The impact of delayed treatment of uncomplicated P. falciparum malaria on progression to severe malaria: A systematic review and a pooled multicentre individual-patient meta-analysis

BACKGROUND

Delay in receiving treatment for uncomplicated malaria (UM) is often reported to increase the risk of developing severe malaria (SM), but access to treatment remains low in most high-burden areas. Understanding the contribution of treatment delay on progression to severe disease is critical to determine how quickly patients need to receive treatment and to quantify the impact of widely implemented treatment interventions, such as 'test-and-treat' policies administered by community health workers (CHWs). We conducted a pooled individual-participant meta-analysis to estimate the association between treatment delay and presenting with SM.

METHODS AND FINDINGS

A search using Ovid MEDLINE and Embase was initially conducted to identify studies on severe Plasmodium falciparum malaria that included information on treatment delay, such as fever duration (inception to 22nd September 2017). Studies identified included 5 case-control and 8 other observational clinical studies of SM and UM cases. Risk of bias was assessed using the Newcastle-Ottawa scale, and all studies were ranked as 'Good', scoring ≥7/10. Individual-patient data (IPD) were pooled from 13 studies of 3,989 (94.1% aged <15 years) SM patients and 5,780 (79.6% aged <15 years) UM cases in Benin, Malaysia, Mozambique, Tanzania, The Gambia, Uganda, Yemen, and Zambia. Definitions of SM were standardised across studies to compare treatment delay in patients with UM and different SM phenotypes using age-adjusted mixed-effects regression. The odds of any SM phenotype were significantly higher in children with longer delays between initial symptoms and arrival at the health facility (odds ratio [OR] = 1.33, 95% CI: 1.07-1.64 for a delay of >24 hours versus ≤24 hours; p = 0.009). Reported illness duration was a strong predictor of presenting with severe malarial anaemia (SMA) in children, with an OR of 2.79 (95% CI:1.92-4.06; p < 0.001) for a delay of 2-3 days and 5.46 (95% CI: 3.49-8.53; p < 0.001) for a delay of >7 days, compared with receiving treatment within 24 hours from symptom onset. We estimate that 42.8% of childhood SMA cases and 48.5% of adult SMA cases in the study areas would have been averted if all individuals were able to access treatment within the first day of symptom onset, if the association is fully causal. In studies specifically recording onset of nonsevere symptoms, long treatment delay was moderately associated with other SM phenotypes (OR [95% CI] >3 to ≤4 days versus ≤24 hours: cerebral malaria [CM] = 2.42 [1.24-4.72], p = 0.01; respiratory distress syndrome [RDS] = 4.09 [1.70-9.82], p = 0.002). In addition to unmeasured confounding, which is commonly present in observational studies, a key limitation is that many severe cases and deaths occur outside healthcare facilities in endemic countries, where the effect of delayed or no treatment is difficult to quantify.

CONCLUSIONS

Our results quantify the relationship between rapid access to treatment and reduced risk of severe disease, which was particularly strong for SMA. There was some evidence to suggest that progression to other severe phenotypes may also be prevented by prompt treatment, though the association was not as strong, which may be explained by potential selection bias, sample size issues, or a difference in underlying pathology. These findings may help assess the impact of interventions that improve access to treatment.

Use of rectal artesunate for severe malaria at the community level, Zambia

Objective

To determine whether the administration of rectal artesunate by trained community health volunteers before referral to a health-care facility reduces the case fatality rate of severe malaria in young children in hard-to-reach communities in Zambia.

Methods

We implemented a pilot project in Serenje District between July 2017 and July 2018. The project involved: (i) training community health volunteers to administer rectal artesunate to children with suspected severe malaria and refer them to a health facility; (ii) ensuring emergency transport with bicycle ambulances was available; (iii) ensuring adequate drug supplies; and (iv) ensuring health-care workers could treat severe malaria with injectable artesunate. Surveys of health facilities, volunteers and bicycle ambulance riders were performed near the beginning and end of the intervention period. In addition, data on severe malaria cases and associated deaths were obtained from health facilities and a community monitoring system.

Findings

In the year before the intervention, 18 deaths occurred in 224 cases of confirmed severe malaria among children younger than 5 years seen at intervention health facilities (case fatality rate: 8%); during the intervention, 3 of 619 comparable children with severe malaria died (case fatality rate: 0.5%).

Conclusion

The administration of pre-referral rectal artesunate treatment to young children with severe malaria by community health volunteers was feasible, safe and effective in hard-to-reach communities in Zambia and was associated with a substantial decrease in the case fatality rate. The project’s approach is highly adaptable and could be used in other countries with a high malaria burden.

Prescribing patterns and compliance with World Health Organization recommendations for the management of severe malaria: a modified cohort event monitoring study in public health facilities in Ghana and Uganda

BACKGROUND

Injectable artesunate (AS) is the World Health Organization (WHO) recommended medication for the treatment of severe malaria followed with an oral artemisinin-based combination therapy (ACT). There are few studies indicating how physicians prescribe injectable AS, injectable quinine (Q) or injectable artemether (AR) and ACT for severe malaria. This study was undertaken to evaluate prescription compliance to the WHO recommendation in 8 public health facilities in Ghana and Uganda. This was a modified cohort event monitoring study involving patients who were administered with injectable anti-malarial for treatment of presumed or confirmed severe malaria. Patients prescribed at least one dose of injectable artesunate, artemether or quinine qualified to enrol in the study. Patients were recruited at inpatient facilities and followed up in the hospital, by phone or at home. Following WHO recommendations, patients are to be prescribed 3 doses of injectable AS, Q or AR for at least 24 h followed with oral ACT. Compliance rate was estimated as the number of patient prescriptions that met the WHO recommendation for treatment of severe malaria divided by the total number of patients who completed the study by end of follow up. Log-binomial regression model was used to identify predictors for compliance. Based on the literature and limitations of available data from the patients' record, the diagnosis results, age, gender, weight, and country were considered as potential predictors of prescriber adherence to the WHO recommendations.

RESULTS

A total of 1191 patients completed the study, of which 93% were prescribed injectable AS, 3.1% (injectable AR or Q) with 32.5% prescribed follow-on oral ACT and 26% on concomitant antibiotics. 391 (32.8%) were in Ghana and 800 (67.2%) in Uganda. There were 582 (48.9%) women. The median age was 3.9 years (IQR = 2, 9) and median weight was 13 kg (IQR = 10, 20). Of the 1191 patients, 329 of the prescriptions complied with the WHO recommendation (compliance rate = 27.6%; 95% CI = [25.2, 30.2]). Diagnostic results (Adjusted prevalence ratio (aPR) = 4.56; 95% = [3.42, 6.08]; p < 0.0001) and weight (20 + kg vs < 10 kg: aPR = 0.65; 95% = [0.44, 0.96]; p = 0.015) were identified as factors independently associated with compliance.

CONCLUSION

Injectable AS is the most commonly prescribed medicine in the management of severe malaria in Ghana and Uganda. However, adherence to the WHO recommendation of at least 3 doses of injectable anti-malarial in 24 h followed by a full course of ACT is low, at less than 30%.

An operational comparative study of quinine and artesunate for the treatment of severe malaria in hospitals and health centres in the Democratic Republic of Congo: the MATIAS study

Background

The Democratic Republic of the Congo (DRC) has the highest number of severe malaria cases in the world. In early 2012, the National Malaria Control Programme (NMCP) changed the policy for treating severe malaria in children and adults from injectable quinine to injectable artesunate. To inform the scaling up of injectable artesunate nationwide, operational research is needed to identify constraints and challenges in the DRC’s specific setting.

Methods

The implementation of injectable quinine treatment in 350 patients aged 2 months or older in eight health facilities from October 2012 to January 2013 and injectable artesunate in 399 patients in the same facilities from April to June 2013 was compared. Since this was an implementation study, concurrent randomized controls were not possible. Four key components were evaluated during each phase: 1) clinical assessment, 2) time and motion, 3) feasibility and acceptability, and 4) financial cost.

Results

The time to discharge was lower in the artesunate (median = 2, 90 % central range 1–9) compared to the quinine group (3 (1–9) days; p <0.001). Similarly, the interval between admission and the start of intravenous (IV) treatment (2 (0–15) compared to 3 (0–20) hours; p <0.001) and parasite clearance time (23 (11–49) compared to 24 (10–82) hours; p <0.001) were lower in the artesunate group. The overall staff pre-administration time (13 (6–38) compared to 20 (7–50) minutes; p <0.001) and the personnel time spent on patient management (9 (1–24) compared to 12 (3–52) minutes; p <0.001) were lower in the artesunate group. In hospitals and health centres, the mean (standard deviation, SD) total cost per patient treated for severe malaria with injectable artesunate was USD 51.94 (16.20) and 19.51 (9.58); and USD 60.35 (17.73) and 20.36 (6.80) with injectable quinine.

Conclusions

This study demonstrates that injectable artesunate in the DRC is easier to use and it costs less than injectable quinine. These findings provide the basis for practical recommendations for rapid national deployment of injectable artesunate in the DRC.

Electronic supplementary material

The online version of this article (doi:10.1186/s12936-015-0732-1) contains supplementary material, which is available to authorized users.

Delayed anemia after treatment with injectable artesunate in the Democratic Republic of the Congo: a manageable issue

Cases of delayed hemolytic anemia have been described after treatment with injectable artesunate, the current World Health Organization (WHO)–recommended first-line drug for the treatment of severe malaria. A total of 350 patients (215 [61.4%] < 5 years of age and 135 [38.6%] ≥ 5 years of age) were followed-up after treatment with injectable artesunate for severe malaria in hospitals and health centers of the Democratic Republic of the Congo. Complete series of hemoglobin (Hb) measurements were available for 201 patients. A decrease in Hb levels between 2 and 5 g/dL was detected in 23 (11.4%) patients during the follow-up period. For five patients, Hb levels decreased below 5 g/dL during at least one follow-up visit. All cases of delayed anemia were clinically manageable and resolved within one month.

FOXO1 and c-jun transcription factors mRNA are modulated in endometriosis

Endometriosis is a polygenic gynaecological condition affecting 5-15% of women of childbearing age. Major symptoms of the disease are pelvic pain and infertility. No clear link has been established between symptoms and the stage of the disease. Although some aspects have begun to be clarified, clinical understanding of endometriosis remains partial at the molecular level. In this perspective, we targeted isolation of differentially expressed genes in the eutopic endometrial tissue. Our assumption was that the endometrial cells of patients presented an unusual gene expression profile, allowing their implantation and survival in an ectopic site, leading to endometriotic lesions. Here, we report that mRNA steady-state levels of two key transcription factors are modulated in endometriosis. FOXO1 (also known as FKHR) levels were 1.6-fold lower in endometriosis compared to the control group at the onset of the secretory phase (day 15-21), while c-jun mRNA was present at higher amounts in endometriosis (1.5-fold) at the proliferative phase of the menstrual cycle. These results were derived from a large sample composed of 157 control subjects and 209 patients with endometriosis. Gene profiling was conducted by real-time quantitative PCR, and data were quality controlled before statistical analysis. Whether protein levels are affected as well remains to be investigated.

Concentration of soluble intercellular adhesion molecule-1 in serum samples from patients with endometriosis collected during the luteal phase of the menstrual cycle

BACKGROUND

Soluble intercellular adhesion molecule-1 (sICAM-1), released by endometriotic lesions, is involved in the regulation of cytotoxic processes. Altered levels of sICAM-1 in the circulation could parallel its deregulation in the peritoneal cavity. We therefore investigated whether sICAM-1 could represent a serum marker for endometriosis.

METHODS

sICAM-1 levels were measured by enzyme-linked immunosorbent assay in serum samples from 176 subjects with surgically confirmed endometriosis (134 patients with stage I-II and 42 patients with stage III-IV) and 198 controls with no surgical evidence of the disease. All serum samples were collected during the luteal phase of the menstrual cycle. Detailed information about demographics, symptoms and clinical profile were collected.

RESULTS

Mean levels of sICAM-1 appeared significantly reduced in patients with stage III-IV endometriosis in a crude comparison of means. However, when means were adjusted for potential confounders such as the pre-operative indication or fertility status, no significant difference between cases with stage III-IV disease and controls was observed.

CONCLUSIONS

Serum levels of sICAM-1 during the luteal phase of the cycle are not able to discriminate women suffering from endometriosis from controls when confounders are taken into account. These results underline the importance of careful identification of confounders, based on patients' demographic and clinical data in studies aiming at discovering diagnostic markers for endometriosis.

Large scale validation of human N-myc Downstream-Regulated Gene (NDRG)-1 expression in endometrium during the menstrual cycle

A major challenge in the comprehension of the endometrial transformations leading to the completion of each menstrual cycle in humans is in the identification of specific molecular pathways underlying these monthly turnovers. Towards this goal we compared, by the differential display technique, the relative expression of mRNA in endometrial biopsies harvested in individuals (n = 48) either at the proliferative or the secretory phase of the menstrual cycle. We isolated a cDNA fragment homologous to NDRG1 (N-myc Downstream-Regulated Gene-1) that is present in markedly higher amounts in the secretory phase. Northern blot analysis and quantitative real time PCR experiments confirmed this result in distinct cohorts of individuals (44 and 560 respectively). A closer examination of data showed that the highest mRNA levels were found during the range of 25-28 days of the uterine cycle. Consistent with the mRNA data, the temporal profile of the NDRG1 protein showed a 15-fold increase during the secretory phase, as demonstrated by using semi-quantitative dot blot analyses (n = 92). Immunohistochemical localization revealed that NDRG1 was expressed both in epithelial and stromal cells. This large scale validation of the NDRG1 mRNA and protein increase in endometrium during the secretory phase is consistent with its differentiation-related function described in other tissues and its potential involvement in the window of implantation of the human endometrium, as suggested by previous chip-based evidence.

Levels of vascular endothelial growth factor (VEGF) in serum of patients with endometriosis

BACKGROUND

Elevated concentrations of vascular endothelial growth factor (VEGF) have been detected in the peritoneal fluid of patients with endometriosis. Furthermore, it was postulated that VEGF is involved in the development of endometriotic lesions. The present study is aimed at determining whether high levels of VEGF could also be found in the serum of patients with endometriosis.

METHODS

VEGF levels were measured by enzyme-linked immunosorbent assay (ELISA) in serum from 131 subjects with surgically confirmed endometriosis and 146 controls with no clinical evidence of the disease or detectable endometriotic lesions at the time of surgical examination. Parameters such as demographics, personal habits, menstrual characteristics and clinical profile were collected from each subject included in this study.

RESULTS

The mean VEGF levels were not significantly modulated in serum samples of cases compared with controls in a crude general linear model and in a model adjusted for possible confounders. VEGF serum levels did not correlate with the score, stage of endometriosis or the presence of benign gynaecological disorders. However, a correlation was found between circulating concentrations of VEGF and body mass index.

CONCLUSION

Although VEGF seems to play a pivotal role locally in the implantation and development of endometriotic lesions, the disease is not associated with a significant modulation in the levels of circulating VEGF.

Detection of a decrease in green fluorescent protein fluorescence for the monitoring of cell death: an assay amenable to high-throughput screening technologies

BACKGROUND

Reliable assessment of cell death is now pivotal to many research programs aiming at generating new anti-tumor compounds or at screening cDNA libraries. Such approaches need to rely on reproducible, easy-to-handle, and rapid microplate-based cytotoxicity assays that are amenable to high-throughput screening (HTS) technologies. We describe a method for the direct measurement of cell death, based on the detection of a decrease in fluorescence observed following death induction in cells expressing enhanced green fluorescent protein (EGFP).

METHODS

Cell death was induced by a variety of apoptotic stimuli in various EGFP-expressing mammalian cell lines, including those routinely used in anti-cancer drug screening. Decrease in fluorescence was assessed either by flow cytometry (and compared with other apoptotic markers) or by a fluorescence microplate reader.

RESULTS

Cells expressing EGFP exhibited a decrease in fluorescence when treated by various agents, such as chemotherapeutic drugs, UV irradiation, or caspase-independent cell death inducers. Kinetics and sensitivity of this EGFP-based assay were comparable to those of traditional apoptosis markers such as annexin-V binding, propidium iodide incorporation, or reactive oxygen species production. We also show that the decrease in EGFP fluorescence is directly quantifiable in a fluorescence-based microplate assay. Furthermore, analysis of EGFP protein content in cells undergoing cell death demonstrates that the decrease in fluorescence does not arise from degradation of the protein.

CONCLUSIONS

This novel GFP-based microplate assay combines sensitivity and rapidity, is easily amenable to HTS setups, making it an assay of choice for cytotoxicity evaluation.

Derivatives of monoglycerides as apoptotic agents in T-cells

Recently, lipids have received considerable attention for their potential to induce apoptosis when added exogenously to cells. In this study, we directly demonstrate that murine T-cells undergo rapid apoptosis following treatment with various forms of monoglycerides, which are a family of naturally occurring lipids consisting of a single fatty acid moiety attached to a glycerol backbone. The potency of these lipids varied depending on their chemical structure, whereas glycerol backbone or corresponding fatty acids alone were ineffective. Moreover, monoglyceride-mediated apoptosis was suppressed either by Bcl-2 overexpression, treatment with a broad inhibitor of caspases, or RNA and protein synthesis inhibitors. In addition, treatment of cells with derivatives of monoglycerides induced a calcium flux, which could be inhibited by both extracellular (EGTA) or intracellular (EGTA-AM) calcium chelators. To our knowledge, this is the first report demonstrating a role for derivatives of monoglycerides as inducers of apoptosis in mammalian cells.

"Anorexia saved my life": coincidental anorexia nervosa and cerebral meningioma

OBJECTIVE

We report on a 13-year-old girl with coincidental occult intracranial tumor and early-onset anorexia nervosa.

METHOD

The cerebral meningioma was discovered fortuitously as the result of a research project using SPECT imaging to locate a neurobiological substrate in patients with anorexia nervosa. Without SPECT, the meningioma would have remained undiagnosed until it had become symptomatic. The two conditions appear to have been completely unrelated.

RESULTS AND DISCUSSION

The case highlights two important points. First, intracranial pathology should also be considered however certain is the diagnosis of early-onset anorexia nervosa. Second, neuroimaging plays an important part in diagnosing early-onset anorexia nervosa, both from a clinical and a research prospective.

Inhibitory effects of T-cell stimulation and co-stimulation observed at high concentrations of plate-bound antibodies

Plate-bound monoclonal antibodies (mAb) are often used as a way of stimulating lymphocytes in vitro. Our observations show that the concentrations of mAb used in functional assays in vitro must be carefully assessed before conclusions are drawn about lymphocyte activation or co-activation.

Implication of tyrosine kinase receptor and steel factor in cell density-dependent growth in cervical cancers and leukemias

Cell-cell interaction is important in the expansion of leukemic cells and of solid tumors. Steel factor (SF) or Kit ligand is produced as a membrane-bound form (mSF) and a soluble form. Because both primary gynecological tumors and primary leukemic cells from patients with acute myeloblastic leukemia (AML) have been shown to coexpress c-Kit and SF, we addressed the question of whether mSF could contribute to cell interaction in these cancers. Investigations on primary cervical carcinomas have been hindered by the fact that the cells do not grow in culture. We report herein the establishment of two cervical carcinoma cell lines, CALO and INBL, that reproduce the pattern of SF/c-Kit expression observed in primary tumor samples. In addition, these cells exhibit marked density-dependent growth much in the same way as AML blasts. Using an antisense strategy with phosphorothioate-modified oligonucleotides that specifically target SF without affecting other surface markers, we provide direct evidence for a role of mSF and c-Kit in cell interaction and cell survival in these gynecological tumor cell lines as well as in primary AML blasts. Finally, our study defines the importance of juxtacrine stimulation, which may be as important, if not more, than autocrine stimulation in cancers.

Steel factor sustains SCL expression and the survival of purified CD34+ bone marrow cells in the absence of detectable cell differentiation

CD34+ cells express the basic helix-loop-helix transcription factor SCL, which is essential for blood cell formation in vivo. In addition, their survival is critically dependent on hemopoietic growth factors. We therefore compared the effects of Steel factor (SF) and GM-CSF on the survival, proliferation, and differentiation of primary human CD34+ cells, as well as the role of SCL during these processes. GM-CSF suppresses apoptosis in CD34+ cells, which proliferate and differentiate into mature granulocytic and monocytic cells (CD34-CD13+) and loose SCL expression. In contrast, SF suppresses apoptosis without a significant increase in cell numbers, and the cells remain CD34+ and SCL+ with a blast-like morphology. Examination of apoptosis by the terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL) reaction and of the cell cycle status indicated that SF is both a survival factor and a mitogenic factor for CD34+ cells. There was, however, constant cell death in a fraction of the population, which could be rescued by GM-CSF. Co-addition of SF and GM-CSF prevents the downregulation of SCL observed in the presence of GM-CSF by itself, allows for prolonged survival and expansion of CD34+ cells in culture, inhibits monocytic differentiation and impairs granulocytic differentiation. Finally, exposure to an antisense SCL but not a control oligonucleotide decreases SCL protein levels and prevents the suppression of apoptosis by SF without affecting GM-CSF-dependent cell survival. These observations suggest that the hemopoietic transcription factor SCL regulates the survival of CD34+ cells in response to SF.

Opposite ability of pre-TCR and alpha beta TCR to induce apoptosis

In early CD4(-)CD8(-) pro-thymocytes, signaling through the pre-TCR is crucial for survival and differentiation into CD4(+)CD8(+) cells. At this more mature stage, interactions between alphabetaTCR and self-Ag/MHC complexes in turn lead either to cell survival and differentiation (positive selection) or to cell death (negative selection). Intrinsic differences must therefore exist between pre-TCR signals in CD4(-)CD8(-) thymocytes and alphabetaTCR signals in CD4(+)CD8(+) cells, since only the latter can mediate a death signal. In this work, we directly compared the capability of pre-TCR and alphabetaTCR to induce apoptosis in a CD4(-)CD8(-) thymoma cell line following receptor cross-linking with mAbs. Cross-linking of alphabetaTCR triggered high levels of programmed cell death, mimicking the negative selection signal usually induced in CD4(+)CD8(+) thymocytes. In contrast, pre-TCR was very inefficient at inducing apoptosis upon cross-linking, despite similar levels of surface receptor expression. Importantly, inefficient apoptosis induction by the pre-TCR did not result from its weak association with TCRzeta chain, since TCRs containing alpha-pTalpha chimeric chains, binding weakly to TCRzeta, were still able to induce apoptosis. Although similar tyrosine phosphorylation and calcium influx were induced after either pre-TCR or alphabetaTCR cross-linking, the two pathways diverged at the level of Fas ligand induction. Among putative transcription factors involved in Fas ligand mRNA induction, Nur77 and NFAT transcriptional activities were readily induced after alphabetaTCR, but not pre-TCR, stimulation. Together, these results support the view that the structure of the pre-TCR and alphabetaTCR directly influences their apoptosis-inducing capabilities by activating distinct signaling pathways.

Frontal analysis method to determine competitive adsorption isotherms

In order to design and to optimise preparative separations, the knowledge of the underlying thermodynamic functions, i.e., the adsorption isotherms, is the most essential information. Usually these functions cannot be predicted and various methods have been suggested to determine them experimentally. In particular, dynamic methods are attractive regarding time requirements and reliability. Frontal analysis (FA) is frequently applied to measure single solute isotherms. The theoretical background of this method is offered by the classical equilibrium theory of adsorption. Although this theory also explains the shape of multicomponent breakthrough curves, FA is only seldom applied to determine competitive isotherms. In this work FA was used to measure adsorption isotherms of three components as single solutes and in binary and ternary mixtures in a reversed-phase system. The obtained equilibrium data were correlated using the competitive Langmuir isotherm equation, a bi-Langmuir model, the ideal adsorbed solution theory and the real adsorbed solution theory. No substantial improvement of the predictions was achieved using the more complex models instead of the most simple Langmuir model.

Competitive displacement of pT alpha by TCR-alpha during TCR assembly prevents surface coexpression of pre-TCR and alpha beta TCR

During alphabeta T cell development, CD4(-)CD8(-) thymocytes first express pre-TCR (pTalpha/TCR-beta) before their differentiation to the CD4(+)CD8(+) stage. Positive selection of self-tolerant T cells is then determined by the alphabeta TCR expressed on CD4(+)CD8(+) thymocytes. Conceivably, an overlap in surface expression of these two receptors would interfere with the delicate balance of thymic selection. Therefore, a mechanism ensuring the sequential expression of pre-TCR and TCR must function during thymocyte development. In support of this notion, we demonstrate that expression of TCR-alpha by immature thymocytes terminates the surface expression of pre-TCR. Our results reveal that expression of TCR-alpha precludes the formation of pTalpha/TCR-beta dimers within the endoplasmic reticulum, leading to the displacement of pre-TCR from the cell surface. These findings illustrate a novel posttranslational mechanism for the regulation of pre-TCR expression, which may ensure that alphabeta TCR expression on thymocytes undergoing selection is not compromised by the expression of pre-TCR.

Identification of a novel pre-TCR isoform in which the accessibility of the TCR beta subunit is determined by occupancy of the 'missing' V domain of pre-T alpha

We have identified a novel pre-TCR isoform that is structurally distinct from conventional pre-TCR complexes and whose TCR beta chains are inaccessible to anti-TCR beta antibodies. We term this pre-TCR isoform the MB (masked beta)-pre-TCR. Pre-T alpha (pT alpha) subunits of MB-pre-TCR complexes have a larger apparent mol. wt due to extensive modification with O:-linked carbohydrates; however, preventing addition of O-glycans does not restore antibody recognition of the TCR beta subunits of MB-pre-TCR complexes. Importantly, accessibility of TCR beta chains in MB-pre-TCR complexes is restored by filling in the 'missing' variable (V) domain of pT alpha with a V domain from TCR alpha. Moreover, the proportion of pre-TCR complexes in which the TCR beta subunits are accessible to anti-TCR beta antibody varies with the cellular context, suggesting that TCR beta accessibility is controlled by a trans-acting factor. The way in which this factor might control TCR beta accessibility as well as the physiologic relevance of TCR beta masking for pre-TCR function are discussed.

Thymic selection generates T cells expressing self-reactive TCRs in the absence of CD45

The CD45 protein tyrosine phosphatase regulates Ag receptor signaling in T and B cells. In the absence of CD45, TCR coupling to downstream signaling cascades is profoundly reduced. Moreover, in CD45-null mice, the maturation of CD4+CD8+ thymocytes into CD4+CD8- or CD4-CD8+ thymocytes is severely impaired. These findings suggest that thymic selection may not proceed normally in CD45-null mice, and may be biased in favor of thymocytes expressing TCRs with strong reactivity toward self-MHC-peptide ligands to compensate for debilitated TCR signaling. To test this possibility, we purified peripheral T cells from CD45-null mice and fused them with the BWalpha-beta- thymoma to generate hybridomas expressing normal levels of TCR and CD45. The reactivity of these hybridomas to self or foreign MHC-peptide complexes was assessed by measuring the amount of IL-2 secreted upon stimulation with syngeneic or allogeneic splenocytes. A very high proportion (55%) of the hybridomas tested reacted against syngeneic APCs, indicating that the majority of T cells in CD45-null mice express TCRs with high avidity for self-MHC-peptide ligands, and are thus potentially autoreactive. Furthermore, a large proportion of TCRs selected in CD45-null mice (H-2b) were also shown to display reactivity toward closely related MHC-peptide complexes, such as H-2bm12. These results support the notion that modulating the strength of TCR-mediated signals can alter the outcome of thymic selection, and demonstrate that CD45, by molding the window of affinity/avidity for positive and negative selection, directly participates in the shaping of the T cell repertoire.

SCL and LMO1 alter thymocyte differentiation: inhibition of E2A-HEB function and pre-T alpha chain expression

Cooperation between the stem cell leukemia (SCL) transcription factor and its nuclear partners LMO1 or LMO2 induces aggressive T cell acute lymphoblastic leukemia when inappropriately expressed in T cells. This study examined the cellular and molecular targets of the SCL-LMO complex at the preleukemic stage. We show that SCL and its partners are coexpressed in the most primitive thymocytes. Maturation to the pre-T cell stage is associated with a down-regulation of SCL and LMO1 and LMO2, and a concomitant up-regulation of E2A and HEB expression. Moreover, enforced expression of SCL-LMO1 inhibits T cell differentiation and recapitulates a loss of HEB function, causing a deregulation of the transition checkpoint from the CD4-CD8- to CD4+CD8+ stages. Finally, we identify the gene encoding pT alpha as a downstream target of HEB that is specifically repressed by the SCL-LMO complex.

GP referral to an eating disorder service: why the wide variation?

BACKGROUND

Early detection and management of patients with eating disorders is thought to improve prognosis, yet little is known about the factors associated with referral of these patients to treatment centres.

AIM

To calculate general practitioner (GP) referral rates to a specialist eating disorder service and determine the association between referral rate and general practice and practitioner factors.

METHOD

Referral rate was calculated from a database of routine referrals to St George's Hospital Eating Disorder Service from January 1990 to May 1996 and correlated with practice and practitioner details obtained from medical directories and health authority data.

RESULTS

There was a wide variation in referral rates. A higher referral rate was found to be associated with practice size, proximity to the clinic, female GPs, GPs having the MRCGP qualification, being United Kingdom qualified, and offering full contraceptive services. Fundholding was associated with lower rates of referral.

CONCLUSION

Patients with eating disorders may be at a disadvantage in certain practices. Educational interventions could be targeted towards low referrals.

Quantification of single solute and competitive adsorption isotherms using a closed-loop perturbation method

A modification of the classical method of perturbation chromatography for measuring isotherms of the adsorption of dissolved components is suggested. The general principle of the method consists in analyzing responses of the chromatographic system to small perturbations at different equilibrium concentrations. Essential advantages of the method are: (a) only retention times or volumes have to be measured and no detector calibration is required and (b) experiments with mixtures can be performed and analyzed efficiently. The modification suggested in this paper is the application of a closed-loop arrangement allowing the efficient exploitation of the sample. Experimental data for four different chromatographic systems are presented to illustrate the method. With the determined adsorption isotherms elution profiles could be predicted satisfactorily.

The connecting peptide domain of pT alpha dictates weak association of the pre-T cell receptor with the TCR zeta subunit

Signals delivered through the pre-TCR, a heterodimer of pT alpha and TCR beta chains, are crucial for the maturation and proliferation of immature alphabeta lineage thymocytes from the CD4- CD8- to the CD4+ CD8+ stage. To gain insight into the structural and functional properties of the pre-TCR, chimeric TCR alpha chains were generated by replacing domains of the alpha chain cytoplasmic, transmembrane and constant regions with homologous domains from the pT alpha chain. All chimeric TCR could be expressed stably at the cell surface and induce Ca2+ mobilization as well as phosphorylation of several protein substrates on tyrosine residues. However, chimeras wherein the connecting peptide of TCR alpha chain was substituted by the one from pT alpha, were weakly associated with the TCR zeta chain, showing that functional but not physical interactions were preserved in such chimeras. In contrast, introduction of the connecting peptide of TCR alpha in the pT alpha chain was insufficient to confer stable association with the TCR zeta chain. These results demonstrate that the inability of the pre-TCR to interact strongly with TCR zeta is attributable to amino acid residues present throughout the region comprised between the intrachain Cys and the transmembrane domain. It remains to be determined whether the weak physical interaction between the pre-TCR alphand the zeta2 homodimer prevents the activation of specific TCR zeta-dependent signaling pathways, and thus confers unique signaling properties upon the pre-TCR. In addition, this structural difference between the pT alpha/beta and alphabeta TCR might constitute a means to regulate the expression of these receptors at the surface of thymocytes, at different stages of their maturation.

Surface antigen detection with non-fluorescent, antibody-coated microbeads: an alternative method compatible with conventional fluorochrome-based labeling

BACKGROUND

Our goal was to devise a new labeling technique allowing the flow cytometric detection of an additional cell surface marker without the need for a supplementary fluorochrome.

METHODS

Non-fluorescent polystyrene latex microbeads (0.1 or 0.5 microm in diameter) were coated with monoclonal antibodies (mAbs) by adsorption. Upon binding to their specific antigen on the surface of the cell, mAb-coated beads induced a dramatic shift in the side scatter channel (SSC), resulting in a well-defined cell population.

RESULTS

We show that expression of CD4 on murine peripheral lymphocytes, labeled with anti-CD4 mAb-coated beads, can be readily detected through an amplification of the SSC signal. Simultaneous labeling of lymphocytes with phycoerythrin- (PE)-conjugated anti-CD4 mAb and anti-CD4 mAb-coated beads, showed that all PE+ cells were SSChigh, thus establishing the specificity of the technique. Hence, we have demonstrated that staining with mAb-coated beads could be combined to conventional labeling methods with fluorochrome-conjugated mAbs. Using a standard 488 nm single laser cytometer, we have performed a five-parameter analysis, simultaneously detecting fluorescein isothiocyanate (FITC), PE, RED670 and RED613, in combination with SSC signal modulation induced by mAb-coated beads. Moreover, we have shown that beads coated with mAbs directed against various antigens (CD45R, Mac-1, and TCRbeta) can be used on various tissues, namely lymph nodes, spleen, or bone marrow.

CONCLUSIONS

mAb-coated latex beads can therefore easily be used as an additional surface label, and provide a simple and reliable mean to upgrade the analysis capabilities of standard flow cytometry units.

CD4+ CD8+ thymocytes are preferentially induced to die following CD45 cross-linking, through a novel apoptotic pathway

Ligation of the protein tyrosine phosphatase CD45 on both mature and immature T cells modulates the amplitude of TCR-mediated signals. In this work, we have evaluated the consequences of CD45 ligation on immature T cells, in the absence of TCR engagement. Cross-linking of CD45 on thymocytes by mAbs led to the induction of cellular death, characterized by a reduction in mitochondrial membrane potential (delta psi(m)), production of reactive oxygen species, loss in membrane asymmetry, exposure of phosphatidylserine residues, and incorporation of vital dyes. In sharp contrast to most stimuli causing thymocyte death, CD45 cross-linking did not lead to DNA degradation. Cell death was not blocked by Bcl-2 overexpression or treatment with caspase inhibitor. However, death was inhibited by the addition of scavengers of reactive oxygen species. We also established that susceptibility to CD45-mediated death is acquired during the transition of early CD4- CD8- TCR- T cell precursors into CD4+ CD8+ TCR- thymocytes and is increased with further acquisition of surface TCR on these cells. Moreover, mature thymocytes were much less sensitive to CD45 cross-linking than CD4+ CD8+ cells. We propose that during T cell development, CD45 ligation could induce the death of those immature thymocytes that do not fulfill the requirements for positive selection.

CD4+ CD8+ thymocytes are preferentially induced to die following CD45 cross-linking, through a novel apoptotic pathway

Ligation of the protein tyrosine phosphatase CD45 on both mature and immature T cells modulates the amplitude of TCR-mediated signals. In this work, we have evaluated the consequences of CD45 ligation on immature T cells, in the absence of TCR engagement. Cross-linking of CD45 on thymocytes by mAbs led to the induction of cellular death, characterized by a reduction in mitochondrial membrane potential (delta psi(m)), production of reactive oxygen species, loss in membrane asymmetry, exposure of phosphatidylserine residues, and incorporation of vital dyes. In sharp contrast to most stimuli causing thymocyte death, CD45 cross-linking did not lead to DNA degradation. Cell death was not blocked by Bcl-2 overexpression or treatment with caspase inhibitor. However, death was inhibited by the addition of scavengers of reactive oxygen species. We also established that susceptibility to CD45-mediated death is acquired during the transition of early CD4- CD8- TCR- T cell precursors into CD4+ CD8+ TCR- thymocytes and is increased with further acquisition of surface TCR on these cells. Moreover, mature thymocytes were much less sensitive to CD45 cross-linking than CD4+ CD8+ cells. We propose that during T cell development, CD45 ligation could induce the death of those immature thymocytes that do not fulfill the requirements for positive selection.

Specific activation of the cysteine protease CPP32 during the negative selection of T cells in the thymus

Cysteine proteases of the CED-3 and ICE family have been recently proposed as the ultimate executioners in several mammalian cell death pathways. Among them, the cysteine protease CPP32 has been shown to participate in programmed cell death (PCD), or apoptosis, affecting lymphoid cells in vitro. In the thymus, negative selection is a mechanism through which developing thymocytes expressing a TcR with high affinity for self peptide-MHC complexes are eliminated by PCD. In order to investigate the role of CPP32 in thymic apoptosis, isolated thymocytes were submitted to cell surface CD3 crosslinking by immobilized anti-CD3 mAb or to dexamethasone treatment. Although apoptosis occurred in the absence or after crosslinking with anti-CD3 mAb, specific activation of CPP32, as assessed by the extent of proteolytic cleavage of the p32 zymogen, was only detected in thymocytes cultured in the presence of the immobilized antibody or dexamethasone. This activation was a very early event during apoptosis as it occurred before the exposure of phosphatidyl serine to the upper side of the cell membrane. This was observed both in anti-CD3- and dexamethasone-induced apoptosis. Moreover, using mice transgenic for pigeon cytochrome C (PCC)-specific TcR, we were able to show that, after injection of PCC, the activation of CPP32 and cleavage of its substrate occurred in thymocytes obtained from mice expressing a permissive MHC haplotype for PCC presentation (H-2k). Moreover, PCC induced apoptosis was blocked by the caspase inhibitor zVAD. While spontaneous apoptosis was not accompanied by detectable levels of CPP32 processing, it was characterized by the proteolysis of poly(ADP-ribose) polymerase (PARP) and was blocked by the cysteine protease inhibitor, zVAD-CH2F. Taken together, these results support the concept that CPP32 is among the earliest effectors of the pathway leading to negative selection of autoreactive thymocytes. Our results also suggest the involvement of a distinct CPP32-like cysteine protease in spontaneous apoptosis of thymocytes.

Novel dimeric Nur77 signaling mechanism in endocrine and lymphoid cells

Within the nuclear receptor family, Nur77 (also known as NGFI-B) distinguishes itself by its ability to bind a target sequence (the NBRE) as a monomer and by its role in T-cell receptor (TCR)-induced apoptosis in T cells. We now report on a novel mechanism of Nur77 action that is mediated by homodimers. These dimers bind a Nur77 response element (NurRE), which has been identified as a target of CRH-induced Nur77 in the pro-opiomelanocortin (POMC) gene promoter. Both halves of the palindromic NurRE are required for responsiveness to physiological signals, like CRH in pituitary-derived AtT-20 cells. Similarly, in T-cell hybridomas, TCR activation induced NurRE but not NBRE reporters. The in vivo signaling function of Nur77 thus appears to be mediated by dimers acting on a palindromic response element of unusual spacing between its half-sites. This mechanism may represent the biologically relevant paradigm of action for this subfamily of orphan nuclear receptors.

Antagonism between Nur77 and glucocorticoid receptor for control of transcription

Two important functions of glucocorticoids (Gc), namely, suppression of immune system function and feedback repression of the hypothalamo-pituitary-adrenal (HPA) axis, are mediated through repression of gene transcription. Previous studies have indicated that this repression is exerted in part through antagonism between the glucocorticoid receptors (GR) and the AP-1 family of transcription factors. However, this mechanism could not account for repression of the pro-opiomelanocortin (POMC) gene, an important regulator of the HPA axis. Our recent identification of the orphan nuclear receptor Nur77 as a mediator of CRH induction of POMC transcription led us, in the present work, to show that Gc antagonize this positive signal at two levels. First, Gc partly blunt the CRH induction of Nur77 mRNA, and second, they antagonize Nur77-dependent transcription. GR repression is exerted by antagonism of Nur77 action on the NurRE element of the POMC gene. Gc antagonism of NurRE activity was observed in response to physiological stimuli in both endocrine (CRH induction of POMC) and lymphoid (T-cell receptor activation) cells. In transfection experiments, transcriptional activation by Nur77 and the repressor activity of liganded GR titrated each other on their cognate DNA target. In vitro binding experiments as well as mutation analysis of GR suggest that the mechanism of GR antagonism of Nur77 is very similar to that of the antagonism between GR and AP-1. The convergence of positive signals mediated by Nur77 (and also probably by related family members) and negative signals exerted by GR appears to be a general mechanism for control of transcription, since it is active in both endocrine and lymphoid cells.

Induction of thymocyte deletion by purified single peptide/major histocompatibility complex ligands

We report a novel in vitro approach that allows study of the consequences of TCR ligation on thymocytes in the absence of thymic stromal cells. Hence, thymocytes were incubated either in the presence of recombinant antigenic peptide/MHC complexes, which represent ligands of physiologic affinities, or with anti-TCR mAb, a ligand of supraphysiologic affinity. Whereas TCR cross-linking with mAb led to thymocyte deletion, incubation with peptide/MHC ligands did not trigger cellular apoptosis. However, the addition of a costimulatory signal (provided by anti-CD28 mAb) allowed the induction of apoptosis following TCR binding to peptide/MHC ligands, and it increased the levels of cell death obtained through mAb-mediated TCR cross-linking. Requirement for accessory signals seen with TCR stimulation by peptide/MHC complexes argues in favor of qualitative differences between TCR engagement by ligands of either physiologic or supraphysiologic affinity.

Induction of thymocyte deletion by purified single peptide/major histocompatibility complex ligands

We report a novel in vitro approach that allows study of the consequences of TCR ligation on thymocytes in the absence of thymic stromal cells. Hence, thymocytes were incubated either in the presence of recombinant antigenic peptide/MHC complexes, which represent ligands of physiologic affinities, or with anti-TCR mAb, a ligand of supraphysiologic affinity. Whereas TCR cross-linking with mAb led to thymocyte deletion, incubation with peptide/MHC ligands did not trigger cellular apoptosis. However, the addition of a costimulatory signal (provided by anti-CD28 mAb) allowed the induction of apoptosis following TCR binding to peptide/MHC ligands, and it increased the levels of cell death obtained through mAb-mediated TCR cross-linking. Requirement for accessory signals seen with TCR stimulation by peptide/MHC complexes argues in favor of qualitative differences between TCR engagement by ligands of either physiologic or supraphysiologic affinity.

Overexpression of HOXB3 in hematopoietic cells causes defective lymphoid development and progressive myeloproliferation

HOXB3 mRNA levels are high in the earliest CD34+ lineage- bone marrow cells and low to undetectable in later CD34+/CD34- cells. To gain some insight into the role this gene may play in hematopoiesis, HOXB3 was overexpressed in murine bone marrow cells using retroviral gene transfer. Thymi of HOXB3 marrow recipients were reduced in size compared with control transplant recipients, with a 24-fold decrease in the absolute number of CD4+ CD8+ cells and a 3-fold increase in the number of CD4- CD8- thymocytes that contained a high proportion of gammadelta TCR+ cells. B cell differentiation was also perturbed in these mice, as indicated by the virtual absence of transduced IL-7-responsive pre-B clonogenic progenitors. Recipients of HOXB3-transduced cells also had elevated numbers of mature granulocyte macrophage colony-forming cells in their bone marrow and spleen. Together these results suggest roles for HOXB3 in proliferation and differentiation processes of both early myeloid and lymphoid developmental pathways.

Modulation of integrin-mediated intercellular adhesion during the interaction of thymocytes with stromal cells expressing VLA-4 and LFA-1 ligands

Mature peripheral T cells closely regulate their intercellular interactions by modulating integrin adhesion functions. The ability of members of the integrin family to mediate intercellular adhesion is dependent on signals from within the cells (inside-out signaling) that increase the avidity of integrins for their ligands. These changes in avidity are independent of the quantitative changes on the number of receptors, and there is evidence to suggest that phosphorylation events play a predominant role in the regulation of the avidity state of the integrins. Whether such regulatory mechanisms are operative during T cell development had hitherto been an opened question. In the present work, we have used an in vitro adhesion assay between thymocytes and target cells expressing VLA-4 and LFA-1 counter ligands to determine how thymocytes can discriminate between integrin-specific signals during T cell development. Our findings are that VLA-4, but not LFA-1, is constitutively expressed in its high-avidity state during the early stages of T cell development, and that the high-avidity state of thymocytes for VCAM-1-expressing cells is closely regulated by signaling through protein kinase C and protein tyrosine kinase pathways. At later stages of development, mature thymocytes prior to leaving the thymus turn off both VLA-4 and LFA-1 adhesion functions. Our results show that the low-affinity state of integrins on peripheral mature T cells is established before mature thymocytes leave the thymus. Only when mature T cells recognize antigenic peptides in the context of major histocompatibility complex in the periphery will they turn on the adhesion function of VLA-4 and/or LFA-1 integrins.

Thymic epithelial cell lines that mediate positive selection can also induce thymocyte clonal deletion

Negative selection of potentially autoreactive thymocytes occurs mainly in the thymus and is thought to be induced primarily by interaction with bone marrow-derived cells. However, some studies have also reported a role for radioresistant thymic cells, which are probably epithelial in origin, in the deletion of thymocytes reacting to endogenous superantigens. We have previously demonstrated that thymic epithelial cell lines could induce thymocyte-positive selection in vivo. In this study, we assessed the potential of these cells to delete thymocytes reacting to the staphylococcal enterotoxin A or B superantigens in vitro. In the presence of staphylococcal enterotoxin A or B we found that all thymic epithelial cell lines used in this study were capable of activating T cell hybrids or deleting CD4+CD8+ thymocytes expressing an appropriate TCR. The extent of superantigen-mediated thymocyte deletion mediated by thymic epithelial cell lines was comparable to that mediated by a thymic macrophage cell line. Similar results were obtained with three phenotypically distinct thymic cell lines, suggesting that the ability to induce thymocyte deletion might be a general feature of various subsets of thymic epithelium. The observations provided in this study, combined with our previous demonstration that the same thymic epithelial cell lines can participate in positive selection, suggest that a given stromal cell population might be capable of taking part both in positive and negative selection of thymocytes.

Iron overload in beta 2-microglobulin-deficient mice

The present paper describes the results of a comparative histological and quantitative analysis of iron distribution in tissues of beta 2m-/- and beta 2m+/- mice of different ages. Progressive hepatic iron overload, indistinguishable from that observed in human hemochromatosis, was found only in mice homozygous for the mutated beta 2m gene. Total iron measurements done by flame atomic absorption showed statistically significant differences between liver samples from 5 beta 2m+/- heterozygotes (468 +/- 174 micrograms/g of dry weight) and 9 mice homozygous for the mutated beta 2m gene with average total hepatic iron levels of 1583 +/- 423 micrograms/g of dry weight.

Thymic epithelial cell lines that mediate positive selection can also induce thymocyte clonal deletion

Negative selection of potentially autoreactive thymocytes occurs mainly in the thymus and is thought to be induced primarily by interaction with bone marrow-derived cells. However, some studies have also reported a role for radioresistant thymic cells, which are probably epithelial in origin, in the deletion of thymocytes reacting to endogenous superantigens. We have previously demonstrated that thymic epithelial cell lines could induce thymocyte-positive selection in vivo. In this study, we assessed the potential of these cells to delete thymocytes reacting to the staphylococcal enterotoxin A or B superantigens in vitro. In the presence of staphylococcal enterotoxin A or B we found that all thymic epithelial cell lines used in this study were capable of activating T cell hybrids or deleting CD4+CD8+ thymocytes expressing an appropriate TCR. The extent of superantigen-mediated thymocyte deletion mediated by thymic epithelial cell lines was comparable to that mediated by a thymic macrophage cell line. Similar results were obtained with three phenotypically distinct thymic cell lines, suggesting that the ability to induce thymocyte deletion might be a general feature of various subsets of thymic epithelium. The observations provided in this study, combined with our previous demonstration that the same thymic epithelial cell lines can participate in positive selection, suggest that a given stromal cell population might be capable of taking part both in positive and negative selection of thymocytes.