Healthier rhythm, healthier brain? Integrity of circadian melatonin and temperature rhythms relates to the clinical state of brain-injured patients.

BACKGROUND: Healthy circadian rhythmicity has been suggested to relate to a better state of brain-injured patients and to support the emergence of consciousness in patient groups characterized by a relative instability thereof such as patients with disorders of consciousness (DOC). METHODS: Going beyond earlier studies, a systems-level perspective was adopted and, using multilevel modelling, the joint predictive value of three indices of circadian rhythm integrity derived from skin temperature variations, melatoninsulfate secretion, and physical activity (wrist actigraphy) patterns was evaluated for the behaviourally assessed state [Coma Recovery Scale - Revised (CRS-R) score] of DOC patients [13 unresponsive wakefulness syndrome; seven minimally conscious (exit) state]. Additionally, it was assessed in a subset of 16 patients whether patients' behavioural repertoire (CRS-R score) varied (i) with time of day or (ii) offset from the body temperature maximum (BTmax ), i.e. when cognitive performance is expected to peak. RESULTS: The results reveal that better integrity of circadian melatoninsulfate and temperature rhythms relate to a richer behavioural repertoire. Moreover, higher CRS-R scores are, by trend, related to assessments taking place at a later daytime or deviating less from the pre-specified time of occurrence of BTmax . CONCLUSIONS: In conclusion, the results suggest that therapeutic approaches aimed at improving circadian rhythms in brain-injured patients are promising and should be implemented in hospitals or nursing homes. Beyond this, it might be helpful to schedule diagnostic procedures and therapies around the (pre-assessed) BTmax (≈4 pm in healthy individuals) as this is when patients should be most responsive.

Late age onset of amyotrophic lateral sclerosis is often not considered in elderly people.

INTRODUCTION: Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease causing an upper and lower motor neuron loss. It is neurology textbook knowledge that the mean age of onset is about 60 years. However, recent investigations show an increasing incidence in older persons. We therefore evaluated whether ALS is potentially not considered in elderly people with ALS symptoms, respectively, not recognized. MATERIALS AND METHODS: We included retrospectively all patients with ALS diagnoses after work-up that were admitted to our neurological and geriatric departments from 2007 to 2010 and collected their clinical data. The diagnosis of ALS was based on the El Escorial criteria. Patients were grouped into three categories according to age (<50, between 50 and 70, >70), and differences in clinical and/ or biographical factors were investigated. RESULTS: We identified 35 patients (18 men and 17 women) with a median age at onset of 71.5 years (range: 36-87 years). When establishing the diagnosis, 51% were older than 70 years, 40% (14/35) between 50 and 70, and only 9% younger than 50. Only in 46 per cent of patients who were sent to our departments with ALS symptoms ALS was considered by the referring physician. CONCLUSION: Late age onset of ALS seems to be more common than formerly assumed and is presumably under-recognized in elderly patients. ALS needs to be considered as a differential diagnosis in older patients. Potential factors accounting for older people being underdiagnosed with ALS relate to frequent presentation with symptoms like dysphagia, frailty or general weakness for other reasons.

Non-eosinophilic airway hyper-reactivity in mice, induced by IFN-γ producing CD4(+) and CD8(+) lung T cells, is responsive to steroid treatment.

Non-eosinophilic asthma is characterized by infiltration of neutrophils into the lung and variable responsiveness to glucocorticoids. The pathophysiological mechanisms have not been characterized in detail. Here, we present an experimental asthma model in mice associated with non-eosinophilic airway inflammation and airway hyper-responsiveness (AHR). For this, BALB/c mice were sensitized by biolistic DNA immunization with a plasmid encoding the model antigen ß-galactosidase (pFascin-ßGal mice). For comparison, eosinophilic airway inflammation was induced by subcutaneous injection of ßGal protein (ßGal mice). Intranasal challenge of mice in both groups induced AHR to a comparable extent as well as recruitment of inflammatory cells into the airways. In contrast to ßGal mice, which exhibited extensive eosinophilic infiltration in the lung, goblet cell hyperplasia and polarization of CD4(+) T cells into Th2 and Th17 cells, pFascin-ßGal mice showed considerable neutrophilia, but no goblet cell hyperplasia and a predominance of Th1 and Tc1 cells in the airways. Depletion studies in pFascin-ßGal mice revealed that CD4(+) and CD8(+) cells cooperated to induce maximum inflammation, but that neutrophilic infiltration was not a prerequisite for AHR induction. Treatment of pFascin-ßGal mice with dexamethasone before intranasal challenge did not affect neutrophilic infiltration, but significantly reduced AHR, infiltration of monocytes and lymphocytes as well as content of IFN-γ in the bronchoalveolar fluid. Our results suggest that non-eosinophilic asthma associated predominantly with Th1/Tc1 cells is susceptible to glucocorticoid treatment. pFascin-ßGal mice might represent a mouse model to study pathophysiological mechanisms proceeding in the subgroup of asthmatics with non-eosinophilic asthma that respond to inhaled steroids.

Assessment of a wireless headband for automatic sleep scoring.

PURPOSE: Classically, professional assessment of sleep is done in the sleep laboratory using whole-night polysomnography (PSG). However, given a misbalance between accredited sleep laboratories and the large amount of patients suffering from sleep disorders, only few receive appropriate diagnostic assessment. Recently, some low-cost home sleep scoring systems have been proposed, yet such systems are rarely tested scientifically. The aim of the present study was to evaluate the staging accuracy of the home sleep scoring system Zeo (Newton, MA, USA). METHODS: A final sample of 21 nights from ten subjects (aged 23-45) was digitally recorded with PSG as well as with the Zeo system. We compared scorings of Zeo (on an epoch-be-epoch basis) with the Somnolyzer 24 × 7 (an automatic staging algorithm), expert scorers as well as the freeware SleepExplorer. RESULTS: It was revealed that Zeo shows moderate overall agreement as compared to our study standard Somnolyzer 24 × 7 (κ = 0.56). The most obvious performance difference between Zeo and both other scoring approaches was stage wake (sleep onset latency + wake after sleep onset). While Zeo detected only 40.8 % of the study standard wake epochs, 70.1 % were detected by the expert scorers and 83.4 % by the SleepExplorer, respectively. CONCLUSIONS: Data suggest that the Zeo system produces acceptable sleep scoring for stage REM, light and deep sleep, with a specific weakness in correctly detecting waking periods.

Disproportion in T-cell subpopulations in immunodeficient mutant hr/hr mice.

Mice of the HRS strain, which carry the mutant gene hr, were examined for abnormalities in representation of the three T-cell sets Ly1, Ly23, and Ly123 in the spleen. The salient feature of hr/hr mice, which are immunologically deficient, in comparison with +/hr segregants, was a gross disproportion in numbers of cells belonging to the Ly1 and Ly123 sets, at the age of 3--3.5 mo. At this age, Ly123 cells of hr/hr spleen outnumbered Ly1 cells by 2:1, whereas in +/hr spleens Ly123 cells were outnumbered by approximately 1:2. Cells from pooled lymph nodes of hr/hr mice did not show a correspondingly gross disporprotion of Ly1 and Ly123 cells. Total counts of splenic T cells, and of B cells, were not significantly different in hr/hr and +/hr mice.

CD4-mediated enhancement or inhibition of T cell activation does not require the CD4:p56lck association.

CD4 is the coreceptor molecule expressed on the surface of T cells specific for or restricted by class II molecules of the major histocompatibility complex (MHC). Its expression on T cells is required for an optimal response to antigen (Ag). Three mechanisms have been invoked for the involvement of CD4 in T cell activation. First, it was shown that CD4 binds to MHC class II molecules on antigen presenting cells (APCs) thereby favoring an adhesion between effector cells and APCs. Association of CD4 to the T cell receptor and to the tyrosine kinase p56lck have also been shown to be critically involved in the positive function of CD4. Here, we demonstrate that the interaction of CD4 with p56lck is not required to enhance the response of two CD4-dependent, Ag-specific T cell hybridomas. Mutant forms of CD4 (TCD4), which lose association to p56lck, were expressed in these T cells and were shown to enhance the Ag-specific response as efficiently as the wild-type CD4. Moreover both CD4-dependent and independent T cell responses were inhibited by CD4-specific mAbs even when CD4 was not associated with p56lck. These results indicate that mechanisms distinct from sequestration of p56lck and/or negative signaling operate in these inhibitions. Results demonstrating enhancement of TCR-mediated signaling by the coaggregation of TCD4 mutant to the TCR further confirm that the association of p56lck to CD4 is not absolutely required for the regulatory functions of CD4. Our results suggest that the mechanisms implicated in the enhancement of T cell stimulation via CD4 depend solely on the extracellular and transmembrane domains of CD4.

Acquisition of an additional antigen specificity after mouse CD4 gene transfer into a T helper hybridoma.

We have transfected the mouse CD4 gene into a beef insulin (BI)-specific murine T helper hybridoma that lacks CD4 surface expression. The CD4-expressing transfectants have acquired an additional reactivity for pork insulin (PI), which was not detectable in the original recipient cell. The transfectants' response to PI can be completely abrogated by anti-CD4 antibodies. The transfected clone showed a 50-fold increased sensitivity towards BI in comparison to the same CD4- hybridoma. These experiments suggest that CD4 may be important in determining the antigen fine specificity and, therefore, may also play a role in altering the T cell repertoire.

Antigen dose-dependent suppression of murine IgE responses is mediated by CD4(-)CD8(-) double-negative T cells.

BACKGROUND: The IgE response against protein antigens is profoundly influenced by the dose used for sensitization. OBJECTIVE: The aim of the study was to identify immune cells that are involved in antigen dose-dependent regulation of IgE formation. METHODS: Wild-type mice as well as T helper (Th)1-deficient IL-12p40(-/-) and IFN-gamma(-/-) mice were immunized by repeated intraperitoneal injection of either low doses (K01 mice) or high doses (K100 mice) of keyhole limpet haemocyanin adsorbed to aluminium hydroxide. Splenocytes of immunized mice were restimulated in vitro and antigen-dependent T cell proliferation and cytokine production were measured. The frequency of regulatory T cell subsets among splenocytes from K01 and K100 mice was compared using fluorocytometry and RT-PCR analysis. Splenocytes or T cell subpopulations were transferred into naïve mice and the effect of lymphocyte transfer on IgE production after priming of recipients with low antigen doses was determined. RESULTS: Specific IgE production was considerably impaired in K100 mice. Antigenic restimulation revealed hypoproliferation of K100 splenocytes and reduced production of Th2 cytokines IL-4, IL-5 and IL-13, but no induction of IFN-gamma production. Moreover, lymphocytes from K01 and K100 mice did not show significant differences in the expression of molecules associated with the phenotype or activity of conventional regulatory T cells. Transfer of splenocytes or purified T cells from K100 mice substantially suppressed the induction of IgE production in the recipients in an antigen- and isotype-specific manner. Neither CD4(+) nor CD8(+) T cells from K100 mice were able to inhibit IgE formation; instead, we identified CD4(-)CD8(-) double-negative T cells (dnT cells) as the principal T cell population, which potently suppressed IgE production. CONCLUSION: Our data demonstrate that CD4(-)CD8(-) dnT cells play a major role in the regulation of IgE responses induced by high antigen doses.

Classification of non-aneurysmal subarachnoid haemorrhage: CT correlation to the clinical outcome.

AIM: To propose a new computed tomography (CT)-based classification system for non-aneurysmal subarachnoid haemorrhage (SAH), which predicts patients' discharge clinical outcome and helps to prioritize appropriate patient management. METHODS AND MATERIALS: A 5-year, retrospective, two-centre study was carried out involving 1486 patients presenting with SAH. One hundred and ninety patients with non-aneurysmal SAH were included in the study. Initial cranial CT findings at admission were correlated with the patients' discharge outcomes measured using the Modified Rankin Scale (MRS). A CT-based classification system (type 1-4) was devised based on the topography of the initial haemorrhage pattern. RESULTS: Seventy-five percent of the patients had type 1 haemorrhage and all these patients had a good clinical outcome with a discharge MRS of

The specificity of the interaction between the agretope of an antigen and an Ia-molecule can depend on the T cell clonotype.

A series of T cell clones was developed from (B10 x B10.BR)F1 mice immunized with the isolated A chain of pig insulin. The T cell clones show considerable diversity as defined by their distinct reactivities to pig, beef, sheep and horse insulins in combination with the same syngeneic Ab alpha Ak beta molecules. These species variants of insulin differ from each other only in amino acid residues in position A8, A9 or A10 within the so-called A chain loop and responsiveness of mice to these variants is under Ir gene control. A detailed analysis of the stimulatory capacity of various insulin/Ia combinations including inhibition experiments with anti-Ia- and -L3T4 antibodies led to the following interpretation: the amino acid residues A8-A10 are involved in the interaction of the insulin A chain with the Ia molecules. This region can, therefore, be regarded as part of the agretope. Structural variations within this region can modify the stimulatory potency of the insulin variants. However, whether a particular amino acid substitution results in an enhancement or a reduction of the response depends on the fine specificity of the T cell clone involved. Thus, an interaction of Ia molecules with antigen cannot solely account for the functional specificity of an agretope, rather this also depends on the structure of the particular T cell receptor that participates in recognition.

Suppression of MHC class I antigens in oncogenic transformants: association with decreased recognition by cytotoxic T lymphocytes.

Cytotoxic T lymphocytes (CTLs) recognize peptide fragments derived from endogenous proteins, processed internally, and presented at the cell surface by major histocompatibility complex (MHC) class I molecules. The use of specific CTL for cancer therapy is limited because of their dependence on effective processing and presentation of appropriate antigenic peptides. Structural alterations, like point mutation or somatic loss, or dysregulation of key elements in the processing or presentation pathway, may allow cells to escape the immune surveillance. Indeed, the expression of MHC class I antigens on the surface of virus- and oncogene-transformed cells is low and correlates with tumorigenicity. Transformation of murine fibroblasts with the ras oncogene results in the suppression of cell surface expression of all H-2 loci as determined by FACScan analysis using a panel of monoclonal antibodies. We then examined whether the oncogene-mediated suppression of MHC class I surface expression was associated with reduced recognition of transformants by CD8+ T lymphocytes. Murine T lymphoma cells were stably transfected by the Ha-ras oncogene. The transfectants expressed distinct levels of the Ha-ras specific protein p21. Again, immunofluorescence analysis demonstrated an inverse correlation between oncogene and MHC class I surface expression in RMAras transformants. Allogeneic H-2Kb-restricted cytotoxic T lymphocytes were able to efficiently lyse the parental T lymphoma cells. In contrast, the CTL-mediated lysis of ras transformants was significantly downregulated compared with untransfected RMA cells. The efficiency of CTL-mediated lysis of RMAras cells was directly associated with reduced MHC class I membrane and high p21ras protein expression. Thus, the oncogene-mediated downregulation of MHC class I surface expression resulted in a reduced CTL response. Attempts are in progress to revert the defects in MHC class I surface expression of oncogenic transformants by introducing the different elements of the antigen presentation pathway. Such studies will not only provide improved understanding of the mechanisms of tumor escape, but also will suggest strategies to repair cellular defects in cancer patients having impaired expression of MHC class I antigens.

Maturation of epidermal Langerhans cells in vitro is accompanied by downregulation of 4F2 (CD98) as determined by differential display.

Following short-term culture, Langerhans cells mature morphologically and functionally into potent immunostimulatory cells. As regulation of gene expression accompanies this maturation process, it is likely that differentially expressed genes are involved in the maturation events. Using the recently described method of differential display, we generated cDNA expression patterns starting with mRNA of murine epidermal Langerhans cells isolated either directly (fLC) or following 3 d cultivation (cLC). Five hundred putative differentially expressed cDNA fragments were recovered from the gel. For a part of the fragments differential expression was confirmed by dot blot and Southern hybridization procedures. These cDNA fragments were subcloned and sequenced following the verification step. Database searches revealed that unknown genes as well as already characterized genes were identified. A cDNA fragment preferentially hybridizing with fLC was identified as the murine surface marker 4F2 (CD98). Downregulation of the activation marker 4F2/CD98 was confirmed by additional analysis at the mRNA and protein level. The downregulation of 4F2 surface expression on cLC is compatible with the notion that the committed, terminally differentiated cLC downregulate proteins involved in proliferation and cell survival.

Expression of the actin-bundling protein fascin in cultured human dendritic cells correlates with dendritic morphology and cell differentiation.

Dendritic cells are key players of the immune system as they efficiently induce primary immune responses by activating naive T cells. We generated human dendritic cells from CD14+ blood precursors and investigated expression of the actin-bundling protein fascin during maturation by western blotting, immunofluorescence, and cytofluorometry. Cells obtained by culture of CD14+ blood precursors in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4, which were only weakly positive for the maturation marker CD83, expressed low amounts of fascin. Addition of a cytokine cocktail including tumor necrosis factor alpha, interleukin-1beta, interleukin-6, and prostaglandin E2 induced maturation of the cells and enhanced fascin expression in parallel with CD83 expression. Isolated mature CD83+ cells displayed especially high fascin levels on western blots, as did gated CD83+ dendritic cells in cytofluorometry. Dendritic cells generated from CD34+ blood precursors expressed high levels of fascin as well. Confocal microscopy revealed that location of fascin within the cell was restricted to the area of the submembranous actin cytoskeleton and to the dendritic processes. Suppression experiments using antisense constructs of fascin hint at a retarded morphologic maturation of dendritic cells, supporting the view that fascin expression is pivotal for dendrite formation. Our data suggest that fascin could serve as a marker molecule to monitor the maturation state of in vitro generated dendritic cells for use in clinical trials.

Mouse langerhans cells differentially express an activated T cell-attracting CC chemokine.

Epidermal Langerhans cells represent an immature population of dendritic cells, not yet able to prime naïve T cells. Following in vitro culture Langerhans cells mature into potent immunostimulatory cells. We constructed a representative cDNA library of in vitro matured murine Langerhans cells. Applying a differential screening procedure 112 differentially expressed cDNA clones were isolated. Thirty-six clones represented cDNA fragments of the same gene, identifying it to be the most actively expressed gene induced in maturing Langerhans cells. A full-length cDNA was sequenced completely. The open reading frame codes for a protein of 92 amino acids containing a leader peptide of 24 amino acids, yielding a mature protein of 7.8 kDa molecular weight. Database searches revealed 99.4% sequence identity on the nucleotide level to the recently described mouse CC chemokine ABCD-1, as well as 74% sequence identity to the human CC chemokine, the macrophage-derived chemokine/stimulated T cell chemotactic protein. Expression was analyzed by reverse transcriptase-polymerase chain reaction on a large panel of cell types. Unlike the macrophage-derived chemokine, expression was not detected in macrophages stimulated by various cytokines. Expression is restricted to cultured Langerhans cells, in vitro cultured dendritic cells, and lipopolysaccharide-activated B cells. Recombinant protein was expressed in the yeast Pichia pastoris and purified to homogeneity. Whereas no chemotactic activity was observed in chemotaxis assays for naïve T cells, B cells, cultured dendritic cells, and Langerhans cells, a strong chemoattractant activity was exerted on activated T cells. Thus, production of this chemokine by dendritic cells may be essential for the establishment and amplification of T cell responses.

Action of complement in the lysis of mouse sarcoma cells sensitized with H-2 alloantibody.

A modified cytotoxicity assay was adapted from classical erythrocytolytic assays, in which complement components were added in sequence to antibody-sensitized cells. This assay was applied to a model system in which mouse sarcoma cells were sensitized with H-2 alloantibody. The stepwise presentation of complement components combined with the stabilization of C2 by iodine treatment considerably augmented the lytic efficiency of human complement. More generally, the techniques adopted for this study provide a new model for obtaining basic information about selective reaction steps concerned in lysis of nucleated cells by alloantibody and complement. Comparisons of the lysis of sheep erythrocytes by xenoantibody with the lysis of mouse sarcoma cells by H-2 alloantibody, in our assay system with oxidized or untreated human complement, disclosed a difference in the kinetics of C142 formation, manifest in a lag phase and a protracted tmax for the sarcoma cells. These data may suggest that multiple complement-mediated functional lesions are necessary for immune lysis of nucleated cells.

PCR-amplified cDNA probes for verification of differentially expressed genes.

Differential display has proven to be a powerful technique for the detection and isolation of differentially expressed genes. By generating reproducible cDNA expression patterns, it is possible to compare gene expression by two or more cell types, developmental stages or tissues and to isolate as yet unknown differentially expressed genes. A sensitive method is necessary to verify the differential expression of the isolated cDNAs. Here we describe the use of adaptor-ligated. PCR-amplified total cDNA of the two cell types compared as a probe for Southern hybridizations with the isolated cDNAs.

Nonradioactive detection of differentially expressed genes using complex RNA or DNA hybridization probes.

The analysis of differential gene expression has become increasingly important in recent years. Typically, differentially expressed genes are identified in a primary screening procedure, yielding candidate genes whose differential expression has to be verified. We provide a highly sensitive, efficient and nonradioactive differential screening procedure to analyze numerous candidate genes in a single step. This comprises labeling of poly(A)+ RNA of the cell types analyzed with DIG Chem-Link and differential hybridization to the candidate genes fixed on dot blots. DIG Chem-Link allows, to our knowledge, for the first time efficient and direct nonradioactive labeling of RNA in vitro. Advantages of this method include extremely short exposure times and the feasibility to re-use the probes after prolonged storage. Using this procedure, we isolated several genes that are differentially expressed in maturing Langerhans cells.

Perpetual proliferation of LYT-1 cells requires repetitive signals for IL-2 receptor induction by antigen-presenting cells.

T cell lines with specificity for bovine insulin and ovalbumin were maintained by serial stimulation with antigen presented on irradiated syngeneic spleen cells, alternating 3 days later with subculture in IL-2 containing medium (CM). When the cultures were repetitively split in CM, with concomitant dilution of antigen-presenting cells, a gradual loss of proliferative capacity of the cells in the presence of CM was observed. Absorption studies revealed a 20-fold reduction of IL-2 receptors on the surface of T blasts assayed 12 days after antigenic stimulation as compared with day 5 blasts. This decrement in the number of IL-2 acceptor sites reflected an actual decrease in cell surface density of IL-2 receptors. Restimulation of the T blasts with antigen and spleen cells induced both a substantial increase in IL-2 receptor density and responsiveness to CM. Furthermore, the permanent presence of antigen and spleen cells during splitting of the T blasts in CM prevented the loss of responsiveness to IL-2. As an interpretation we propose that the Lyt-1 cells studied here clear their IL-2 receptors from the cell surface after interaction with IL-2. Thus, each new round of replication of the daughter cells would be dependent on induction of IL-2 receptors by activating signals provided by antigen/Ia structures on accessory cells as well as possibly accessory cell products such as IL-1, rendering Lyt-1 cells sensitive to regulatory influences.

Characterization of lymphokine-mediated activation of macrophages for antigen presentation: studies with long-term cultured bone marrow-derived macrophages and cloned T cells.

In cultures of bone marrow (BM) supplemented with L cell-derived colony-stimulating factor a pure population of macrophages (M phi) differentiates, which can be further propagated with a doubling time of 3.8 days. "Young" BMM phi obtained on day 8 of culture were shown to act as antigen-presenting cells inducing the antigen-specific proliferation of the cloned T cell line ST2/K.9, whereas "old" M phi had lost this ability. However, at any time tested (up to 132 days) the presentation function of old BMM phi could be completely restored by pulsing the cells with lymphokines (LK). A duration of 11 hr for the LK-pulse was sufficient to trigger the M phi to exert an optimal presentation function. This activity could be maintained when the LK-treatment was prolonged (tested up to 17 days). Activation was accompanied by a deceleration of growth. The LK effective in M phi activation were found to be contained in the supernatants of T cell lines stimulated by antigen or mitogen, and could be substituted by a low dose (5-10 units/ml) of recombinant interferon-gamma. In direct comparison LK-triggered BMM phi presented antigen as efficiently as peritoneal exudate M phi activated in vivo by ConA. Moreover, primed lymph node T cells responded to antigen-presenting BMM phi in a similar way as ST2/K.9 T cells. Therefore, these findings obtained with long-term cultured cells can be expected to reflect a physiological mechanism for the amplification of the immune response.

Consequences of antigen self-presentation by tumor-specific cytotoxic T cells.

CD8-positive cytotoxic T cells (CTL) recognize antigenic peptides in combination with major histocompatibility complex (MHC) class I molecules on the surface of syngeneic antigen presenting cells (APC). In the present paper we show that cells from tumor antigen-specific CTL clones present their cognate antigenic peptide to other CTL from the same clone. Inter-CTL peptide presentation resulted in activation of the cells of one CTL clone to MHC-unrestricted lysis of bystander cells. In contrast to the behaviour of this clone, another CTL clone did not lyse bystander cells after incubation with the cognate peptide, but was activated to self-destruction. The human herpes virus Epstein-Barr virus is involved in the pathogenesis of a broad spectrum of human neoplasias. Using freshly established non-clonal T cells with specificity for a peptide derived from an Epstein-Barr virus encoded antigen we found again lysis of MHC mismatched bystander cells as a consequence of inter-CTL peptide presentation, indicating that bystander lysis following antigen self-presentation is not a phenomenon restricted to long-term in vitro cultured T cell clones. The potential implications for immunosurveillance against cancer and for tumor escape mechanisms are discussed.