus is sufficient to initiate polyclonal B cell activation, ANA production and mild GN, similar to NZB mice. A B cell intrinsic defect was found to be responsible for initiating the abnormal cellular phenotype in B6.NZBc13 mice. Functional analyses of the B cell subset in B6.NZBc13 mice revealed normal BCR-signaling responses and tolerance mechanisms; however, they were hyper-responsive to TLR3 stimulation, resulting in increased survival and proliferation. Thus, the study of these NZB congenic mouse strains has been instrumental in confirming the presence of loci on NZB chromosomes 4 and 13 that modulate the development of disease and highlights that disease onset is mediated by a balance of both susceptibility and suppressor alleles. Collectively, these findings contribute to the current field of lupus immunogenetics and confirm the power of congenic mouse models in understanding the genetic basis of SLE.