Regulatory CD4+Foxp3+ T Cells Control the Severity of Anaphylaxis

Objective

Anaphylaxis is a life-threatening outcome of immediate-type hypersensitivity to allergen, consecutive to mast cell degranulation by allergen-specific IgE. Regulatory T cells (Treg) can control allergic sensitization and mast cell degranulation, yet their clinical benefit on anaphylactic symptoms is poorly documented. Here we investigated whether Treg action during the effector arm of the allergic response alleviates anaphylaxis.

Methods

We used a validated model of IgE-mediated passive systemic anaphylaxis, induced by intravenous challenge with DNP-HSA in mice passively sensitized with DNP-specific IgE. Anaphylaxis was monitored by the drop in body temperature as well as plasma histamine and serum mMCP1 levels. The role of Treg was analyzed using MHC class II-deficient (Aβ^°/°) mice, treatment with anti-CD25 or anti-CD4 mAbs and conditional ablation of Foxp3⁺ Treg in DEREG mice. Therapeutic efficacy of Treg was also evaluated by transfer experiments using FoxP3-eGFP knock-in mice.

Results

Anaphylaxis did not occur in mast cell-deficient W/W^v mutant mice and was only moderate and transient in mice deficient for histamine receptor-1. Defects in constitutive Treg, either genetic or induced by antibody or toxin treatment resulted in a more severe and/or sustained hypothermia, associated with a rise in serum mMCP1, but not histamine. Adoptive transfer of Foxp3⁺ Treg from either naïve or DNP-sensitized donors similarly alleviated body temperature loss in Treg-deficient DEREG mice.

Conclusion

Constitutive Foxp3⁺ Treg can control the symptomatic phase of mast cell and IgE-dependent anaphylaxis in mice. This might open up new therapeutic avenues using constitutive rather than Ag-specific Treg for inducing tolerance in allergic patients.     

In Vitro and In Vivo Models of Cerebral Ischemia Show Discrepancy in Therapeutic Effects of M2 Macrophages

The inflammatory response following ischemic stroke is dominated by innate immune cells: resident microglia and blood-derived macrophages. The ambivalent role of these cells in stroke outcome might be explained in part by the acquisition of distinct functional phenotypes: classically (M1) and alternatively activated (M2) macrophages. To shed light on the crosstalk between hypoxic neurons and macrophages, an in vitro model was set up in which bone marrow-derived macrophages were co-cultured with hippocampal slices subjected to oxygen and glucose deprivation. The results showed that macrophages provided potent protection against neuron cell loss through a paracrine mechanism, and that they expressed M2-type alternative polarization. These findings raised the possibility of using bone marrow-derived M2 macrophages in cellular therapy for stroke. Therefore, 2 million M2 macrophages (or vehicle) were intravenously administered during the subacute stage of ischemia (D4) in a model of transient middle cerebral artery occlusion. Functional neuroscores and magnetic resonance imaging endpoints (infarct volumes, blood-brain barrier integrity, phagocytic activity assessed by iron oxide uptake) were longitudinally monitored for 2 weeks. This cell-based treatment did not significantly improve any outcome measure compared with vehicle, suggesting that this strategy is not relevant to stroke therapy.     

Deciphering the Glycan Preference of Bacterial Lectins by Glycan Array and Molecular Docking with Validation by Microcalorimetry and Crystallography

Recent advances in glycobiology revealed the essential role of lectins for deciphering the glycocode by specific recognition of carbohydrates. Integrated multiscale approaches are needed for characterizing lectin specificity: combining on one hand high-throughput analysis by glycan array experiments and systematic molecular docking of oligosaccharide libraries and on the other hand detailed analysis of the lectin/oligosaccharide interaction by x-ray crystallography, microcalorimetry and free energy calculations. The lectins LecB from Pseudomonas aeruginosa and BambL from Burkholderia ambifaria are part of the virulence factors used by the pathogenic bacteria to invade the targeted host. These two lectins are not related but both recognize fucosylated oligosaccharides such as the histo-blood group oligosaccharides of the ABH(O) and Lewis epitopes. The specificities were characterized using semi-quantitative data from glycan array and analyzed by molecular docking with the Glide software. Reliable prediction of protein/oligosaccharide structures could be obtained as validated by existing crystal structures of complexes. Additionally, the crystal structure of BambL/Lewis x was determined at 1.6 Å resolution, which confirms that Lewis x has to adopt a high-energy conformation so as to bind to this lectin. Free energies of binding were calculated using a procedure combining the Glide docking protocol followed by free energy rescoring with the Prime/Molecular Mechanics Generalized Born Surface Area (MM-GBSA) method. The calculated data were in reasonable agreement with experimental free energies of binding obtained by titration microcalorimetry. The established predictive protocol is proposed to rationalize large sets of data such as glycan arrays and to help in lead discovery projects based on such high throughput technology.     

Novel Plasmodium falciparum Maurer's clefts protein families implicated in the release of infectious merozoites

The pathogenicity of the most deadly human malaria parasite, Plasmodium falciparum, relies on the export of virulence factors to the surface of infected erythrocytes. A novel membrane compartment, referred to as Maurer's clefts, is transposed to the host erythrocyte, acting as a marshal platform in the red blood cell cytoplasm, for exported parasite proteins addressed to the host cell plasma membrane. We report here the characterization of three new P. falciparum multigene families organized in 9 highly conserved clusters with the Pfmc‐2tm genes in the subtelomeric regions of parasite's chromosomes and expressed at early trophozoite stages. Like the PfMC‐2TM proteins, the PfEPF1, 3 and 4 proteins encoded by these families are exported to the Maurer's clefts, as peripheral or integral proteins of the Maurer's cleft membrane and largely exposed to the red cell cytosolic face of this membrane. A promoter titration approach was used to question the biological roles of these P. falciparum‐specific exported proteins. Using the Pfepf1 family promoter, we observed the specific downregulation of all four families, correlating with the inefficient release of merozoites while the parasite intra‐erythrocytic maturation and Maurer's clefts morphology were not impacted.     

Thermal and hydrodynamic modelling of active catheters for interventional radiology

Interventional radiologists desire to improve their operating tools such as catheters. Active catheters in which the tip is moved using shape memory alloy actuators activated using the Joule effect present a promising approach for easier navigation in the small vessels. However, the increase in temperature caused by this Joule effect must be controlled in order to prevent damage to blood cells and tissues. This paper is devoted to the simulation and experimental validation of a fluid-thermal model of an active catheter prototype. Comparisons between computer-predicted and experimentally measured temperatures are presented for both experiments in air and water at 37°C. Good agreement between the computational and experimental results is found, demonstrating the validity of the developed computer model. These comparisons enable us to highlight some important issues in the modelling process and to determine the optimal current for the activation of the catheter.     

Effect of low temperature on emergence, fecundity, longevity and host-feeding by Trichogramma brassicae

The occurrence of sub-optimal temperatures during development of immature parasitoids can have important consequences on adult fitness. We investigated the impact of different regimes of low temperature on emergence, differential mortality, longevity and fecundity in Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae). The host-feeding behaviour of adult females was also measured as an indicator of energy reserve at emergence. Acclimation of 30 days at 10 °C or 24 days at 13 °C allowed T. brassicae immatures to develop with a lower mortality than those exposed directly at 5 °C. Longevity and fecundity of females decreased at a lower rate with acclimation at 10 °C suggesting that acclimation at 13 °C may have depleted the energy reserves of individuals more than acclimation at 10 °C. Short photoperiod exposure during the maternal generation had no effect on progeny’s fitness. We found no difference among the treatments in females’ host-feeding behaviours, in differential mortality at emergence, in female’s mobility and in F1 sex ratio.