Cytotoxic T-lymphocytes secrete soluble factors that induce caspase-mediated apoptosis in glioblastoma cell lines

We have previously shown that factors secreted by activated CTLs induce apoptosis in a panel of glioblastoma lines. In this study, we analyzed the expression of death receptors, activation of caspases and mRNA expression of 96 apoptotic genes in glioblastoma lines either sensitive or resistant to supernatant of activated CTLs. Our results indicate that exposure to supernatant triggers several pathways of caspase activation in glioblastoma lines involved in the initiation of both extrinsic and intrinsic apoptosis. High steady-state levels of Bcl-2 were identified as potentially accounting for the resistance of a proportion of glioblastoma lines to factors secreted by activated CTLs.

Mitochondrial-mediated apoptosis in neural stem cells exposed to manganese

Manganese is an essential nutrient for humans that has to be maintained at proper levels for normal brain functioning. However, manganese also acts as a toxicant to the brain, and several studies have linked exposure to excessive manganese to neurotoxicity in adults. A recent report has suggested that ingesting high doses of manganese via drinking water can impede intellectual functions in children. It is known that during development, the nervous system is particularly vulnerable to different types of injuries and toxicants. Neural stem cells (NSCs) play an essential role in both the developing nervous system and the adult brain where the capacity for self-renewal may be important. In the present study, we have used NSCs to investigate the molecular mechanisms involved in manganese developmental neurotoxicity. The results show that primary cultures of rat embryonic cortical NSCs as well as the murine-derived multipotent NSC line C17.2 undergo apoptotic cell death via a mitochondrial-mediated pathway in response to manganese. Exposed cells exhibit typical apoptotic features, such as chromatin condensation and cell shrinkage, mitochondrial cytochrome c release, activation of caspase-3, and caspase-specific cleavage of the endogenous substrate poly (ADP-ribose) polymerase. In addition, our data also show that reactive oxygen species formation plays a role in the onset of manganese toxicity in NSCs.

Soluble factors released by virus specific activated cytotoxic T-lymphocytes induce apoptotic death of astroglioma cell lines

Astrocytomas and astrogliomas represent the most common types of primary tumors in human central nervous system and are associated with high mortality due to the absence of efficient therapy. Here we demonstrate that, upon antigen-specific activation, cytotoxic T-lymphocytes (CTLs) secrete products that inhibit proliferation and induce apoptosis in a significant proportion of astroglioma cell lines. This effect is tumor specific in that normal cultured astrocytes do not develop apoptotic changes upon exposure to supernatant of activated CTLs. Experiments with purified lymphokines and lymphokine specific blocking antibodies indicate that synergistic activities of tumor necrosis factor (TNF)-alpha and interferon (INF)-gamma are required for the apoptosis inducing effect on some astroglioma cell lines. However, this effect appears to be dependent on additional factors produced by activated CTLs. Our results suggest that local application of factors released by activated CTLs or induction of CTL migration and activation in the tumor site may have a therapeutic effect in patients with astrogliomas.

Astrocyte activation and apoptosis: their roles in the neuropathology of HIV infection

Astrogliosis is a common neuropathological finding in the brains of HIV infected individuals; both activation and apoptosis of astrocytes are seen. This review aims to discuss the Fas pathway in the context of proliferation and apoptosis of astrocytes during HIV infection, and as a result of astrogliosis, the dysregulation of astrocyte-neuron networks. The presence of molecules reflecting astrocyte activation, which are derived from the solubilization of receptor/ligand from the surface of proliferating astrocytes, in the cerebrospinal fluid may be used to evaluate the degree of brain cell activation during HAART therapy. A better understanding of the molecular pathway(s) leading to increase activation and apoptosis of astrocytes, in parallel with studies conducted to unravel the molecules involved in T-cell apoptosis during HIV infection, may lead to the development of new therapeutic strategies for controlling HIV replication and tissue damage.

Modulation of sFas indicates apoptosis in human herpes simplex encephalitis

Herpes simplex encephalitis (HSE) is the most common cause of non-epidemic, acute and fatal viral encephalitis. A pronounced mortality and morbidity remains in HSE despite antiviral treatment. There is evidence of a vigorous intrathecal immune activity in acute phases of HSE and of persistently increased activity at follow-ups after years. The role of apoptosis of neuronal cells in HSE patients as a mechanism of damage has been brought up lately. We hypothesize that the severity and the progression of the cerebral injury resulting from HSE can be evaluated by quantitative measurement of a compartment of immune activation molecules i.e. soluble Fas (sFas) involved in apoptosis through the Fas/Fas Ligand pathway. Consecutive cerebrospinal fluid (CSF) samples from a prospectively followed cohort, included in an antiviral treatment trial in HSE, were enrolled for quantitative measurement of sFas using commercial capture ELISA. In total, CSF samples from 49 patients with HSE, 63 patients with non-HSE encephalitis and 18 healthy individuals were studied. High levels of sFas were expressed in CSF samples collected between days 0-45 after neurological onset in 41/49 (84%) HSE patients, whereas only 21/63 (33%) of non-HSE patients and none of 18 healthy controls demonstrated measurable levels of sFas. Following the consecutive CSF sFas levels over the time and considering the clinical state of patients at admission, their neurological or lethal outcome at 12 months, and antiviral treatment, we observed that HSE patients with severe neurological sequels revealed an increase in changes of CSF sFas as compared to patients with mild or moderate neurological outcome (57.6+/-55.6 pg/ml, n=10 versus 26.3+/-97.5 pg/ml, n=14; P=0.008). Also HSE patients undergoing vidarabine treatment expressed significantly higher levels of changes of CSF sFas when compared to acyclovir-treated patients (63.7+/-52.8 pg/ml, n=9 versus 26.1+/-98.4 pg/ml, n=14; P=0.003). Interestingly, regardless of the clinical state at admission, and subsequent disease progression of the HSE patients, we could not observe any significant differences in the CSF sFas levels during the first 7 days of neurological symptoms. These observations underline the role of immunological response throughout the course of HSV infection in the brain and the role of the Fas/FasL pathway in particular in disease progression of HSE. The findings further enforce the need of expanding the knowledge of the pathogenesis of HSE to direct to more effective, in particular not only antiviral but also anti-apoptotic or anti-inflammatory treatment.

Incidence and pathogenesis of clinical relapse after herpes simplex encephalitis in adults

OBJECTIVES

To study the occurrence of relapse of herpes simplex encephalitis (HSE) and to find out whether soluble activity markers in cerebrospinal fluid (CSF) indicate direct viral or immune- mediated events.

METHODS

A consecutive series of 32 adult survivors of HSE were followed to determine the incidence of clinical relapse of HSE. Four patients had neurological deterioration interpreted as relapsing HSE. Four non-relapsing HSE cases were selected as matched controls. Fifty nine batched, paired CSF and serum samples from the eight HSE patients were analysed for soluble activity markers, predominantly cytokines and mediators (interferon-gamma, soluble CD8, tumour necrosis factor-alpha, and interleukin-10), amount of HSV-DNA and markers of glial and neuronal destruction (neurofilament protein, glial fibrillary acidic protein, S-100-beta, and neuron specific enolase).

RESULTS

Relapse of HSE was diagnosed in 3 of 26 (12 %) acyclovir-treated patients (5 episodes during 6.1 years of followup) and in 1 of 6 vidarabine-recipients. All relapses occurred from 1 to 4 months after acute HSE, except for a second relapse after 3.3 years in one patient. Computer tomography at relapses revealed few abnormalities apart from those found during the primary disease. Intravenous acyclovir and corticosteroids were given for 7-21 days in all the relapse patients. All relapse patients seemed to recover to the pre-relapse condition. HSV-DNA was demonstrated in CSF in all patients during the acute stage but not in any of 13 CSF samples taken during relapse phases. The HSV viral load during the acute stage of HSE was not higher or of longer duration in the relapsing patients than in the non-relapsing HSE controls. The levels of sCD8 were increased in nearly all CSF samples tested with peaks of sCD8 at one month of acute HSE. In all episodes of relapse, sCD8 peaks were detected during the first week at high levels. CSF levels of neuron-specific enolase, S-100 and glial fibrillary acidic protein were markedly lower at relapse than at the acute stage of HSV-1 encephalitis.

CONCLUSION

The lack of demonstrable HSV DNA in CSF, the lack of acute CSF signs and the lack of signs of neural and glia cells destruction indicate that a direct viral cytotoxicity is not the major pathogenic mechanism in relapse. Instead, the pronounced CSF proinflammatory immunological response and the relative lack of CSF anti-inflammatory cytokine IL-10 response suggest immunologically-mediated pathogenicity.

Alteration of Fas and Fas ligand expression during human visceral leishmaniasis

Several studies in murine systems have suggested a role of apoptosis in the pathogenesis of leishmaniasis. However, the role of apoptosis in visceral leishmaniasis in man has not been explored. In this study, we show that patients with visceral leishmaniasis demonstrate significant dysregulation of Fas and Fas ligand. Levels of soluble Fas (sFas) and soluble Fas ligand (sFasL) were elevated in plasma of patients with active visceral leishmaniasis (VL) and individuals co-infected with VL-HIV-1 compared to healthy controls. The levels of sFas and sFasL were normalized 6 months after successful treatment. In VL patients, the expression of membrane bound Fas, and to a lower extent FasL, were up-regulated on Leishmania donovani-infected spleen cells, the site of parasite multiplication. Expression of Fas and FasL on peripheral blood mononuclear cells was within normal range, probably reflecting that the blood is not a normal site of L. donovani infection. Furthermore, this is suggested by the finding that in vitro infection of macrophages with L. donovani up-regulated Fas expression on the surface of infected cells and enhanced the levels of sFasL in supernatants from infected cultures. How this dysregulation may affect the pathogenesis of human visceral leishmaniasis is discussed.

Elevated levels of soluble Fas and Fas ligand in cerebrospinal fluid of patients with AIDS dementia complex

We measured the levels of sFas and sFasL in CSF and serum of HIV-1 infected patients and related them to AIDS dementia complex (ADC). Specimens were obtained from 51 HIV-1 infected individuals (29 with ADC) and 39 HIV negative individuals. The sFas was detectable in all sera and 98% of CSF specimens. Measurable levels of sFasL were found in 79% of the CSF and 98% of sera samples. According to the presence or absence of ADC, we observed significant differences in CSF sFas (median and IQR 116, 132 vs. 30, 23 pg/ml, P<0.001) and sFasL (median and IQR 127, 290 vs. 15, 73 pg/ml, P<0.001) levels. The sFas in serum differed significantly between HIV-1 infected subjects and non-infected controls (P<0.001), with no correlation to ADC. On the contrary, sFasL in serum differed among HIV-1 infected subjects according to clinical signs of ADC. In the cross-sectional study, the number of cells present in CSF and CD4+ T cell counts in blood did not correlate to the levels of CSF sFas and sFasL. Interestingly, the number of HIV RNA copies in CSF correlated significantly to the levels of CSF sFasL (P=0.001) but not to sFas in the same compartment. Antiretroviral therapy reduced viral load and sFas levels in CSF in the majority of patients. sFas is a useful marker for ADC diagnosis and follow-up during antiviral treatment.

Nonproductive human immunodeficiency virus type 1 infection of human fetal astrocytes: independence from CD4 and major chemokine receptors

Human immunodeficiency virus type 1 (HIV-1) infection of the brain is associated with neurological manifestations both in adults and in children. The primary target for HIV-1 infection in the brain is the microglia, but astrocytes can also be infected. We tested 26 primary HIV-1 isolates for their capacity to infect human fetal astrocytes in culture. Eight of these isolates, independent of their biological phenotype and chemokine receptor usage, were able to infect astrocytes. Although no sustained viral replication could be demonstrated, the virus was recovered by coculture with receptive cells such as macrophages or on stimulation with interleukin-1beta. To gain knowledge into the molecular events that regulate attachment and penetration of HIV-1 in astrocytes, we investigated the expression of several chemokine receptors. Fluorocytometry and calcium-mobilization assay did not provide evidence of expression of any of the major HIV-1 coreceptors, including CXCR4, CCR5, CCR3, and CCR2b, as well as the CD4 molecule on the cell surface of human fetal astrocytes. However, mRNA transcripts for CXCR4, CCR5, Bonzo/STRL33/TYMSTR, and APJ were detected by RT-PCR. Furthermore, infection of astrocytes by HIV-1 isolates with different chemokine receptor usage was not inhibited by the chemokines SDF-1beta, RANTES, MIP-1beta, or MCP-1 or by antibodies directed against the third variable region or the CD4 binding site of gp120. These data show that astrocytes can be infected by primary HIV-1 isolates via a mechanism independent of CD4 or major chemokine receptors. Furthermore, astrocytes are potential carriers of latent HIV-1 and on activation may be implicated in spreading the infection to other neighbouring cells, such as microglia or macrophages.