Re-examination of the Southern Hemisphere truffle genus Amylascus (Pezizaceae, Ascomycota) and characterization of the sister genus Nothoamylascus gen. nov

Amylascus is a genus of ectomycorrhizal truffles within Pezizaceae that is known from Australia and contains only two described species, A. herbertianus and A. tasmanicus. Species of Amylascus are closely related to truffles (Pachyphlodes, Luteoamylascus) and cup fungi (Plicariella) from the Northern Hemisphere. Here we reevaluate the species diversity of Amylascus and related taxa from southern South America and Australia based on new morphological and molecular data. We identify previously undocumented diversity and morphological variability in ascospore color, ascospore ornamentation, hymenial construction, epithecium structure and the amyloid reaction of the ascus in Melzer's reagent. We redescribe two Amylascus species from Australia and describe seven new Amylascus species, five from South America and two from Australia. This is the first report of Amylascus species from South America. We also describe the new South American genus Nothoamylascus as sister lineage to the Pachyphlodes-Amylascus-Luteoamylascus clade (including Amylascus, Luteoamylascus, Pachyphlodes, and Plicariella). We obtained ITS sequences of mitotic spore mats from Nothoamylascus erubescens gen. & sp. nov. and four of the seven newly described Amylascus species, providing the first evidence of mitotic spore mats in Amylascus. Additional ITS sequences from mitotic spore mats reveal the presence of nine additional undescribed Amylascus and one Nothoamylascus species that do not correspond to any sampled ascomata. We also identify three additional undescribed Amylascus species based on environmental sequences from the feces of two grounddwelling bird species from Chile, Scelorchilus rubecula and Pteroptochos tarnii. Our results indicate that ascomata from Amylascus and Nothoamylascus species are rarely collected, but molecular data from ectomycorrhizal roots and mitotic spore mats indicate that these species are probably common and widespread in southern South America. Finally, we present a time-calibrated phylogeny that is consistent with a late Gondwanan distribution. The time since the most recent common ancestor of: 1) the family Pezizaceae had a mean of 276 Ma (217-337 HPD); 2) the Amylascus-Pachyphlodes-Nothoamylascus-Luteoamylascus clade had a mean of 79 Ma (60-100 HPD); and 3) the Amylascus-Pachyphlodes clade had a mean of 50 Ma (38-62 HPD). The crown age of Pachyphlodes had a mean of 39 Ma (25-42 HPD) and Amylascus had a mean age of 28 Ma (20-37 HPD), falling near the Eocene-Oligocene boundary and the onset of the Antarctic glaciation (c. 35 Ma). Citation: Healy RA, Truong C, Castellano MA, et al. 2023. Re-examination of the Southern Hemisphere truffle genus Amylascus (Pezizaceae, Ascomycota) and characterization of the sister genus Nothoamylascus gen. nov. Persoonia 51: 125-151. doi: 10.3767/persoonia.2023.51.03.

Dental practitioner approaches to bruxism: Preliminary findings from the national dental practice-based research network

OBJECTIVE

Bruxism is a repetitive masticatory muscle activity. This study investigates dental practitioners' approaches to bruxism assessment and treatment in practices.

METHODS

A brief 5 question questionnaire ("Quick Poll") on bruxism was conducted.

RESULTS

A total of 397 practitioners responded. More than half (55%) initiated treatment for bruxism on one to three patients per month. The majority believed that stress (97%) and sleep patterns (82%) affected bruxism in their patients. Interestingly, 96% offered an occlusal guard/appliance and 46% made occlusal adjustments.

CONCLUSION

This study highlights inconsistencies in practitioner approaches to bruxism assessment and management in clinical settings, suggesting gaps in practitioner knowledge evidenced by the varied responses.

ABBREVIATIONS

PBRN - Practice-Based Research NetworkMMA - Masticatory muscle activitySB - Sleep bruxismAB - Awake bruxismTMJ - Temporomandibular jointOSA - Obstructive sleep apnea.

Mammalian Mycophagy: a Global Review of Ecosystem Interactions Between Mammals and Fungi

The consumption of fungi by animals is a significant trophic interaction in most terrestrial ecosystems, yet the role mammals play in these associations has been incompletely studied. In this review, we compile 1 154 references published over the last 146 years and provide the first comprehensive global review of mammal species known to eat fungi (508 species in 15 orders). We review experimental studies that found viable fungal inoculum in the scats of at least 40 mammal species, including spores from at least 58 mycorrhizal fungal species that remained viable after ingestion by mammals. We provide a summary of mammal behaviours relating to the consumption of fungi, the nutritional importance of fungi for mammals, and the role of mammals in fungal spore dispersal. We also provide evidence to suggest that the morphological evolution of sequestrate fungal sporocarps (fruiting bodies) has likely been driven in part by the dispersal advantages provided by mammals. Finally, we demonstrate how these interconnected associations are widespread globally and have far-reaching ecological implications for mammals, fungi and associated plants in most terrestrial ecosystems.

Abstract LB189: Pharmacodynamic assessment of a-TIGIT mAb EOS-448 highlights multiple FcγR-mediated mode-of-actions in blood and tumor of patients with advanced solid tumors

T cell immunoglobulin and ITIM domain (TIGIT) is an immune checkpoint inhibitor expressed mainly on NK and T cell populations which has demonstrated clinical proof of concept in NSCLC for its inhibition in combination with a-PD(L)-1 agents1. EOS-448 (also named GSK4428859A) is an antagonistic anti-TIGIT human immunoglobulin G1 (hIgG1) antibody showing picomolar activity both to prevent ligand binding and to engage Fc gamma receptors (FcγR).

EOS-448 was selected based on its potent affinity to TIGIT, translating into strong antagonist and functional activity to restore T cell functions and potent antitumor activity in murine models2. Building EOS-448 on an isotype allowing to engage FcγR added potential additional mechanisms of action (MoAs), including the FcγR-induced activation of myeloid/NK populations and antibody-mediated depletion of TIGIT high cells.

To characterize and experimentally validate the multiple MoA triggered by EOS-448, we tested, both in preclinical and clinical settings, its potential to (i) activate effector T cells (ii) modulate antigen-presenting through FcγR engagement, and (iii) deplete suppressive regulatory T cells and terminally exhausted CD8 T cells that express the highest levels of TIGIT.

Our results obtained in murine models confirm the strong potential for the a-TIGIT + a-PD1 combination as well as major differences in activity depending on isotype, with only the Fc-engaging format inducing strong antitumor effect correlating with Treg depletion and CD8 T cell activation within the tumor. Similarly, activation markers on DC and antigen-mediated activation were only observed with the Fc-engaging version but totally absent with the Fc-dead format. In addition, we demonstrated, ex-vivo on human samples, that EOS-448 could preferentially deplete Tregs over effector CD8 T cells and progenitor-like exhausted T cells (Tpex) with low effector function over stem-like memory T cells (Tstem) with stronger effector potential3.

In a first-in-human trial, EOS-448 demonstrated a good tolerability profile with early signs of efficacy4. Pharmacodynamic assessment made by flow cytometry in the blood of patients treated across multiple dose levels of EOS-448 confirmed the multiple MoAs triggered by the drug with (i) increased Ki67 expression in memory CD8 T cells during the first treatment cycle, (ii) sustained depletion of suppressive Tregs, and (iii) of TIGIT high CD8+ T cells, known to be terminally exhausted5, overall resulting in an increased effector CD8/Treg ratio. This activity also translated into a significant decrease in the detection of TIGIT+ cells by immunohistochemistry (IHC), including FoxP3+ double stained cells, in 21 out of 22 tested paired biopsies, with EOS-448 being the first reported a-TIGIT mAb to engage TIGIT within patient tumor.

Overall, the preclinical and clinical evaluation demonstrate the multiple MoAs of EOS-448 supporting its clinical development as a differentiated a-TIGIT mAb to restore anti-tumor immune response. Multiple randomized studies are planned to be initiated in 2022.

1.Cho BC, et al. Abstract #LBA2 ESMO-IO; 2021 2.Preillon J, et al. Mol Cancer Ther ; 2021. 3.Galletti G, et al. Nat Immunol ; 2020. 4.Van den Mooter TF et al. Abstract #CT118 AACR; 2021. 5.Guo X et al. Nat Medicine ; 2018.

Citation Format: Julia Cuende, Julie Preillon, Noemie Wald, Marjorie Mercier, Paola Tieppo, Iain Welsby, Veronique Bodo, Yvonne McGrath, Tom F. Van Den Mooter, Jean-Pascal Machiels, Clarisse Truong, Olivier De Henau, Gregory Driessens, Marion Libouban. Pharmacodynamic assessment of a-TIGIT mAb EOS-448 highlights multiple FcγR-mediated mode-of-actions in blood and tumor of patients with advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB189.

Precipitation of greigite and pyrite induced by Thermococcales: an advantage to live in Fe- and S-rich environments?

Thermococcales, a major order of archaea inhabiting the iron- and sulfur-rich anaerobic parts of hydrothermal deep-sea vents, have been shown to rapidly produce abundant quantities of pyrite FeS₂ in iron-sulfur-rich fluids at 85°C, suggesting that they may contribute to the formation of 'low temperature' FeS₂ in their ecosystem. We show that this process operates in Thermococcus kodakarensis only when zero-valent sulfur is directly available as intracellular sulfur vesicles. Whether in the presence or absence of zero-valent sulfur, significant amounts of Fe₃ S₄ greigite nanocrystals are formed extracellularly. We also show that mineralization of iron sulfides induces massive cell mortality but that concomitantly with the formation of greigite and/or pyrite, a new generation of cells can grow. This phenomenon is observed for Fe concentrations of 5 mM but not higher suggesting that above a threshold in the iron pulse all cells are lysed. We hypothesize that iron sulfides precipitation on former cell materials might induce the release of nutrients in the mineralization medium further used by a fraction of surviving non-mineralized cells allowing production of new alive cells. This suggests that biologically induced mineralization of iron-sulfides could be part of a survival strategy employed by Thermococcales to cope with mineralizing high-temperature hydrothermal environments.

Resurrecting the genus Geomorium: Systematic study of fungi in the genera Underwoodia and Gymnohydnotrya (Pezizales) with the description of three new South American species

Molecular phylogenetic analyses have addressed the systematic position of several major Northern Hemisphere lineages of Pezizales but the taxa of the Southern Hemisphere remain understudied. This study focuses on the molecular systematics and taxonomy of Southern Hemisphere species currently treated in the genera Underwoodia and Gymnohydnotrya. Species in these genera have been identified as the monophyletic /gymnohydnotrya lineage, but no further research has been conducted to determine the evolutionary origin of this lineage or its relationship with other Pezizales lineages. Here, we present a phylogenetic study of fungal species previously described in Underwoodia and Gymnohydnotrya, with sampling of all but one described species. We revise the taxonomy of this lineage and describe three new species from the Patagonian region of South America. Our results show that none of these Southern Hemisphere species are closely related to Underwoodia columnaris, the type species of the genus Underwoodia. Accordingly, we recognize the genus Geomorium described by Spegazzini in 1922 for G. fuegianum. We propose the new family, Geomoriaceae fam. nov., to accommodate this phylogenetically and morphologically unique Southern Hemisphere lineage. Molecular dating estimated that Geomoriaceae started to diverge from its sister clade Tuberaceae c. 112 MYA, with a crown age for the family in the late Cretaceous (c. 67 MYA). This scenario fits well with a Gondwanan origin of the family before the split of Australia and South America from Antarctica during the Paleocene-Eocene boundary (c. 50 MYA).

The role of self-disclosure by peer mentors: Using personal narratives in depression care

OBJECTIVE

Self-disclosure is recognized as an important aspect of peer support, but little is known about its use by peers. This study aimed to qualitatively understand peer self-disclosure in the context of depression care delivery to older adults.

METHODS

69 audio-recordings of peer-client meetings were coded for self-disclosure using the Roter Interaction Analysis System (RIAS). Peer self-disclosure was defined as a statement describing personal life experience with physical and/or emotional relevance for the client. A total of 3421 discrete statements were organized into 770 disclosure episodes. The episodes were qualitatively analyzed to identify themes related to the content and function of self-disclosure within the peer-counseling context.

RESULTS

Peer self-disclosure was used to 1) counsel through reframing perspectives, modeling positive behaviors, offering coping skills, and sharing mental health resources and health information; 2) establish rapport by emphasizing similarities unrelated to depression; and 3) show empathy and understanding of personal struggles. In addition, self-disclosure rarely only focused on the peer experience without relevance for the client.

CONCLUSIONS & PRACTICE IMPLICATIONS

Peer self-disclosure can be purposively used in depression care delivery with older adults. Training and supervision in appropriate self-disclosure should be provided to peers to ensure purposive use.

Challenges on the road to recovery: Exploring attitudes and experiences of clients in a community-based buprenorphine program in Baltimore City

OBJECTIVE

This qualitative study identifies and describes experiences and challenges to retention of individuals with opioid use disorder (OUD) who participated in a low-threshold combined buprenorphine-peer support treatment program in Baltimore.

METHODS

In-depth semi-structured interviews with staff and former clients of the Project Connections Buprenorphine Program (PCBP) (9 people) and focus group discussions with current and previous clients of PCBP (7 people) were conducted. Content analysis was used to extract themes regarding barriers to enrolling and remaining in, and transitioning from the program.

RESULTS

Primary challenges identified by the participants included struggles with cravings and symptoms of withdrawal, comorbid mental health issues, criminal justice system involvement, medication stigma, and conflicts over level of flexibility regarding program requirements and the role of employment.

CONCLUSIONS

This study identified several obstacles clients face when seeking care through a combined buprenorphine-peer support model. Findings highlight potential programmatic factors that can be improved and additional resources that may support treatment retention rates and better outcomes. Despite challenges, low-threshold and community-based programs can increase access to effective maintenance treatment for OUD, especially among vulnerable populations who may not have access to formal health services.

The impact of young age on outcome in colon cancer

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Background: The early age of diagnosis (<40 years) of colon cancer (CC) is generally considered to be associated with a particularly grave prognosis. Our objective was to determine the prognostic relevance of young age on outcome in CC. Methods: Retrospective cohort study from Region 5 of the California Cancer Registry (R5 CCR). Survival by Kaplan- Meier with significance assessed by log-rank test, T-test and Chi Square where appropriate. Results: Between January 1,1994 and December 31, 2003 10,730 patients with CC were diagnosed in R5 CCR. The patients ranged in age from 18–103 years (mean 71.1 years). Two hundred fourteen patients (2%) were 40 years of age or younger. The mean age of young patients was 34.6 years (range 18–40) and for old patients 71.3 years (range 41–103). The mean number of nodes examined were 18.5 in the young CC patient and 18.4 in the remainder of CC patients. There was no significant difference in the anatomic sub-site of the primary between younger and older CC patients (p=0.43). Young patients presented with more advanced primary tumors (T4 18.7% vs. 11.6%, p=0.03), more frequently with more extensive nodal involvement (N+ (54.4% vs. 40.2%, p<0.0001), and more frequently with distant metastatic disease (M1 25.7% vs. 18.3%, p=0.005). Despite these adverse characteristics, young patients had a significantly better disease specific survival (DSS) compared to their older counterparts (5 year survival 70.1% vs. 62.3%, p=0.02). Young patients had a suggestion of improved DSS compared to older patients in Stage I disease (5 yr DSS 96.0% vs. 90.5%, p=0.34) with more certain evidence of improved DSS in Stage II (5 yr DSS 94.8% vs. 79.9%, p=0.02), Stage III (5 yr DSS 73.4% vs. 57.2%, p=0.01) and most profoundly in Stage IV (5 yr DSS 20.1% vs. 0.08%, p=0.002). Conclusions: Despite adverse characteristics at diagnosis, young CC patients have a better DSS than their older counterparts. This is in contrast to the generally held opinion that young CC patients fare worse. This may reflect the ability of young CC patients to accept and tolerate more intense and aggressive therapies.

No significant financial relationships to disclose.

Rapidly progressive neurological deterioration in a child with Alpers syndrome exhibiting a previously unremarkable brain MRI

Alpers syndrome is a fatal disorder due to mutations in the POLG gene encoding the catalytic subunit of mitochondrial DNA polymerase gamma (Pol gamma) involved in mitochondrial DNA (mtDNA) replication. We describe a case of Alpers syndrome due to POLG mutations, with rapidly progressive course, a fatal outcome, and an essentially normal brain MRI in the early oligo-symptomatic phase. Our observation suggests that Alpers syndrome should be considered even in patients with an initially unremarkable brain MRI. The patient was found to harbor the p.Q497H, p.W748S and p.E1143G mutations in cis on one allele, and a fourth mutation, the p.G848S on the other allele. Although the individual mutations detected in the presented case have been previously reported, the specific genotype formed by the particular combination of these is novel.

Clinical and molecular features of mitochondrial DNA depletion due to mutations in deoxyguanosine kinase

Published mutations in deoxyguanosine kinase (DGUOK) cause mitochondrial DNA depletion and a clinical phenotype that consists of neonatal liver failure, nystagmus and hypotonia. In this series, we have identified 15 different mutations in the DGUOK gene from 9 kindreds. Among them, 12 have not previously been reported. Nonsense, splice site, or frame-shift mutations that produce truncated proteins predominate over missense mutations. All patients who harbor null mutations had early onset liver failure and significant neurological disease. These patients have all died before 2-years of age. Conversely, two patients carrying missense mutations had isolated liver disease and are alive in their 4th year of life without liver transplant. Five subjects were detected by newborn screening, with elevated tyrosine or phenylalanine. Consequently, this disease should be considered if elevated tyrosine is identified by newborn screening. Mitochondrial DNA content was below 10% of controls in liver in all but one case and modestly reduced in blood cells. With this paper a total of 39 different mutations in DGUOK have been identified. The most frequent mutation, c.763_c.766dupGATT, occurs in 8 unrelated kindreds. 70% of mutations occur in only one kindred, suggesting full sequencing of this gene is required for diagnosis. The presentation of one case with apparent viral hepatitis, without neurological disease, suggests that this disease should be considered in patients with infantile liver failure regardless of the presence of neurological features or apparent infectious etiology.

Recent invasion of the mountain birch Betula pubescens ssp. tortuosa above the treeline due to climate change: genetic and ecological study in northern Sweden

Mountain birch, Betula pubescens ssp. tortuosa, forms the treeline in northern Sweden. A recent shift in the range of the species associated with an elevation of the treeline is commonly attributed to climate warming. Using microsatellite markers, we explored the genetic structure of populations along an altitudinal gradient close to the treeline. Low genetic differentiation was found between populations, whereas high genetic diversity was maintained within populations. High level of gene flow compensated for possible losses of genetic diversity at higher elevations and dissipated the founding effect of newly established populations above the treeline. Spatial autocorrelation analysis showed low spatial genetic structure within populations because of extensive gene flow. At the treeline, significant genetic structure within the juvenile age class at small distances did not persist in the adult age class, indicating recent expansion of young recruits due to the warming of the climate. Finally, seedling performance above the treeline was positively correlated with parameters related to temperature. These data confirm the high migration potential of the species in response to fluctuating environmental conditions and indicate that it is now invading higher altitudes due to the recent warming of the climate.

Anesthetic management of a parturient with mixed mitral valve disease and uncontrolled atrial fibrillation

This case report describes the anesthetic management of a 32-year-old parturient with combined severe mitral regurgitation and moderate mitral stenosis, complicated by fast atrial fibrillation. The advantageous effects of epidural analgesia during labor and vaginal delivery and the importance of invasive monitoring are discussed. We also report the rare complication of right bundle branch block related to the use of a pulmonary artery catheter.

An ORF2 protein-based ELISA for porcine circovirus type 2 antibodies in post-weaning multisystemic wasting syndrome

Porcine circovirus type 2 (PCV2) plays a crucial role in the pathogenesis of post-weaning multisystemic wasting syndrome (PMWS) in swine. As PCV2 displays significant homology with PCV1 (a non-pathogenic virus) at the nucleotide and amino-acid level, a discriminative antigen is needed for specific serological diagnosis. The ORF2-encoded capsid protein from PCV2 was used to develop an indirect enzyme-linked immunosorbent assay (ELISA). GST-fused capsid protein from PCV2 and GST alone (both expressed in recombinant baculovirus-infected cells) were used as antigens for serodiagnosis. The specificity of the ELISA for detection of PCV2 antibodies was demonstrated in sera from pigs experimentally infected with PCV1, PCV2 and other swine viruses. The semi-quantitative nature of the test was evaluated versus an immunoperoxidase monolayer assay (IPMA). The ELISA was performed on 322 sera from pigs in eight Brittany herds and compared with IPMA. The sensitivity (98.2%) and specificity (94.5%) of this test were considered suitable for individual serological detection. High PCV2 seroprevalence was found in sows and pigs at the end of the growth phase (18-19 weeks) in all eight herds. The seroprevalence in piglets (11-17 weeks) was statistically correlated with clinical symptoms of PMWS (93% in affected versus 54%, in non-affected farms). A cohort study performed in PMWS-free farms showed that 57% of piglets exhibited active seroconversion after 13 weeks, indicating that PCV2 infection occurred earlier in PMWS-affected piglets.

An experimental model for post-weaning multisystemic wasting syndrome (PMWS) in growing piglets

Post-weaning multisystemic wasting syndrome (PMWS) is a comparatively new disease of swine, and known to occur in France since 1996. A porcine circovirus type 2 (PCV2) is found in the lesions of affected piglets. Six piglets aged 10-13 weeks were obtained from a French PMWS-affected farm. Two showing characteristic signs of PMWS (palor, weakness and emaciation) remained in poor condition and were finally killed 6 and 9 days after their arrival in the experimental unit. Tissue homogenates from these two piglets were used to reproduce mild PMWS in specific pathogen-free (SPF) piglets. This mild PMWS consisted of pyrexia (up to 41.7 degrees C) and growth retardation (up to 30% of weight reduction compared with controls) commencing 1 week after infection and lasting 3 weeks. In seven additional trials, pyrexia, growth retardation and lesions characteristic of PMWS were consistently produced in SPF and conventional piglets. However, only four of 55 inoculated SPF piglets (7.2%) showed severe wasting disease. One died and the others had to be killed 3 to 4 weeks after inoculation. None of the inoculated animals developed antibodies to any common swine viruses or bacteria, but clear evidence of PCV2 seroconversion was obtained. Our results therefore strongly suggest that PCV2 is the primary aetiological agent of PMWS.

Identification of an immunorelevant ORF2 epitope from porcine circovirus type 2 as a serological marker for experimental and natural infection

Post-weaning multisystemic wasting syndrome (PMWS) is a recently identified disease of pigs linked to the emergence of a new porcine circovirus (PCV2). We report here the characterization of immunorelevant linear B-cell epitopes of the Open Reading Frame 2-encoded protein (Orf2) from PCV2 by an enzyme-linked immunosorbent assay (ELISA) using experimental antisera collected from pigs inoculated with a PCV2 isolate. Two epitopes spanning residues 69 to 83 and 117 to 131 were specific to PCV2. Antibodies to the 117 to 131 epitope (B- 133) were detected in 22% and 100% of specific pathogen-free (SPF) pig sera 6 and 11 weeks post inoculation, respectively. Cross-sectional studies performed with field sera collected from PMWS-affected herds showed B-133 antibodies in 5% of 8 to 10 week-old pigs, 38% of 13-14 week-old pigs, 62% of 16 to 19 week-old pigs, 56% of 20 to 25 week-old pigs and 45% of 26 to 31 week-old pigs. All these data suggest that epitope B- 133 is a serological marker of PCV2 infection that could be used for the detection of PCV2 antibody response.

Differential recognition of ORF2 protein from type 1 and type 2 porcine circoviruses and identification of immunorelevant epitopes

Two types of porcine circovirus (PCV) have been isolated and are referred to as PCV1 and PCV2. PCV1 represents an apathogenic virus, whereas PCV2 is associated with post-weaning multisystemic wasting syndrome. The two PCVs are related, since they display about 70% identity based on nucleotide sequences. In order to discriminate between common and type-specific antigens, an immunocytological approach was used following transfections with cloned circovirus DNAs, as well as recombinant proteins expressed by either baculovirus or plasmid vectors. The ORF1-encoded proteins in the two viruses were shown to be antigenically related, whereas the ORF2 proteins were recognized differentially by polyclonal anti-PCV2 antibodies. Furthermore, PEPSCAN analysis performed on overlapping fragments of the genes encoding part of ORF1 and the entire ORF2 and ORF3 led to the identification of five dominant immunoreactive areas, one located on ORF1 and four on ORF2. However, only some ORF2 peptides proved to be immunorelevant epitopes for virus type discrimination. The potential use of ORF2-derived antigens as diagnostic tools is demonstrated.

Direct selection for mutators in Escherichia coli

We have constructed strains that allow a direct selection for mutators of Escherichia coli on a single plate medium. The plate selection is based on using two different markers whose reversion is enhanced by a given mutator. Plates containing limiting amounts of each respective nutrient allow the growth of ghost colonies or microcolonies that give rise to full-size colonies only if a reversion event occurs. Because two successive mutational events are required, mutator cells are favored to generate full-size colonies. Reversion of a third marker allows direct visualization of the mutator phenotype by the large number of blue papillae in the full-size colonies. We also describe plate selections involving three successive nutrient markers followed by a fourth papillation step. Different frameshift or base substitution mutations are used to select for mismatch-repair-defective strains (mutHLS and uvrD). We can detect and monitor mutator cells arising spontaneously, at frequencies lower than 10(-5) in the population. Also, we can measure a mutator cascade, in which one type of mutator (mutT) generates a second mutator (mutHLS) that then allows stepwise frameshift mutations. We discuss the relevance of mutators arising on a single medium as a result of cells overcoming successive growth barriers to the development and progression of cancerous tumors, some of which are mutator cell lines.

Comparison of antibody responses to different forms of HIV-1 core antigens by epitope mapping

The specificity of antibodies to HIV-1 capsid (p24CA) and matrix (p17MA) proteins, produced in mice against unprocessed immature assembled polyprotein (wild-type p55 virus-like particles or chimeric p55 virus-like particles) or against the monomeric mature form (rp24CA/rp17MA), was analyzed by a microplate epitope mapping assay using a panel of synthetic peptides covering the entire p24CA plus p17MA sequences of HIV-1LAI. All immunized mice developed anti-p24CA and anti-p17MA antibodies, although the spectrum of specificity of these antibodies was different. Four p24 CA epitopes (residues 176-192, 201-218, 233-253, 285-304) were recognized by anti-rp24CA/rp17MA antibodies, whereas one p17MA epitope (residues 11-25) and one p24CA epitope (residues 176-192) were constantly recognized by anti-p55 virus-like particle antibodies. These results suggest a different specificity pattern of anti-p24CA and anti-p17MA antibodies depending on whether they are produced against the soluble mature form or the immature assembled form of the gag proteins.

Assembly and immunogenicity of chimeric Gag-Env proteins derived from the human immunodeficiency virus type 1

We evaluated the potential of the precursor Gag protein (Pr55) of the human immunodeficiency virus type 1 (HIV-1) as a carrier for the presentation of envelope epitopes. Recombinant chimeric core-envelope protein-expressing constructs were derived by deletion of regions within the gag gene, especially of regions encoding p24 capsid epitopes. Sequences encoding either the principal neutralization determinant (PND) and/or the CD4-binding domains (CD4BS) were then inserted. Deletion of residues 196-226 within the p24 capsid protein did not prevent self-assembly into virus-like particles (VLPs) whereas deletion of residues 299-328 completely abolished VLP formation. Thus the major homology region (MHR) and proximal sequences are required for capsid assembly. An immunization study in mice showed that assembled chimeric proteins elicited strong anti-Gag, weak anti-envelope, and no neutralizing humoral responses. Nonassembled chimeric proteins were poor immunogens. Mapping of Pr55 antigenic sites using sera from immunized mice and peptides overlapping the entire Gag precursor showed that p24 capsid and p17 matrix epitopes presented to the immune system differed from the mature form (p24 or p17) and the multimeric immature form (Pr55).

A simple procedure to generate chimeric Pr55gag virus-like particles expressing the principal neutralization domain of human immunodeficiency virus type 1

The Pr55gag human immunodeficiency virus type 1 (HIV-1) precursor protein that is capable of auto-assembling was used as a carrier for a consensus sequence of the principal neutralization domain (PND) of the HIV-1 envelope. For this purpose, a modified HIV-1 gag gene with deletion of the sequence encoding a previously described p24 epitope (amino acids 196-228 of Pr55gag) was first obtained using PCR with degenerate primers, and then cloned. This deleted gag gene allowed in a second time the insertion of a synthetic oligonucleotide cassette encoding the North American/European consensus PND precisely in place of the p24 epitope. The chimeric gene was then inserted into a baculovirus transfer vector and expressed in insect cells. The construct formed 100-140 nm virus-like particles that were released into the extracellular medium. The use of a serum-free medium that supports growth of insect cells facilitated the downstream purification of the extracellular particles. The chimeric particles were recognized by monoclonal antibodies directed to V3 by Western blot but not by immune electron microscopy, suggesting that, although the inserted sequence was still antigenic it was not exposed at the surface of the particles. The results show the ability of Pr55gag to serve as a carrier for easy insertion, in a precisely defined region, of selected epitopes of gp120 surface envelope protein, and to still auto-assemble in virus-like particles. However, the data indicate that exposed epitopes of the mature p24 protein are not presented similarly in the Pr55 precursor, and therefore that different constructs with various insertions in different places must be generated. Such constructs offer an attractive approach for HIV vaccine development and will need evaluation for both antigenicity and immunogenicity.