Immunogenic peptides require an undisturbed phospholipid cell membrane environment and must be amphipathic to immobilize Ia on B cells

Ia-reactive immunogenic peptides have been shown to immobilize Ia molecules on the B cell surface and to facilitate their aggregation with specific alloantibody. We show that to immobilize Ia the peptide must be amphipathic. Polar peptides appear to bind to Ia molecules as judged by competitive inhibition, but do not immobilize the MHC molecule. This suggests the possibility that peptides establish the immobilizing membrane contact via a lipophilic group. Examining the B cell membrane lipid environment, we found that treatment of B cells with phospholipase C prevents peptide-mediated immobilization of Ia. The requirement of a lipophilic peptide portion as well as of phospholipase-sensitive membrane components for effective peptide-mediated Ia aggregation on B cell membranes suggests a role for membrane phospholipids in this process. We advance the speculation that immunodominant amphipathic peptides immobilize Ia molecules by attaching them to cell surface phospholipids which we tentatively refer to as immobilizing phospholipids.     

Variation du taux d’infestation par Thaumetopoea pityocampa du pin d’Alep : effet sur les paramètres dendrométriques dans les forêts de la région de Djelfa (Atlas saharien,Algérie)

The forests of the Saharan Atlas represent the southern edge of the natural range of the Aleppo pine (Pinus halepensis Mill.). These are exposed to climatic stress in relation to drought and attacks of the pine processionary moth (Thaumetopoea pityocampa Schiff., denoted by CP in the French text). The purpose of our work is to study the variation of the infestation rate by the pine processionary moth and its density with climatic factors and dendrometric parameters. The infestation rate (7.82%) by the pine processionary moth and its density (2.74 ± 2.61 nests/tree) were lower in our pine forests than in the northern ones. It appeared that the attacks of the moth increase mainly with the number of days of frost and heatwave. The dendrometric parameters were negatively correlated with the moth's density per tree. On the other hand, the latter was positively correlated with the defoliation rate. The results were discussed in a biogeographic framework in the light of the current knowledge of the distribution of the pine processionary moth in the Aleppo pine, in relation with the climatic conditions.     

Modulation of tetracycline-phospholipid interactions by tuning of pH at the water-air interface

This paper is part of a systematic study of the interactions of tetracycline antibiotics with phospholipid monolayers at the water-air interface. Tetracyclines are widespread antibiotics that undergo a series of protonation equilibria in solution, depending on the pH. The surface activity of tetracyclines was determined by means of surface tension measurements for three different systems, i.e. water, TRIS and McIlvaine-EDTA buffer. Surface pressure-molecular area and surface potential-molecular area isotherms were acquired for dipalmitoylphosphatidic acid monolayers on TRIS buffer (pH=7.0) and McIlvaine-EDTA buffer (pH=4.0) solution as a function of tetracycline concentration in the subphase. Comparative analysis of surface potential data, with the molecular dipole moment of tetracycline obtained from semiempirical calculations, provided information on the orientation of tetracycline at the interface. Surface pressure measurements as a function of monolayer compression were described, applying either a continuous partition model or Langmuir adsorption isotherms. The results obtained in the case of buffer solutions were compared to those obtained for tetracycline in water subphases. The analysis of the results indicated that electrostatic interactions dictate the migration of tetracycline to the monolayer interface. Penetration of the molecule to the lipophilic portion of the monolayer was unlikely, especially at high surface pressures. The results showed that stronger interactions are established between the zwitterionic tetracycline and the deprotonated phosphatidic group in TRIS buffer solution; in this case, tetracycline binds at the monolayer interface following a Langmuir type adsorption. In the case of water, where the monodeprotonated acid and the tetracycline zwitterions are the only species involved, the data can be described by continuous partition of tetracycline between interfacial and bulk phases. The same holds for McIlvaine-EDTA buffer subphases, although the high concentrations of citrate ions in this buffer competitively interfere with tetracycline association at the monolayer interface.     

A characteristic Mls-1a response precedes Mls-1a anergy in vivo

T cells expressing V beta 6 variable gene segments of the T cell receptor undergo blast formation and divide in mice after injection of lymphoid cells bearing minor lymphocyte-stimulating (Mls)-1a gene products. This in vivo Mls-1a response resembles in vitro Mls-1a stimulation; it is dose dependent, not MHC-class II haplotype restricted, but requires expression of functional IE gene products. The in vivo Mls-1a response is followed by a complete and specific in vivo Mls-1a anergy and a partial in vitro Mls-1a anergy. The measurement of a Mls-1a response in vivo and of the establishment of in vivo anergy to it provides a convenient method to assay Mls-1a reactivity of T cells in vivo on a cell-by-cell basis in terms of cell surface phenotype, size, and mitotic activity.     

Effect of the phospholipid head group in antibiotic-phospholipid association at water-air interface

We studied the interactions of tetracycline antibiotics, TCs, with phospholipid monolayers with the two-fold aim of elucidating the mechanism of action of TCs and to provide a first step for the realization of bio-mimetic sensor for such drugs by means of the Langmuir-Blodgett technique. Preliminary surface tension studies demonstrated that surface activity of tetracycline is moderate and dependent on the pH of the subphase. We selected three phospholipids having hydrophobic chains of the same length but differing in the polar head structures, i.e. dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylethanolamine, and dipalmitoylphosphatidic acid. Surface pressure- and surface potential- area isotherms were employed to investigate the behavior of the phospholipid monolayers at the water-air interface when tetracycline was added to the aqueous subphase. Analysis of the results indicated that the electrostatic interaction is the driving force for migration of tetracycline towards the interface where localized adsorption to the head groups occurs. Nevertheless, such interactions appear to be insufficient to promote penetration of tetracycline through the hydrophobic layer.     

Effects of intercropping on field-scale phosphorus acquisition processes in a calcareous soil

Plant and Soil - Calcium uptake by plants and the ratio of calcium to phosphorus (Ca/P) in the uptake have been recently identified as important drivers of P acquisition in neutral to alkaline...     

On possible trypsin-induced biases in peptides analysis with aerolysin nanopore

Nanopore-based single-molecule analysis technique is a promising approach in the field of proteomics. In this Technical Brief, the interaction between the biological nanopore of Aerolysin (AeL) and peptides is investigated, focusing on potential biases depending on the AeL activation protocol. Our results reveal that residual trypsin, which may be unintentionally introduced in analyte solution when using a classical AeL activation protocol, can induce a significant formation of shorter peptides by enzymatic degradation of longer ones, which may lead to unwanted effects and/or misinterpretations. AeL free-trypsin activation protocol eliminates this bias and appears more appropriate for peptide/proteins analysis, specifically in the perspective of nanopore-based molecular fingerprinting or of low-abundance species characterization.     

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.     

Criterion validity and between-day reliability of an inertial-sensor-based trunk postural stability test during unstable sitting

IntroductionAdequate neuromuscular control of the lumbar spine is required to prevent lumbar injuries. A trunk postural stability test has been proposed earlier, using a chair wobbling on a central pivot and four springs with adjustable positions to modulate task difficulty. An inertial sensor is fixed on the chair to measure postural sway. The aim of this study is to assess the criterion validity and between-day reliability of the calibration and testing components.MethodsThirty six subjects (with and without low back pain) followed a calibration procedure, four practice trials and three 60-s trials on 2 days. The criterion validity of the inertial sensor was tested against an optoelectronic system and a force platform. The reliability of 38 body sway measures obtained from the inertial sensor angular measures was estimated.ResultsThe inertial sensor led to valid estimates of postural sway. The reliability of the calibration procedure was moderate. Practically no learning effect was detected except for a few body sway measures in patients with CLBP. Three 60-s trials provided acceptable reliability for approximately half of the body sway measures, although this is more difficult to achieve in patients with CLBP.DiscussionThe use of an easy to use inertial sensor led to valid measures of postural sway. A number of body sway measures were identified as reliable tools for individual follow-ups but inter-subject comparisons were anticipated as more difficult when patients with CLBP are involved.     

Induction of neonatal tolerance to the Mls-1a self-super-antigen. Time kinetics and MHC restriction.

We examined the accessibility of the thymus to a self-super-Ag encoded by the Mls-1a region of chromosome 1 and the process by which this Ag establishes immunologic tolerance. Intravenously administered Mls-1a Ag accumulates quickly in peripheral organs of adult or newborn Mls-1a- recipients, where it mounts an immune response. The Ag does not enter the thymus in detectable amounts and does not induce an immune response of Mls-1a-responsive T cells present in this organ. Instead, the thymus of newborn Mls-1a- recipients of Mls-1a+ lymphoid cells continues for several days to export Mls-1a-reactive T cells, which respond to Mls-1a Ag when they encounter it in peripheral organs. This response peaks around day 3 or day 4 and declines very rapidly thereafter. The deletion of intrathymic Mls-1a-reactive T cells ensues simultaneously with this decline. It has previously been shown that Mls-1a Ag causes deletion or anergy of Mls-1a-reactive peripheral T cells, subsequent to their activation. We see the same time kinetics in producing deletion or anergy of Mls-1a-reactive T cells in the thymus of newborn animals, with the exception that the activation phase that precedes the deletion of Mls-1a-reactive T cells occurs in the periphery and not in the thymus. This observation indicates that thymic Mls-1a-specific T cells are not deleted through activation. Whether their deletion depends on a feed-back from the peripheral activation of Mls-1a-reactive cells, as the time relationship could suggest, is not clear. The finding establishes, however, that the deletion of functionally mature Mls-1a-reactive T cells and the activation of such cells are not necessarily related events, which may or may not utilize a common trigger mechanism, such as the engagement of the TCR. Concerning the trigger mechanism, we report that Mls-1a-specific deletion of T cells is an MHC-restricted process, whereas Mls-1a-specific activation of T cells is not MHC restricted.