Splenic retention of Plasmodium falciparum gametocytes to block the transmission of malaria.

Plasmodium falciparum is transmitted from humans to Anopheles mosquito vectors via the sexual erythrocytic forms termed gametocytes. Erythrocyte filtration through microsphere layers (microsphiltration) had shown that circulating gametocytes are deformable. Compounds reducing gametocyte deformability would induce their splenic clearance, thus removing them from the blood circulation and blocking malaria transmission. The hand-made, single-sample prototype for microsphiltration was miniaturized to a 96-well microtiter plate format, and gametocyte retention in the microsphere filters was quantified by high-content imaging. The stiffening activity of 40 pharmacological compounds was assessed in microtiter plates, using a small molecule (calyculin) as a positive control. The stiffening activity of calyculin was assessed in spleen-mimetic microfluidic chips and in macrophage-depleted mice. Marked mechanical retention (80% to 90%) of mature gametocytes was obtained in microplates following exposure to calyculin at concentrations with no effect on parasite viability. Of the 40 compounds tested, including 20 antimalarials, only 5 endoperoxides significantly increased gametocyte retention (1.5- to 2.5-fold; 24 h of exposure at 1 µM). Mature gametocytes exposed to calyculin accumulated in microfluidic chips and were cleared from the circulation of macrophage-depleted mice as rapidly as heat-stiffened erythrocytes, thus confirming results obtained using the microsphiltration assay. An automated miniaturized approach to select compounds for their gametocyte-stiffening effect has been established. Stiffening induces gametocyte clearance both in vitro and in vivo. Based on physiologically validated tools, this screening cascade can identify novel compounds and uncover new targets to block malaria transmission. Innovative applications in hematology are also envisioned.

A mathematical perspective on CD4(+) T cell quorum-sensing.

We analyse a mathematical model of the peripheral CD4(+) T cell population, based on a quorum-sensing mechanism, by which an optimum number of regulatory T cells can be established and maintained. We divide the population of a single T cell receptor specificity into four pools: naive, IL-2 producing, IL-2 non-producing, and regulatory CD4(+) T cells. Proliferation, death and differentiation of cells are introduced as transition probabilities of a stochastic Markov model, with the assumption that the amount of IL-2 available to CD4(+) T cells is proportional to the size of the population of IL-2 producing CD4(+) T cells. We explore the population dynamics both in the absence and in the presence of specific antigen. We study the establishment of the peripheral CD4(+) T cell pool from thymic output in the absence of antigen, and its return to homeostasis after an immune challenge, by steady state analysis of the deterministic approximation. The number of regulatory T cells at steady state is greater in the presence of antigen than in its absence. We also consider the stochastic dynamics of the model after an immune challenge, in particular the behaviour leading to ultimate extinction of the IL-2 producing and regulatory T cell populations.

Valuing genetic and genomic testing in France: current challenges and latest evidence.

High-throughput next-generation sequencing technologies have seen an increase in use in most developed countries. The translation of genomic testing into clinical practice challenges the traditional model of medical care in France and raises numerous medical, legal, ethical, organizational, and financial issues. In order to allow the population to use this revolution to its advantage, France has conceived the French Plan for Genomic Medicine 2025. Its aim is to improve health and quality of life, to organize new pathways of care and counseling, and to make decisions about insurance coverage. It has also been designed to drive innovation and promote economic growth in France by incorporating genomic medicine into the French health care system. These issues can be addressed through evaluations developed to aid the decision-making process in the context of resource scarcity. Health economists can help to resolve these resource allocation challenges by measuring the impact of this technological revolution on patients, caregivers, providers, and the health care system. In this paper, we will review challenges associated with implementing genomic testing in France. One of the pilot studies of the French Plan for Genomic Medicine 2025 will be presented as an illustration of the role of health economists in overcoming some of the challenges of this technological revolution.

microRNA-mediated regulation of mTOR complex components facilitates discrimination between activation and anergy in CD4 T cells.

T cell receptor (TCR) signals can elicit full activation with acquisition of effector functions or a state of anergy. Here, we ask whether microRNAs affect the interpretation of TCR signaling. We find that Dicer-deficient CD4 T cells fail to correctly discriminate between activating and anergy-inducing stimuli and produce IL-2 in the absence of co-stimulation. Excess IL-2 production by Dicer-deficient CD4 T cells was sufficient to override anergy induction in WT T cells and to restore inducible Foxp3 expression in Il2-deficient CD4 T cells. Phosphorylation of Akt on S473 and of S6 ribosomal protein was increased and sustained in Dicer-deficient CD4 T cells, indicating elevated mTOR activity. The mTOR components Mtor and Rictor were posttranscriptionally deregulated, and the microRNAs Let-7 and miR-16 targeted the Mtor and Rictor mRNAs. Remarkably, returning Mtor and Rictor to normal levels by deleting one allele of Mtor and one allele of Rictor was sufficient to reduce Akt S473 phosphorylation and to reduce co-stimulation-independent IL-2 production in Dicer-deficient CD4 T cells. These results show that microRNAs regulate the expression of mTOR components in T cells, and that this regulation is critical for the modulation of mTOR activity. Hence, microRNAs contribute to the discrimination between T cell activation and anergy.

IL-2 coordinates IL-2-producing and regulatory T cell interplay.

Many species of bacteria use quorum sensing to sense the amount of secreted metabolites and to adapt their growth according to their population density. We asked whether similar mechanisms would operate in lymphocyte homeostasis. We investigated the regulation of the size of interleukin-2 (IL-2)-producing CD4(+) T cell (IL-2p) pool using different IL-2 reporter mice. We found that in the absence of either IL-2 or regulatory CD4(+) T (T reg) cells, the number of IL-2p cells increases. Administration of IL-2 decreases the number of cells of the IL-2p cell subset and, pertinently, abrogates their ability to produce IL-2 upon in vivo cognate stimulation, while increasing T reg cell numbers. We propose that control of the IL-2p cell numbers occurs via a quorum sensing-like feedback loop where the produced IL-2 is sensed by both the activated CD4(+) T cell pool and by T reg cells, which reciprocally regulate cells of the IL-2p cell subset. In conclusion, IL-2 acts as a self-regulatory circuit integrating the homeostasis of activated and T reg cells as CD4(+) T cells restrain their growth by monitoring IL-2 levels, thereby preventing uncontrolled responses and autoimmunity.

Quorum-Sensing in CD4(+) T Cell Homeostasis: A Hypothesis and a Model.

Homeostasis of lymphocyte numbers is believed to be due to competition between cellular populations for a common niche of restricted size, defined by the combination of interactions and trophic factors required for cell survival. Here we propose a new mechanism: homeostasis of lymphocyte numbers could also be achieved by the ability of lymphocytes to perceive the density of their own populations. Such a mechanism would be reminiscent of the primordial quorum-sensing systems used by bacteria, in which some bacteria sense the accumulation of bacterial metabolites secreted by other elements of the population, allowing them to "count" the number of cells present and adapt their growth accordingly. We propose that homeostasis of CD4(+) T cell numbers may occur via a quorum-sensing-like mechanism, where IL-2 is produced by activated CD4(+) T cells and sensed by a population of CD4(+) Treg cells that expresses the high-affinity IL-2Rα-chain and can regulate the number of activated IL-2-producing CD4(+) T cells and the total CD4(+) T cell population. In other words, CD4(+) T cell populations can restrain their growth by monitoring the number of activated cells, thus preventing uncontrolled lymphocyte proliferation during immune responses. We hypothesize that malfunction of this quorum-sensing mechanism may lead to uncontrolled T cell activation and autoimmunity. Finally, we present a mathematical model that describes the key role of IL-2 and quorum-sensing mechanisms in CD4(+) T cell homeostasis during an immune response.

Pteridium aquilinum and its ptaquiloside toxin induce DNA damage response in gastric epithelial cells, a link with gastric carcinogenesis.

The multifactorial origin of gastric cancer encompasses environmental factors mainly associated with diet. Pteridium aquilinum-bracken fern-is the only higher plant known to cause cancer in animals. Its carcinogenic toxin, ptaquiloside, has been identified in milk of cows and groundwater. Humans can be directly exposed by consumption of the plant, contaminated water or milk, and spore inhalation. Epidemiological studies have shown an association between bracken exposure and gastric cancer. In the present work, the genotoxicity of P. aquilinum and ptaquiloside, including DNA damaging effects and DNA damage response, was characterized in human gastric epithelial cells and in a mouse model. In vitro, the highest doses of P. aquilinum extracts (40 mg/ml) and ptaquiloside (60 µg/ml) decreased cell viability and induced apoptosis. γH2AX and P53-binding protein 1 analysis indicated induction of DNA strand breaks in treated cells. P53 level also increased after exposure, associated with ATR-Chk1 signaling pathway activation. The involvement of ptaquiloside in the DNA damage activity of P. aquilinum was confirmed by deregulation of the expression of a panel of genes related to DNA damage signaling pathways and DNA repair, in response to purified ptaquiloside. Oral administration of P. aquilinum extracts to mice increased gastric cell proliferation and led to frameshift events in intron 2 of the P53 gene. Our data demonstrate the direct DNA damaging and mutagenic effects of P. aquilinum. These results are in agreement with the carcinogenic properties attributed to this fern and its ptaquiloside toxin and support their role in promoting gastric carcinogenesis.

Surface alpha 2-3- and alpha 2-6-sialylation of human monocytes and derived dendritic cells and its influence on endocytosis.

Several glycoconjugates are involved in the immune response. Sialic acid is frequently the glycan terminal sugar and it may modulate immune interactions. Dendritic cells (DCs) are antigen-presenting cells with high endocytic capacity and a central role in immune regulation. On this basis, DCs derived from monocytes (mo-DC) are utilised in immunotherapy, though many features are ignored and their use is still limited. We analyzed the surface sialylated glycans expressed during human mo-DC generation. This was monitored by lectin binding and analysis of sialyltransferases (ST) at the mRNA level and by specific enzymatic assays. We showed that alpha 2-3-sialylated O-glycans and alpha 2-6- and alpha 2-3-sialylated N-glycans are present in monocytes and their expression increases during mo-DC differentiation. Three main ST genes are committed with this rearrangement: ST6Gal1 is specifically involved in the augmented alpha 2-6-sialylated N-glycans; ST3Gal1 contributes for the alpha2-3-sialylation of O-glycans, particularly T antigens; and ST3Gal4 may contribute for the increased alpha2-3-sialylated N-glycans. Upon mo-DC maturation, ST6Gal1 and ST3Gal4 are downregulated and ST3Gal1 is altered in a stimulus-dependent manner. We also observed that removing surface sialic acid of immature mo-DC by neuraminidase significantly decreased its endocytic capacity, while it increased in monocytes. Our results indicate the STs expression modulates the increased expression of surface sialylated structures during mo-DC generation, which is probably related with changes in cell mechanisms. The ST downregulation after mo-DC maturation probably results in a decreased sialylation or sialylated glycoconjugates involved in the endocytosis, contributing to the downregulation of one or more antigen-uptake mechanisms specific of mo-DC.