Mpox vaccine and infection-driven human immune signatures: an immunological analysis of an observational study

BACKGROUND

Monkeypox virus has recently infected more than 88 000 people, raising concerns about our preparedness against this emerging viral pathogen. Licensed and approved for mpox, the JYNNEOS vaccine has fewer side-effects than previous smallpox vaccines and has shown immunogenicity against monkeypox in animal models. This study aims to elucidate human immune responses to JYNNEOS vaccination compared with mpox-induced immunity.

METHODS

Peripheral blood mononuclear cells and sera were obtained from ten individuals vaccinated with one or two doses of JYNNEOS and six individuals diagnosed with monkeypox virus infection. Samples were obtained from seven individuals before vaccination to serve as a baseline. We examined the polyclonal serum (ELISA) and single B-cell (heavy chain gene and transcriptome data) antibody repertoires and T-cell responses (activation-induced marker and intracellular cytokine staining assays) induced by the JYNNEOS vaccine versus monkeypox virus infection.

FINDINGS

All participants were men between the ages of 21 and 60 years, except for one woman in the group of mpox-convalescent individuals, and none had previous orthopoxvirus exposure. All mpox cases were mild. Vaccinee samples were collected 6-33 days after the first dose and 5-40 days after the second dose. Mpox-convalescent samples were collected 20-102 days after infection. In vaccine recipients, gene-level plasmablast and antibody responses were negligible and sera displayed moderate binding to recombinant orthopoxviral proteins (A29L, A35R, E8L, A30L, A27L, A33R, B18R, and L1R) and native proteins from the 2022 monkeypox outbreak strain. By contrast, recent monkeypox virus infection (within 20-102 days) induced robust serum antibody responses to monkeypox virus proteins and to native monkeypox virus proteins from a viral isolate obtained during the 2022 outbreak. JYNNEOS vaccine recipients presented robust orthopoxviral CD4+ and CD8+ T-cell responses.

INTERPRETATION

Infection with monkeypox virus resulted in robust B-cell and T-cell responses, whereas immunisation with JYNNEOS elicited more robust T-cell responses. These data can help to inform vaccine design and policies for preventing mpox in humans.

FUNDING

National Cancer Institute (National Institutes of Health), National Institute of Allergy and Infectious Diseases (National Institutes of Health), and Icahn School of Medicine.

Development of a novel serological assay for the detection of mpox infection in vaccinated populations

In 2022 the World Health Organization declared a Public Health Emergency for an outbreak of mpox, the zoonotic Orthopoxvirus (OPV) affecting at least 104 nonendemic locations worldwide. Serologic detection of mpox infection is problematic, however, due to considerable antigenic and serologic cross-reactivity among OPVs and smallpox-vaccinated individuals. In this report, we developed a high-throughput multiplex microsphere immunoassay using a combination of mpox-specific peptides and cross-reactive OPV proteins that results in the specific serologic detection of mpox infection with 93% sensitivity and 98% specificity. The New York State Non-Vaccinia Orthopoxvirus Microsphere Immunoassay is an important tool to detect subclinical mpox infection and understand the extent of mpox spread in the community through retrospective analysis.

Development of a Novel Serological Assay for the Detection of Mpox Infection in Vaccinated Populations

In 2022 the World Health Organization declared a Public Health Emergency for an outbreak of mpox, the zoonotic Orthopoxvirus (OPV) affecting at least 103 non-endemic locations world-wide. Serologic detection of mpox infection is problematic, however, due to considerable antigenic and serologic cross-reactivity among OPVs and smallpox-vaccinated individuals. In this report, we developed a high-throughput multiplex microsphere immunoassay (MIA) using a combination of mpox-specific peptides and cross-reactive OPV proteins that results in the specific serologic detection of mpox infection with 93% sensitivity and 98% specificity. The New York State Non-Vaccinia Orthopoxvirus Microsphere Immunoassay is an important diagnostic tool to detect subclinical mpox infection and understand the extent of mpox spread in the community through retrospective analysis.

Pharmacokinetics of convalescent plasma therapy in a COVID-19 patient with X-linked Agammaglobulinemia

Convalescent plasma (CP) has been the first line of defense against numerous infectious diseases throughout history. The COVID-19 pandemic created a need for a quick, easily accessible, and effective treatment for severe disease and CP was able to meet that immediate need. The utility of CP warrants a better understanding of the pharmacokinetics of CP treatment. Here we present the case of a COVID-19 patient with a genetic deficiency in antibody production who received CP as a part of the treatment regimen. In depth serological analysis revealed a surprising lack of SARS-CoV-2 specific antibodies and reduced serum IgG following CP infusion. Our study highlights plasma dilution and accelerated antibody clearance as potential mechanisms for the variable efficacy of CP therapy.

Durable Immunity to Ricin Toxin Elicited by Intranasally Administered Monoclonal Antibody-Based Immune Complexes

Inhalation of ricin toxin (RT) elicits profuse inflammation and cell death within the upper and lower airways, ultimately culminating in acute respiratory distress syndrome. We previously reported that the effects of pulmonary RT exposure in mice are nullified by intranasal administration of an mAb mixture consisting of PB10, directed against ricin's enzymatic subunit (RTA), and SylH3, directed against ricin's binding subunit (RTB). We now report that delivery of PB10 and SylH3 as an RT-mAb immune complex (RIC) to mice by the intranasal or i.p. routes stimulates the rapid onset of RT-specific serum IgG that persists for months. RIC administration also induced high-titer, toxin-neutralizing Abs. Moreover, RIC-treated mice were immune to a subsequent 5 × LD₅₀ RT challenge on days 30 or 90. Intranasal RIC administration was more effective than i.p. delivery at rendering mice immune to intranasal RT exposure. Finally, we found that the onset of RT-specific serum IgG following RIC delivery was independent of FcγR engagement, as revealed through FcγR knockout mice and RICs generated with PB10/SylH3 LALA (leucine to alanine) derivatives. In conclusion, a single dose of RICs given intranasally to mice was sufficient to stimulate durable protective immunity to RT by an FcγR-independent pathway.

The Serological Sciences Network (SeroNet) for COVID-19: Depth and Breadth of Serology Assays and Plans for Assay Harmonization

Background

In October 2020, the National Cancer Institute (NCI) Serological Sciences Network (SeroNet) was established to study the immune response to COVID-19, and "to develop, validate, improve, and implement serological testing and associated technologies." SeroNet is comprised of 25 participating research institutions partnering with the Frederick National Laboratory for Cancer Research (FNLCR) and the SeroNet Coordinating Center. Since its inception, SeroNet has supported collaborative development and sharing of COVID-19 serological assay procedures and has set forth plans for assay harmonization.

Methods

To facilitate collaboration and procedure sharing, a detailed survey was sent to collate comprehensive assay details and performance metrics on COVID-19 serological assays within SeroNet. In addition, FNLCR established a protocol to calibrate SeroNet serological assays to reference standards, such as the U.S. SARS-CoV-2 serology standard reference material and First WHO International Standard (IS) for anti-SARS-CoV-2 immunoglobulin (20/136), to facilitate harmonization of assay reporting units and cross-comparison of study data.

Results

SeroNet institutions reported development of a total of 27 ELISA methods, 13 multiplex assays, 9 neutralization assays, and use of 12 different commercial serological methods. FNLCR developed a standardized protocol for SeroNet institutions to calibrate these diverse serological assays to reference standards.

Conclusions

SeroNet institutions have established a diverse array of COVID-19 serological assays to study the immune response to SARS-CoV-2 virus and vaccines. Calibration of SeroNet serological assays to harmonize results reporting will facilitate future pooled data analyses and study cross-comparisons.

COVID-19 Serology Control Panel Using the Dried-Tube Specimen Method

The dried-tube specimen (DTS) procedure was used to develop the COVID-19 serology control panel (CSCP). The DTS offers the benefit of shipping materials without a cold chain, allowing for greater access without deterioration of material integrity. Samples in the panel were sourced from COVID-19 convalescent persons from March to May 2020. The immunoglobulin subtypes (total Ig, IgM, and IgG) and their respective reactivity to severe acute respiratory syndrome coronavirus 2 nucleocapsid, spike, and receptor-binding domain antigens of the samples were delineated and compared with the WHO International Standard to elucidate the exact binding antibody units of each CSCP sample and ensure the CSCP provides adequate reactivity for different types of serological test platforms. We distribute the CSCP as a kit with five coded tubes to laboratories around the world to be used to compare test kits for external quality assurance, for harmonizing laboratory testing, and for use as training materials for laboratory workers.

Glycolipid-Containing Nanoparticle Vaccine Engages Invariant NKT Cells to Enhance Humoral Protection against Systemic Bacterial Infection but Abrogates T-Independent Vaccine Responses

CD4⁺ T cells enable the critical B cell humoral immune protection afforded by most effective vaccines. We and others have recently identified an alternative source of help for B cells in mice, invariant NK T (iNKT) cells. iNKT cells are innate glycolipid-specific T cells restricted to the nonpolymorphic Ag-presenting molecule CD1d. As such, iNKT cells respond to glycolipids equally well in all people, making them an appealing adjuvant for universal vaccines. We tested the potential for the iNKT glycolipid agonist, α-galactosylceramide (αGC), to serve as an adjuvant for a known human protective epitope by creating a nanoparticle that delivers αGC plus antigenic polysaccharides from Streptococcus pneumoniae αGC-embedded nanoparticles activate murine iNKT cells and B cells in vitro and in vivo, facilitate significant dose sparing, and avoid iNKT anergy. Nanoparticles containing αGC plus S. pneumoniae polysaccharides elicits robust IgM and IgG in vivo and protect mice against lethal systemic S. pneumoniae However, codelivery of αGC via nanoparticles actually eliminated Ab protection elicited by a T-independent S. pneumoniae vaccine. This is consistent with previous studies demonstrating iNKT cell help for B cells following acute activation, but negative regulation of B cells during chronic inflammation. αGC-containing nanoparticles represent a viable platform for broadly efficacious vaccines against deadly human pathogens, but their potential for eliminating B cells under certain conditions suggests further clarity on iNKT cell interactions with B cells is warranted.

Serological analysis reveals an imbalanced IgG subclass composition associated with COVID-19 disease severity

Coronavirus disease 2019 (COVID-19) is associated with a wide spectrum of disease presentation, ranging from asymptomatic infection to acute respiratory distress syndrome (ARDS). Paradoxically, a direct relationship has been suggested between COVID-19 disease severity and the levels of circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibodies, including virus-neutralizing titers. A serological analysis of 536 convalescent healthcare workers reveals that SARS-CoV-2-specific and virus-neutralizing antibody levels are elevated in individuals that experience severe disease. The severity-associated increase in SARS-CoV-2-specific antibody is dominated by immunoglobulin G (IgG), with an IgG subclass ratio skewed toward elevated receptor binding domain (RBD)- and S1-specific IgG3. In addition, individuals that experience severe disease show elevated SARS-CoV-2-specific antibody binding to the inflammatory receptor FcɣRIIIa. Based on these correlational studies, we propose that spike-specific IgG subclass utilization may contribute to COVID-19 disease severity through potent Fc-mediated effector functions. These results may have significant implications for SARS-CoV-2 vaccine design and convalescent plasma therapy.

Potency determination of ricin toxin using a monoclonal antibody-based competition assay

Mouse challenge studies with death as an endpoint remain the gold standard in assessing the potency of ricin toxin, a Category B biothreat agent derived from the castor bean (Ricinus communis). However, animal studies are expensive, time consuming and ethically concerning. In an effort to reduce reliance on animals in vaccine development, we developed a monoclonal antibody (MAb)-based ricin competition ELISA (RiCoE) that indicates conformation integrity of ricin toxin. In forced degradation (heat-denaturation) experiments with native ricin holotoxin, we demonstrate a correlation between the decline in MAb reactivity in RiCoE and a corresponding loss of toxin potency in Vero cells (IC₅₀) and mice (LD₅₀). The RiCoE assay was applied to differentially sourced commercial lots of ricin toxin derived from R. communis blends and compared to toxin potency in mice. There was near perfect congruence between RiCoE values with two different MAbs (PB10, SyH7) and ricin potency in the mouse model using morbidity as an endpoint. In conclusion, we propose that RiCoE can serve as a rapid and sensitive substitute to mouse lethal dose challenge studies as a means to determine ricin toxin potency and will be valuable at various stages of vaccine development.

Endpoint and epitope-specific antibody responses as correlates of vaccine-mediated protection of mice against ricin toxin

The successful licensure of vaccines for biodefense is contingent upon the availability of well-established correlates of protection (CoP) in at least two animal species that can be applied to humans, without the need to assess efficacy in the clinic. In this report we describe a multivariate model that combines pre-challenge serum antibody endpoint titers (EPT) and values derived from an epitope profiling immune-competition capture (EPICC) assay as a predictor in mice of vaccine-mediated immunity against ricin toxin (RT), a Category B biothreat. EPICC is a modified competition ELISA in which serum samples from vaccinated mice were assessed for their ability to inhibit the capture of soluble, biotinylated (b)-RT by a panel of immobilized monoclonal antibodies (mAbs) directed against four immunodominant toxin-neutralizing regions on the enzymatic A chain (RTA) of RT. In a test cohort of mice (n = 40) vaccinated with suboptimal doses of the RTA subunit vaccine, RiVax®, we identified two mAbs, PB10 and SyH7, which had EPICC inhibition values in pre-challenge serum samples that correlated with survival following a challenge with 5 × LD₅₀ of RT administered by intraperitoneal (IP) injection. Analysis of a larger cohort of mice (n = 645) revealed that a multivariate model combining endpoint titers and EPICC values for PB10 and SyH7 as predictive variables had significantly higher statistical power than any one of the independent variables alone. Establishing the correlates of vaccine-mediated protection in mice represents an important steppingstone in the development of RiVax® as a medical countermeasure under the United States Food and Drug Administration's "Animal Rule."

Thermal stability and epitope integrity of a lyophilized ricin toxin subunit vaccine

Biodefense vaccine are destined to be stockpiled for periods of time and deployed in the event of a public health emergency. In this report, we compared the potency of liquid and lyophilized (thermostabilized) formulations of a candidate ricin toxin subunit vaccine, RiVax, adsorbed to aluminum salts adjuvant, over a 12-month period. The liquid and lyophilized formulations were stored at stressed (40 °C) and unstressed (4 °C) conditions and evaluated at 3, 6 and 12-month time points for potency in a mouse model of lethal dose ricin challenge. At the same time points, the vaccine formulations were interrogated in vitro by competition ELISA for conformational integrity using a panel of three monoclonal antibodies (mAbs), PB10, WECB2, and SyH7, directed against known immunodominant toxin-neutralizing epitopes on RiVax. We found that the liquid vaccine under stress conditions declined precipitously within the first three months, as evidenced by a reduction in in vivo potency and concomitant loss of mAb recognition in vitro. In contrast, the lyophilized RiVax vaccine retained in vivo potency and conformational integrity for up to one year at 4 °C and 40 °C. We discuss the utility of monitoring the integrity of one or more toxin-neutralizing epitopes on RiVax as a possible supplement to animal studies to assess vaccine potency.

Alpha-galactosylceramide (αGalCer) enhances vaccine-induced protection in a model of ricin intoxication

Alpha-galactosylceramide (αGalCer) is a glycolipid derived from a marine sponge that is a potent activator of both mouse and human invariant natural killer T (iNKT) cells. For that reason, αGalCer is a promising vaccine adjuvant that has been shown to improve both humoral and cellular immunity when co-administered with various vaccines, including candidate vaccines for biodefense. In the current study, we tested the effectiveness of αGalCer as an adjuvant for the clinically-relevant ricin toxin subunit vaccine, RiVax. αGalCer had a potent adjuvant effect, as shown by a rapid onset of anti-ricin IgG titers, accelerated development of serum toxin-neutralizing activity, and enhanced protection from lethal ricin challenge in a mouse model. These results underscore the potential of αGalCer to augment the protective immune response to a vaccine designed to counteract ricin toxin, a fast-acting biothreat agent.

Early derivation of IgM memory cells and bone marrow plasmablasts

IgM memory cells are recognized as an important component of B cell memory in mice and humans. Our studies of B cells elicited in response to ehrlichial infection identified a population of CD11c-positive IgM memory cells, and an IgM bone marrow antibody-secreting cell population. The origin of these cells was unknown, although an early T-independent spleen CD11c- and T-bet-positive IgM plasmablast population precedes both, suggesting a linear relationship. A majority of the IgM memory cells detected after day 30 post-infection, also T-bet-positive, had undergone somatic hypermutation, indicating they expressed activation-induced cytidine deaminase (AID). Therefore, to identify early AID-expressing precursor B cells, we infected an AID-regulated tamoxifen-inducible Cre-recombinase-EYFP reporter strain. Tamoxifen administration led to the labeling of both IgM memory cells and bone marrow ASCs on day 30 and later post-infection. High frequencies of labeled cells were identified on day 30 post-infection, following tamoxifen administration on day 10 post-infection, although IgM memory cells were marked when tamoxifen was administered as early as day 4 post-infection. Transcription of Aicda in the early plasmablasts was not detected in the absence of CD4 T cells, but occurred independently of TLR signaling. Unlike the IgM memory cells, the bone marrow IgM ASCs were elicited independent of T cell help. Moreover, Aicda was constitutively expressed in IgM memory cells, but not in bone marrow ASCs. These studies demonstrate that two distinct long-term IgM-positive B cell populations are generated early in response to infection, but are maintained via separate mechanisms.

Identification of secreted and membrane-bound bat immunoglobulin using a Microchiropteran-specific mouse monoclonal antibody

Bat immunity has received increasing attention because some bat species are being decimated by the fungal disease, White Nose Syndrome, while other species are potential reservoirs of zoonotic viruses. Identifying specific immune processes requires new specific tools and reagents. In this study, we describe a new mouse monoclonal antibody (mAb) reactive with Eptesicus fuscus immunoglobulins. The epitope recognized by mAb BT1-4F10 was localized to immunoglobulin light (lambda) chains; hence, the mAb recognized serum immunoglobulins and B lymphocytes. The BT1-4F10 epitope appeared to be restricted to Microchiropteran immunoglobulins and absent from Megachiropteran immunoglobulins. Analyses of sera and other E. fuscus fluids showed that most, if not all, secreted immunoglobulins utilized lambda light chains. Finally, mAb BT1-4F10 permitted the identification of B cell follicles in splenic white pulp. This Microchiropteran-specific mAb has potential utility in seroassays; hence, this reagent may have both basic and practical applications for studying immune process.

Neutrophils license iNKT cells to regulate self-reactive mouse B cell responses

The innate responsiveness of the immune system is important not only for quick responses to pathogens but also for the initiation and shaping of the subsequent adaptive immune response. Activation via the cytokine IL-18, a product of inflammasomes, gives rise to a rapid response that includes the production of self-reactive antibodies. As increased concentrations of this cytokine are found in inflammatory diseases, we investigated the origin of the B cell response and its regulation. We identified an accumulation of B cell-helper neutrophils in the spleen that interacted with innate-type invariant natural killer T cells (iNKT cells) to regulate B cell responses. We found that neutrophil-dependent expression of the death-receptor ligand FasL by iNKT cells was needed to restrict autoantibody production. Neutrophils can thus license iNKT cells to regulate potentially harmful autoreactive B cell responses during inflammasome-driven inflammation.

T cell-dependent IgM memory B cells generated during bacterial infection are required for IgG responses to antigen challenge

Immunological memory has long considered to be harbored in B cells that express high-affinity class-switched IgG. IgM-positive memory B cells can also be generated following immunization, although their physiological role has been unclear. In this study, we show that bacterial infection elicited a relatively large population of IgM memory B cells that were uniquely identified by their surface expression of CD11c, CD73, and programmed death-ligand 2. The cells lacked expression of cell surface markers typically expressed by germinal center B cells, were CD138 negative, and did not secrete Ab ex vivo. The population was also largely quiescent and accumulated somatic mutations. The IgM memory B cells were located in the region of the splenic marginal zone and were not detected in blood or other secondary lymphoid organs. Generation of the memory cells was CD4 T cell dependent and required IL-21R signaling. In vivo depletion of the IgM memory B cells abrogated the IgG recall responses to specific Ag challenge, demonstrating that the cell population was required for humoral memory, and underwent class-switch recombination following Ag encounter. Our findings demonstrate that T cell-dependent IgM memory B cells can be elicited at high frequency and can play an important role in maintaining long-term immunity during bacterial infection.

SSR-marker analysis of the intracultivar phenotypic variation discovered within 3 soybean cultivars

Genetic variation within homogeneous gene pools in various crops is assumed to be very limited. One objective of this study was to use 144 simple sequence repeat (SSR) markers to determine if the single-plant lines selected at ultra-low plant density in honeycomb designs within the soybean cultivars Benning, Haskell, and Cook had unique SSR genetic fingerprints. Another objective was to investigate if the variation found was the result of residual genetic heterozygosity that could be detected in the original gene pool where selection initiated. Our results showed that the phenotypic variation for seed protein content and seed weight has a genotypic component identified by the SSR band variation. The 7 lines from Haskell had a total of 63 variant alleles, the 5 lines from Benning had 34 variant alleles, and the 7 lines from Cook had 34 variant alleles, therefore, possessing unique genetic fingerprints. Most of the intracultivar SSR band variation discovered was the result of residual heterozygosity in the initial plant selected to become the cultivar. More specifically, 82% of the SSR variant alleles were traced in the Benning Foundation seed source, 93% in the Haskell seed source, and 82% in the Cook seed source. The remaining variant bands (18% for Benning, 7% for Haskell, and 18% for Cook) could not be detected in the Foundation seed source and were likely the result of mutation or some other mechanism generating de novo variation. These results provide evidence that genetic variation among individual plants is present even in homogeneous gene pools and can be further utilized in breeding programs.

Collaborative learning in radiologic science education

CONTEXT

Radiologic science is a complex health profession, requiring the competent use of technology as well as the ability to function as part of a team, think critically, exercise independent judgment, solve problems creatively and communicate effectively.

OBJECTIVE

This article presents a review of literature in support of the relevance of collaborative learning to radiologic science education. In addition, strategies for effective design, facilitation and authentic assessment of activities are provided for educators wishing to incorporate collaborative techniques into their program curriculum.

RESULTS

The connection between the benefits of collaborative learning and necessary workplace skills, particularly in the areas of critical thinking, creative problem solving and communication skills, suggests that collaborative learning techniques may be particularly useful in the education of future radiologic technologists.

SUMMARY

This article summarizes research identifying the benefits of collaborative learning for adult education and identifying the link between these benefits and the necessary characteristics of medical imaging technologists.

Fine mapping of the nematode resistance gene Mi-3 in Solanum peruvianum and construction of a S. lycopersicum DNA contig spanning the locus

Currently, the only genetic resistance against root-knot nematodes in the cultivated tomato Solanum lycopersicum (Lycopersicon esculentum) is due to the gene Mi-1. Another resistance gene, Mi-3, identified in the related wild species Solanum peruvianum (Lycopersicon peruvianum) confers resistance to nematodes that are virulent on tomato lines that carry Mi-1, and is effective at temperatures at which Mi-1 is not effective (above 30 degrees C). Two S. peruvianum populations segregating for Mi-3 were used to develop a high-resolution map of the Mi-3 region of chromosome 12. S. lycopersicum BACs carrying flanking markers were identified and used to construct a contig spanning the Mi-3 region. Markers generated from BAC-end sequences were mapped in S. peruvianum plants in which recombination events had occurred near Mi-3. Comparison of the S. peruvianum genetic map with the physical map of S. lycopersicum indicated that marker order is conserved between S. lycopersicum and S. peruvianum. The 600 kb contig between Mi-3-flanking markers TG180 and NR18 corresponds to a genetic distance of about 7.2 cM in S. peruvianum. We have identified a marker that completely cosegregates with Mi-3, as well as flanking markers within 0.25 cM of the gene. These markers can be used to introduce Mi-3 into cultivated tomato, either by conventional breeding or cloning strategies.

Replication from oriP of Epstein-Barr virus requires exact spacing of two bound dimers of EBNA1 which bend DNA

oriP is a 1.7-kb region of the Epstein-Barr virus (EBV) chromosome that supports replication and stable maintenance of plasmids in human cells that contain EBV-encoded protein EBNA1. Plasmids that depend on oriP are replicated once per cell cycle by cellular factors. The replicator of oriP is an approximately 120-bp region called DS which depends on either of two pairs of closely spaced EBNA1 binding sites. Here we report that changing the distance between the EBNA1 sites of a functional pair by inserting or deleting 1 or 2 bp abolished replication activity. The results indicated that, while the distance separating the binding sites is critical, the specific nucleotide sequence between them is unlikely to be important. The use of electrophoretic mobility shift assays to investigate binding by EBNA1 to the sites with normal or altered spacing revealed that EBNA1 induces DNA to bend significantly when it binds, with the center of bending coinciding with the center of binding. EBNA1 binding to a functional pair of sites which are spaced 21 bp apart center to center and which thus are in helical phase induces a larger symmetrical bend, which based on electrophoretic mobility approximates the sum of two separate EBNA1-induced DNA bends. The results imply that replication from oriP requires a precise structure in which DNA forms a large bend around two EBNA1 dimers.

Human DNA replication initiation factors, ORC and MCM, associate with oriP of Epstein-Barr virus

The 165-kb chromosome of Epstein-Barr virus (EBV) is replicated by cellular enzymes only once per cell cycle in human cells that are latently infected. Here, we report that the human origin recognition complex, ORC, can be detected in association with an EBV replication origin, oriP, in cells by using antibodies against three different subunits of human ORC to precipitate crosslinked chromatin. Mcm2, a subunit of the MCM replication licensing complex, was found to associate with oriP during G(1) and to dissociate from it during S phase. The detection of ORC and Mcm2 at oriP was shown to require the presence of the 120-bp replicator of oriP. Licensing and initiation of replication at oriP of EBV thus seem to be mediated by ORC. This is an example of a virus apparently using ORC and associated factors for the propagation of its genome.

Initiation of DNA replication within oriP is dispensable for stable replication of the latent Epstein-Barr virus chromosome after infection of established cell lines

The 165-kb circularized chromosome of Epstein-Barr virus (EBV) is replicated in latently infected cells once per cell cycle by host proteins during S phase. Replication initiates at multiple sites on latent EBV chromosomes, including within a 1.8-kb region called oriP, which can provide both replication and stabilization for recombinant plasmids in the presence of the EBV-encoded protein, EBNA-1. Replication initiates at or near the dyad symmetry component (DS) of oriP, which depends on multiple EBNA-1 binding sites for activity. To test the importance of the replication function of oriP, the DS was deleted from the viral genome. EBV mutants lacking the DS and carrying a selectable gene could establish latent infections in BL30 cells, in which circular, mutant viral chromosomes were stably maintained. Analysis of replication fork movement using two-dimensional gel electrophoresis showed that the deletion of the DS reduced the initiation events to an undetectable level within the oriP region so that this segment was replicated exclusively by forks entering the region from either direction. A significant slowing or stalling of replication forks that occurs normally at the approximate position of the DS was also eliminated by deletion of the DS. The results confirm the DS as both a replication origin and a place where replication forks pause. Since the replication function of oriP is dispensable at least in certain cell lines, the essential role of EBNA-1 for infection of these cell lines is likely to be that of stabilizing the EBV chromosome by associating with the 30-bp repeats of oriP. The results also imply that in established cell lines, the EBV chromosome can be efficiently replicated entirely from origins that are activated by cellular factors. Presumably, initiation of replication at the DS, mediated by EBNA-1, is important for the natural life cycle of EBV, perhaps in establishing latent infections of normal B cells.

The minimal replicator of Epstein-Barr virus oriP

oriP is a 1.7-kb region of the Epstein-Barr virus (EBV) chromosome that supports the replication and stable maintenance of plasmids in human cells. oriP contains two essential components, called the DS and the FR, both of which contain multiple binding sites for the EBV-encoded protein, EBNA-1. The DS appears to function as the replicator of oriP, while the FR acts in conjunction with EBNA-1 to prevent the loss of plasmids from proliferating cells. Because of EBNA-1's role in stabilizing plasmids through the FR, it has not been entirely clear to what extent EBNA-1 might be required for replication from oriP per se, and a recent study has questioned whether EBNA-1 has any direct role in replication. In the present study we found that plasmids carrying oriP required EBNA-1 to replicate efficiently even when assayed only 2 days after plasmids were introduced into the cell lines 143B and 293. Significantly, using 293 cells it was demonstrated that the plasmid-retention function of EBNA-1 and the FR did not contribute significantly to the accumulation of replicated plasmids, and the DS supported efficient EBNA-1-dependent replication in the absence of the FR. The DS contains two pairs of closely spaced EBNA-1 binding sites, and a previous study had shown that both sites within either pair are required for activity. However, it was unclear from previous work what additional sequences within the DS might be required. We found that each "half" of the DS, including a pair of closely spaced EBNA-1 binding sites, had significant replicator activity when the other half had been deleted. The only significant DNA sequences that the two halves of the DS share in common, other than EBNA-1 binding sites, is a 9-bp sequence that is present twice in the "left half" and once in the "right half." These nonamer repeats, while not essential for activity, contributed significantly to the activity of each half of the DS. Two thymines occur at unique positions within EBNA-1 binding sites 1 and 4 at the DS and become sensitive to oxidation by permanganate when EBNA-1 binds, but mutation of each to the consensus base, adenine, actually improved the activity of each half of the DS slightly. In conclusion, the DS of oriP is an EBNA-1-dependent replicator, and its minimal active core appears to be simply two properly spaced EBNA-1 binding sites.

Genetic evidence that EBNA-1 is needed for efficient, stable latent infection by Epstein-Barr virus

Replication and maintenance of the 170-kb circular chromosome of Epstein-Barr virus (EBV) during latent infection are generally believed to depend upon a single viral gene product, the nuclear protein EBNA-1. EBNA-1 binds to two clusters of sites at oriP, an 1, 800-bp sequence on the EBV genome which can support replication and maintenance of artificial plasmids introduced into cell lines that contain EBNA-1. To investigate the importance of EBNA-1 to latent infection by EBV, we introduced a frameshift mutation into the EBNA-1 gene of EBV by recombination along with a flanking selectable marker. EBV genomes carrying the frameshift mutation could be isolated readily after superinfecting EBV-positive cell lines, but not if recombinant virus was used to infect EBV-negative B-cell lines or to immortalize peripheral blood B cells. EBV mutants lacking almost all of internal repeat 3, which encode a repetitive glycine and alanine domain of EBNA-1, were generated in the same way and found to immortalize B cells normally. An EBNA-1-deficient mutant of EBV was isolated and found to be incapable of establishing a latent infection of the cell line BL30 at a detectable frequency, indicating that the mutant was less than 1% as efficient as an isogenic, EBNA-1-positive strain in this assay. The data indicate that EBNA-1 is required for efficient and stable latent infection by EBV under the conditions tested. Evidence from other studies now indicates that autonomous maintenance of the EBV chromosome during latent infection does not depend on the replication initiation function of oriP. It is therefore likely that the viral chromosome maintenance (segregation) function of oriP and EBNA-1 is what is required.

CD21-Dependent infection of an epithelial cell line, 293, by Epstein-Barr virus

Epstein-Barr virus (EBV) is invariably present in undifferentiated nasopharyngeal carcinomas, is found sporadically in other carcinomas, and replicates in the differentiated layer of the tongue epithelium in lesions of oral hairy leukoplakia. However, it is not clear how frequently or by what mechanism EBV infects epithelial cells normally. Here, we report that a human epithelial cell line, 293, can be stably infected by EBV that has been genetically marked with a selectable gene. We show that 293 cells express a relatively low level of CD21, that binding of fluorescein-labeled EBV to 293 cells can be detected, and that both the binding of virus to cells and infection can be blocked with antibodies specific for CD21. Two proteins known to form complexes with CD21 on the surface of lymphoid cells, CD35 and CD19, could not be detected at the surface of 293 cells. All infected clones of 293 cells exhibited tight latency with a pattern of gene expression similar to that of type II latency, but productive EBV replication and release of infectious virus could be induced inefficiently by forced expression of the lytic transactivators, R and Z. Low levels of mRNA specific for the transforming membrane protein of EBV, LMP-1, as well as for LMP-2, were detected; however, LMP-1 protein was either undetectable or near the limit of detection at less than 5% of the level typical of EBV-transformed B cells. A slight increase in expression of the receptor for epidermal growth factor, which can be induced in epithelial cells by LMP-1, was detected at the cell surface with two EBV-infected 293 cell clones. These results show that low levels of surface CD21 can support infection of an epithelial cell line by EBV. The results also raise the possibility that in a normal infection of epithelial cells by EBV, the LMP-1 protein is not expressed at levels that are high enough to be oncogenic and that there might be differences in the cells of EBV-associated epithelial cancers that have arisen to allow for elevated expression of LMP-1.

An imperfect correlation between DNA replication activity of Epstein-Barr virus nuclear antigen 1 (EBNA1) and binding to the nuclear import receptor, Rch1/importin alpha

Epstein-Barr virus (EBV) replicates as a stable multicopy episome in latently infected mammalian cells. Latent cycle DNA replication requires only two viral elements, the cis-acting origin of plasmid replication (oriP) and the trans-acting origin binding protein (EBNA1). EBNA1 binds multiple recognition sites in oriP, but has not other enzymatic activities associated with replication functions. To identify human cellular proteins that mediate EBNA1 function, we designed a one-hybrid assay in yeast to select for proteins that bind to EBNA1 when bound to criP in vivo. A human cDNA encoding the Rch1/hSRP1 alpha/ importin alpha protein was isolated and shown to bind to full-length EBNA1, but not to an amino terminal deletion mutant of EBNA1 when bound to oriP in yeast. The interaction of EBNA1 with Rch1 was confirmed biochemically by coimmunoprecipitation from nuclear extracts and by direct binding of recombinant proteins in vitro. Internal deletion mutations in EBNA1 which compromised DNA replication activity were similarly reduced for binding to Rch1. Mutations with no effect on DNA replication activity were similarly unaffected for Rch1 binding. Rch1/importin alpha has been shown to bind to the nuclear localization sequence (NLS) of several proteins and stimulate nuclear import. A substitution mutation in the EBNA1 nuclear localization sequence reduced Rch1 binding, but had no effect on DNA replication function, indicating that Rch1 binding affinity does not correspond precisely with replication activity. Nevertheless, the identification of a stable interaction between Rch1 and EBNA1 at the origin of viral DNA replication raises the intriguing possibility that Rch1 contributes to the nuclear functions of EBNA1.

Characterization of accessory molecules in murine lung dendritic cell function: roles for CD80, CD86, CD54, and CD40L

Lung dendritic cells (DCs) from mice were enriched to 92-99% purity using a multistep enrichment protocol which included fluorescence-activated cell sorting. DCs were analyzed for expression of cell surface molecules, function in a mixed leukocyte reaction (MLR), and dependence on accessory molecules in stimulating an MLR. DCs possessed potent accessory properties in vitro, while interstitial macrophages (IM), which are Ia-negative, displayed little MLR-stimulating function of their own. However, IM were capable of enhancing DC-initiated T cell proliferation via a cell contact mechanism. These results indicated that murine lung DCs functioned as stimulators of primary T cell responses, and that cells in the local environment influenced their function. Lung DCs expressed surface molecules typical of DCs from other sites including CD11a, CD54, CD80, and CD86. As is true for DCs in other sites, costimulatory molecules including CD80, CD86, CD40L, CD2, CD54, and CD11a played important roles in lung DC-initiated T cell proliferation. Interestingly, anti-CD86 monoclonal antibody (mAb) had little inhibitory effect on the MLR unless it was added in combination with anti-CD80 mAb. These studies suggest that CD80 on lung DCs can provide a costimulatory signal to allogeneic T cells in the absence of CD86 signaling, but that CD86 functions poorly except when CD80 is also engaged.

The failed Patient Self-Determination Act and policy alternatives for the right to die

The empirical evidence regarding the implementation and impact of the federal Patient Self-Determination Act is examined in this article. The Act was designed to increase the use of advance medical directives in light of the U.S. Supreme Court's Cruzan decision. Research shows that the law has had little effect and that the use of advance directives has scant relation to medical treatment and care. Various policy alternatives for the right to die are also examined. The authors conclude with an analysis of the likely impact of medical costs, fruitless treatment, and rationed health care on limiting life-prolonging treatment.

Comparison of the EBNA1 proteins of Epstein-Barr virus and herpesvirus papio in sequence and function

The EBNA1 protein of Epstein-Barr virus (EBV) supports replication and maintenance of the circularized viral chromosome in cells that are latently infected. We have isolated, sequenced, and functionally characterized the EBNA1 gene of herpesvirus papio (HVP), an EBV-like virus that infects baboons. The amino acid sequences of EBNA1 of HVP and EBV are 56% identical, if the difference in the length of the glycine and alanine containing repetitive region, which is much shorter for HVP EBNA1, is omitted for the calculation. The key structural features of the DNA-binding/dimerization domain (the carboxyl-terminal domain) appear to have been conserved, as have amino acids in the two regions thought to be most critical for DNA binding. Most of the salient features of the amino-terminal two-thirds of EBNA1 (the amino-terminal domain), including a dearth of sequences predictive of alpha-helical or beta-sheet structures, are shared by the two sequences, although numerous gaps in this region were needed for alignment of the sequences. The amino-terminal fifty amino acids of EBNA1 of both EBV and HVP weakly resemble the amino terminus of rat ribosomal protein S2. Plasmids carrying oriP of either virus replicated stably in mammalian cells and supported efficient outgrowth of colonies under selection when supported by EBNA1 from either virus, although with each oriP there was a noticeable preference for EBNA1 to be from the same virus. HVP EBNA1 was less effective than EBV EBNA1 at activating the enhancer function of EBV oriP and under certain conditions was less effective than EBV EBNA1 at supporting maintenance of plasmids carrying EBV oriP. Results obtained with hybrid EBNA1 molecules indicated that differences in the amino-terminal and carboxyl-terminal domains, respectively, are primarily responsible for the differences in transcriptional activation and plasmid maintenance, respectively. The results showed that changes within EBNA1 can differentially alter its transcriptional and replicational activities.

Constitutive binding of EBNA1 protein to the Epstein-Barr virus replication origin, oriP, with distortion of DNA structure during latent infection

Replication of the circular, 170 kb genome of Epstein-Barr virus (EBV) during latent infection is performed by the cellular replication machinery under cell-cycle control. A single viral protein, EBNA1, directs the cellular replication apparatus to initiate replication within the genetically defined replication origin, oriP, at a cluster of four EBNA1 binding sites, referred to here as the physical origin of bidirectional replication, or OBR. A second cluster of EBNA1 binding sites within oriP, the 30 bp repeats, serves an essential role as a replication enhancer and also provides a distinct episome maintenance function that is unrelated to replication. We examined the functional elements of oriP for binding by EBNA1 and possibly other proteins in proliferating Raji cells by generating in vivo footprints using two reagents, dimethylsulfate (DMS) and KMnO4. We also employed deoxyribonuclease I (DNase I) with permeabilized cells. The in vivo and permeabilized cell footprints at the EBNA1 binding sites, particularly those obtained using DMS, gave strong evidence that all of these sites are bound by EBNA1 in asynchronously dividing cells. No consistent evidence was found to suggest binding by other proteins at any other sites within the functional regions of oriP. Thymines at symmetrical positions of the OBR within oriP were oxidized when cells were treated with permanganate, suggestive of bends or other distortions of DNA structure at these positions; binding of EBNA1 in vitro to total DNA from Raji cells induced reactivity to permanganate at identical positions. The simplest interpretation of the results, which were obtained using asynchronously dividing cells, is that EBNA1 binds to its sites at oriP and holds the OBR in a distorted conformation throughout most of the cell cycle, implying that replication is initiated by a cellular mechanism and is not limited by an availability of EBNA1 for binding to oriP.

Mutants of Epstein-Barr virus with a selective marker disrupting the TP gene transform B cells and replicate normally in culture

We have isolated mutants of Epstein-Barr virus (EBV) which carry a dominant selectable marker inserted into the third exon of the gene encoding two membrane proteins, TP1 and TP2 (or LMP2A and LMP2B), which are expressed in latently infected, growth-transformed B cells. One of the mutants also acquired a 260-bp deletion beginning in the first intron a few base pairs from the terminal repeats and removing most of the second TP exon, including the initial coding sequences of TP2. These EBV mutants transform human B cells in culture, and the transformed B-cell clones carrying them release EBV at approximately normal frequencies.

The role of T lymphocytes in pulmonary microbial defense mechanisms

Understanding how lung immunity develops against pulmonary pathogens should lead to more rational approaches in vaccine design and to the use of recombinant cytokines in lung disease. T lymphocytes are central to the development of effective immune responses; therefore, understanding how lung immunity develops will require a study of how and where T cells respond to respiratory antigens. Our laboratory has helped define the phenotype and function of lung dendritic cells, which likely play an essential role in stimulating naive T cells to respond to antigens. We found that both interstitial and alveolar macrophages can regulate the function of these cells, the former to enhance activity, the latter to suppress. In addition, we developed a murine pulmonary infection model using the fungus, Cryptococcus neoformans, in which T-cell-mediated immunity is essential for effective host clearance of the organism. The role of T cells in this model is to recruit and activate effector cells to resolve the lung infection; both CD4 and CD8 T-cell subsets are required for optimal effector cell recruitment. These studies are summarized as examples of current approaches to understanding pulmonary immunity.

A role for TGF-beta in the suppression by murine bronchoalveolar cells of lung dendritic cell initiated immune responses

Effective pulmonary immune responses likely require both local antigen presenting cells (APC) and regulatory suppressor cells. Bronchoalveolar cells (BAC), which consist primarily of alveolar macrophages (AM), are poor APC in most species and are often suppressive. However, dendritic cell (DC)-enriched populations from both lung interstitium and BAC have potent APC activity as measured by their capacity to stimulate both alloantigen and antigen-induced lymphoproliferative T cell responses. To determine if BAC could down-regulate pulmonary immune responses, BAC were mixed with DC-enriched loosely adherent lung interstitial cells (LAd) in a mixed leukocyte reaction (MLR). With high numbers of BAC, MLRs were consistently suppressed and suppression was partially reversed by the addition of indomethacin and catalase. Supernatants from BAC cultured with either syngeneic or allogeneic T lymphocytes in the presence of indomethacin and catalase markedly suppressed an MLR, while supernatants from BAC cultured alone were inconsistently suppressive. Antibodies to TGF-beta completely reversed the BAC-T cell supernatant-induced suppression of the MLR. However, TGF-beta antibody only partially reversed BAC-induced suppression when BAC were added directly to MLR cultures that contained indomethacin and catalase, suggesting that, in addition to TGF-beta, prostaglandins, and H2O2, BAC in culture with LAd and allogeneic T cells also produced short-lived suppressive factors and/or mediated suppression by direct cell contact. Thus, resident BAC likely utilize multiple mechanisms including TGF-beta secretion to suppress intra-alveolar immune responses initiated by lung DC.

Targeted gene disruption in Epstein-Barr virus

We report the development of a method that should allow the insertion of a selective marker into any region of the Epstein-Barr virus (EBV) genome of strain B95-8 through homologous recombination with plasmids. In this method, EBV recombinants are isolated as G418-resistant, immortalized B-cell clones or as G418-resistant, latently infected subclones of Burkitt lymphoma cell lines. The presence of the productive replication origin of EBV, oriLyt, on the plasmid was found to increase the number of observed recombinant viruses by approximately 100-fold; this stimulation was observed when oriLyt was separated from the sites of recombination by several kilobases of nonhomologous DNA. Long segments of EBV DNA flanking the marker on the plasmid and/or a large plasmid size were inferred to be important for obtaining a high proportion of recombinant genomes that had recombined on both sides of the selective marker; otherwise, the recombinants that predominated had acquired the entire plasmid by recombining only on one side of the inserted marker. Therefore, to facilitate targeted insertion of genetic markers into the EBV genome, a cosmid vector carrying oriLyt was constructed and tested by using it to generate EBV mutants with the BALF2 open-reading frame disrupted.

BHRF1 of Epstein-Barr virus, which is homologous to human proto-oncogene bcl2, is not essential for transformation of B cells or for virus replication in vitro

The Epstein-Barr virus (EBV) genome contains an open reading frame, BHRF1, that encodes a presumptive membrane protein with sequence similarity to the proto-oncogene bcl2, which is linked to human B-cell follicular lymphoma. Potential roles for BHRF1 in EBV's ability to growth transform human B cells and to replicate in B cells in culture were investigated by generating EBV mutants that lack most of the open reading frame. This was accomplished by recombination of plasmids carrying mutations in BHRF1 with the transformation-defective EBV strain P3HR1. Because BHRF1 resides close to the deletion in P3HR1 that renders this strain transformation defective, B-cell transformation could be used to select for recombination events in the region. B-cell clones were established by recombinants which lacked most of the BHRF1 open reading frame, although most of these initial B-cell transformants also carried nonrecombinant (BHRF1+) P3HR1 genomes, at levels ranging from a fraction of a copy to four copies per cell. Secondary B-cell transformants that lacked BHRF1+ EBV at detectable levels were found to release transforming, BHRF1-deficient EBV at levels that were within the normal range for EBV-immortalized B-cell clones. These studies demonstrate that BHRF1 is nonessential for growth transformation of B cells and for virus replication and release from these cells in culture.

Immunity to a pulmonary Cryptococcus neoformans infection requires both CD4+ and CD8+ T cells

The role of CD4+ and CD8+ T cells in mediating pulmonary clearance of a cryptococcal infection was investigated. Intratracheal inoculation of BALB/c and C.B-17 mice with a moderately virulent strain of Cryptococcus neoformans (52D) resulted in a pulmonary infection, which was cleared by a T cell-dependent mechanism. During this clearance, there was a significant influx of both CD4+ and CD8+ T cells into the lungs. Depletion of CD4+ T cells by injections of CD4-specific monoclonal antibody (mAb) prevented pulmonary clearance and also resulted in significant colonization of the brain and spleen of infected mice. CD4 depletion did not prevent the influx of CD8+ T cells into the lungs. Surprisingly, depletion of CD8+ T cells by mAb also ablated pulmonary clearance. CD8-depleted mice also had a small but significant increase in brain and spleen colony-forming unit compared to control mice by the end of the study. CD4+ T cell pulmonary influx was independent of the presence of CD8+ T cells. The lungs of T cell-depleted mice were examined histologically. CD4+ and CD8+ T cells each mediated a degree of inflammatory influx seen in the lungs of infected mice and raised the possibility that CD4+ and CD8+ T cells may synergize to generate the inflammatory response in the lungs. Numerous phagocytized but intact cryptococci were seen in the inflammatory foci of CD8-depleted mice but not in control or CD4-depleted mice. We propose that CD4+ T cells may recruit and activate effector phagocytes while CD8+ T cells predominantly function to lyse cryptococcus-laden unactivated phagocytes similar to the function of CD8+ T cells during listeria and mycobacteria infections.

T cell-mediated immunity in the lung: a Cryptococcus neoformans pulmonary infection model using SCID and athymic nude mice

T cells are important in systemic anticryptococcal defenses, but a role in controlling an initial pulmonary infection has not been demonstrated. A murine model with intratracheal inoculation was developed to study the acquisition and expression of pulmonary T cell-mediated immunity against Cryptococcus neoformans. Infections with four strains of C. neoformans (305, 68A, 613D, and 52D) in two strains of mice (BALB/c and C57BL/6) were examined. Unencapsulated strain 305 and slowly growing strain 68A were readily controlled apparently by nonimmune pulmonary defenses, and no extrapulmonary dissemination was detected. Strain 613D grew progressively in the lungs and disseminated to the brain and spleen. Strain 52D initially grew rapidly in the lungs and disseminated to the spleen, but a clearance mechanism developed in the lungs after day 7 postinfection and in the spleen after day 28. SCID and athymic nude mice were unable to clear a strain 52D pulmonary infection, and a lethal disseminated infection occurred. Pulmonary clearance could be adoptively transferred into SCID mice infected with strain 52D by use of immune T cells from the spleen and lungs and hilar lymph nodes of infected immunocompetent donors. Furthermore, pulmonary clearance was almost 100-fold better in SCID mice that received immune T cells from the lungs and hilar lymph nodes than in those that received immune T cells from the spleen, even though equivalent levels of delayed-type hypersensitivity were transferred by both cell populations. These adoptive transfer studies suggested that the lung and hilar lymph node T cells from immune animals either are enriched in such a way as to mediate protective immunity or home to the lungs better than do splenic T cells.

Epstein-Barr virus-derived plasmids replicate only once per cell cycle and are not amplified after entry into cells

Some possible ways in which replication of plasmids containing the Epstein-Barr virus (EBV) plasmid maintenance origin, oriP, might be controlled were investigated. Virtually all plasmid molecules were found to replicate no more than once per cell cycle, whether replication was observed after stable introduction of the plasmids into cells by drug selection or during the first few cell divisions after introducing the DNA into cells. The presence in the cells of excess amounts of EBNA1, the only viral protein needed for oriP function, did not increase the number of oriP-replicated plasmids maintained by cells under selection. In the cell lines studied, EBNA1 and oriP seem to lack the capacity to override the cellular controls that limit DNA replication to one initiation event per DNA molecule per S phase. The multicopy status of EBV-derived, selectable plasmids appears to result from the initial uptake by cells of large numbers of plasmid molecules, the efficient maintenance of these plasmids, and the pressure of genetic selection against plasmid loss. Other unknown controls must be responsible for the amplification of EBV genomes soon after latent infection of cells.

Multiple EBNA1-binding sites are required to form an EBNA1-dependent enhancer and to activate a minimal replicative origin within oriP of Epstein-Barr virus

EBNA1 activates the EBV plasmid maintenance sequence oriP by binding to its two essential regions. One region is a family of 30-base-pair (bp) repeats and is activated by EBNA1 to act as a transcriptional enhancer. The other region contains a 65-bp dyad symmetry and lacks enhancer function. To explore the functional differences between the two regions, we determined oriP activities as functions of the number of 30-bp repeats and compared them with activities determined when tandem copies of the dyad symmetry region were used to replace the 30-bp repeats. Three conclusions have been drawn. (i) Activation of the 30-bp repeats by EBNA1 to enhance transcription or to permit plasmid maintenance is a highly cooperative process involving at least six or seven 30-bp repeats for full activity. (ii) Tandem copies of the dyad symmetry region cooperatively enhance transcription but are less effective than 30-bp repeats providing a similar number of EBNA1-binding sites. (iii) Tandem copies of the dyad symmetry region alone cooperatively activate replication, suggesting that the region contains the actual origin of replication. We also report that while rodent-derived cell lines do not support replication of EBV-derived plasmids they do permit EBNA1-dependent enhancer activity. EBV plasmid replication thus requires the interaction of EBNA1 or oriP with a host factor that is not required for enhancement of transcription.

Ultraviolet light and ultraviolet light-activated composite resins

In a comparison of the UV light--activated composite resins, Estilux was polymerized to a significantly greater depth than the other composite resins. In general, Lee-fill polymerized the least. When comparing the UV light sources, the Lee light and the Duralux light did not significantly differ from each other, but both polymerized the materials tested to a significantly greater depth than the other light sources. Of the two time exposures, 60-second exposure provided a significantly greater depth of polymerization than 20 seconds for each light with each material.

Identification of ribosomal protein S7 as a repressor of translation within the str operon of E. coli

A DNA-directed in vitro protein-synthesizing system was used to demonstrate that r protein S7 has the capacity to inhibit the translation of mRNA for the second and third gene products of the str operon (S7 and EF-G) but not for the first gene product (S12). Translation of mRNA of the last gene product in the operon (EF-Tu) is also probably not inhibited by S7. In addition, we localized the target site for S7 repressor action on the polycistronic str mRNA by examining the repressor activity of S7 in vitro using various template DNAs that contain the gene. The target site was found not to include a promoter-proximal portion of the mRNA for S12. To test for regulatory properties of S7 in vivo, we inserted the S7 gene into a plasmid vector containing the ara regulatory elements such that S7 synthesis was placed under ara control. A specific increase in S7 synthesis caused by stimulation in transcription originating from the arabinose promoter decreased the synthetic rate for EF-G but had no effect on S12 or EF-Tu synthesis.

Feedback regulation of ribosomal protein synthesis in E. coli: localization of the mRNA target sites for repressor action of ribosomal protein L1

E. coli ribosomal protein L1 is a translational repressor of the synthesis in vitro of both proteins encoded in the L11 operon (L11 and L1). L1 is shown to act at a single target site within the first 160 bases of the bicistronic mRNA, near (or at) the translation initiation site of the L11 cistron. Synthesis of L1 apparently requires translation of the preceding L11 cistron, allowing regulation of the synthesis of both proteins froma single mRNA target site. This observation suggests a sequential translation mechanism that results in the equimolar synthesis rates of the two proteins observed in vivo. It was found that the presence of 23S rRNA, but not 16S rRNA, relieves translational inhibition by L1. L1 presumably recognizes structural features of the mRNA target site that are homologous to the L1-binding site of 23S rRNA. Although previous work indicated that translationally inhibited ribosomal protein mRNA is degraded in vivo, L1 repressor action in the present in vitro system was found not to involve mRNA degradation.