Modulation of invariant NKT cell activity by cytokines and receptors in human disease

Invariant natural killer T (NKT) cells are innate-like lymphocytes with both immunoregulatory and cytotoxic functions that play a role as activators and regulators of the immune response in many diseases. NKT cells are believed to bridge the innate and adaptive immune systems by rapidly producing large quantities of cytokines after recognition of CD1d-presented lipid antigens. NKT cells can be divided into two phenotypically and functionally distinct subsets based on the expression of CD4. How the NKT cells and their subsets are regulated, and how they integrate signals from their environment to modulate immune responses is still not fully understood. In this thesis I have investigated how the activity of NKT cells can be modulated by factors other than the TCR, such as cell surface receptors and cytokines. These investigations have been based on blood samples from healthy controls, and from patients suffering from HIV-1 infection or atopic eczema (AE). We have found that CD4- NKT cells are able to degranulate and kill target cells in an NKG2D-dependent but TCR-independent manner in response to NKG2D stimulus. Moreover, we have shown that NKG2D+ NKT cells frequently express perforin that polarizes toward NKG2D-ligand expressing tumor cells. These data demonstrate that the CD4- subset of human NKT cells can mediate direct lysis of CD1d-negative target cells upon NKG2D engagement. We have further characterized the phenotype and function of NKT cells in patients with chronic diseases. In patients with chronic HIV- 1 infection, the CD4- NKT cell subset showed increased expression of the inhibitory programmed death-1 (PD-1) receptor, and displayed severe functional defects. However, the functional impairment was not caused by PD-1 expression per se because the defect could not be reversed by PD-1 blockade. In addition, we have studied the effect of interleukin-2 (IL-2) on NKT cells and natural killer (NK) cells in patients with chronic HIV-1 infection. Material for this study was obtained from a longitudinally study, where administration of IL-2 was added to the antiretroviral treatment (ART) for one year. We found that NKT cells and NK cells responded with different kinetics and in different ways to the IL-2 administration. The NKT cells responded with a gradual numerical increase, but with no significant functional changes. NK cells responded rapidly with an expansion of the cytotoxic CD56dim NK cell subset and increased IFN-γ production. However, the effects of IL-2 on these cells were generally not sustained post treatment. NKT cells were also studied in the chronic inflammatory skin disease AE where the patients have elevated levels of plasma IL-18. Our data provide evidence that IL-18 is a potent activator of human NKT cells promoting an acute pro-inflammatory CD1d-dependent response, even in the absence of exogenous lipid antigens. Interestingly, chronic exposure of NKT cells to IL-18 is inhibitory and skews the NKT cell pool by selectively suppressing the proliferation of CD4+ NKT cells. Importantly, our in vitro data are reflected in AE patients where reduced numbers of CD4+ NKT cells are associated with elevated levels of IL-18 and disease severity. In conclusion, the work presented here contributes to our understanding of the function and role of NKT cells in human diseases including infections and allergie

Evolution of DC-SIGN use revealed by fitness studies of R5 HIV-1 variants emerging during AIDS progression

<p>Abstract</p> <p>Background</p> <p>At early stages of infection CCR5 is the predominant HIV-1 coreceptor, but in approximately 50% of those infected CXCR4-using viruses emerge with disease progression. This coreceptor switch is correlated with an accelerated progression. However, those that maintain virus exclusively restricted to CCR5 (R5) also develop AIDS. We have previously reported that R5 variants in these "non-switch virus" patients evolve during disease progression towards a more replicative phenotype exhibiting altered CCR5 coreceptor interactions. DC-SIGN is a C-type lectin expressed by dendritic cells that HIV-1 may bind and utilize for enhanced infection of T cells in <it>trans</it>. To further explore the evolution of the R5 phenotype we analyzed sequential R5 isolates obtained before and after AIDS onset, i.e. at the chronic stage and during end-stage disease, with regard to efficiency of DC-SIGN use in <it>trans</it>-infections.</p> <p>Results</p> <p>Results from binding and <it>trans</it>-infection assays showed that R5 viruses emerging during end-stage AIDS disease displayed reduced ability to use DC-SIGN. To better understand viral determinants underlying altered DC-SIGN usage by R5 viruses, we cloned and sequenced the HIV-1 <it>env </it>gene. We found that end-stage R5 viruses lacked potential N-linked glycosylation sites (PNGS) in the gp120 V2 and V4 regions, which were present in the majority of the chronic stage R5 variants. One of these sites, amino acid position 160 (aa160) in the V2 region, also correlated with efficient use of DC-SIGN for binding and <it>trans</it>-infections. In fitness assays, where head-to-head competitions between chronic stage and AIDS R5 viruses were setup in parallel direct and DC-SIGN-mediated infections, results were further supported. Competitions revealed that R5 viruses obtained before AIDS onset, containing the V2 PNGS at aa160, were selected for in the <it>trans</it>-infection. Whereas, in agreement with our previous studies, the opposite was seen in direct target cell infections where end-stage viruses out-competed the chronic stage viruses.</p> <p>Conclusion</p> <p>Results of our study suggest R5 virus variants with diverse fitness for direct and DC-SIGN-mediated <it>trans</it>-infections evolve within infected individuals at end-stage disease. In addition, our results point to the importance of a glycosylation site within the gp120 V2 region for efficient DC-SIGN use of HIV-1 R5 viruses.</p

Lower cytokine secretion ex vivo by natural killer T cells in HIV-infected individuals is associated with higher CD161 expression

Objective: Natural killer T (NKT) cells are efficiently targeted by HIV and severely reduced in numbers in the circulation of infected individuals. the functional capacity of the remaining NKT cells in HIV-infected individuals is poorly characterized. This study measured NKT cell cytokine production directly ex vivo and compared these responses with both the disease status and NKT subset distribution of individual patients.Methods: NKT cell frequencies, subsets, and ex-vivo effector functions were measured in the peripheral blood mononuclear cells of HIV-infected patients and healthy controls by flow cytometry. We measured cytokines from NKT cells after stimulation with either a-galactosyl ceramide-loaded CD1d dimers (DimerX-alpha GalCer) or phorbol myristate acetate and ionomycin.Results: the frequencies of NKT cells secreting interferon-gamma and tumor necrosis factor-alpha were significantly lower in HIV-infected patients than healthy controls after DimerX-alpha GalCer treatment, but responses were similar after treatment with phorbol myristate acetate and ionomycin. the magnitude of the interferon-gamma response to DimerX-alpha GalCer correlated inversely with the number of years of infection. Both interferon-gamma and tumor necrosis factor-alpha production in response to DimerX-alpha GalCer correlated inversely with CD161 expression.Conclusion: the ex-vivo Th1 responses of circulating NKT cells to CD1d-glycolipid complexes are impaired in HIV-infected patients. NKT cell functions may be progressively lost over time in HIV infection, and CD161 is implicated in the regulation of NKT cell responsiveness. (C) 2009 Wolters Kluwer Health vertical bar Lippincott Williams & WilkinsNIAIDBrazilian Program for STD and AIDSMinistry of HealthSão Paulo City Health DepartmenFundacao de Arnparo a Pesquisa do Estado de São PauloJohn E. Fogarty International CenterAIDS Research Institute of the AIDS Biology ProgramCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Brazilian Ministry of EducationUniv Calif San Francisco, Div Expt Med, Dept Med, San Francisco, CA 94110 USAUniversidade Federal de São Paulo, São Paulo, BrazilUniv São Paulo, São Paulo, BrazilKarolinska Univ Hosp, CIM, Dept Med, Karolinska Inst, Stockholm, SwedenSan Francisco Gen Hosp, Posit Hlth Program, San Francisco, CA 94110 USAAlbert Einstein Coll Med, Jacobi Med Ctr, Bronx, NY 10467 USAUniversidade Federal de São Paulo, São Paulo, BrazilNIAID: R37-A152731Ministry of Health: 914/BRA/3014 - UNESCO/KallasSão Paulo City Health Departmen: 20040.168.922-7/KallasFundacao de Arnparo a Pesquisa do Estado de São Paulo: 04/15856-9/KallasJohn E. Fogarty International Center: D43 TW00003Web of Scienc