Graduation date: 1998

Lisbon, ca. 2004--Basiert auf Diss. von D.L. Milutinović, 2004.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 113-136). Also available in print.

Thesis (Ph. D.)--University of Chicago, Committee on immunology, August 2003. / Includes bibliographical references. Also available on the Internet.

The causative agent of AIDS (acquired immune deficiency syndrome), HIV (human immunodeficiency virus), is one of the most extensively studied pathogens in modern history. The virus has multiple mechanisms of persisting in the host including evading host immune response. Since HIV-1 depends heavily on the host machinery for various aspects of its life cycle, unraveling the complex interplay between the host and HIV-1 could provide new clues to therapeutic avenues. In T cells, HIV assembles and subsequently buds through the plasma membrane incorporating host derived proteins and lipids in the viral envelope. HIV is thought to utilize a pre-existing mechanism for the budding of normal cellular vesicles called microvesicles to exit host cells. The evidence for this theory comes from reports of similarities between HIV and microvesicles observed for a small subset of proteins and lipids, leading to controversies about its validity. To further test this hypothesis, we utilized lectin microarrays to obtain a comprehensive glycomic profile of HIV and microvesicles derived from a panel of T cell lines. Glycosylation is critical to protein sorting and has a crucial role in HIV-1 biology, making it an ideal marker to compare the particles and the host cell membrane. We observed similar glycomic profiles for HIV-1 and microvesicles strongly suggesting an analogous mode of egress. Glycosylation of both particles seems to vary based on the parent cell line, providing additional evidence for this hypothesis. Microvesicles are involved in immune response modulation; hence the incorporation of microvesicular proteins could influence interactions of HIV with the immune system. The differences in glycosylation between these two particles could be potentially explained by the heavily glycosylated viral envelope glycoprotein. I also demonstrated that these vesicles bud from particular glycan enriched domains of the plasma membrane. Additionally, this work sheds light on the potential mode of interaction between galectin, an immune lectin and HIV-1. This work strongly argues for a conserved mechanism of exocytosis for both particles and sets the stage for examining the role of glycosylation in trafficking of proteins to the sites of microvesicular and viral budding. / text

The outbreaks of human influenza caused by highly pathogenic avian influenza H5N1 virus have attracted a lot of attention and public concern. Effective and universal vaccines may be the best means for prevention and control of the influenza. Taking into account that viral clearance and recovery from influenza A virus infection have been demonstrated to be correlated to specific cytoxic T lymphocyte (CTL) instead of neutralizing antibodies, it is important to develop effective vaccines which are capable of inducing not only neutralizing antibody but also CTL responses. Furthermore, T cell epitopes are usually more conserved than neutralizing epitopes. However, rare information concerning human T cell epitopes specific to H5N1 virus has been reported so far. This study was designed to test our hypothesis that novel and potent human CTL and Th epitopes specific to NP protein of H5N1 virus may be identified in vaccinated and/or infected HLA-A2/DR1 transgenic mice (SURE/L1), while protective epitopes may be further defined from the identified T cell epitopes in the mice challenged with lethal dose of the virus. We used SURE/L1 mouse model because it contains HLA-A2 (*0201) and -DR1 (*0701), both are the second highest frequency of HLA class I and II in Chinese. Since the NP gene is relatively conserved among different clades or strains of H5N1 virus, we selected viral protein NP as the target. Furthermore, we screened the T cell epitopes in splenocytes not only from vaccinated mice but also from survived mice infected with gradually increased dose of H5N1 virus, because the T cell epitopes identified in both vaccinated and infected mice or in infected mice alone might have higher potential to be protective epitopes. In this study, a novel HLA-DR1 (class II) restricted T cell epitope NP368-382, NPII-7, was identified in both vaccinated and infected mice. Two doses of NPII-7 peptide boosting in the mice induced very strong Th1 and CTL responses but no NP specific antibody responses. The vaccination of additional 2 doses of NPII-7 also provided partial protection against lethal challenge of H5N1 virus in the mice, whereas NP DNA vaccination alone did not show any protective effect. The protective effect may be attributed to the strong Th1 and CTL responses induced by the NPII-7 vaccination, because both NP DNA and NPII-7 vaccinations could not induce neutralizing antibody response. Notably, a HLA class II restricted peptide, NPII-7, may induce not only Th1 responses but also more strong HLA class I restricted T cell (CTL) responses. It may probably due to that the HLA-DR1 restricted T cell epitope (NENMEAMDSNTLELR) contained the full sequence of a reported HLA-A2 restricted CTL epitope (AMDSNTLEL), named NP-17 in this study. Although it needs to be further defined whether this novel epitope is really a HLA-DR1 restricted T cell epitope, or it shares the activity of HLA-A2 restricted T cell epitope, or it is just an alternate HLA-A2 restricted T cell epitope, this study has identified a novel T cell epitope and proved that it is a protective T cell epitope. / published_or_final_version / Microbiology / Master / Master of Philosophy

Cordyceps cicadae, a parasitic fungus, has been used as a traditional Chinese herb for treatment of illnesses related to immune dysfunction. However, mechanistic actions are not entirely clear. The specific aim of the present study is to investigate the immunological mechanisms of C. cicadae on human T lymphocytes in vitro. The two main objectives carried out in the present study in order to achieve the aim are: i. to investigate the immunological effects of the water extract of C.cicadae on human resting and proliferating T lymphocytes; 2. to investigate the adjuvant property of C.cicadae with the immunosuppressant Cyclosporin A (CsA) on the control of human T cells proliferation, cell death and cytokines secretion. C. cicadae has demonstrated a dual effect of enhancing the activity of resting Tlymphocytes and inhibiting that of PHA-stimulated cells. In resting T cells, C. cicadae increased cell activity, cytokines secretion, expression of IL-2α receptor (CD25) and the population of Th17 as well as Treg cells without affecting the cell cycle progression. In the viability and cell death test, C. cicadae has been found not to exert toxicity on T cells. These results reveal the role of C. cicadae as an invigorant to improve the immunity as a whole in healthy individuals. In PHA-stimulated proliferating T-lymphocytes, C. cicadae inhibited the cell proliferation by arresting them at G0/G1 phase and decreasing both S and G2/M phase cell populations. The inhibitory effect was not through the induction of cell death as both PHA- and CsA-induced cell apoptosis and necrosis were reduced by C. cicadae treatment. It was believed that C. cicadae affects the progression of inflammatory responses by selectively suppressing the secretion of Th1 cytokines and enhancing that of Th2 cytokines, but it seemed unable to influence the CD25 expression in PHA- and CsA-treated T cells. An increased population of Treg cells by C. cicadae was also observed in PHA-stimulated T cells. C. cicadae adjuvant to CsA showed greater inhibition of cell proliferation and Th1 cytokines production. However, C. cicadae antagonized the effect of CsA in the secretion of IL-10, a Th2 and Treg cytokine. These results suggest a potential role of C. cicadae as an adjuvantive agent with CsA in the therapy of autoimmune diseases and organ transplantation. Furthermore, C. cicadae demonstrated superior immunomodulatory properties over CsA as it can act selectively between resting and proliferating T cells, and also protect them from apoptosis and necrosis, alleviating the toxic effect caused by CsA. In summary, this study showed the potential of C. cicadae as an immunomodulator from which both healthy individuals and inflammatory disease patients can benefit. / published_or_final_version / Biological Sciences / Master / Master of Philosophy

Hepatocellular carcinoma (HCC) is the sixth most common cancer and the second leading cause of cancer-related deaths in the world. It is a disease with poor prognosis with unsatisfactory long-term survival of patients, and thus new strategies to control this disease are warranted. T helper (Th) 17 cells and IL-17 have recently been detected with increased frequency in a number of tumors including HCC. Its role in tumor remains controversial but its presence in HCC has been linked to disease progression, possibly involving angiogenesis. Th17 cells could be homed to inflammatory sites such as tumor microenvironment via CCR6/CCL20 axis and expand locally, and studies from other inflammatory diseases such as autoimmune disease has shown that the gut is the potential source of Th17, where its induction is affected by signals from gut microbiota. Yet this link is not yet shown in extra-intestinal tumors. Probiotics are living microorganisms, which when administered in adequate amounts confer a health benefit on the host. They have been reported to relieve chronic inflammatory diseases in animal and in human intervention studies. It is believed that probiotics regulate signals to gut antigen-presenting cells, which act as the pivot in modulating the systemic immune responses and inactivated bacteria also exhibited immunomodulatory effects in this regard. Accordingly, it was hypothesized that oral feeding of probiotics to HCCbearing animals may affect Th17 polarization and distribution and thereby modulate tumor microenvironment, which may have beneficial effect in tumor development, possibly via affecting angiogenesis. To address this hypothesis, wild-type C57BL/6 mice were fed with different heat-inactivated or viable probiotics– Lactobacillus rhamnosus GG (LGG), Escherichia coli Nissle 1917 (EcN), VSL#3 or mixture of probiotics − Prohep (heat-inactivated LGG, heatinactivated VSL#3 and viable EcN) either one week in advance or at the time of subcutaneous tumor inoculation. Probiotic feeding had improved survival in tumor-bearing mice, slowed down tumor growth and reduced tumor burden when monitored for 38 days. Probiotics showed better efficacy when feeding was given in advance. The anti-tumor effect was related to reduced angiogenesis and reduced IL-17 serum and gene expression within tumor. The mechanistic link between IL-17 modulation and tumor development was further studied in animals by IL-17 neutralization. The anti-tumor efficacy of probiotics, in relation to tumor growth and angiogenesis, was lost after IL-17 neutralization, which was linked to recruitment of myeloid suppressor cells. Since cells from both adaptive and innate immune systems could secrete IL-17, the source of IL-17 production was then identified, and found that Th17 was the major IL-17 secretor being modulated by probiotic feeding. Reduced homing of Th17 to tumor via circulation, with a tendency being recruited from gut was observed. Probiotics-mediated Th17 cell modulation in the gut by inducing the skewing of IL-10 secreting type1 regulatory T cells via dendritic cells may link to limited IL-17 mediated angiogenesis in the tumor microenvironment. With better understanding of the immunomodulation properties of probiotics, prophylactic or therapeutic efficacy in management of other inflammation-associated cancer can be availed. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

Diseases caused by fungi are increasing worldwide and are often associated with high mortality rates. In particular, the normally harmless commensal Candida albicans can cause serious disease if immunological and physiological barriers are perturbed, leading to systemic infection, which is fatal in up to 45% of cases. The adaptive immune response is believed to be important in protection against systemic candidiasis, however, the roles of different helper T (Th) cell subsets, particularly Foxp3+ regulatory T (Treg) cells, remain largely unexplored. The aims of this study were to adapt a mouse model of systemic C. albicans infection to test whether the numbers of Th1, Th2, Th17 and Foxp3+ Treg cells increase in mice with systemic C. albicans infection, and determine their contribution to disease. C. albicans drove the expansion of Th1, Th2 and Th17 cells, as well as multiple Foxp3+ populations that displayed characteristics of natural Treg, induced Treg, Th17 and Th1 cells in vitro and in vivo. The expanded Foxp3+ T cells inhibited Th1 and Th2, but promoted Th17, responses to C. albicans antigens in vitro and exacerbated disease, since their depletion in vivo reduced kidney fungal burden and inflammatory lesions. Furthermore, systemic infection with a weakly virulent C. albicans strain was associated with reduced Treg responses compared to those induced during lethal systemic infection. These data lead to a model for systemic candidiasis whereby Treg expansion promotes Th17 responses that drive pathology, and have implications for future immunotherapy.

The extensive infiltration of immune cells in the joints of patients affected by rheumatoid arthritis (RA), and the subsequent production of pro-inflammatory cytokines triggers bone erosion through the extensive stimulation of bone resorbing osteoclasts (OCs). The activity of γδ T cells has been implicated to influence the onset and severity of the disease pathology in murine models of human RA. With this study the effects of γδ T cells for influencing OC differentiation and resorptive activity were assessed in vitro. Activated γδ T cells exerted inhibitory effects on OC differentiation and resorptive activity, these effects were mediated by the release of soluble factors, since similar inhibitory effects were obtained using conditioned medium (CM) from activated γδ T cells. The primary mediator of such effects was determined to be IFN, since neutralisation markedly restored OC differentiation and resorptive activity. γδ T cell proliferation, activation and survival following culture with autologous mature OCs were assessed by flow cytometry. Interestingly, OCs and OC-derived CM induced activation of γδ T cells as determined by the expression of the early activation marker CD69. A mediator of this stimulatory effect on T cells was found to be TNF, since neutralisation of TNFα decreased the stimulatory effect of OCs on CD69 expression. Consistently, OCs, but not OC-derived CM, increased the proliferation of IL-2-stimulated γδ T cells and also supported the survival of resting γδ T cells. This study provides new insights into the in vitro interactions between human γδ T cells and OCs, moreover it defines osteoclasts as immune competent cells capable of influencing the activation status and the viability of T lymphocytes, and provide evidence for a novel stimulatory effect of OCs on γδ T cells.