Lysis of CD4+ T cells expressing HIV-1 gag peptides by gag-specific CD8+ cytotoxic T cells

The vast majority of in vitro experiments testing the cytotoxic T lymphocytes (CTL) activity in HIV infection has been performed with target cells consisting of autologous EBV-transformed B lymphoblastoid cell lines (B-LCLs) expressing Human immunodeficiency virus type I (HIV-1) proteins. However data concerning the lysis of primary CD4+ T lymphocytes expressing HIV-1 antigens by CTLs is still lacking. To study the CTL activity against such primary targets, we used a system involving PBMCs of an HIV+ asymptomatic patient (PT) as effector cells and the CD4+ lymphocytes or B-LCLs of his healthy HLA-identical twin brother (HTW) as target cells. These syngeneic targets were either infected with recombinant vaccinia virus containing HIV-1 gag gene (gag-vac), or coated with HIV-1 gag peptides. We demonstrate in this study that PT CTLs (which were CD3+, CD4-, CD8+, TCRalphabeta+, TCRgammadelta-, CD56-) specifically lysed both types of syngeneic target cells expressing gag-vac; however, CD4+ T cells expressing HIV gag proteins were lysed less efficiently than B-LCLs expressing the same HIV epitopes. On the other hand, no specific lysis was detected when the target cells were uninfected or infected by wild-type vaccinia virus.     

Lack of infection in HIV-exposed individuals is associated with a strong CD8(+) cell noncytotoxic anti-HIV response

Individuals repeatedly exposed to HIV, but who remain uninfected, form a population enriched for persons likely to have either natural or acquired resistance to the virus. We have studied four such exposed uninfected cohorts, representing 60 individuals, for evidence of protective immunity. This population included participants exposed to HIV through anal or vaginal receptive intercourse on multiple occasions over many years. We observed CD8(+)-cell noncytotoxic inhibition of HIV replication in acutely infected CD4(+) cells in the vast majority of individuals most recently exposed to the virus (within 1 year). The levels of this CD8(+)-cell response were sufficient to inhibit the in vitro infection of the exposed subjects' peripheral blood mononuclear cells. We found no evidence of a significant role for CCR5 Delta32 mutation in this population, nor did CD4(+) cell susceptibility to infection or HIV-specific cytotoxic T-lymphocytes correlate with resistance to infection in the individuals tested. Therefore, the observed strong noncytotoxic CD8(+)-cell anti-HIV responses may be an antiviral immune activity contributing to the apparent protection from infection in these exposed uninfected individuals.     

Primary CD8+ cells from HIV-infected individuals can suppress productive infection of macrophages independent of beta-chemokines

The productive infection of human monocyte-derived macrophages (Mphi) by HIV was suppressed by primary CD8+ cells from asymptomatic HIV-infected individuals. This anti-HIV response was noncytotoxic; removal of the CD8+ cells from the infected Mphi leads to virus production. CD8+ cells inhibited HIV replication when separated from the infected Mphi by a transwell filter insert, indicating a diffusible factor made by the CD8+ cells suppressed productive infection of Mphi. Three beta-chemokines, which can be secreted by activated CD8+ cells, RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein (MIP)-1alpha and MIP-1beta prevented HIV replication in the Mphi cultures. In addition, incubation of acutely infected Mphi with a mixture of neutralizing antibodies to RANTES, MIP-1alpha, and MIP-1beta enhanced virus replication. Nevertheless, neutralization of beta-chemokines with specific antibodies did not abolish the suppression by CD8+ cells of HIV replication in Mphi. Thus, even though beta-chemokines decrease HIV replication in Mphi, these cytokines are not responsible for the ability of CD8+ cells to inhibit HIV production in these cells.     

Critical role for CD4(+) T cells in controlling retrovirus replication and spread in persistently infected mice

Reactivations of persistent viral infections pose a significant medical problem in immunocompromised cancer, transplant, and AIDS patients, yet little is known about how persistent viral infections are immunologically controlled. Here we describe a mouse model for investigating the role of the immune response in controlling a persistent retroviral infection. We demonstrate that, following recovery from acute Friend virus infection, a small number of B cells evade immunological destruction and harbor persistent virus. In vivo depletions of T-cell subsets in persistently infected mice revealed a critical role for CD4(+) T cells in controlling virus replication, spread to the erythroid lineage, and induction of erythroleukemia. The CD4(+) T-cell effect was independent of CD8(+) T cells and in some cases was also independent of virus-neutralizing antibody responses. Thus, the CD4(+) T cells may have had a direct antiviral effect. These results may have relevance for human immunodeficiency virus (HIV) infections where loss of CD4(+) T cells is associated with an increase in HIV replication, reactivation of persistent viruses, and a high incidence of virus-associated cancers.     

Viral immune evasion due to persistence of activated T cells without effector function

We examined the regulation of virus-specific CD8 T cell responses during chronic lymphocytic choriomeningitis virus (LCMV) infection of mice. Our study shows that within the same persistently infected host, different mechanisms can operate to silence antiviral T cell responses; CD8 T cells specific to one dominant viral epitope were deleted, whereas CD8 T cells responding to another dominant epitope persisted indefinitely. These virus-specific CD8 T cells expressed activation markers (CD69(hi), CD44(hi), CD62Llo) and proliferated in vivo but were unable to elaborate any antiviral effector functions. This unresponsive phenotype was more pronounced under conditions of CD4 T cell deficiency, highlighting the importance of CD8- CD4 T cell collaboration in controlling persistent infections. Importantly, in the presence of CD4 T cell help, adequate CD8 effector activity was maintained and the chronic viral infection eventually resolved. The persistence of activated virus-specific CD8 T cells without effector function reveals a novel mechanism for silencing antiviral immune responses and also offers new possibilities for enhancing CD8 T cell immunity in chronically infected hosts.     

Expression of class II, but not class I, major histocompatibility complex molecules is required for granuloma formation in infection with Schistosoma mansoni

Previous studies have suggested that granulomatous inflammation in schistosomiasis is mediated by CD4+ T helper lymphocytes sensitized to parasite egg antigens. However, CD8+ T cells have also frequently been associated with the immune response to schistosome eggs. To examine more precisely the role of CD4+ and CD8+ T cells in the pathology of the schistosomal infection, we used mice with targeted mutations in major histocompatibility complex (MHC) class II or class I molecules. These mutations lead, respectively, to the virtual absence of CD4+ and CD8+ T cells. The results clearly show that schistosome-infected MHC class II mutant mice failed to form granulomas around parasite eggs. In contrast, infected MHC class I mutant mice displayed characteristic granulomatous lesions that were comparable to those in wild-type control mice. Moreover, lymphoid cells from MHC class II mutant mice were unable to react to egg antigens with either proliferative or cytokine [interferon-gamma, interleukin (IL)-4, IL-10] responses; nor were they able to present egg antigens to specifically sensitized CD4+ T helper cells from infected syngeneic control mice. By comparison, cells from MHC class I mutant mice exercised all these functions in a manner comparable with those from wild-type controls. These observations clearly demonstrate that schistosomal egg granulomas are mediated by MHC class II-restricted CD4+ T helper cells. They also suggest that CD8+ T cells do not become sensitized to egg antigens and play little role, if any, in the pathogenesis of schistosomiasis.     

Alloantigen-stimulated anti-HIV activity

A number of studies have suggested that an immune response to human leukocyte antigen (HLA) alloantigens may contribute to protection against HIV infection. In the present study, we examined the effect of alloantigen-stimulated cell lines obtained from peripheral blood mononuclear cells (PBMC) of HIV-uninfected (HIV-) individuals and the soluble factors produced by these cell lines on HIV-1 replication. Multiple in vitro restimulation with irradiated allogeneic PBMC from HIV- donors resulted in the expansion of CD8(+) T-cell lines that inhibited HIV-1 replication when cocultured with either autologous or heterologous in vitro-infected phytohemagglutinin (PHA) blasts. Supernatants from the alloantigen-stimulated cell lines also inhibited HIV replication in both PHA blasts and a chronically infected cell line. The alloantigen-stimulated cell lines and the factors they produced inhibited both T-cell-tropic (T) and macrophage-tropic (M) isolates of HIV-1. Blocking experiments using anti-chemokine antibodies suggested that this inhibition of HIV replication was not due to the beta-chemokines present in cocultures of cell lines with HIV-infected blasts. These results indicate that alloantigen-stimulation of PBMC from HIV- individuals activates CD8(+) T cells that produce soluble factor(s) that inhibit HIV replication of a wide spectrum of HIV-1 isolates through a chemokine-independent mechanism. This is a US government work. There are no restrictions on its use.     

Dual role of dendritic cells in the induction and down-regulation of antigen-specific cutaneous inflammation

We have previously reported that contact sensitivity (CS) to dinitrofluorobenzene (DNFB) in C57BL/6 mice was mediated by MHC class I-restricted CD8+ T cells and down-regulated by MHC class II-restricted CD4+ T cells. In this study, we analyzed the contribution of dendritic cells (DC) in the induction of these two T cell subsets endowed with opposite functions. Hapten-pulsed skin- and bone marrow-derived DC, obtained from either normal C57BL/6 mice or from MHC class II (I+ II-) and MHC class I (I- II+)-deficient mice, were tested for their ability to prime normal mice for CS to dinitrofluorobenzene. Expression of MHC class I molecules by transferred DC was mandatory both for the induction of CS and for the generation of hapten-specific CD8+ T cells in lymphoid organs. I+ II- DC were as potent as I+ II+ DC in priming for CS, demonstrating that activation of effector CD8+ T cells can occur independently of CD4+ T cell help. I- II+ DC could not immunize for CS, although they could sensitize for a delayed-type hypersensitivity reaction to protein Ags. Moreover, I- II+ DC injected simultaneously with cutaneous sensitization down-regulated the inflammatory response, suggesting that hapten presentation by MHC class II molecules could prime regulatory CD4+ T cells. These results indicate that DC can present haptenated peptides by both MHC class I and class II molecules and activate Ag-specific CD8+ effector and CD4+ regulatory T cell subsets, concurrently and independently.     

Liver damage preferentially results from CD8(+) T cells triggered by high affinity peptide antigens

Little is understood of the anatomical fate of activated T lymphocytes and the consequences they have on the tissues into which they migrate. Previous work has suggested that damaged lymphocytes migrate to the liver. This study compares class I versus class II major histocompatibility complex (MHC)-restricted ovalbumin-specific T cell antigen receptor (TCR) transgenic mice to demonstrate that after in vivo activation with antigen the emergence of CD4(-)CD8(-)B220(+) T cells occurs more frequently from a CD8(+) precursor than from CD4(+) T cells. Furthermore, this change in phenotype is conferred only by the high affinity native peptide antigen and not by lower affinity peptide variants. After activation of CD8(+) cells with only the high affinity peptide, there is also a dramatically increased number of liver lymphocytes with accompanying extensive hepatocyte damage and elevation of serum aspartate transaminase. This was not observed in mice bearing a class II MHC-restricted TCR. The findings show that CD4(-)CD8(-)B220(+) T cells preferentially derive from a CD8(+) precursor after a high intensity TCR signal. After activation, T cells can migrate to the liver and induce hepatocyte damage, and thereby serve as a model of autoimmune hepatitis.     

The theory and practice of health education applied to nursing: a bi-polar approach

Because CD1-restricted T cells lack CD4 but produce IFN-gamma in response to nonpeptide mycobacterial antigens, they could play a unique role in immunity to tuberculosis. We studied CD1-restricted T cells in the context of HIV infection by expanding CD4(-) T cell lines from 10 HIV-infected patients. Upon stimulation with Mycobacterium tuberculosis antigen or upon exposure to macrophages infected with M. tuberculosis, these T cell lines proliferated, produced IFN-gamma, and showed cytolytic T cell (CTL) activity against macrophages pulsed with mycobacterial antigen, findings consistent with a protective role against M. tuberculosis. Anti-CD1b antibodies abrogated T cell proliferation, IFN-gamma production, and CTL activity, demonstrating that these T cells are CD1 restricted. IFN-gamma production in response to M. tuberculosis was enhanced by antitransforming growth factor-beta in 8/10 lines, and by IL-15 in 2/10 lines. IFN-gamma production was augmented in a nonantigen-specific manner by IL-12 in 4/8 lines. When live HIV was cocultured with CD1-restricted T cell lines, p24 antigen and proviral DNA were not detected, indicating that the T cells were not infectable with HIV. Vaccination strategies aimed at activation and expansion of M. tuberculosis-reactive CD1-restricted T cells in HIV-infected patients may constitute a novel means to provide protection against tuberculosis, while minimizing the risk of enhancing HIV replication through stimulation of CD4(+) cells.     

CD40 ligand is pivotal to efficient control of virus replication in mice infected with lymphocytic choriomeningitis virus

CD40 ligand (CD40L) is an important molecule that is known to be involved in T-B collaboration and certain aspects of cell-mediated immunity. However, its role in antiviral immunity has not been clearly defined as of yet. Therefore, mice with a targeted defect in the gene encoding this molecule were infected with one of two strains of lymphocytic choriomeningitis virus differing markedly in their capacity to spread in the host. Infection with lymphocytic choriomeningitis virus is initially controlled primarily by CD8+ effector cells, whereas long-term immune surveillance also depends upon CD4+ cells and B cells. Our results reveal that the primary activation, clonal expansion, and differentiation of CD8+ T cells does not require expression of CD40L. However, lack of expression results in rapid impairment of CTL responsiveness and failure to permanently control virus replication. This happens not only in mice infected with the rapidly spreading virus strain but also at a late stage in mice infected with the strain of more limited potential for spreading. In the latter mice, virus replication is initially controlled very efficiently, but high levels of virus can be detected in the blood and internal organs approximately 6 mo after virus inoculation. Since the impairment of immune function seems to be more pronounced in CD40L-deficient mice than in mice lacking either CD4+ cells or B cells, these results indicate that CD40L is pivotal to sustain efficient antiviral immune surveillance, including CD8+ T cells, and suggest that CD40L is critically involved in cellular interactions in addition to T-B cooperation.     

The central role of CD4(+) T cells in the antitumor immune response

The induction of optimal systemic antitumor immunity involves the priming of both CD4(+) and CD8(+) T cells specific for tumor-associated antigens. The role of CD4(+) T helper cells (Th) in this response has been largely attributed to providing regulatory signals required for the priming of major histocompatibility complex class I restricted CD8(+) cytolytic T lymphocytes, which are thought to serve as the dominant effector cell mediating tumor killing. However, analysis of the effector phase of tumor rejection induced by vaccination with irradiated tumor cells transduced to secrete granulocyte/macrophage colony-stimulating factor indicates a far broader role for CD4(+) T cells in orchestrating the host response to tumor. This form of immunization leads to the simultaneous induction of Th1 and Th2 responses, both of which are required for maximal systemic antitumor immunity. Cytokines produced by these CD4(+) T cells activate eosinophils as well as macrophages that produce both superoxide and nitric oxide. Both of these cell types then collaborate within the site of tumor challenge to cause its destruction.     

Detection of Borrelia burgdorferi-specific CD8+ cytotoxic T cells in patients with Lyme arthritis

T cells are believed to play an important role in the pathogenesis of Lyme arthritis (LA), an inflammatory joint disease caused by the spirochete Borrelia burgdorferi (Bb). The presence or absence of certain Bb-specific CD4+ T helper cells has been associated with prognosis. Since recent observations suggested the activation of CD8+ T cells during infection with Bb, we searched for CD8+ cytotoxic T lymphocytes in patients with LA. CD8+ T cell lines were generated from peripheral blood and synovial fluid of five patients with LA. In addition, CD8+ T cells were expanded by Ag-specific stimulation in bulk cultures. A cytotoxicity assay was established using target cells infected with recombinant vaccinia viruses expressing the borrelial proteins outer surface protein (Osp) A, OspB, or flagellin. We found Bb-specific CTL lines derived from the peripheral blood of three patients with LA with specificity for flagellin, OspA, and OspB. All Bb-specific CTL lines were CD3+, CD8+, and TCRalphabeta, and cytotoxic activity was HLA class I restricted. Moreover, CD8+ T cells expanded by Ag-specific stimulation in vitro demonstrated Bb-specific and HLA class I-restricted lysis toward individual borrelial proteins. Interestingly, Bb-specific lytic activity was only detected in patient samples obtained after the disappearance of arthritis. We report the detection of Bb-specific cytotoxic CD8+ T cells in patients with LA. The induction of specific CD8+ T cells may play an important role in disease control and may have important bearings for the development of effective vaccines against Lyme borreliosis.     

Antagonist peptide selects thymocytes expressing a class II major histocompatibility complex-restricted T cell receptor into the CD8 lineage

CD4/CD8 lineage decision is an important event during T cell maturation in the thymus. CD8 T cell differentiation usually requires corecognition of major histocompatibility complex (MHC) class I by the T cell receptor (TCR) and CD8, whereas CD4 T cells differentiate as a consequence of MHC class II recognition by the TCR and CD4. The involvement of specific peptides in the selection of T cells expressing a particular TCR could be demonstrated so far for the CD8 lineage only. We used mice transgenic for an MHC class II-restricted TCR to investigate the role of antagonistic peptides in CD4 T cell differentiation. Interestingly, antagonists blocked the development of CD4(+) cells that normally differentiate in thymus organ culture from those mice, and they induced the generation of CD8(+) cells in thymus organ culture from mice impaired in CD4(+) cell development (invariant chain-deficient mice). These results are in line with recent observations that antagonistic signals direct differentiation into the CD8 lineage, regardless of MHC specificity.     

Helicobacter pylori infection in immunized mice lacking major histocompatibility complex class I and class II functions

The role of major histocompatibility complex (MHC) class I- and class II-restricted functions in Helicobacter pylori infection and immunity upon oral immunization was examined in vivo. Experimental challenge with H. pylori SS1 resulted in significantly greater (P 相似文献   

Derivation of herpesvirus saimiri-transformed CD8+ T cell lines with noncytotoxic anti-HIV activity

Herpesvirus saimiri (HVS), strain 488-77, was used to derive continuously growing transformed human CD8+ T cell lines that can suppress HIV replication in CD4+ cells via the production of an antiviral factor(s). Transformed CD8+ cell lines were obtained by HVS infection of peripheral blood mononuclear cells or purified CD8- T cells from HIV-infected or uninfected individuals. Suppression of primary or laboratory isolates of HIV was mediated by factor permeation of a transwell membrane or by cell-free culture supernatants. Suppressing and nonsuppressing cell lines were IL-2-dependent for good growth and showed a similar activated cell surface phenotype. The cell lines produced varying amounts of the cytokines IL-8, IL-10, TNF-alpha, TNF-beta, RANTES, MIP-1 alpha, and MIP-1 beta, but not IFN-alpha. No correlation was observed between the level of any of these cytokines and the presence or absence of antiviral activity in cell line culture supernatants. These cell lines have become an important resource for studying antiviral factors produced by CD8+ T cells from HIV-infected individuals.