Earlier Onset of δ-Retrovirus-Induced Leukemia after Splenectomy

Infection by δ-retroviruses such as human T-lymphotropic virus type 1 (HTLV-1) and bovine leukemia virus (BLV) is mostly asymptomatic. Indeed, only a minority (<5%) of δ-retrovirus infected hosts will develop either lymphoproliferative or neurodegenerative diseases after long latency periods. In fact, the host immune response is believed to tightly control viral replication but this assumption has not been definitely proven in vivo. Here, we provide direct experimental evidence demonstrating that integrity of the spleen is required to control pathogenesis. In the BLV model, we show that asplenia decreases efficiency of the immune response and induces an imbalance in cell dynamics resulting in accelerated onset of leukemia. These observations enlighten a potential threat in splenectomized HTLV-1 carriers and justify a regular preventive evaluation.     

Immune impairment in HIV infection: Existence of risky and immunodeficiency thresholds

Results of several studies show that some DC populations are susceptible to HIV. Modulation of DCs by HIV infection, in particular interference of the antigen-presenting function of DCs, is a key aspect in viral pathogenesis and contributes to viral evasion from immunity because the loss of the DC function engenders some impairment effects for a proliferation of CTL responses, which play an important role in the immune response to HIV. As described herein, we use a simple mathematical model to examine virus-immune dynamics over the course of HIV infection in the context of the immune impairment effects. A decrease of the DC number and function during the course of HIV-1 infection is observed. Therefore, we simply assumed that the immune impairment rate increases over the HIV infection. Under the assumption, four processes of the disease progression dynamics of our model are classifiable according to their virological properties. It is particularly interesting a typical disease progression presents a “risky threshold” and an “immunodeficiency threshold”. Regarding the former, the immune system might collapse when the impairment rate of HIV exceeds a threshold value (which corresponds to a transcritical bifurcation point). For the latter, the immune system always collapses when the impairment rate exceeds the value (which corresponds to a saddle-node bifurcation point). To test our theoretical framework, we investigate the existence and distribution of these thresholds in 10 patients.     

Early increases in superantigen-specific Foxp3+ regulatory T cells during mouse mammary tumor virus infection

Mouse mammary tumor virus (MMTV) is a milk-borne betaretrovirus that has developed strategies to exploit and subvert the host immune system. Here, we show in a natural model of MMTV infection that the virus causes early and progressive increases in superantigen (SAg)-specific Foxp3⁺ regulatory T cells (T_reg) in Peyer's patches (PP). These increases were shown to be dependent on the presence of dendritic cells. CD4⁺ CD25⁺ T cells from the PP of infected mice preferentially suppress the proliferative response of T cells to SAg-expressing antigen-presenting cells ex vivo. We investigated the influence of the depletion of CD25⁺ cells at different stages of the infection. When CD25⁺ cells were depleted before MMTV infection, an increase in the number of PP SAg-cognate Foxp3⁻ T cells was found at day 6 of infection. Since the SAg response is associated with viral amplification, the possibility exists that T_reg cells attenuate the increase in viral load at the beginning of the infection. In contrast, depletion of CD25⁺ cells once the initial SAg response has developed caused a lower viral load, suggesting that at later stages T_reg cells may favor viral persistence. Thus, our results indicated that T_reg cells play an important and complex role during MMTV infection.     

Partitioning of small organic molecules in aqueous biphasic systems

Aqueous biphasic systems (ABS) are suitable for the separation of small organic molecules in industrial and environmental applications and thus, it is important to correlate partitioning behavior of model organic solutes with their structure in order to develop predictive models. The partitioning behavior of five, uncharged, substituted benzenes (benzene, toluene, chlorobenzene, 1,4-dichlorobenzene and 1,2,4-trichlorobenzene) were studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts (K₃PO₄, K₂CO₃, (NH₄)₂SO₄ and NaOH). For a given solute and a defined concentration of salt, the partition coefficients increase as the ΔG_hyd value of the salt anion becomes more negative (e.g., D_benzene increases in the order OH⁻<SO₄²⁻<CO₃²⁻<PO₄³⁻). In a given salt, the distribution ratios increase in the order benzene<toluene<chlorobenzene<1,4-dichlorobenzene<1,2,4-trichlorobenzene. The partitioning behavior of the solutes in PEG–salt ABS was found to be strongly correlated with their partitioning coefficients in 1-octanol–water biphasic systems.     

CD4+ CCR5+ T-cell dynamics during simian immunodeficiency virus infection of Chinese rhesus macaques

Simian immunodeficiency virus (SIV) infection of rhesus macaques (RMs) provides a reliable model to study the relationship between lentivirus replication, cellular immune responses, and CD4⁺ T-cell dynamics. Here we investigated, using SIVmac251-infected RMs of a Chinese genetic background (which experience a slower disease progression than Indian RMs), the dynamics of CD4⁺ CCR5⁺ T cells, as this subset of memory/activated CD4⁺ T cells is both a preferential target of virus replication and a marker of immune activation. As expected, we observed that the number of circulating CD4⁺ CCR5⁺ T cells decreases transiently at the time of peak viremia. However, at 60 days postinfection, i.e., when set-point viremia is established, the level of CD4⁺ CCR5⁺ T cells was increased compared to the baseline level. Interestingly, this increase correlated with faster disease progression, higher plasma viremia, and early loss of CD4⁺ T-cell function, as measured by CD4⁺ T-cell count, the fraction of memory CD4⁺ T cells, and the recall response to purified protein derivative. Taken together, these data show a key difference between the dynamics of the CD4⁺ CCR5⁺ T-cell pool (and its relationship with disease progression) in Chinese RMs and those described in previous reports for Indian SIVmac251-infected RMs. As the SIV-associated changes in the CD4⁺ CCR5⁺ T-cell pool reflect the opposing forces of SIV replication (which reduces this cellular pool) and immune activation (which increases it), our data suggest that in SIV-infected Chinese RMs the impact of immune activation is more prominent than that of virus replication in determining the size of the pool of CD4⁺ CCR5⁺ T cells in the periphery. As progression of HIV infection in humans also is associated with a relative expansion of the level of CD4⁺ CCR5⁺ T cells, we propose that SIV infection of Chinese RMs is a very valuable and important animal model for understanding the pathogenesis of human immunodeficiency virus infection.     

Differential CD4+ versus CD8+ T-cell responses elicited by different poxvirus-based human immunodeficiency virus type 1 vaccine candidates provide comparable efficacies in primates

Poxvirus vectors have proven to be highly effective for boosting immune responses in diverse vaccine settings. Recent reports reveal marked differences in the gene expression of human dendritic cells infected with two leading poxvirus-based human immunodeficiency virus (HIV) vaccine candidates, New York vaccinia virus (NYVAC) and modified vaccinia virus Ankara (MVA). To understand how complex genomic changes in these two vaccine vectors translate into antigen-specific systemic immune responses, we undertook a head-to-head vaccine immunogenicity and efficacy study in the pathogenic HIV type 1 (HIV-1) model of AIDS in Indian rhesus macaques. Differences in the immune responses in outbred animals were not distinguished by enzyme-linked immunospot assays, but differences were distinguished by multiparameter fluorescence-activated cell sorter analysis, revealing a difference between the number of animals with both CD4⁺ and CD8⁺ T-cell responses to vaccine inserts (MVA) and those that elicit a dominant CD4⁺ T-cell response (NYVAC). Remarkably, vector-induced differences in CD4⁺/CD8⁺ T-cell immune responses persisted for more than a year after challenge and even accompanied antigenic modulation throughout the control of chronic infection. Importantly, strong preexposure HIV-1/simian immunodeficiency virus-specific CD4⁺ T-cell responses did not prove deleterious with respect to accelerated disease progression. In contrast, in this setting, animals with strong vaccine-induced polyfunctional CD4⁺ T-cell responses showed efficacies similar to those with stronger CD8⁺ T-cell responses.     

Surviving Mousepox Infection Requires the Complement System

Poxviruses subvert the host immune response by producing immunomodulatory proteins, including a complement regulatory protein. Ectromelia virus provides a mouse model for smallpox where the virus and the host''s immune response have co-evolved. Using this model, our study investigated the role of the complement system during a poxvirus infection. By multiple inoculation routes, ectromelia virus caused increased mortality by 7 to 10 days post-infection in C57BL/6 mice that lack C3, the central component of the complement cascade. In C3^−/− mice, ectromelia virus disseminated earlier to target organs and generated higher peak titers compared to the congenic controls. Also, increased hepatic inflammation and necrosis correlated with these higher tissue titers and likely contributed to the morbidity in the C3^−/− mice. In vitro, the complement system in naïve C57BL/6 mouse sera neutralized ectromelia virus, primarily through the recognition of the virion by natural antibody and activation of the classical and alternative pathways. Sera deficient in classical or alternative pathway components or antibody had reduced ability to neutralize viral particles, which likely contributed to increased viral dissemination and disease severity in vivo. The increased mortality of C4^−/− or Factor B^−/− mice also indicates that these two pathways of complement activation are required for survival. In summary, the complement system acts in the first few minutes, hours, and days to control this poxviral infection until the adaptive immune response can react, and loss of this system results in lethal infection.     

Low Frequency Magnetic Fields Enhance Antitumor Immune Response against Mouse H22 Hepatocellular Carcinoma

Objective

Many studies have shown that magnetic fields (MF) inhibit tumor growth and influence the function of immune system. However, the effect of MF on mechanism of immunological function in tumor-bearing mice is still unclear.

Methods

In this study, tumor-bearing mice were prepared by subcutaneously inoculating Balb/c mice with hepatocarcinoma cell line H22. The mice were then exposed to a low frequency MF (0.4 T, 7.5 Hz) for 30 days. Survival rate, tumor growth and the innate and adaptive immune parameters were measured.

Results

MF treatment could prolong survival time (n = 28, p<0.05) and inhibit tumor growth (n = 9, p<0.01) in tumor-bearing mice. Moreover, this MF suppressed tumor-induced production of cytokines including interleukin-6 (IL-6), granulocyte colony- stimulating factor (G-CSF) and keratinocyte-derived chemokine (KC) (n = 9–10, p<0.05 or 0.01). Furthermore, MF exposure was associated with activation of macrophages and dendritic cells, enhanced profiles of CD4⁺ T and CD8⁺ T lymphocytes, the balance of Th17/Treg and reduced inhibitory function of Treg cells (n = 9–10, p<0.05 or 0.01) in the mice model.

Conclusion

The inhibitory effect of MF on tumor growth was related to the improvement of immune function in the tumor-bearing mice.     

Cytotoxic T-lymphocyte elicited therapeutic vaccine candidate targeting cancer against MAGE-A11 carcinogenic protein

Immunotherapy is a breakthrough approach for cancer treatment and prevention. By exploiting the fact that cancer cells have overexpression of tumor antigens responsible for its growth and progression, which can be identified and removed by boosting the immune system. In silico techniques have provided efficient ways for developing preventive measures to ward off cancer. Herein, we have designed a potent cytotoxic T-lymphocyte epitope to elicit a desirable immune response against carcinogenic melanoma-associated antigen-A11. Potent epitope was predicted using reliable algorithms and characterized by advanced computational avenue CABS molecular dynamics simulation, for full flexible binding with HLA-A*0201 and androgen receptor to large-scale rearrangements of the complex system. Results showed the potent immunogenic construct (KIIDLVHLL), from top epitopes using five algorithms. Molecular docking analyses showed the strong binding of epitope with HLA-A*0201 and androgen receptor with docking score of −780.6 and −641.06 kcal/mol, respectively. Molecular dynamics simulation analysis revealed strong binding of lead epitope with androgen receptor by involvement of 127 elements through atomic-model study. Full flexibility study showed stable binding of epitope with an average root mean square deviation (RMSD) 2.21 Å and maximum RMSD value of 6.48 Å in optimal cluster density area. The epitope also showed remarkable results with radius of gyration 23.0777 Å, world population coverage of 39.08% by immune epitope database, and transporter associated with antigen processing (TAP) affinity IC₅₀ value of 2039.65 nm. Moreover, in silico cloning approach confirmed the expression and translation capacity of the construct within a suitable expression vector. The present study paves way for a potential immunogenic construct for prevention of cancer.     

Early Assessment of the Efficacy of Temozolomide Chemotherapy in Experimental Glioblastoma Using [18F]FLT-PET Imaging

Addition of temozolomide (TMZ) to radiation therapy is the standard treatment for patients with glioblastoma (GBM). However, there is uncertainty regarding the effectiveness of TMZ. Considering the rapid evolution of the disease, methods to assess TMZ efficacy early during treatment would be of great benefit. Our aim was to monitor early effects of TMZ in a mouse model of GBM using positron emission tomography (PET) with 3′-deoxy-3′-[¹⁸F]fluorothymidine ([¹⁸F]FLT).

Methods

Human glioma cells sensitive to TMZ (Gli36dEGFR-1) were treated with sub-lethal doses of TMZ to obtain cells with lower sensitivity to TMZ (Gli36dEGFR-2), as measured by growth and clonogenic assays. Gli36dEGFR-1 and Gli36dEGFR-2 cells were subcutaneously (s.c.) or intracranially (i.c.) xenografted into nude mice. Mice were treated for 7 days with daily injection of 25 or 50 mg/kg TMZ. Treatment efficacy was measured using [¹⁸F]FLT-PET before treatment and after 2 days. Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) were used to determine tumor volumes before treatment and after 7 days.

Results

A significant difference was observed between TMZ and DMSO treated tumors in terms of variations of [¹⁸F]FLT T/B ratio as soon as day 2 in the i.c. as well as in the s.c. mouse model. Variations of [¹⁸F]FLT T/B uptake ratio between days 0 and 2 correlated with variations of tumor size between days 0 and 7 (s.c. model: n_tumor = 17 in n_mice = 11, P<0.01; i.c. model: n_tumor/mice = 9, P<0.01).

Conclusions

Our results indicate that [¹⁸F]FLT-PET may be useful for an early evaluation of the response of GBM to TMZ chemotherapy in patients with glioma.     

Conductive and Kinetic Properties of Connexin45 Hemichannels Expressed in Transfected HeLa Cells

Human HeLa cells transfected with mouse connexin Cx45 were used to examine the conductive and kinetic properties of Cx45 hemichannels. The experiments were carried out on single cells using a voltage-clamp method. Lowering the [Ca²⁺]_o revealed an extra current. Its sensitivity to extracellular Ca²⁺ and gap junction channel blockers (18α-glycyrrhetinic acid, palmitoleic acid, heptanol), and its absence in non-transfected HeLa cells suggested that it is carried by Cx45 hemichannels. The conductive and kinetic properties of this current, I _hc, were determined adopting a biphasic pulse protocol. I _hc activated at positive V _m and deactivated partially at negative V _m. The analysis of the instantaneous I _hc yielded a linear function g _hc,inst = f(V _m) with a hint of a negative slope (g _hc,inst: instantaneous conductance). The analysis of the steady-state I _hc revealed a sigmoidal function g _hc,ss = f(V _m) best described with the Boltzmann equation: V _m,0 = −1.08 mV, g _hc,min = 0.08 (g _hc,ss: steady-state conductance; V _{m, 0}:V _m at which g _hc,ss is half-maximally activated; g _hc,min: minimal conductance; major charge carriers: K⁺ and Cl⁻). The g _hc was minimal at negative V _m and maximal at positive V _m. This suggests that Cx45 connexons integrated in gap junction channels are gating with negative voltage. I _hc deactivated exponentially with time, giving rise to single time constants, τ_d. The function τ_d = f(V _m) was exponential and increased with positive V _m (τ_d = 7.6 s at V _m = 0 mV). The activation of I _hc followed the sum of two exponentials giving rise to the time constants, τ_a1 and τ_a2. The function τ_a1 = f(V _m) and τ_a2 = f(V _m) were bell-shaped and yielded a maximum of ≅ 0.6 s at V _m ≅ −20 mV and ≅ 4.9 s at V _m ≅ 15 mV, respectively. Neither τ_a1 = f(V _m) nor τ_a2 = f(V _m) coincided with τ_d = f(V _m). These findings conflict with the notion that activation and deactivation follow a simple reversible reaction scheme governed by first-order voltage-dependent processes.     

T-wave width as an index for quantification of ventricular repolarization dispersion: Evaluation in an isolated rabbit heart model

This study examined the significance of ECG-derived indexes in quantifying ventricular repolarization dispersion (VRD) given its value as a risk marker for severe myocardial arrhythmia. Multilead ECG recordings from an isolated rabbit heart model, including control and globally increased VRD (IVRD) beats, were studied. The IVRD was induced by supplying d-Sotalol (DS) or premature ventricular stimulation (PVS). ECG indexes came from (a) the absolute ECG summation signal, from which we obtained the amplitude and area of the T-wave, and the T-wave width (T_W), which we consider as IVRD indexes, and (b) the Singular Value Decomposition (SVD) of the ECG, from which the θ_PT (angle between the first SVD principal axis and the repolarization axis), T-wave residuum (T_WR), T-wave morphology dispersion (T_MD), unnormalized T_MD (UT_MD), and θ_RT (the angle between the depolarization and the repolarization vectors) were estimated as IVRD indexes. Results were compared with the classical QT-based VRD indexes (σ_QTe, standard deviation of QT end). The main results are T_W: 78.0±10.3 vs. 133.6±29.6 ms, for control vs. IVRD generated using DS, p<0.005 and 95.2±7.9 vs. 118.5±15.7 ms when PVS was used, p<0.007; σ_QTe: gives 6.5±1.4 vs. 11.6±1.9 ms, for DS p<0.007 and 7.6±2.2 vs. 13.0±3.4 ms for PVS, p<0.007; respectively. θ_PT: 35±51° vs. 117±49°, p<0.009 in DS. We concluded that globally induced IVRD is well reflected by the T_W parameter, being the most sensitive of the studied ones. The IVRD can also be quantified by using the θ_PT index.     

Effects of Forest Age on Soil Autotrophic and Heterotrophic Respiration Differ between Evergreen and Deciduous Forests

We examined the effects of forest stand age on soil respiration (SR) including the heterotrophic respiration (HR) and autotrophic respiration (AR) of two forest types. We measured soil respiration and partitioned the HR and AR components across three age classes ∼15, ∼25, and ∼35-year-old Pinus sylvestris var. mongolica (Mongolia pine) and Larix principis-rupprechtii (larch) in a forest-steppe ecotone, northern China (June 2006 to October 2009). We analyzed the relationship between seasonal dynamics of SR, HR, AR and soil temperature (ST), soil water content (SWC) and normalized difference vegetation index (NDVI, a plant greenness and net primary productivity indicator). Our results showed that ST and SWC were driving factors for the seasonal dynamics of SR rather than plant greenness, irrespective of stand age and forest type. For ∼15-year-old stands, the seasonal dynamics of both AR and HR were dependent on ST. Higher Q₁₀ of HR compared with AR occurred in larch. However, in Mongolia pine a similar Q₁₀ occurred between HR and AR. With stand age, Q₁₀ of both HR and AR increased in larch. For Mongolia pine, Q₁₀ of HR increased with stand age, but AR showed no significant relationship with ST. As stand age increased, HR was correlated with SWC in Mongolia pine, but for larch AR correlated with SWC. The dependence of AR on NDVI occurred in ∼35-year-old Mongolia pine. Our study demonstrated the importance of separating autotrophic and heterotrophic respiration components of SR when stimulating the response of soil carbon efflux to environmental changes. When estimating the response of autotrophic and heterotrophic respiration to environmental changes, the effect of forest type on age-related trends is required.     

Modification of tumor cells by a low dose of Newcastle disease virus

Summary Augmented tumor-specific T cell responses were observed against the high metastatic murine lymphoma variant ESb when using as immunogen ESb tumor cells that had been modified by infection with a low dose of Newcastle disease virus (NDV). Such virus-modified inactivated tumor cells (ESb-NDV) were potent tumor vaccines when applied postoperatively for active specific immunotherapy of ESb metastases. We demonstrate here that immune spleen cells from mice immunized with ESb-NDV contain enhanced immune capacity in both the CD4⁺, CD8^– and the CD4^–, CD8⁺ T cell compartments to mount a secondary-tumor-specific cytotoxic T cell response in comparison with immune cells from mice immunized with ESb. ESb-NDV immune CD4⁺, CD8^– helper T cells also produced more interleukin 2 after antigen stimulation than the corresponding ESb immune cells. There was no participation of either CD4⁺ or CD8⁺ virus-specific cells in the augmented response. The specificity of the T cells for the tumor-associated antigen remaind unchanged. Thus, there is the paradox that the virus-mediated augmentation of the tumor-specific T cell response in this system involves increased T helper activity but does not involve the recognition of viral epitopes as potential new helper determinants.Abbreviations CTL cytolytic T lymphocytes - IL-2 interleukin 2 - rIL-2 recombinant IL-2 - mAb monoclonal antibody - NDV Newcastle disease virus - SSC syngeneic spleen cell     

Induction of specific human primary immune responses to a Semliki Forest virus–based tumor vaccine in a Trimera mouse model

Recombinant Semliki Forest virus (rSFV) enables high-level, transient expression of heterologous proteins in vivo, and is believed to be a superior vector for genetic vaccination, compared with the conventional DNA plasmid. Nonetheless, the efficacy of rSFV-based vaccine in eliciting human immune responses has not been tested. We used a Trimera mouse model, consisting of lethally irradiated BALB/c host reconstituted with nonobese diabetes/severe combined immunodeficiency (NOD/SCID) bone marrow plus human peripheral blood mononuclear cells (PBMCs), to characterize the in vivo immune responses against rSFV-encoded human melanoma antigen MAGE-3. MAGE-3–specific antibody and cytotoxic T lymphocyte (CTL) activity were detected by ELISA and ⁵¹Cr-release assay, respectively, and the responses were compared with those induced by a plasmid DNA vaccine encoding the same antigen. The results showed that rSFV vaccine could elicit human MAGE-3–specific antibody and CTL response in the Trimera mice, and the antitumor responses were more potent than those by plasmid DNA vaccination. This is the first report to evaluate human immune responses to an rSFV-based tumor vaccine in the Trimera mouse model. Our data suggest that rSFV vector is better than DNA plasmid in inducing protective immunity, and the Trimera model may serve as a general tool to evaluate the efficacy of tumor vaccines in eliciting human primary immune response in vivo.     

In vivo evaluation of epidermal growth factor and transforming growth factor β1 in mouse tumor models

The influence of modulating circulating levels of epidermal growth factor (EGF) and transforming growth factor β₁ (TGF-β₁) on tumorgrowth was examined in a variety of mouse models. Removal of the EGF-rich submandibular gland from host mice failed to alter the growth of a variety of human tumor xenografts or a C3H mouse tumor. Infusion of EGF from Alzet minipumps raised circulating EGF levels. However, only the A549 human tumor xenograft showed any significant increase in growth in the presence of EGF infusion and this response was marginal. The growth of Wehi 3BD+ and A549 tumor lines in culture was inhibited by TGF-β₁. The growth of these lines in vivo, however, was not significantly altered by the administration of TGF-β₁ via a variety of routes.     

Brain regional distribution of GABAA receptors exhibiting atypical GABA agonism: Roles of receptor subunits

The major inhibitory neurotransmitter in the brain, γ-aminobutyric acid (GABA), has only partial efficacy at certain subtypes of GABA_A receptors. To characterize these minor receptor populations in rat and mouse brains, we used autoradiographic imaging of t-butylbicyclophosphoro[³⁵S]thionate ([³⁵S]TBPS) binding to GABA_A receptors in brain sections and compared the displacing capacities of 10 mM GABA and 1 mM 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP), a competitive GABA-site agonist. Brains from GABA_A receptor α1, α4, δ, and α4 + δ subunit knockout (KO) mouse lines were used to understand the contribution of these particular receptor subunits to “GABA-insensitive” (GIS) [³⁵S]TBPS binding. THIP displaced more [³⁵S]TBPS binding than GABA in several brain regions, indicating that THIP also inhibited GIS-binding. In these regions, GABA prevented the effect of THIP on GIS-binding. GIS-binding was increased in the cerebellar granule cell layer of δ KO and α4 + δ KO mice, being only slightly diminished in that of α1 KO mice. In the thalamus and some other forebrain regions of wild-type mice, a significant amount of GIS-binding was detected. This GIS-binding was higher in α4 KO mice. However, it was fully abolished in α1 KO mice, indicating that the α1 subunit was obligatory for the GIS-binding in the forebrain.Our results suggest that native GABA_A receptors in brain sections showing reduced displacing capacity of [³⁵S]TBPS binding by GABA (partial agonism) minimally require the assembly of α1 and β subunits in the forebrain and of α6 and β subunits in the cerebellar granule cell layer. These receptors may function as extrasynaptic GABA_A receptors.     

Modelling the Evolutionary Dynamics of Viruses within Their Hosts: A Case Study Using High-Throughput Sequencing

Uncovering how natural selection and genetic drift shape the evolutionary dynamics of virus populations within their hosts can pave the way to a better understanding of virus emergence. Mathematical models already play a leading role in these studies and are intended to predict future emergences. Here, using high-throughput sequencing, we analyzed the within-host population dynamics of four Potato virus Y (PVY) variants differing at most by two substitutions involved in pathogenicity properties. Model selection procedures were used to compare experimental results to six hypotheses regarding competitiveness and intensity of genetic drift experienced by viruses during host plant colonization. Results indicated that the frequencies of variants were well described using Lotka-Volterra models where the competition coefficients β_ij exerted by variant j on variant i are equal to their fitness ratio, r_j/r_i. Statistical inference allowed the estimation of the effect of each mutation on fitness, revealing slight (s = −0.45%) and high (s = −13.2%) fitness costs and a negative epistasis between them. Results also indicated that only 1 to 4 infectious units initiated the population of one apical leaf. The between-host variances of the variant frequencies were described using Dirichlet-multinomial distributions whose scale parameters, closely related to the fixation index F _ST, were shown to vary with time. The genetic differentiation of virus populations among plants increased from 0 to 10 days post-inoculation and then decreased until 35 days. Overall, this study showed that mathematical models can accurately describe both selection and genetic drift processes shaping the evolutionary dynamics of viruses within their hosts.