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(1/1118) Cell-mediated immunity: dealing a direct blow to pathogens.

Cytotoxic T lymphocytes are essential for defence against viral infections. Recent data demonstrating direct killing of intracellular bacteria by granulysin, a protein released from the granules of cytotoxic T lymphocytes, emphasize the contribution of these lymphocytes to the control of tuberculosis.  (+info)

(2/1118) Clearance of Chlamydia trachomatis from the murine genital mucosa does not require perforin-mediated cytolysis or Fas-mediated apoptosis.

The molecular mechanisms of resistance to genital infection with the mouse pneumonitis (MoPn) strain of Chlamydia trachomatis are unknown. A role for major histocompatibility complex class II-restricted, interleukin-12-dependent CD4(+) T cells has been established, but the functional activity of these cells does not depend on secretion of gamma interferon. Here we examined the potential contribution of T-cell-mediated cytotoxicity and apoptosis to mucosal clearance of MoPn by using mice deficient in the molecular mediators of target cell lysis. Animals lacking perforin, Fas, Fas ligand, or both perforin and Fas ligand were infected genitally with C. trachomatis MoPn and monitored for expression of immunity to chlamydial antigens and clearance of MoPn from the genital mucosa. In each case, the profile of spleen cytokine production, the magnitude of the host antibody response, and the kinetics of chlamydial clearance were similar to those of genetically intact controls. Compensatory overproduction of tumor necrosis factor alpha, an alternate mediator of apoptosis in certain cell types, did not appear to account for the ability of mutant mice to resolve Chlamydia infections. These results fail to support CD4(+) T-cell-mediated apoptosis or CD8(+) T-cell-mediated cytotoxicity as being critical to the clearance of C. trachomatis MoPn urogenital infections.  (+info)

(3/1118) Resistance of paroxysmal nocturnal hemoglobinuria cells to the glycosylphosphatidylinositol-binding toxin aerolysin.

Paroxysmal nocturnal hemoglobinuria (PNH) is a clonal stem cell disorder caused by a somatic mutation of the PIGA gene. The product of this gene is required for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors; therefore, the phenotypic hallmark of PNH cells is an absence or marked deficiency of all GPI-anchored proteins. Aerolysin is a toxin secreted by the bacterial pathogen Aeromonas hydrophila and is capable of killing target cells by forming channels in their membranes after binding to GPI-anchored receptors. We found that PNH blood cells (erythrocytes, lymphocytes, and granulocytes), but not blood cells from normals or other hematologic disorders, are resistant to the cytotoxic effects of aerolysin. The percentage of lysis of PNH cells after aerolysin exposure paralleled the percentage of CD59(+) cells in the samples measured by flow cytometry. The kinetics of red blood cell lysis correlated with the type of PNH erythrocytes. PNH type III cells were completely resistant to aerolysin, whereas PNH type II cells displayed intermediate sensitivity. Importantly, the use of aerolysin allowed us to detect PNH populations that could not be detected by standard flow cytometry. Resistance of PNH cells to aerolysin allows for a simple, inexpensive assay for PNH that is sensitive and specific. Aerolysin should also be useful in studying PNH biology.  (+info)

(4/1118) Cytotoxicity is mandatory for CD8(+) T cell-mediated contact hypersensitivity.

Contact hypersensitivity (CHS) is a T cell-mediated skin inflammation induced by epicutaneous exposure to haptens in sensitized individuals. We have previously reported that CHS to dinitrofluorobenzene in mice is mediated by major histocompatibility complex (MHC) class I-restricted CD8(+) T cells. In this study, we show that CD8(+) T cells mediate the skin inflammation through their cytotoxic activity. The contribution of specific cytotoxic T lymphocytes (CTLs) to the CHS reaction was examined both in vivo and in vitro, using mice deficient in perforin and/or Fas/Fas ligand (FasL) pathways involved in cytotoxicity. Mice double deficient in perforin and FasL were able to develop hapten-specific CD8(+) T cells in the lymphoid organs but did not show CHS reaction. However, they did not generate hapten-specific CTLs, demonstrating that the CHS reaction is dependent on cytotoxic activity. In contrast, Fas-deficient lpr mice, FasL-deficient gld mice, and perforin-deficient mice developed a normal CHS reaction and were able to generate hapten-specific CTLs, suggesting that CHS requires either the Fas/FasL or the perforin pathway. This was confirmed by in vitro studies showing that the hapten-specific CTL activity was exclusively mediated by MHC class I-restricted CD8(+) T cells which could use either the perforin or the Fas/FasL pathway for their lytic activity. Thus, cytotoxic CD8(+) T cells, commonly implicated in the host defence against tumors and viral infections, could also mediate harmful delayed-type hypersensitivity reactions.  (+info)

(5/1118) From myocarditis to cardiomyopathy: mechanisms of inflammation and cell death: learning from the past for the future.

A progression from viral myocarditis to dilated cardiomyopathy has long been hypothesized, but the actual extent of this progression has been uncertain. However, a causal link between viral myocarditis and dilated cardiomyopathy has become more evident than before with the tremendous developments in the molecular analyses of autopsy and endomyocardial biopsy specimens, new techniques of viral gene amplification, and modern immunology. The persistence of viral RNA in the myocardium beyond 90 days after inoculation, confirmed by the method of polymerase chain reaction, has given us new insights into the pathogenesis of dilated cardiomyopathy. Moreover, new knowledge of T-cell-mediated immune responses in murine viral myocarditis has contributed a great deal to the understanding of the mechanisms of ongoing disease processes. Apoptotic cell death may provide the third concept to explain the pathogenesis of dilated cardiomyopathy, in addition to persistent viral RNA in the heart tissue and an immune system-mediated mechanism. Beneficial effects of alpha1-adrenergic blocking agents, carteolol, verapamil, and ACE inhibitors have been shown clinically and experimentally in the treatment of viral myocarditis and dilated cardiomyopathy. Antiviral agents should be more extensively investigated for clinical use. The rather discouraging results obtained to date with immunosuppressive agents in the treatment of viral myocarditis indicated the importance of sparing neutralizing antibody production, which may be controlled by B cells, and raised the possibility of promising developments in immunomodulating therapy.  (+info)

(6/1118) Cytokine-based tumor cell vaccine is equally effective against parental and isogenic multidrug-resistant myeloma cells: the role of cytotoxic T lymphocytes.

Tumor cells that survive initial courses of chemotherapy may do so by acquiring a multidrug-resistant phenotype. This particular mechanism of drug resistance may also confer resistance to physiological effectors of apoptosis that could potentially reduce the efficacy of immune therapies that use these pathways of cell death. We have previously demonstrated high efficacy for a cytokine-based tumor cell vaccine in a murine MPC11 myeloma model. In the present study, the effects of this vaccination were compared in MPC11 cells and their isogenic sublines selected for mdr1/P-glycoprotein (Pgp)-mediated multidrug resistance (MDR). Immunization with MPC11 cells expressing granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-12 (IL-12) led to long-lasting protection of mice against subcutaneous (sc) challenge with both parental cells or their MDR variants. Similarly, immunization with GM-CSF/IL-12-transfected MDR sublines caused rejection of transplantation of both parental cells and the MDR sublines. Whereas MPC11 cells and their MDR variants were resistant to APO-1/CD95/Fas ligand, the immunization generated potent granzyme B/perforin-secreting cytotoxic T lymphocytes (CTLs) that were similarly effective against both parental and isogenic MDR cells. We conclude that MDR mediated by mdr1/Pgp did not interfere with lysis by pore-forming CTLs. Immunotherapy based on pore-forming CTLs may be an attractive approach to the treatment of drug-resistant myeloma.  (+info)

(7/1118) Characterization of the culture filtrate-specific cytotoxic T lymphocyte response induced by Bacillus Calmette-Guerin vaccination in H-2b mice.

Although CD8+ T cells are supposed to play an important role in protective immunity to mycobacteria, cytotoxic T lymphocyte (CTL) responses in this infection remain poorly characterized. We previously demonstrated that bacillus Calmette-Guerin (BCG) immunization of H-2b mice induced CTL able to recognize and kill macrophages incubated with proteins from mycobacterial culture supernatant [culture filtrate (CF) antigens]. In the present study, we have further characterized the lytic activity of these CTL and the processing pathway used for the presentation of CF proteins. We show that they use the degranulation pathway (secretion of perforins and granzymes) as the main lytic mechanism of cytotoxicity and also secrete IFN-gamma upon incubation with CF-pulsed macrophages. The in vitro presentation of CF proteins to CTL required a processing step inhibited in the cold but insensitive to Brefeldin A. Transporter-associated protein (TAP)-2-deficient RMA-S cells were efficiently recognized and killed by CF-specific CTL, demonstrating the lack of TAP requirement for this presentation. However, recognition of target cells by CTL was abolished when carried out in the presence of chloroquine. These results indicate that a non-classical MHC class I-processing pathway allows the recognition of a CF protein by CTL in BCG-vaccinated H-2b mice.  (+info)

(8/1118) Differentiation of human CD8 T cells: implications for in vivo persistence of CD8+ CD28- cytotoxic effector clones.

CD8 T cells contain a distinct subset of CD8+ CD28- cells. These cells are not present at birth and their frequency increases with age. They frequently contain expanded clones using various TCRalphabeta receptors and these clones can represent >50% of all CD8 cells, specially in old subjects or patients with chronic viral infections such as HIV-1. Herein, it is shown that a large fraction of CD8+ CD28- cells expresses intracellular perforin by three-color flow cytometry, in particular when this subset is expanded. Together with their known ability to exert potent re-directed cytotoxicity, this indicates that CD8+ CD28- T cells comprise cytotoxic effector cells. With BrdU labeling, we show that CD8+ CD28- cells derive from CD8+ CD28+ precursors in vitro. In addition, sorted CD8+ CD28+ cells gave rise to a population of CD8+ CD28- cells after allo-stimulation. Moreover, ex vivo CD8+ CD28+ cells contain the majority of CD8 blasts, supporting the notion that they contain the proliferative precursors of CD8+ CD28- cells. CD95 (Fas) expression was lower in CD8+ CD28- cells, and this subset was less prone to spontaneous apoptosis in ex vivo samples and more resistant to activation-induced cell death induced by a superantigen in vitro. Thus, the persistence of expanded clones in vivo in the CD8+ CD28- subset may be explained by antigen-driven differentiation from CD8+ CD28+ memory precursors, with relative resistance to apoptosis as the clones become perforin(+) effector cells.  (+info)