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Cytotoxic Mechanisms (cytotoxic + mechanism)

Distribution by Scientific Domains

Medical Sciences	83%

Selected Abstracts

Cytotoxic mechanisms in different forms of T-cell-mediated drug allergies

ALLERGY, Issue 6 2004
P. C. Kuechler
Background:, Cytotoxic mechanisms are involved in different forms of drug induced exanthems. Methods:, Here we compare the killing pathways of CD4+, CD8+ and CD4/CD8+ T-cell lines (TCL) and clones derived from patients suffering from maculopapular, bullous and pustular drug eruptions. In vitro, perforin and Fas-mediated killing was analysed in cytotoxicity assays against autologous Epstein,Barr virus (EBV)-transformed B-cell lines, Fas-transfected mouse lymphoblasts and natural killer (NK)-target cells. In addition, affected skin lesions and the TCL and clones were stained for perforin and FasL-expression. Results:, We detected perforin and some FasL-mediated killing in all three types of exanthems. Some of the drug-specific T-cell clones analysed exerted mainly perforin-, other more FasL-mediated killing showing no strict relationship between their perforin- and Fas-mediated cytotoxic capacity. Using a cell culture method focusing on the generation of cytotoxic T cells, we detected drug-specific CD8+, TCR,,+ T cells, which failed to proliferate to drug presentation by antigen presenting cells but killed in a drug dependent way. Interestingly, these cells had substantial natural killer-like T cell(s) like features as they were CD56+ and CD94+ and had the ability to kill the NK-sensitive cell line K562. Conclusion:, Our data underline the important role of cytotoxic mechanisms in different forms of drug induced exanthems and suggest that even some T cells with NK-like characteristics may be involved in drug hypersensitivity. [source]

Influence of intracellular Ca2+, mitochondria membrane potential, reactive oxygen species, and intracellular ATP on the mechanism of microcystin-LR induced apoptosis in Carassius auratus lymphocytes in vitro

ENVIRONMENTAL TOXICOLOGY, Issue 6 2007
H. Zhang
Abstract Microcystin-LR (MCLR), the most toxic microcystin up to date, could induce apoptosis in many kinds of fish and mammalian cells. For the fish immunotoxicity, it was found that MCLR could induce apoptosis in Carassius auratus lymphocytes in vitro. So this study focused on the role of intracellular Ca2+, mitochondrial membrane potential, reactive oxygen species (ROS), and intracellular ATP in response to the mechanisms of MCLR-induced apoptosis in fish lymphocytes. MCLR (10 nM) administration resulted in a massive elevation in ROS, intracellular Ca2+, decreased ATP, and rapid mitochondrial membrane potential (,,m) disruption. When compared to controls, both a fourfold significant (P < 0.001) elevation in O2, in 1.5 h and an approximately twofold increase in Ca2+ in 0.5 h were observed. After 6 h of treatment, an approximately 30% decrease for ,,m but about 75% decline for ATP were found. Together, the results demonstrated that MCLR-induced apoptosis was associated with a massive calcium influx, resulting in O2, elevation, ,,m disruption, and ATP depletion. This study provided a possible cytotoxic mechanism of fish lymphocytes caused by MCLR. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 559,564, 2007. [source]

Cytotoxic action mode of a novel porphyrin derivative isolated from harmful red tide dinoflagellate Heterocapsa circularisquama

JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 3 2008
Daekyung Kim
Abstract Heterocapsa circularisquama is known to cause lethal effect on bivalves, but toxic effect on fish has not been reported yet. Recently, we have found that H. circularisquama has potent light-dependent hemolytic toxins. Based on the chemical structural analysis, one of the hemolytic toxins named H2-a was found to be a novel porphyrin derivative with similar structure to pyropheophorbide a methyl ester (PME), a well-known photoactive hemolytic agent (Miyazaki et al., Aquatic Toxicol. 2005;73:382--393). To clarify the cytotoxic action mode of H2-a, we examined the effects of H2-a on HeLa cells in comparison with PME. The cytotoxicities of both reagents were strictly light dependent, and no significant cytotoxic effects including cellular morphological changes were induced without light illumination. The dose response curves revealed that H2-a showed stronger cytotoxicity to HeLa cells than PME. Fluorescence microscopic observation suggested that H2-a tends to accumulate in the plasma membrane, whereas PME seems to distribute entire cytoplasm. Although PME induced typical apoptotic nuclear morphological changes and DNA fragmentation in HeLa cells, no such apoptosis-inducing ability of H2-a was observed. Among the radical scavengers, histidine significantly inhibited the cytotoxic activity of H2-a, suggesting the involvement of singlet oxygen in the cytotoxicity. These results suggest that the cytotoxic mechanism of H2-a is necrotic rather than apoptosis differing from PME, even though these are structurally quite similar to each other. The relatively high affinity of H2-a to the plasma membrane might result in the potent and quick cytotoxicity without induction of apoptotic signal transduction. © 2008 Wiley Periodicals, Inc. J Biochem Mol Toxicol 22:158,165, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20216 [source]

Tumour necrosis factor-, affects blood,brain barrier permeability and tight junction-associated occludin in acute liver failure

LIVER INTERNATIONAL, Issue 8 2010
Sa Lv
Abstract Background: Cerebral oedema leading to cerebral herniation is a major cause of death during acute liver failure (ALF), but the underlying mechanism is not clear. Aims: We investigated the role of tumour necrosis factor (TNF)-, in changing the permeability of the blood,brain barrier (BBB) during ALF. Methods: ALF animal models were generated by administering d -galactosamine (GalN) and lipopolysaccharide, or GalN and TNF-,. ALF induction was blocked by first administering anti-TNF-,,IgG or anti-TNF-,-R1. We investigated the BBB permeability with Evans blue staining, and the structure with electron microscopy. Results: BBB permeability increased in ALF mice and correlated with elevated serum TNF-, levels. No vascular endothelial cell (EC) apoptosis was detected, but electron microscopy of cells from human and mouse ALF tissues revealed tight junction (TJ) disruptions and EC shrinkage, as well as increased vesicles and vacuoles. In addition, the expression of the TJ-associated protein occludin was significantly decreased in both ALF mice and patients, although the expression of occludin mRNA did not change. Changes in BBB permeability, brain tissue ultrastructure and occludin expression in ALF-induced mice could be prevented by prophylaxis treatment with either antibody to TNF-,,IgG or antibody to TNF-,-R1. Conclusions: Our results suggest that TNF-, plays a critical role in the development of brain oedema in ALF, and that both vasogenic and cytotoxic mechanisms may be involved. Increased BBB permeability may be because of the disruption of TJs, and loss of the TJ-associated protein occludin. [source]

Cytotoxic mechanisms in different forms of T-cell-mediated drug allergies

Antitumor activity and mechanism of action of the iron chelator, Dp44mT, against leukemic cells,

AMERICAN JOURNAL OF HEMATOLOGY, Issue 3 2009
Egarit Noulsri
Iron chelators have been reported to induce apoptosis and cell cycle arrest in cancer cells. Recent studies suggest broad and selective antitumor activity of the new iron chelator, di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT; Whitnall et al., Proc Natl Acad Sci USA 2006;103:14901,14906). However, little is known concerning its effects on hematological malignancies. Using acute leukemia cells, the effect of Dp44mT on apoptosis, cell cycle, caspase-3 activation, and mitochondrial trans-membrane potential has been examined by flow cytometry. Dp44mT acted to induce a G1/S arrest in NB4 promyelocytic leukemia cells at low concentrations (0.5,2.5 ,M), being far more effective than the clinically used chelator, desferrioxamine (DFO). Moreover, Dp44mT induced apoptosis of NB4 cells in a dose- and time-dependent manner with markedly less effect on nonproliferating cells. The apoptosis-inducing activity of Dp44mT was significantly more effective than DFO. Furthermore, this study also showed that Dp44mT had broad activity, inducing apoptosis in several types of acute leukemia and also multiple myeloma cell lines. Additional studies examining the cytotoxic mechanisms of Dp44mT showed that a reduction in the mitochondrial trans-membrane potential and caspase-3 activation could be involved in the mechanism of apoptosis. Our results suggest that Dp44mT possesses potential as an effective cytotoxic agent for the chemotherapeutic treatment of acute leukemia. Am. J. Hematol. 2009. © 2008 Wiley-Liss, Inc. [source]

T Cell-mediated Rejection of Kidney Transplants: A Personal Viewpoint

AMERICAN JOURNAL OF TRANSPLANTATION, Issue 5 2010
P. F. Halloran
In kidney allografts, T cell mediated rejection (TCMR) is characterized by infiltration of the interstitium by T cells and macrophages, intense IFNG and TGFB effects, and epithelial deterioration. Recent experimental and clinical studies provide the basis for a provisional model for TCMR. The model proposes that the major unit of cognate recognition in TCMR is effector T cells engaging donor antigen on macrophages. This event creates the inflammatory compartment that recruits effector and effector memory CD4 and CD8 T cells, both cognate and noncognate, and macrophage precursors. Cognate T cells cross the donor microcirculation to enter the interstitium but spare the microcirculation. Local inflammation triggers dedifferentiation of the adjacent epithelium (e.g. loss of transporters and expression of embryonic genes) rather than cell death, via mechanisms that do not require known T-cell cytotoxic mechanisms or direct contact of T cells with the epithelium. Local epithelial changes trigger a response of the entire nephron and a second wave of dedifferentiation. The dedifferentiated epithelium is unable to exclude T cells, which enter to produce tubulitis lesions. Thus TCMR is a cognate recognition-based process that creates local inflammation and epithelial dedifferentiation, stereotyped nephron responses, and tubulitis, and if untreated causes irreversible nephron loss. [source]

Donor Fas Is Not Necessary for T-Cell-Mediated Rejection of Mouse Kidney Allografts

AMERICAN JOURNAL OF TRANSPLANTATION, Issue 10 2008
D. Kayser
It is important to resolve whether T-cell-mediated rejection (TCMR) is mediated by contact-dependent cytotoxicity or by contact-independent inflammatory mechanisms. We recently showed that the cytotoxic molecules perforin and granzymes A and B are not required for TCMR of mouse kidney transplants. Nevertheless, TCMR could still be mediated by cytotoxicity via Fas on donor cells engaging Fas ligand on host T cells. We examined whether the diagnostic TCMR lesions would be abrogated if donor Fas was absent, particularly in hosts deficient in perforin or granzymes A and B. Kidneys from Fas-deficient donors transplanted into major histocompatibility complex (MHC)- mismatched hosts developed tubulitis and diffuse interstitial infiltration indistinguishable from wild-type (WT) allografts, even in hosts deficient in perforin and granzymes A and B. Gene expression analysis revealed similar molecular disturbances in Fas-deficient and WT allografts at day 21 transplanted into WT, perforin and granzyme A/B-deficient hosts, indicating epithelial injury and dedifferentiation. Thus, donor Fas is not necessary for TCMR diagnostic lesions or molecular changes, even in the absence of perforin,granzyme mechanisms. We propose that in TCMR, interstitial effector T cells mediate parenchymal injury by inflammatory mechanisms that require neither the perforin,granzyme nor the Fas,Fas ligand cytotoxic mechanisms. [source]

Islet Allograft Rejection by Contact-Dependent CD8+ T cells: Perforin and FasL Play Alternate but Obligatory Roles,

AMERICAN JOURNAL OF TRANSPLANTATION, Issue 8 2007
M. Sleater
Though CD8+ T lymphocytes are important cellular mediators of islet allograft rejection, their molecular mechanism of rejection remains unidentified. Surprisingly, while it is generally assumed that CD8+ T cells require classic cytotoxic mechanisms to kill grafts in vivo, neither perforin nor FasL (CD95L) are required for acute islet allograft rejection. Thus, it is unclear whether such contact-dependent cytotoxic pathways play an essential role in islet rejection. Moreover, both perforin and CD95L have been implicated in playing roles in peripheral tolerance, further obscuring the role of these effector pathways in rejection. Therefore, we determined whether perforin and/or FasL (CD95L) were required by donor MHC-restricted (,direct') CD8+ T cells to reject islet allografts in vivo. Islet allograft rejection by primed, alloreactive CD8+ T cells was examined independently of other lymphocyte subpopulations via adoptive transfer studies. Individual disruption of T-cell-derived perforin or allograft Fas expression had limited impact on graft rejection. However, simultaneous disruption of both pathways prevented allograft rejection in most recipients despite the chronic persistence of transferred T cells at the graft site. Thus, while there are clearly multiple cellular pathways of allograft rejection, perforin and FasL comprise alternate and necessary routes of acute CD8+ T-cell-mediated islet allograft rejection. [source]

Tubulitis and Epithelial Cell Alterations in Mouse Kidney Transplant Rejection Are Independent of CD103, Perforin or Granzymes A/B

AMERICAN JOURNAL OF TRANSPLANTATION, Issue 9 2006
G. Einecke
One of the defining lesions of kidney allograft rejection is epithelial deterioration and invasion by inflammatory cells (tubulitis). We examined epithelial changes and their relationship to effector T cells and to CD103/E-cadherin interactions in mouse kidney allografts. Rejecting allografts showed interstitial mononuclear infiltration from day 5. Loss of epithelial mass, estimated by tubular surface area, and tubulitis were minimal through day 7 and severe by day 21. Tubules in day 21 allografts manifested severe reduction of E-cadherin and Ksp-cadherin by immunostaining with redistribution to the apical membrane, indicating loss of polarity. By flow cytometry T cells isolated from allografts were 25% CD103+. Laser capture microdissection and RT-PCR showed increased CD103 mRNA in the interstitium and tubules. However, allografts in hosts lacking CD103 developed tubulitis, cadherin loss, and epithelial deterioration similar to wild-type hosts. The loss of cadherins and epithelial mass was also independent of perforin and granzymes A and B. Thus rejection is characterized by severe tubular deterioration associated with CD103+ T cells but not mediated by CD103/cadherin interactions or granzyme-perforin cytotoxic mechanisms. We suggest that alloimmune effector T cells mediate epithelial injury by contact-independent mechanisms related to delayed type hypersensitivity, followed by invasion of the altered epithelium to produce tubulitis. [source]

Perforin expression in peripheral blood lymphocytes and skin-infiltrating cells in patients with lichen planus

BRITISH JOURNAL OF DERMATOLOGY, Issue 2 2004
L. Prpi, Massari
Summary Background, Current evidence suggests that lichen planus is a T-cell-mediated autoimmune disease in which cytotoxic mechanisms have been poorly investigated. Objectives, We investigated the expression of perforin in subpopulations of peripheral blood lymphocytes (PBL) in exacerbation and remission phases of the disease as well as in skin lesions. Methods, We performed a simultaneous detection of perforin (intracellular molecule) and cell surface antigens on PBL by flow cytometry, and skin lesions were investigated by immunohistochemistry. Results, The most interesting finding was a significant increase of perforin expression in cytotoxic T lymphocytes (CD3+ perforin+ cells) in the exacerbation phase of disease (P < 0·05), which was mostly located in the CD8+ subpopulation (CD8+ perforin+) (P < 0·01). Using immunohistochemistry we confirmed the infiltration of T lymphocytes in skin lesions, especially of CD4+ and CD8+ phenotypes, compared with uninvolved (P < 0·05) and healthy skin (P < 0·01). The expression of perforin was also significantly higher in lesional skin compared with nonlesional and healthy skin (P < 0·05). Conclusions, Our results clearly show the upregulation of perforin expression in peripheral blood as well as in lesions of patients with lichen planus and therefore suggest an important role for perforin in this autoimmune disease. [source]