Ingestion of polyethylene terephthalate microplastic water contaminants by Xenopus laevis tadpoles negatively affects their resistance to ranavirus infection and antiviral immunity.

Small plastic debris (0.1 µm-5 mm) or microplastics (MPs) have become major pollutants of aquatic ecosystems worldwide and studies suggest that MPs exposure can pose serious threats to human and wildlife health. However, to date the potential biological impacts of MPs accumulating in low amount in tissues during early life remains unclear. Here, for a more realistic assessment, we have used environmentally representative, mildly weathered, polyethylene terephthalate microplastics (PET MPs), cryomilled (1-100 µm) and fluorescently labelled. We leveraged the amphibian Xenopus laevis tadpoles as an animal model to define the biodistribution of PET MPs and determine whether exposure to PET MPs induce perturbations of antiviral immunity. Exposure to PET MPs for 1-14 days resulted in detectable PET MPs biodistribution in intestine, gills, liver, and kidney as determined by fluorescence microscopy on whole mount tissues. PET MPs accumulation rate in tissues was further evaluated via a novel in situ enzymatic digestion and subsequent filtration using silicon nanomembranes, which shows that PET MPs rapidly accumulate in tadpole intestine, liver and kidneys and persist over a week. Longer exposure (1 month) of tadpoles to relatively low concentration of PET MPs (25 µg/ml) significantly increased susceptibility to viral infection and altered innate antiviral immunity without inducing overt inflammation. This study provides evidence that exposure to MPs negatively impact immune defenses of aquatic vertebrates.

The Binding, Infection, and Promoted Growth of Batrachochytrium dendrobatidis by the Ranavirus FV3.

Increasing reports suggest the occurrence of co-infection between Ranaviruses such as Frog Virus 3 (FV3) and the chytrid fungus Batrachochytrium dendrobatidis (Bd) in various amphibian species. However, the potential direct interaction of these two pathogens has not been examined to date. In this study, we investigated whether FV3 can interact with Bd in vitro using qPCR, conventional microscopy, and immunofluorescent microscopy. Our results reveal the unexpected ability of FV3 to bind, promote aggregation, productively infect, and significantly increase Bd growth in vitro. To extend these results in vivo, we assessed the impact of FV3 on Xenopus tropicalis frogs previously infected with Bd. Consistent with in vitro results, FV3 exposure to previously Bd-infected X. tropicalis significantly increased Bd loads and decreased the host's survival.

Survival of patients living with HIV and cancer in Cali, Colombia.

Background: People living with HIV have an increased risk of cancer compared to the general population. However, with the increase in life expectancy and advances in antiretroviral therapy, the survival of patients with cancer and HIV has changed. Objective: To determine the survival of patients living with HIV and cancer in Cali, Colombia. Methods: A retrospective cohort study was conducted at the Fundación Valle del Lili, Cali, Colombia. Data from the HIV database was crossed with data from the hospital and population-based cancer registries between 2011-2019. Patients <18 years, limited available clinical information on the diagnosis and treatment of HIV and cancer, and non-oncological tumor diagnosis were excluded. Results: A total of 173 patients were included. The frequencies of AIDS-defining neoplasms were: Non-Hodgkin lymphoma (42.8%), Kaposi sarcoma (27.8%), and cervical cancer (4.6%). Overall survival was 76.4% (95% CI 68.9-82.3) at five years. Poorer survival was found in patients with AIDS-defining infections (56.9% vs. 77.8%, p=0.027) and non-AIDS-defining infections (57.8% vs. 84.2%, p=0.013), while there was better survival in patients who received antiretroviral therapy (65.9% vs. 17.9%, p=0.021) and oncological treatment (66.7% vs. 35.4%, p<0.001). The presence of non-AIDS-defining infections increases the risk of dying (HR = 2.39, 95% CI 1.05-5.46, p=0.038), while oncological treatment decreases it (HR = 0.33, 95% CI 0.14-0.80, p=0.014). Conclusions: In people living with HIV, Non-Hodgkin lymphoma and Kaposi sarcoma are the most common neoplasms. Factors such as AIDS-associated and non-AIDS-associated infections have been identified as determinants of survival. Cancer treatment seems to improve survival.

Antecedentes: Las personas que viven con VIH tienen un riesgo mayor de cáncer en comparación con la población general. Sin embargo, con el aumento de la esperanza de vida y los avances en la terapia antirretroviral, la supervivencia de los pacientes con cáncer y VIH ha cambiado. Objetivo: Determinar la supervivencia de los pacientes que viven con VIH y cáncer en Cali, Colombia. Métodos: Se realizó un estudio de cohorte retrospectivo en la Fundación Valle del Lili, Cali, Colombia. Los datos de la base de datos de VIH se cruzaron con los datos de los registros de cáncer de base hospitalaria y poblacional entre 2011-2019. Se excluyeron los pacientes <18 años, con información clínica limitada disponible sobre el diagnóstico y tratamiento del VIH y el cáncer y los casos con diagnóstico de tumor no oncológico. Resultados: Se incluyeron un total de 173 pacientes. Las frecuencias de neoplasias definitorias de SIDA fueron: linfoma no Hodgkin (42.8%), sarcoma de Kaposi (27.8%) y cáncer cervical (4.6%). La supervivencia global fue del 76.4% (IC 95% 68.9-82.3) a los cinco años. Se encontró una peor supervivencia en pacientes con infecciones definitorias de SIDA (56.9% vs. 77.8%, p=0.027) e infecciones no definitorias de SIDA (57.8% vs. 84.2%, p=0.013), mientras que hubo una mejor supervivencia en pacientes que recibieron terapia antirretroviral (65.9% vs. 17.9%, p=0.021) y tratamiento oncológico (66.7% vs. 35.4%, p<0.001). La presencia de infecciones no definitorias de SIDA aumentó el riesgo de morir (HR = 2.39, IC 95% 1.05-5.46, p=0.038), mientras que el tratamiento oncológico lo disminuyó (HR = 0.33, IC 95% 0.14-0.80, p=0.014). Conclusiones: En las personas que viven con VIH, el linfoma no Hodgkin y el sarcoma de Kaposi son las neoplasias más comunes. Se han identificado factores como las infecciones asociadas al SIDA y las infecciones no asociadas al SIDA como determinantes de la supervivencia. El tratamiento del cáncer parece mejorar la supervivencia.

Larval T Cells Are Functionally Distinct from Adult T Cells in Xenopus laevis.

The amphibian Xenopus laevis tadpole provides a unique comparative experimental organism for investigating the roles of innate-like T (iT) cells in tolerogenic immunity during early development. Unlike mammals and adult frogs, where conventional T cells are dominant, tadpoles rely mostly on several prominent distinct subsets of iT cells interacting with cognate nonpolymorphic MHC class I-like molecules. In the present study, to investigate whole T cell responsiveness ontogenesis in X. laevis, we determined in tadpoles and adult frogs the capacity of splenic T cells to proliferate in vivo upon infection with two different pathogens, ranavirus FV3 and Mycobacterium marinum, as well as in vitro upon PHA stimulation using the thymidine analogous 5-ethynyl-2'-deoxyuridine and flow cytometry. We also analyzed by RT-quantitative PCR T cell responsiveness upon PHA stimulation. In vivo tadpole splenic T cells showed limited capacity to proliferate, whereas the in vitro proliferation rate was higher than adult T cells. Gene markers for T cell activation and immediate-early genes induced upon TCR activation were upregulated with similar kinetics in tadpole and adult splenocytes. However, the tadpole T cell signature included a lower amplitude in the TCR signaling, which is a hallmark of mammalian memory-like T cells and iT or "preset" T cells. This study suggests that reminiscent of mammalian neonatal T cells, tadpole T cells are functionally different from their adult counterpart.

Survival of patients living with HIV and cancer in Cali, Colombia

Background: People living with HIV have an increased risk of cancer compared to the general population. However, with the increase in life expectancy and advances in antiretroviral therapy, the survival of patients with cancer and HIV has changed. Objective: To determine the survival of patients living with HIV and cancer in Cali, Colombia Methods: A retrospective cohort study was conducted at the Fundación Valle del Lili, Cali, Colombia. Data from the HIV database was crossed with data from the hospital and population-based cancer registries between 2011-2019. Patients <18 years, limited available clinical information on the diagnosis and treatment of HIV and cancer, and non-oncological tumor diagnosis were excluded. Results: A total of 173 patients were included. The frequencies of AIDS-defining neoplasms were: Non-Hodgkin lymphoma (42.8%), Kaposi sarcoma (27.8%), and cervical cancer (4.6%). Overall survival was 76.4% (95% CI 68.9-82.3) at five years. Poorer survival was found in patients with AIDS-defining infections (56.9% vs. 77.8%, p=0.027) and non-AIDS-defining infections (57.8% vs. 84.2%, p=0.013), while there was better survival in patients who received antiretroviral therapy (65.9% vs. 17.9%, p=0.021) and oncological treatment (66.7% vs. 35.4%, p<0.001). The presence of non-AIDS-defining infections increases the risk of dying (HR = 2.39, 95% CI 1.05-5.46, p=0.038), while oncological treatment decreases it (HR = 0.33, 95% CI 0.14-0.80, p=0.014). Conclusions: In people living with HIV, Non-Hodgkin lymphoma and Kaposi sarcoma are the most common neoplasms. Factors such as AIDS-associated and non-AIDS-associated infections have been identified as determinants of survival. Cancer treatment seems to improve survival.

Antecedentes: Las personas que viven con VIH tienen un riesgo mayor de cáncer en comparación con la población general. Sin embargo, con el aumento de la esperanza de vida y los avances en la terapia antirretroviral, la supervivencia de los pacientes con cáncer y VIH ha cambiado. Objetivo: Determinar la supervivencia de los pacientes que viven con VIH y cáncer en Cali, Colombia. Métodos: Se realizó un estudio de cohorte retrospectivo en la Fundación Valle del Lili, Cali, Colombia. Los datos de la base de datos de VIH se cruzaron con los datos de los registros de cáncer de base hospitalaria y poblacional entre 2011-2019. Se excluyeron los pacientes <18 años, con información clínica limitada disponible sobre el diagnóstico y tratamiento del VIH y el cáncer y los casos con diagnóstico de tumor no oncológico. Resultados: Se incluyeron un total de 173 pacientes. Las frecuencias de neoplasias definitorias de SIDA fueron: linfoma no Hodgkin (42.8%), sarcoma de Kaposi (27.8%) y cáncer cervical (4.6%). La supervivencia global fue del 76.4% (IC 95% 68.9-82.3) a los cinco años. Se encontró una peor supervivencia en pacientes con infecciones definitorias de SIDA (56.9% vs. 77.8%, p=0.027) e infecciones no definitorias de SIDA (57.8% vs. 84.2%, p=0.013), mientras que hubo una mejor supervivencia en pacientes que recibieron terapia antirretroviral (65.9% vs. 17.9%, p=0.021) y tratamiento oncológico (66.7% vs. 35.4%, p<0.001). La presencia de infecciones no definitorias de SIDA aumentó el riesgo de morir (HR = 2.39, IC 95% 1.05-5.46, p=0.038), mientras que el tratamiento oncológico lo disminuyó (HR = 0.33, IC 95% 0.14-0.80, p=0.014). Conclusiones: En las personas que viven con VIH, el linfoma no Hodgkin y el sarcoma de Kaposi son las neoplasias más comunes. Se han identificado factores como las infecciones asociadas al SIDA y las infecciones no asociadas al SIDA como determinantes de la supervivencia. El tratamiento del cáncer parece mejorar la supervivencia.

Usefulness of Electoral Models for COVID-19 Vaccine Distribution.

Purpose of Review: In response to the COVID-19 pandemic, there has been a remarkably accelerated development of vaccines worldwide. However, an effective distribution system is crucial for vaccination at a national level. Ecuador was one of the first Latin American countries to be most severely affected by the pandemic. It has been struggling to expand its vaccination drive and requires a strategy that provides an achievable vaccination rate and maintains its primary care services. This study aims to provide an efficient vaccination model to achieve herd immunity by utilizing the country's existing infrastructure (the centralized electoral system) for mass vaccination. Recent Findings: The national electoral data from 2017 and 2021 were used to create estimates for the proposed vaccination model. Two model variations, total personnel, needed, and the number of days needed to vaccinate 50%, 75%, and 100% of the population were considered. The numbers of vaccines needed, and vaccination sites were estimated based on the current number of registered voters and polling stations. The results from the proposed model show that 17,892,353 people can be vaccinated, at 40,093 polling stations, by 90,209 personnel if one vaccinator was available per polling station. Summary: Based on this model, even a conservative estimate shows that 12.56 days are needed to achieve herd immunity, and 16.74 days are needed to vaccinate the entire population of Ecuador. Additionally, we propose that this vaccination model can be used as a blueprint for any country to address similar catastrophes in the future. Supplementary Information: The online version contains supplementary material available at 10.1007/s40475-022-00251-y.

Virus-Targeted Transcriptomic Analyses Implicate Ranaviral Interaction with Host Interferon Response in Frog Virus 3-Infected Frog Tissues.

Ranaviruses (Iridoviridae), including Frog Virus 3 (FV3), are large dsDNA viruses that cause devastating infections globally in amphibians, fish, and reptiles, and contribute to catastrophic amphibian declines. FV3's large genome (~105 kb) contains at least 98 putative open reading frames (ORFs) as annotated in its reference genome. Previous studies have classified these coding genes into temporal classes as immediate early, delayed early, and late viral transcripts based on their sequential expression during FV3 infection. To establish a high-throughput characterization of ranaviral gene expression at the genome scale, we performed a whole transcriptomic analysis (RNA-Seq) using total RNA samples containing both viral and cellular transcripts from FV3-infected Xenopus laevis adult tissues using two FV3 strains, a wild type (FV3-WT) and an ORF64R-deleted recombinant (FV3-∆64R). In samples from the infected intestine, liver, spleen, lung, and especially kidney, an FV3-targeted transcriptomic analysis mapped reads spanning the full-genome coverage at ~10× depth on both positive and negative strands. By contrast, reads were only mapped to partial genomic regions in samples from the infected thymus, skin, and muscle. Extensive analyses validated the expression of almost all of the 98 annotated ORFs and profiled their differential expression in a tissue-, virus-, and temporal class-dependent manner. Further studies identified several putative ORFs that encode hypothetical proteins containing viral mimicking conserved domains found in host interferon (IFN) regulatory factors (IRFs) and IFN receptors. This study provides the first comprehensive genome-wide viral transcriptome profiling during infection and across multiple amphibian host tissues that will serve as an instrumental reference. Our findings imply that Ranaviruses like FV3 have acquired previously unknown molecular mimics, interfering with host IFN signaling during evolution.

Targeted Transcriptomics of Frog Virus 3 in Infected Frog Tissues Reveal Non-Coding Regulatory Elements and microRNAs in the Ranaviral Genome and Their Potential Interaction with Host Immune Response.

Background: Frog Virus 3 (FV3) is a large dsDNA virus belonging to Ranaviruses of family Iridoviridae. Ranaviruses infect cold-blood vertebrates including amphibians, fish and reptiles, and contribute to catastrophic amphibian declines. FV3 has a genome at ~105 kb that contains nearly 100 coding genes and 50 intergenic regions as annotated in its reference genome. Previous studies have mainly focused on coding genes and rarely addressed potential non-coding regulatory role of intergenic regions. Results: Using a whole transcriptomic analysis of total RNA samples containing both the viral and cellular transcripts from FV3-infected frog tissues, we detected virus-specific reads mapping in non-coding intergenic regions, in addition to reads from coding genes. Further analyses identified multiple cis-regulatory elements (CREs) in intergenic regions neighboring highly transcribed coding genes. These CREs include not only a virus TATA-Box present in FV3 core promoters as in eukaryotic genes, but also viral mimics of CREs interacting with several transcription factors including CEBPs, CREBs, IRFs, NF-κB, and STATs, which are critical for regulation of cellular immunity and cytokine responses. Our study suggests that intergenic regions immediately upstream of highly expressed FV3 genes have evolved to bind IRFs, NF-κB, and STATs more efficiently. Moreover, we found an enrichment of putative microRNA (miRNA) sequences in more than five intergenic regions of the FV3 genome. Our sequence analysis indicates that a fraction of these viral miRNAs is targeting the 3'-UTR regions of Xenopus genes involved in interferon (IFN)-dependent responses, including particularly those encoding IFN receptor subunits and IFN-regulatory factors (IRFs). Conclusions: Using the FV3 model, this study provides a first genome-wide analysis of non-coding regulatory mechanisms adopted by ranaviruses to epigenetically regulate both viral and host gene expressions, which have co-evolved to interact especially with the host IFN response.

TLR5-Mediated Reactivation of Quiescent Ranavirus FV3 in Xenopus Peritoneal Macrophages.

Ranaviruses such as frog virus 3 (FV3) are large double-stranded DNA (dsDNA) viruses causing emerging infectious diseases leading to extensive morbidity and mortality of amphibians and other ectothermic vertebrates worldwide. Among the hosts of FV3, some are highly susceptible, whereas others are resistant and asymptomatic carriers that can take part in disseminating the infectious virus. To date, the mechanisms involved in the processes of FV3 viral persistence associated with subclinical infection transitioning to lethal outbreaks remain unknown. Investigation in Xenopus laevis has revealed that in asymptomatic FV3 carrier animals, inflammation induced by heat-killed (HK) Escherichia coli stimulation can provoke the relapse of active infection. Since Toll-like receptors (TLRs) are critical for recognizing microbial molecular patterns, we investigated their possible involvement in inflammation-induced FV3 reactivation. Among the 10 different TLRs screened for changes in expression levels following FV3 infection and HK E. coli stimulation, only TLR5 and TLR22, both of which recognize bacterial products, showed differential expression, and only the TLR5 ligand flagellin was able to induce FV3 reactivation similarly to HK E. coli Furthermore, only the TLR5 ligand flagellin induced FV3 reactivation in peritoneal macrophages both in vitro and in vivo These data indicate that the TLR5 signaling pathway can trigger FV3 reactivation and suggest a role of secondary bacterial infections or microbiome alterations (stress or pollution) in initiating sudden deadly disease outbreaks in amphibian populations with detectable persistent asymptomatic ranavirus.IMPORTANCE This study in the amphibian Xenopus laevis provides new evidence of the critical role of macrophages in the persistence of ranaviruses in a quiescent state as well as in the reactivation of these pathogens into a virulent infection. Among the multiple microbial sensors expressed by macrophages, our data underscore the preponderant involvement of TLR5 stimulation in triggering the reactivation of quiescent FV3 in resident peritoneal macrophages, unveiling a mechanistic connection between the reactivation of persisting ranavirus infection and bacterial coinfection. This suggests a role for secondary bacterial infections or microbiome alterations (stress or pollution) in initiating sudden deadly disease outbreaks in amphibian populations with detectable persistent asymptomatic ranavirus.

The myeloid lineage is required for the emergence of a regeneration-permissive environment following Xenopus tail amputation.

Regeneration-competent vertebrates are considered to suppress inflammation faster than non-regenerating ones. Hence, understanding the cellular mechanisms affected by immune cells and inflammation can help develop strategies to promote tissue repair and regeneration. Here, we took advantage of naturally occurring tail regeneration-competent and -incompetent developmental stages of Xenopus tadpoles. We first establish the essential role of the myeloid lineage for tail regeneration in the regeneration-competent tadpoles. We then reveal that upon tail amputation there is a myeloid lineage-dependent change in amputation-induced apoptosis levels, which in turn promotes tissue remodelling, and ultimately leads to the relocalization of the regeneration-organizing cells responsible for progenitor proliferation. These cellular mechanisms failed to be executed in regeneration-incompetent tadpoles. We demonstrate that regeneration incompetency is characterized by inflammatory myeloid cells whereas regeneration competency is associated with reparative myeloid cells. Moreover, treatment of regeneration-incompetent tadpoles with immune-suppressing drugs restores myeloid lineage-controlled cellular mechanisms. Collectively, our work reveals the effects of differential activation of the myeloid lineage on the creation of a regeneration-permissive environment and could be further exploited to devise strategies for regenerative medicine purposes.

Critical Role of an MHC Class I-Like/Innate-Like T Cell Immune Surveillance System in Host Defense against Ranavirus (Frog Virus 3) Infection.

Besides the central role of classical Major Histocompatibility Complex (MHC) class Ia-restricted conventional Cluster of Differentiation 8 (CD8) T cells in antiviral host immune response, the amphibian Xenopuslaevis critically rely on MHC class I-like (mhc1b10.1.L or XNC10)-restricted innate-like (i)T cells (iVα6 T cells) to control infection by the ranavirus Frog virus 3 (FV3). To complement and extend our previous reverse genetic studies showing that iVα6 T cells are required for tadpole survival, as well as for timely and effective adult viral clearance, we examined the conditions and kinetics of iVα6 T cell response against FV3. Using a FV3 knock-out (KO) growth-defective mutant, we found that upregulation of the XNC10 restricting class I-like gene and the rapid recruitment of iVα6 T cells depend on detectable viral replication and productive FV3 infection. In addition, by in vivo depletion with XNC10 tetramers, we demonstrated the direct antiviral effector function of iVα6 T cells. Notably, the transitory iV6 T cell defect delayed innate interferon and cytokine gene response, resulting in long-lasting negative inability to control FV3 infection. These findings suggest that in Xenopus and likely other amphibians, an immune surveillance system based on the early activation of iT cells by non-polymorphic MHC class-I like molecules is important for efficient antiviral immune response.

Developmental exposure to chemicals associated with unconventional oil and gas extraction alters immune homeostasis and viral immunity of the amphibian Xenopus.

Although aquatic vertebrates and humans are increasingly exposed to water pollutants associated with unconventional oil and gas extraction (UOG), the long-term effects of these pollutants on immunity remains unclear. We have established the amphibian Xenopus laevis and the ranavirus Frog Virus 3 (FV3) as a reliable and sensitive model for evaluating the effects of waterborne pollutants. X. laevis tadpoles were exposed to a mixture of equimass amount of UOG chemicals with endocrine disrupting activity (0.1 and 1.0 µg/L) for 3 weeks, and then long-term effects on immune function at steady state and following viral (FV3) infection was assessed after metamorphosis. Notably, developmental exposure to the mixture of UOG chemicals at the tadpole stage affected metamorphic development and fitness by significantly decreasing body mass after metamorphosis completion. Furthermore, developmental exposure to UOGs resulted in perturbation of immune homeostasis in adult frogs, as indicated by significantly decreased number of splenic innate leukocytes, B and T lymphocytes; and a weakened antiviral immune response leading to increased viral load during infection by the ranavirus FV3. These findings suggest that mixture of UOG-associated waterborne endocrine disruptors at low but environmentally-relevant levels have the potential to induce long-lasting alterations of immune function and antiviral immunity in aquatic vertebrates and ultimately human populations.

Assessing Antibody Responses to Pathogens or Model Antigens in Xenopus by Enzyme-Linked Immunosorbent Assay (ELISA).

Xenopus laevis-specific monoclonal antibodies recognize IgM and IgY antibodies not only from X. laevis but also X. tropicalis as well as a variety of amphibian species including Ranidae, Bufonidae, and even some salamanders. These reagents are very useful to assess antibody responses from the serum or other animal secretions (e.g., peritoneal fluid). We present here an enzyme-linked immunosorbent assay (ELISA) optimized for amphibians that permits users to detect and titrate the presence of each type of antibody (IgM and IgY) produced against particular pathogens (e.g., virus, bacteria, or fungus) or antigens (e.g., DNP-KLH).

Evaluating Blood Cell Populations in Xenopus Using Flow Cytometry and Differential Counts by Cytospin.

Analyses by flow cytometry and differential counts by cytospin of peripheral blood leukocytes are two reliable and convenient methods used to assess the immune status and immune responses in the amphibian Xenopus. Here, we describe these methods and discuss their challenges and limitations.

Water Contaminants Associated With Unconventional Oil and Gas Extraction Cause Immunotoxicity to Amphibian Tadpoles.

Chemicals associated with unconventional oil and gas (UOG) operations have been shown to contaminate surface and ground water with a variety of endocrine disrupting compounds (EDCs) inducing multiple developmental alteration in mice. However, little is known about the impacts of UOG-associated contaminants on amphibian health and resistance to an emerging ranavirus infectious disease caused by viruses in the genus Ranavirus, especially at the vulnerable tadpole stage. Here we used tadpoles of the amphibian Xenopus laevis and the ranavirus Frog virus 3 (FV3) as a model relevant to aquatic environment conservation research for investigating the immunotoxic effects of exposure to a mixture of 23 UOG-associated chemicals with EDC activity. Xenopus tadpoles were exposed to an equimass mixture of 23 UOG-associated chemicals (range from 0.1 to 10 µg/l) for 3 weeks prior to infection with FV3. Our data show that exposure to the UOG chemical mixture is toxic for tadpoles at ecological doses of 5 to 10 µg/l. Lower doses significantly altered homeostatic expression of myeloid lineage genes and compromised tadpole responses to FV3 through expression of TNF-α, IL-1ß, and Type I IFN genes, correlating with an increase in viral load. Exposure to a subset of 6 UOG chemicals was still sufficient to perturb the antiviral gene expression response. These findings suggest that UOG-associated water pollutants at low but environmentally relevant doses have the potential to induce acute alterations of immune function and antiviral immunity.

Long term effects of carbaryl exposure on antiviral immune responses in Xenopus laevis.

Water pollutants associated with agriculture may contribute to the increased prevalence of infectious diseases caused by ranaviruses. We have established the amphibian Xenopus laevis and the ranavirus Frog Virus 3 (FV3) as a reliable experimental platform for evaluating the effects of common waterborne pollutants, such as the insecticide carbaryl. Following 3 weeks of exposure to 10 ppb carbaryl, X. laevis tadpoles exhibited a marked increase in mortality and accelerated development. Exposure at lower concentrations (0.1 and 1.0 ppb) was not toxic, but it impaired tadpole innate antiviral immune responses, as evidenced by significantly decreased TNF-α, IL-1ß, IFN-I, and IFN-III gene expression. The defect in IFN-I and IL-1ß gene expression levels persisted after metamorphosis in froglets, whereas only IFN-I gene expression in response to FV3 was attenuated when carbaryl exposure was performed at the adult stage. These findings suggest that the agriculture-associated carbaryl exposure at low but ecologically-relevant concentrations has the potential to induce long term alterations in host-pathogen interactions and antiviral immunity.

Frog Virus 3 dissemination in the brain of tadpoles, but not in adult Xenopus, involves blood brain barrier dysfunction.

While increasing evidence points to a key role of monocytes in amphibian host defenses, monocytes are also thought to be important in the dissemination and persistent infection caused by ranavirus. However, little is known about the fate of infected macrophages or if ranavirus exploits immune privileged organs, such as the brain, in order to establish a reservoir. The amphibian Xenopus laevis and Frog Virus 3 (FV3) were established as an experimental platform for investigating in vivo whether ranavirus could disseminate to the brain. Our data show that the FV3 infection alters the BBB integrity, possibly mediated by an inflammatory response, which leads to viral dissemination into the central nervous system in X. laevis tadpole but not adult. Furthermore, our data suggest that the macrophages play a major role in viral dissemination by carrying the virus into the neural tissues.

Characterization of Frog Virus 3 knockout mutants lacking putative virulence genes.

To identify ranavirus virulence genes, we engineered Frog Virus 3 (FV3) knockout (KO) mutants defective for a putative viral caspase activation and recruitment domain-containing (CARD) protein (Δ64R-FV3) and a ß-hydroxysteroid dehydrogenase homolog (Δ52L-FV3). Compared to wild type (WT) FV3, infection of Xenopus tadpoles with Δ64R- or Δ52L-FV3 resulted in significantly lower levels of mortality and viral replication. We further characterized these and two earlier KO mutants lacking the immediate-early18kDa protein (FV3-Δ18K) or the truncated viral homolog of eIF-2α (FV3-ΔvIF-2α). All KO mutants replicated as well as WT-FV3 in non-amphibian cell lines, whereas in Xenopus A6 kidney cells replication of ΔvCARD-, ΔvßHSD- and ΔvIF-2α-FV3 was markedly reduced. Furthermore, Δ64R- and ΔvIF-2α-FV3 were more sensitive to interferon than WT and Δ18-FV3. Notably, Δ64R-, Δ18K- and ΔvIF-2α- but not Δ52L-FV3 triggered more apoptosis than WT FV3. These data suggest that vCARD (64R) and vß-HSD (52L) genes contribute to viral pathogenesis.

Nonclassical MHC-Restricted Invariant Vα6 T Cells Are Critical for Efficient Early Innate Antiviral Immunity in the Amphibian Xenopus laevis.

Nonclassical MHC class Ib-restricted invariant T (iT) cell subsets are attracting interest because of their potential to regulate immune responses against various pathogens. The biological relevance and evolutionary conservation of iT cells have recently been strengthened by the identification of iT cells (invariant Vα6 [iVα6]) restricted by the nonclassical MHC class Ib molecule XNC10 in the amphibian Xenopus laevis. These iVα6 T cells are functionally similar to mammalian CD1d-restricted invariant NKT cells. Using the amphibian pathogen frog virus 3 (FV3) in combination with XNC10 tetramers and RNA interference loss of function by transgenesis, we show that XNC10-restricted iVα6 T cells are critical for early antiviral immunity in adult X. laevis. Within hours following i.p. FV3 infection, iVα6 T cells were specifically recruited from the spleen into the peritoneum. XNC10 deficiency and concomitant lack of iVα6 T cells resulted in less effective antiviral and macrophage antimicrobial responses, which led to impaired viral clearance, increased viral dissemination, and more pronounced FV3-induced kidney damage. Together, these findings imply that X. laevis XNC10-restricted iVα6 T cells play important roles in the early anti-FV3 response and that, as has been suggested for mammalian invariant NKT cells, they may serve as immune regulators polarizing macrophage effector functions toward more effective antiviral states.