The Effect of gadolinium on the ESR response of alanine and ammonium tartrate exposed to thermal neutrons

Many efforts have been made to develop neutron capture therapy (NCT) for cancer treatment. Among the challenges in using NCT is the characterization of the features of the mixed radiation field and of its components. In this study, we examined the enhancement of the ESR response of pellets of alanine and ammonium tartrate with gadolinium oxide exposed to a thermal neutron beam. In particular, the ESR response of these dosimeters as a function of the gadolinium content inside the dosimeter was analyzed. We found that the addition of gadolinium improves the sensitivity of both alanine and ammonium tartrate. However, the use of gadolinium reduces or abolishes tissue equivalence because of its high atomic number (Z(Gd) = 64). Therefore, it is necessary to find the optimum compromise between the sensitivity to thermal neutrons and the reduction of tissue equivalence. Our analysis showed that a low concentration of gadolinium oxide (of the order of 5% of the total mass of the dosimeter) can enhance the thermal neutron sensitivity more than 13 times with an insignificant reduction of tissue equivalence.     

A structural analytic method on the phase space data of Linac 4 MV photons based on the real world

PurposeIt was given that the characteristics of the fluence distribution and the energy spectrum structure of 4MV photons on the Phase Space (PhSp) plane and a method to analyzing the characteristics.MethodsAfter the PhSp file of 4 MV photons was acquired by the method of Monte Carlo (MC) calculation, the photons recorded by PhSp file were grouped based on the energy bin, and it was analyzed that the spatial distribution and energy spectrum structure of the photons. The photons in each energy group were continually grouped to sub-files according to momentum bin, and the primary and scattered photons could be separated according to the character of the fluence distribution of the photons in the sub-files.ResultsThe energy of 4 MV beam is a continuous spectrum. The energy constituent on a pixel at different distances from the center point is different, and the average energy on the center axis of the field is the highest; The photons with 0–1.0 MeV had 42.6% of all; that with energy more than 3.0 MeV had 11.7%; greater than 4 MeV, just 1.5%. The primary and scattered photons were easy collected according to the distribution characteristics of sub-groups.ConclusionsThe work to acquire and analyze the PhSp file of the 4 MV beam is significant. 4 MV, 6 MV, 8 MV, 10 MV and 15 MV energy beams basically cover the beams of radiotherapy, and a database of the energy beams could be built for the MC related research of other scholars.     

Radiation-induced hemopoietic death in mice as a function of photon energy and dose rate

Radiation-induced hemopoietic death was measured in mice exposed to photons of four different energies: 250-kVp X rays, 60Co gamma rays (1.25 MeV), and 6- and 25-MV photons from a linear accelerator. For each radiation source, the lethal dose which killed 50% of the population in 30 days (LD50/30) associated with the hemopoietic syndrome was determined in groups of mice exposed to graded doses from 600 to 1150 cGy at dose rates of 20, 40, and 80 cGy/min. The calculated LD50/30 values for 25 and 6 MV were significantly different from each other at all exposure rates while no difference was observed between 6 MV and 60Co. Using 60Co gamma rays as the standard, the relative biologic effectiveness was as follows: 250 kVp greater than 25 MV greater than 6 MV = 60Co. The data suggest that there may be a greater damage to tissue within the marrow cavities following exposure to very high megavoltage radiation, a factor which must be considered with the increasing utilization of linear accelerators in the clinic and laboratory.     

Alanine radicals,part 4: relative amounts of radical species in alanine dosimeters after exposure to 6-19 MeV electrons and 10 kV-15 MV photons

The amino acid l-alpha-alanine can be used for high-precision dosimetry over a wide dose range, using EPR spectroscopy for monitoring radical concentrations. It is important, however, to understand the underlying composition of the observed EPR spectrum. In previous work, it was shown that the EPR signal from irradiated alanine consists of at least three different radical species, with the relative importance of each of these being almost independent of absorbed dose. However, it was not known whether the relative importance of each radical is independent of the radiation quality responsible for the EPR signal. In the present work, the relative contributions of the different radical species to the total EPR signal from alanine dosimeters irradiated with 6-19 MeV electrons and 10 kV-15 MV photons at a dose of 10 Gy were examined. By spectrum reconstruction using benchmark spectra generated from a simulation procedure, the relative amounts of the three different radical species were shown to be virtually independent of these radiation beam qualities.     

Evaluation of ferrous benzoic methylthymol-blue gel as a dosimeter via magnetic resonance imaging

PurposeIn previous studies, methylthymol-blue and benzoic acid have been introduced as a diffuser limiter and sensitivity enhancer in the gel dosimeter composition, respectively. This work focused on analyzing a formulation of the Fricke gel dosimeter consisting of methylthymol-blue and benzoic acid through magnetic resonance imaging.MethodsThe gel dosimeter samples were irradiated using 6, 10, and 15 MV photons with different levels of doses and read using a 1.5 T scanner in order to evaluate the dose–response sensitivity and to study the effect of benzoic acid concentration, diffusion coefficient and temperature and to determine the temporal stability of the gel dosimeter.ResultsInspection of radiological properties revealed that this gel dosimeter can be considered as a tissue equivalent medium. Within the dose range 0 to 1000 cGy, the R1 sensitivity and R2 sensitivity of the gel dosimeter equaled 0.058 ± 0.003 and 0.092 ± 0.004 s⁻¹Gy⁻¹, respectively. The diffusion coefficient was less than 0.85 ± 0.02mm²h⁻¹ for doses higher than 200 cGy. In addition, by changing the temperature from 15C to 25, the R1 sensitivity and R2 sensitivity decreased about 5 and 11%, respectively. Further, no significant energy and dose rate dependence were observed over photon energies of 6, 10, and 15 MV and over the range 65 to 525 cGy min⁻¹.ConclusionsBased on our observation, the ferrous benzoic acid methylthymol-blue gel dosimeter can be suggested to measure the dose distribution. Further analysis is required to clarify its performance in clinical situations.     

Surface dose measurements with GafChromic EBT film for 6 and 18 MV photon beams

The aim of this study was to determine the surface doses using GafChromic EBT films and compare them with plane-parallel ionization chamber measurements for 6 and 18 MV high energy photon beams. The measurements were made in a water equivalent solid phantom in the build-up region of the 6 and 18 MV photon beams at 100 cm SSD for various field sizes. Markus type plane-parallel ion chamber with fixed-separation between collecting electrodes was used to measure the percent depth doses. GafChromic EBT film measurements were performed both on the phantom surface and maximum dose depth at the same geometry with ion chamber measurements. The surface doses found using GafChromic EBT film were 15%, 20%, 29%and 39% ± 2% (1SD) for 6 MV photons, 6%, 11%, 23% and 32% ± 2% (1SD) for 18 MV photons at 5, 10, 20 and 30 cm² field sizes, respectively. GafChromic EBT film provides precise measurements for surface dose in the high energy photons. Agreement between film and plane-parallel chamber measurements was found to be within ±3% for 18 MV photon beams. There was 5% overestimate on the surface doses when compared with the plane-parallel chamber measurements for all field sizes in the 6 MV photon beams.     

Monte Carlo studies in Gold Nanoparticles enhanced radiotherapy: The impact of modelled parameters in dose enhancement

PurposeOver the last decades, Gold Nanoparticles (AuNPs) have been presented as an innovative approach in radiotherapy (RT) enhancement. Several studies have proven that the irradiation of tumors containing AuNPs could lead to more effective tumor control than irradiation alone. Studies with low kV photons and AuNPs conclude in encouraging results regarding the level of radioenhancement. However, experimental and theoretical studies with MV photons report controversial findings concerning the correlation between dose enhancement effect and tumor cell killing. The great variation in the experimental protocols and simulations complicates the comparison of their outcomes and depicts the need for limiting the variety of investigated parameters. Our purpose is to point out a possible direction for building realistic Monte Carlo (MC) models that could end up with promising results in MV photons RT enhancement.MethodsWe explored published in silico studies concerning AuNPs enhanced RT from 2010 to 2019. In this review, we discuss the different AuNPs and MV photon beams characteristics that have been reported and their effect in dose enhancement.ResultsAuNPs size, concentration, type of distribution along with photon beams energy and the presence of flattening filter in linear accelerators seem to be the major parameters that determine AuNPs radioenhancement in silico.ConclusionsPrior to AuNPs clinical translation in photon radiotherapy, in silico studies should emphasize on nanodosimetry and track structure codes than condensed history ones. Toxicity estimation and biological aspects should be implemented in MC simulations so as to achieve accurate and realistic modelling of AuNPs driven RT.     

T cell microvilli simulations show operation near packing limit and impact on antigen recognition

T cells are immune cells that continuously scan for foreign-derived antigens on the surfaces of nearly all cells, termed antigen-presenting cells (APCs). They do this by dynamically extending numerous protrusions called microvilli (MVs) that contain T cell receptors toward the APC surface in order to scan for antigens. The number, size, and dynamics of these MVs, and the complex multiscale topography that results, play a yet unknown role in antigen recognition. We develop an anatomically informed model that confines antigen recognition to small areas representing MVs that can dynamically form and dissolve and use the model to study how MV dynamics impact antigen sensitivity and discrimination. We find that MV surveillance reduces antigen sensitivity compared with a completely flat interface, unless MV are stabilized in an antigen-dependent manner, and observe that MVs have only a modest impact on antigen discrimination. The model highlights that MV contacts optimize the competing demands of fast scanning speeds of the APC surface with antigen sensitivity. Our model predicts an interface packing fraction that corresponds closely to those observed experimentally, indicating that T cells operate their MVs near the limits imposed by anatomical and geometric constraints. Finally, we find that observed MV contact lifetimes can be largely influenced by conditions in the T cell/APC interface, with these lifetimes often being longer than the simulation or experimental observation period. This work highlights the role of MVs in antigen recognition.     

Redox regulation of diaphragm proteolysis during mechanical ventilation

Prevention of oxidative stress via antioxidants attenuates diaphragm myofiber atrophy associated with mechanical ventilation (MV). However, the specific redox-sensitive mechanisms responsible for this remain unknown. We tested the hypothesis that regulation of skeletal muscle proteolytic activity is a critical site of redox action during MV. Sprague-Dawley rats were assigned to five experimental groups: 1) control, 2) 6 h of MV, 3) 6 h of MV with infusion of the antioxidant Trolox, 4) 18 h of MV, and 5) 18 h of MV with Trolox. Trolox did not attenuate MV-induced increases in diaphragmatic levels of ubiquitin-protein conjugation, polyubiquitin mRNA, and gene expression of proteasomal subunits (20S proteasome alpha-subunit 7, 14-kDa E2, and proteasome-activating complex PA28). However, Trolox reduced both chymotrypsin-like and peptidylglutamyl peptide hydrolyzing (PGPH)-like 20S proteasome activities in the diaphragm after 18 h of MV. In addition, Trolox rescued diaphragm myofilament protein concentration (mug/mg muscle) and the percentage of easily releasable myofilament protein independent of alterations in ribosomal capacity for protein synthesis. In summary, these data are consistent with the notion that the protective effect of antioxidants on the diaphragm during MV is due, at least in part, to decreasing myofilament protein substrate availability to the proteasome.     

Ultrasound-assisted investigation of photon triggered vaporization of poly(vinylalcohol) phase-change nanodroplets: A preliminary concept study with dosimetry perspective

PurposeWe investigate the vaporization of phase-change ultrasound contrast agents using photon radiation for dosimetry perspectives in radiotherapy.MethodsWe studied superheated perfluorobutane nanodroplets with a crosslinked poly(vinylalcohol) shell. The nanodroplets' physico-chemical properties, and their acoustic transition have been assessed firstly. Then, poly(vinylalcohol)-perfluorobutane nanodroplets were dispersed in poly(acrylamide) hydrogel phantoms and exposed to a photon beam. We addressed the effect of several parameters influencing the nanodroplets radiation sensitivity (energy/delivered dose/dose rate/temperature). The nanodroplets-vaporization post-photon exposure was evaluated using ultrasound imaging at a low mechanical index.ResultsPoly(vinylalcohol)-perfluorobutane nanodroplets show a good colloidal stability over four weeks and remain highly stable at temperatures up to 78 °C. Nanodroplets acoustically-triggered phase transition leads to microbubbles with diameters <10 μm and an activation threshold of mechanical index = 0.4, at 7.5 MHz. A small number of vaporization events occur post-photon exposure (6MV/15MV), at doses between 2 and 10 Gy, leading to ultrasound contrast increase up to 60% at RT. The nanodroplets become efficiently sensitive to photons when heated to a temperature of 65 °C (while remaining below the superheat limit temperature) during irradiation.ConclusionsNanodroplets’ core is linked to the degree of superheat in the metastable state and plays a critical role in determining nanodroplet’ stability and sensitivity to ionizing radiation, requiring higher or lower linear energy transfer vaporization thresholds. While poly(vinylalcohol)-perfluorobutane nanodroplets could be slightly activated by photons at ambient conditions, a good balance between the degree of superheat and stability will aim at optimizing the design of nanodroplets to reach high sensitivity to photons at physiological conditions.     

Monte Carlo Study of Radiation Dose Enhancement by Gadolinium in Megavoltage and High Dose Rate Radiotherapy

MRI is often used in tumor localization for radiotherapy treatment planning, with gadolinium (Gd)-containing materials often introduced as a contrast agent. Motexafin gadolinium is a novel radiosensitizer currently being studied in clinical trials. The nanoparticle technologies can target tumors with high concentration of high-Z materials. This Monte Carlo study is the first detailed quantitative investigation of high-Z material Gd-induced dose enhancement in megavoltage external beam photon therapy. BEAMnrc, a radiotherapy Monte Carlo simulation package, was used to calculate dose enhancement as a function of Gd concentration. Published phase space files for the TrueBeam flattening filter free (FFF) and conventional flattened 6MV photon beams were used. High dose rate (HDR) brachytherapy with Ir-192 source was also investigated as a reference. The energy spectra difference caused a dose enhancement difference between the two beams. Since the Ir-192 photons have lower energy yet, the photoelectric effect in the presence of Gd leads to even higher dose enhancement in HDR. At depth of 1.8 cm, the percent mean dose enhancement for the FFF beam was 0.38±0.12, 1.39±0.21, 2.51±0.34, 3.59±0.26, and 4.59±0.34 for Gd concentrations of 1, 5, 10, 15, and 20 mg/mL, respectively. The corresponding values for the flattened beam were 0.09±0.14, 0.50±0.28, 1.19±0.29, 1.68±0.39, and 2.34±0.24. For Ir-192 with direct contact, the enhanced were 0.50±0.14, 2.79±0.17, 5.49±0.12, 8.19±0.14, and 10.80±0.13. Gd-containing materials used in MRI as contrast agents can also potentially serve as radiosensitizers in radiotherapy. This study demonstrates that Gd can be used to enhance radiation dose in target volumes not only in HDR brachytherapy, but also in 6 MV FFF external beam radiotherapy, but higher than the currently used clinical concentration (>5 mg/mL) would be needed.     

Optimal planning parameters for simultaneous boost IMRT treatment of prostate cancer using a Beam Modulator™

ObjectiveTo determine the optimum energy and beam arrangement for prostate intensity-modulated radiation therapy (IMRT) delivery using an Elekta Beam Modulator? linear accelerator, in order to inform decisions when commissioning IMRT for prostate cancer.MethodsCMS XiO was used to create IMRT plans for a prostate patient. Arrangements with 3, 5, 7, 9 and 11 equally spaced fields, containing both a direct anterior and a direct posterior beam were used, with both 6 MV and 10 MV photons. The effects of varying the maximum number of iterations, leaf increment, number of intensity levels and minimum segment size were investigated. Treatment plans were compared using isodose distributions, conformity indices for targets and critical structures, target dose homogeneity, body dose and plan complexity.ResultsTarget dose conformity and homogeneity and sparing of critical structures improved with an increasing number of beams, although any improvements were small for plans containing more than five fields. Set-ups containing a direct posterior field provided superior conformality around the rectum to anterior beam arrangements. Mean non-target dose and total number of monitor units were higher with 6 MV for all beam arrangements. The dose distribution resulting from seven 6 MV beams was considered clinically equivalent to that with five 10 MV beams.ConclusionMethods have been developed to plan IMRT treatments using XiO for delivery with a Beam Modulator? that fulfil demanding dose criteria, using many different set-ups. This study suggests that 6 MV photons can produce prostate IMRT plans that are comparable to those using 10 MV. Work is ongoing to develop a complete class solution.     

Spectrophotometric and electron spin resonance studies on the substrate interactions of ferredoxin-linked nitrite reductase from spinach

Interactions of ferredoxin-linked nitrite reductase (NiR) from spinach with its substrate were studied by spectrophotometry and electron spin resonance (ESR) spectroscopy. Siroheme was extractable from NiR with 2.5% (W/V) trichloroacetic acid (TCA) and with acetone containing 0.01 N HCl. The addition of nitrite or sulfite to these extracts resulted in shifts of the absorption spectra of siroheme. The HCl-acetone extract showed ESR signals of symmetrical high spin heme, which disappeared on addition of nitrite. Spectral titration indicated a high affinity of extracted siroheme to nitrite and sulfite. The addition of nitrite or sulfite to protoheme dissolved in 0.01 N HCl-acetone did not cause a shift of the absorption spectrum. The extractability of siroheme with 0.01 N HCl-acetone was suppressed by the addition of nitrite to the NiR preparation. Moreover, a substrate-induced difference spectrum with peaks at about 295 and 287 nm was observed on addition of nitrite to NiR. These observations indicated an intrinsic strong affinity of siroheme to nitrite and sulfite, formation of rhombicity of siroheme by binding to the protein moiety, and also a probable conformational change of NiR on binding to the substrate. In agreement with previous reports, ESR signals of the heme-NO complex were observed with NiR in the presence of nitrite, methyl viologen (MV), and dithionite. In the present study, the same signals of similar intensity were also observed on omission of MV, under which conditions no catalytic reduction of nitrite occurred. Furthermore, the signal of the heme-NO complex was not observed when MV was replaced by spinach ferredoxin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of varying dose-per-pulse and average dose rate in X-ray beam irradiation on cultured cell survival

Characterizing the biological effects of flattening filter-free (FFF) X-ray beams from linear accelerators is of importance, due to their increasing clinical availability. The purpose of this work is to determine whether in vitro cell survival is affected by the higher dose-per-pulse present in FFF beams in comparison with flattened X-ray beams. A Varian TrueBeam^® linear accelerator was used to irradiate the T98G, V79-4 and U87-MG cell lines with a single fraction of 5 Gy or 10 Gy doses of X-rays. Beams with energies of 6 MegaVolt (MV), 6 MV FFF and 10 MV FFF were used, with doses-per-pulse as measured at the monitor chamber of 0.28, 0.78 and 1.31 mGy/pulse for 6 MV, 6 MV FFF and 10 MV FFF, respectively. The dose delivered to each Petri dish was verified by means of ionization chamber measurements. No statistically significant effects on survival fraction were observed for any of the cell lines considered, either as a function of dose-per-pulse, average dose rate or total dose delivered. Biological effects of higher instantaneous rates should not be excluded on the basis of in vitro experimental results such as the ones presented in this work. The next step toward an assessment of the biological impact of FFF beams will require in vivo studies.     

基于壳聚糖的搭载光源可溶性微针的制备与评价

光动力疗法与给药微针(microneedle, MN)相结合为治疗肿瘤提供了一种安全有效的途径。本文设计了一种基于壳聚糖搭载高能光子的可控缓释型载药微针贴片(LED-losartan-HEMA/ CS-MN, LLH-CSMN),重点研究了其制备工艺,并且以氯沙坦为模型药物对微针阵列的形貌尺寸进行了表征,探究了LLH-CSMN的力学性能、皮肤穿刺性能、缓释性能以及高能光子在长时间工作下的光热性能。结果表明,基于壳聚糖搭载高能光子的微针贴片能够有效地在皮肤表面打开通道进行药物递送,并进行光动力治疗。同时,体外透皮扩散试验表明,以氯沙坦为模型药物制备的微针在1 h内释放了约30%的药物,在1 d内总共释放了约60%的药物,随后进行缓慢释放,在6 d后最终释放了93%的药物,LLH-CSMN具有可控缓释特性以及良好的长效光辅助治疗效果,为肿瘤治疗提供了一个新的安全有效途径。     

Parameter estimation from experimental laboratory data of HSV-1 by using alternative regression method

In this paper, an estimation of model parameters is performed by using the Alternative Regression (AR) approach on an experimental data set of Herpes Simplex Virus type-1 (HSV-1) infection with innate immune response. Throughout the specified course of time, the measurements of monocytes, neutrophils, and viral load were obtained from the corneas of infected mice. C57BL/6 (B6) mice were used at Oakland University, Department of Biological Sciences, and the outcome measurements were divided into training and testing data sets. The HSV-1 nonlinear dynamic model is proposed based on the observed data patterns and biological system information. The simulation results of the proposed model showed that they consistently fit the experimental data set. In addition, the sensitivity test and model validation diagnostics are considered to determine the most significant key parameters that affect the dynamics of the HSV-1 system.     

SAXS-data-based structural modeling of DNA–gadolinium complexes fixed in particles of cholesteric liquid-crystalline dispersions

Structure of cholesteric liquid-crystalline dispersions (CLCDs) formed by double-stranded DNA molecules and treated with gadolinium salts was studied by small-angle X-ray scattering (SAXS). The obtained SAXS data open the way for structural modeling of these complexes to obtain a reasonable explanation for the correlated decrease in amplitude of an abnormal negative band in the circular dichroism (CD) spectra and the characteristic Bragg peak in the experimental small-angle X-ray scattering curves observed on treatment of CLCD by gadolinium salts. Model simulations of different kinds of structural organizations of the DNA–gadolinium complex were performed using novel SAXS data analysis methods in combination with several new, complementary modeling techniques, enabling us to build low-resolution three-dimensional structural models of DNA–gadolinium complexes fixed in CLCD particles. The obtained models allow us to suggest that a change takes place in the helical twist of quasinematic layers formed by these molecules at high concentrations of gadolinium salt. This change in the twist can be used to explain the experimentally observed increase in amplitude of an abnormal band in the CD spectra of DNA CLCD.     

Gene expression profiles of arabidopsis under the stress of methyl viologen: a microarray analysis

Methyl viologen (MV) is the main ingredient of Paraquat. It is little known about how plants respond to this compound. To understand the mode of MV action and molecular mechanism of plant response, we performed experiments of microarray on Arabidopsis. In MV treated seedling, approximately 6 % genes were altered at mRNA levels, including 818 genes increased, whereas 1,440 genes decreased. Studies of these genes expression patterns provided some new information on the reaction process of plant after the treatment with MV. These included signaling molecules for MV response and reactive oxygen species formation, enzymes required for secondary metabolism and, cell wall maintenance and strategy of photostasis balance. The expression kinetics of the genes induced by MV will provides useful information for the abiotic stress defense mechanism in plants.     

Luminescent probing of the simplest chiral α‐amino acid–alanine in an enantiopure and racemic state

Luminescent spectroscopy combined with the technique of luminescent probing with rare earth ions (europium, gadolinium, terbium) and an actinide ion (uranyl) was used to differentiate enantiopure and racemic alanine, the simplest chiral proteinogenic amino acid. Using the achiral luminescent probes, small differences between pure L and DL alanine in the solid state were strongly amplified. Based on the observed electronic transitions of the probes, the position of the triplet level of the coordinated alanine was estimated. Formation of homo‐ and heterochiral complexes between enantiomers of alanine and the metal ions is discussed as a possible mechanism of chiral self‐discrimination.     

CD150 (SLAM) is a receptor for measles virus but is not involved in viral contact-mediated proliferation inhibition

Measles virus (MV) interacts with cellular receptors on the surface of peripheral blood lymphocytes (PBL) which mediate virus binding and uptake. Simultaneously, the direct contact of the viral glycoproteins with the cell surface induces a negative signal blocking progression to the S phase of the cell cycle, resulting in a pronounced proliferation inhibition. We selected a monoclonal antibody (MAb 5C6) directed to the surface of highly MV-susceptible B cells (B95a), which inhibits binding to and infection of cells with MV wild-type and vaccine strains. By screening a retroviral cDNA library from human splenocytes (ViraPort; Stratagene) with this antibody, we cloned and identified the recognized molecule as signaling lymphocytic activation molecule (SLAM; CD150), which is identical to the MV receptor recently found by H. Tatsuo et al. (Nature 406:893-897, 2000). After infection of cells, and after surface contact with MV envelope proteins, SLAM is downregulated from the cell surface of activated PBL and cell lines. Although anti-SLAM and/or anti-CD46 antibodies block virus binding, they do not interfere with the contact-mediated proliferation inhibition. In addition, the cell-type-specific expression of SLAM does not correlate with the sensitivity of cells for proliferation inhibition. The data indicate that proliferation inhibition induced by MV contact is independent of the presence or absence of the virus-binding receptors SLAM and CD46.