Selection of neutralizing antibody escape mutants with type A influenza virus HA-specific polyclonal antisera: possible significance for antigenic drift

Ten antisera were produced in rabbits by two or three intravenous injections of inactivated whole influenza type A virions. All contained haemagglutination-inhibition (HI) antibody directed predominantly to an epitope in antigenic site B and, in addition, various amounts of antibodies to an epitope in site A and in site D. The ability of untreated antisera to select neutralization escape mutants was investigated by incubating virus possessing the homologous haemagglutinin with antiserum adjusted to contain anti-B epitope HI titres of 100, 1000 and 10000 HIU/ml. Virus-antiserum mixtures were inoculated into embryonated hen's eggs, and progeny virus examined without further selection. Forty percent of the antisera at a titre of 1000 HIU/ml selected neutralizing antibody escape mutants as defined by their lack of reactivity to Mab HC10 (site B), and unchanged reactivity to other Mabs to site A and site D epitopes. All escape mutant-selecting antisera had a ratio of anti-site B (HC10)-epitope antibody[ratio]other antibodies of [gt-or-equal, slanted]2·0[ratio]1. The antiserum with the highest ratio (7·4[ratio]1) selected escape mutants in all eggs tested in four different experiments. No antiserum used at a titre of 10000 HIU/ml allowed multiplication of any virus. All antisera used at a titre of 100 HIU/ml permitted virus growth, but this was wild-type (wt) virus. We conclude that a predominant epitope-specific antibody response, a titre of [gt-or-equal, slanted]1000 HIU/ml, and a low absolute titre of other antibodies ([less-than-or-eq, slant]500 HIU/ml) are three requirements for the selection of escape mutants. None of the antisera in this study could have selected escape mutants without an appropriate dilution factor, so the occurrence of an escape mutant-selecting antiserum in nature is likely to be a rare event

Measuring forces between protein fibers by microscopy

We propose a general scheme for measuring the attraction between mechanically frustrated semiflexible fibers by measuring their thermal fluctuations and shape. We apply this analysis to a system of sickle hemoglobin (HbS) fibers that laterally attract one another. These fibers appear to “zip” together before reaching mechanical equilibrium due to the existence of cross-links into a dilute fiber network. We are also able to estimate the rigidities of the fibers. These rigidities are found to be consistent with sickle hemoglobin “single” fibers 20 nm in diameter, despite recent experiments indicating that fiber bundling sometimes occurs. Our estimate of the magnitude of the interfiber attraction for HbS fibers is in the range 8 ± 7 kBT/μm, or 4 ± 3 kBT/μm if the fibers are assumed, a priori to be single fibers (such an assumption is fully consistent with the data). This value is sufficient to bind the fibers, overcoming entropic effects, although extremely chemically weak. Our results are compared to models for the interfiber attraction that include depletion and van der Waals forces. This technique should also facilitate a similar analysis of other filamentous protein assembles in the future, including β-amyloid, actin, and tubulin

SO ORDERED: A Textual Analysis of United States’ Governors’ Press Release Responses to the COVID-19 Pandemic

The COVID-19 pandemic presents a unique environment from which each individual state, in the United States, has been forced to address their publics. In order to understand how each state has engaged with this pandemic, a textual analysis of each state’s governor’s first press release was conducted; five thematic trends were identified. Through use of the social trust approach to risk communication and the contingency theory of strategic conflict management (using external threat variables), the implications of these press releases are discussed

Assessing morphological changes to the periaqueductal gray and the corpus callosum in response to opioid exposure in an adolescent rat model

The risk-taking behavior that occurs during adolescence, as well as the brain development that coincides with this period, makes adolescents vulnerable to trying and becoming addicted to drugs of abuse, such as opioids. Drug addiction causes changes to the brain at the chemical scale (triggering or inhibiting neurotransmitter release), the cellular scale (strengthening or weakening neural connections), and at the gross anatomical scale (i.e., changes detected on brain scans). The goals of this investigation are to 1) refine gross neuroanatomical imaging techniques and 2) apply the techniques to a rat model of adolescent opioid addiction. I used a nascent soft-tissue imaging technique called diceCT (diffusible iodine-based contrast-enhanced computed tomography), which allowed me to digitally analyze small neuroanatomical structures without dissection. First, I tested the efficacy of two diceCT protocols: the standard approach of fixation, staining, and scanning specimens, and another approach that adds a tissue-stabilization step, which is reported to limit the tissue shrinkage that can occur when a specimen is exposed to high concentrations of iodine. MicroCT visualizations from this experiment revealed that tissue stabilization is not routinely necessary to obtain satisfactory brain scans, as elliptical Fourier analysis found no significant shape differences when neuroanatomical structures were compared between stabilized and non-stabilized brains. Then, for a second experiment, I used the same adolescent rat brains to determine if opioid exposures during life can be associated with gross anatomical changes to the periaqueductal gray (PAG) and corpus callosum. I found highly significant changes to the cross-sectional shape of both the PAG and the corpus callosum in the opioid-exposed group compared to the drug-naïve group. Whether these anatomical changes translate into functional or behavioral consequences should be the target of future investigations. Potential limitations to this experiment are the low sample size (n = 18) and the complicated design of drug exposures. While further research is necessary to overcome these limitations, the implications of this preliminary investigation are troubling, especially given adolescents’ increasing access to opioids

STR-923: FATIGUE OF STUD SHEAR CONNECTORS IN STEEL-PRECAST COMPOSITE BRIDGES

Modular bridge systems consisting of precast concrete deck panels connected to steel girders are becoming increasingly popular due to their rapid construction and optimal material utilization. The shear connection is a critical element of the system, having significant impacts on construction time, economic and environmental cost, structural integrity, and durability. Today welded shear studs are by far the most common type of shear connection. In steel-precast composite bridges, the studs are commonly grouped together so that the precast deck panels can be affixed to the girders by providing full depth “shear pockets” filled with grout. A laboratory beam testing program is underway at the University of Waterloo to investigate the effect of cyclic loading on stud shear connectors in cast-in-place and precast bridge girders. The program consists of twelve beam specimens, uniquely tested using a variable amplitude load history simulating Canadian highway truck traffic. In addition to yielding valuable S-N (stress plotted vs. the number of cycles until fatigue failure) data, initial test results provide evidence of the benefits of redundancy in the structural system and the value of beam tests over push-out tests. Calculating connector stresses in a composite beam is made complicated by interfacial slip and neutral axis migration. The end goal of this research is to provide Canadian bridge designers and erectors with improved design and construction recommendations in order to improve the efficiency and economy of this structural system for rapid bridge replacement projects

Temporal inabilities and decision-making capacity in depression

We report on an interview-based study of decision-making capacity in two classes of patients suffering from depression. Developing a method of second-person hermeneutic phenomenology, we articulate the distinctive combination of temporal agility and temporal inability characteristic of the experience of severely depressed patients. We argue that a cluster of decision-specific temporal abilities is a critical element of decision-making capacity, and we show that loss of these abilities is a risk factor distinguishing severely depressed patients from mildly/moderately depressed patients. We explore the legal and clinical consequences of this result