Dynamics of semi-flexible fibres in viscous flow

The dynamics of semi-flexible fibres in shear flow and the effect of flexibility on the swimming speed of helical flagella are investigated. High aspect ratio particles such as carbon and glass fibres are often added as fillers to processed polymers. Although these materials have high rigidity, the large aspect ratiomakes the fibres liable to bending during flow. Other high aspect ratio fibres that behave as semi-flexible fibres include carbon nano-tubes, paper fibres and semi-flexible polymers such as the muscle protein f-actin. Most theoretical studies assume that fibres are either rigid or completely flexible, but in this thesis fibres with a finite bending modulus are considered. A semi-flexible fibre is modelled as a chain of shorter rods linked together. A bending torque is included at the joints between the rods to account for the rigidity. In shear flow the simulation reproduces the C and S turns observed in experiments on semi-flexible fibres. The results for finite aspect ratio fibres predict changes to the period of rotation and drift between Jeffery orbits. The direction of drift for a flexible fibre depends on both the intial orientation and the fibre’s flexiblity. We also present a linear analysis of how small distortions to a straight semi-flexible fibre grow when the flow places the fibre under compression. These results are in agreement with our full simulations and the growth rates of the distortions to a straight fibre allow us to predict the most unstable mode at a particular flow rate. To allow for intrinsically bent or helical equilibrium shapes a second simulation method is developed that includes a twisting torque at the joints between the rods as well as a bending torque. Using this simulation we measure the period of rotation and orbit drift of permanently deformed fibres in shear flow and show that due to the asymmetry of a helix, shear induced rotation results in translation and orbit drift for both rigid and semi-flexible fibres. Bacteria such as Vibrio alginolyticus and Escherichia coli swim by rotating one or more helical flagella. Vibrio alginolyticus has only one flagella and changes direction by altering its sense of rotation. Experimental observations of Vibrio alginolyticus have found that backwards swimming is 50% faster than forwards swimming speed however, previous numerical simulation results have shown only a 4% difference for flagella of the same dimensions. We use our simulation to consider how flexiblity affects the swimming speed of helical flagella and show that for a constant angular velocity, difference between forwards and backwards swimming speed ranges between 0-23%depending on the exact stiffness chosen. We explain the differences in swimming speeds of semi-flexible fibres by investigating the shape changes which occur and comparing them to the results for swimming speeds of rigid flagella of varying dimensions.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Soluble HIV-1 Env trimers in adjuvant elicit potent and diverse functional B cell responses in primates

Broadly neutralizing antibodies (bNAbs) against the HIV-1 envelope glycoproteins (Envs) have proven difficult to elicit by immunization. Therefore, to identify effective Env neutralization targets, efforts are underway to define the specificities of bNAbs in chronically infected individuals. For a prophylactic vaccine, it is equally important to define the immunogenic properties of the heavily glycosylated Env in healthy primates devoid of confounding HIV-induced pathogenic factors. We used rhesus macaques to investigate the magnitude and kinetics of B cell responses stimulated by Env trimers in adjuvant. Robust Env-specific memory B cell responses and high titers of circulating antibodies developed after trimer inoculation. Subsequent immunizations resulted in significant expansion of Env-specific IgG-producing plasma cell populations and circulating Abs that displayed increasing avidity and neutralization capacity. The neutralizing activity elicited with the regimen used was, in most aspects, superior to that elicited by a regimen based on monomeric Env immunization in humans. Despite the potency and breadth of the trimer-elicited response, protection against heterologous rectal simian-HIV (SHIV) challenge was modest, illustrating the challenge of eliciting sufficient titers of cross-reactive protective NAbs in mucosal sites. These data provide important information for the design and evaluation of vaccines aimed at stimulating protective HIV-1 immune responses in humans

Immune response to SARS-CoV-2 mRNA vaccination in multiple sclerosis patients after rituximab treatment interruption

Peripheral B cell depletion via anti-CD20 treatment is a highly effective disease-modifying treatment for reducing new relapses in multiple sclerosis (MS) patients. A drawback of rituximab (RTX) and other anti-CD20 antibodies is a poor immune response to vaccination. While this can be mitigated by treatment interruption of at least six months prior to vaccination, the timing to resume treatment while maintaining subsequent vaccine responses remains undetermined. Here, we characterized SARS-CoV-2 S-directed antibody and B cell responses throughout three BNT162b2 mRNA vaccine doses in RTX-treated MS patients, with the first two doses given during treatment interruption. We examined B-cell mediated immune responses in blood samples from patients with RTX-treated MS throughout three BNT162b2 vaccine doses, compared to an age- and sex-matched healthy control group. The first vaccine dose was given 1.3 years (median) after the last RTX infusion, the second dose one month after the first, and the third dose four weeks after treatment re-initiation. We analyzed SARS-CoV-2 S-directed antibody levels using enzyme-linked immunosorbent assay (ELISA), and the neutralization capacity of patient serum against SARS-CoV-2 S-pseudotyped lentivirus using luciferase reporter assay. In addition, we assessed switched memory (CD19+CD20+CD27+IgD-), unswitched memory (CD19+CD20+CD27+IgD+), naïve (CD19+CD20+CD27-IgD+), and double negative (DN, CD19+CD20+CD27-IgD-) B cell frequencies, as well as their SARS-CoV-2 S-specific (CoV+) and Decay Accelerating Factor-negative (DAF-) subpopulations, using flow cytometry. After two vaccine doses, S-binding antibody levels and neutralization capacity in SARS-CoV-2-naïve MS patients were comparable to vaccinated healthy controls, albeit with greater variation. Higher antibody response levels and CoV+-DN B cell frequencies after the second vaccine dose were predictive of a boost effect after the third dose, even after re-initiation of rituximab treatment. MS patients also exhibited lower frequencies of DAF- memory B cells, a suggested proxy for germinal centre activity, than control individuals. S-binding antibody levels in RTX-treated MS patients after two vaccine doses could help determine which individuals would need to move up their next vaccine booster dose or postpone their next RTX infusion. Our findings also offer first indications on the potential importance of antigenic stimulation of DN B cells and long-term impairment of germinal centre activity in rituximab-treated MS patients

Probabilistic classification of anti-SARS-CoV-2 antibody responses improves seroprevalence estimates.

OBJECTIVES: Population-level measures of seropositivity are critical for understanding the epidemiology of an emerging pathogen, yet most antibody tests apply a strict cutoff for seropositivity that is not learnt in a data-driven manner, leading to uncertainty when classifying low-titer responses. To improve upon this, we evaluated cutoff-independent methods for their ability to assign likelihood of SARS-CoV-2 seropositivity to individual samples. METHODS: Using robust ELISAs based on SARS-CoV-2 spike (S) and the receptor-binding domain (RBD), we profiled antibody responses in a group of SARS-CoV-2 PCR+ individuals (n = 138). Using these data, we trained probabilistic learners to assign likelihood of seropositivity to test samples of unknown serostatus (n = 5100), identifying a support vector machines-linear discriminant analysis learner (SVM-LDA) suited for this purpose. RESULTS: In the training data from confirmed ancestral SARS-CoV-2 infections, 99% of participants had detectable anti-S and -RBD IgG in the circulation, with titers differing > 1000-fold between persons. In data of otherwise healthy individuals, 7.2% (n = 367) of samples were of uncertain serostatus, with values in the range of 3-6SD from the mean of pre-pandemic negative controls (n = 595). In contrast, SVM-LDA classified 6.4% (n = 328) of test samples as having a high likelihood (> 99% chance) of past infection, 4.5% (n = 230) to have a 50-99% likelihood, and 4.0% (n = 203) to have a 10-49% likelihood. As different probabilistic approaches were more consistent with each other than conventional SD-based methods, such tools allow for more statistically-sound seropositivity estimates in large cohorts. CONCLUSION: Probabilistic antibody testing frameworks can improve seropositivity estimates in populations with large titer variability

B Cell Recognition of the Conserved HIV-1 Co-Receptor Binding Site Is Altered by Endogenous Primate CD4

The surface HIV-1 exterior envelope glycoprotein, gp120, binds to CD4 on the target cell surface to induce the co-receptor binding site on gp120 as the initial step in the entry process. The binding site is comprised of a highly conserved region on the gp120 core, as well as elements of the third variable region (V3). Antibodies against the co-receptor binding site are abundantly elicited during natural infection of humans, but the mechanism of elicitation has remained undefined. In this study, we investigate the requirements for elicitation of co-receptor binding site antibodies by inoculating rabbits, monkeys and human-CD4 transgenic (huCD4) rabbits with envelope glycoprotein (Env) trimers possessing high affinity for primate CD4. A cross-species comparison of the antibody responses showed that similar HIV-1 neutralization breadth was elicited by Env trimers in monkeys relative to wild-type (WT) rabbits. In contrast, antibodies against the co-receptor site on gp120 were elicited only in monkeys and huCD4 rabbits, but not in the WT rabbits. This was supported by the detection of high-titer co-receptor antibodies in all sera from a set derived from human volunteers inoculated with recombinant gp120. These findings strongly suggest that complexes between Env and (high-affinity) primate CD4 formed in vivo are responsible for the elicitation of the co-receptor-site-directed antibodies. They also imply that the naïve B cell receptor repertoire does not recognize the gp120 co-receptor site in the absence of CD4 and illustrate that conformational stabilization, imparted by primary receptor interaction, can alter the immunogenicity of a type 1 viral membrane protein

Varför väljer anställda att stanna i en organisation? : Hur en stor svensk organisation med låg personalomsättning aktivt arbetar för att bibehållande anställda

Då arbetsmarknaden numera kännetecknas av en hög rörlighet, där individer som ofta byterarbete, behöver organisationer förstå varför anställda väljer att stanna kvar. Syftet med studienär att öka förståelsen för varför anställda väljer att stanna i en organisation samt att dra lärdomarfrån hur en organisation aktivt arbetar med bibehållandet. Som underlag till analysen av studiens resultat identifierades, med hjälp av tidigare forskning, tre faktorer som anses påverka bibehållandet av anställda. Faktorerna har i tidigare forskning gett förklaring till personalomsättning och i enstaka fall varför anställda stannar kvar. Det empiriska materialet i studien bygger på nio intervjuer med anställda på ICA Sverige AB, varav fyra är HR-chefer. Utifrån resultatet identifierades en tillkommande faktor, intern rekrytering. Utifrån studiens slutsatser anses faktorerna arbetsklimat, passform, organisatoriskt stöd och internrekrytering ha betydande roll i varför anställda väljer att stanna kvar i en organisation

Varför väljer anställda att stanna i en organisation? : Hur en stor svensk organisation med låg personalomsättning aktivt arbetar för att bibehållande anställda

Då arbetsmarknaden numera kännetecknas av en hög rörlighet, där individer som ofta byterarbete, behöver organisationer förstå varför anställda väljer att stanna kvar. Syftet med studienär att öka förståelsen för varför anställda väljer att stanna i en organisation samt att dra lärdomarfrån hur en organisation aktivt arbetar med bibehållandet. Som underlag till analysen av studiens resultat identifierades, med hjälp av tidigare forskning, tre faktorer som anses påverka bibehållandet av anställda. Faktorerna har i tidigare forskning gett förklaring till personalomsättning och i enstaka fall varför anställda stannar kvar. Det empiriska materialet i studien bygger på nio intervjuer med anställda på ICA Sverige AB, varav fyra är HR-chefer. Utifrån resultatet identifierades en tillkommande faktor, intern rekrytering. Utifrån studiens slutsatser anses faktorerna arbetsklimat, passform, organisatoriskt stöd och internrekrytering ha betydande roll i varför anställda väljer att stanna kvar i en organisation

Regulation of Subunit-Specific Germinal Center B Cell Responses to the HIV-1 Envelope Glycoproteins by Antibody-Mediated Feedback

The regulation of germinal center (GC) B cell responses to single epitopes is well investigated. How monoclonal B cells are regulated within the polyclonal B cell response to protein antigens is less so. Here, we investigate the primary GC B cell response after injection of mice with HIV-1 envelope glycoproteins. We demonstrate that single GCs are seeded by a diverse number of B cell clones shortly after a single immunization and that the presence of Env-specific antibodies can inhibit the development of early GC B cells. Importantly, the suppression was dependent on the GC B cells and the infused antibodies to target the same subunit of the injected HIV-1 envelope glycoproteins. An affinity-dependent antibody feedback has previously been shown to regulate GC B cell development. Here, we propose that this antibody-based feedback acts on GC B cells only if they target the same or overlapping epitopes. This study provides important basic information of GC B cell regulation, and for future vaccine designs with aim to elicit neutralizing antibodies against HIV-1

Intravenous immunoglobulin therapy for COVID-19 in immunocompromised patients : A retrospective cohort study

Objectives: To investigate the effectiveness of intravenous immunoglobulin (IVIG) as treatment for COVID-19 in immunocompromised patients. Methods: This retrospective study investigated outcomes for immunocompromised, vaccine non-responsive, patients that between September 2022 and April 2023 received IVIG as treatment for COVID-19 in the region of Västerbotten, Sweden. We analyzed clinical data, viral load, and anti-SARS-CoV-2 IgG binding and neutralization levels of patient serum samples and IVIG production batches. Primary and secondary outcomes were clinical cure and viral clearance, respectively. Results: Sixteen patients were analyzed. After a median COVID-19 duration of 4 weeks, a median 60 g IVIG infusion increased SARS-CoV-2 binding and neutralizing antibody levels, with broad in vitro activity against tested variants. The treatment resulted in abrogation of viremia in all patients and general improvement in 15 survivors that all met the primary endpoint. Thirteen patients met the secondary endpoint at follow-up after a median of four months. Two subjects with persistent SARS-CoV-2 carriage relapsed but were successfully retreated with IVIG. Conclusions: Antibodies in IVIG efficiently neutralized several SARS-CoV-2 variants. Treatment with IVIG was associated with clinical cure and viral clearance in immunocompromised patients. Our data suggests that IVIG could be a novel treatment alternative for COVID-19 for this patient category

Immune response to SARS-CoV-2 mRNA vaccination in multiple sclerosis patients after rituximab treatment interruption

Peripheral B cell depletion via anti-CD20 treatment is a highly effective disease-modifying treatment for reducing new relapses in multiple sclerosis (MS) patients. A drawback of rituximab (RTX) and other anti-CD20 antibodies is a poor immune response to vaccination. While this can be mitigated by treatment interruption of at least six months prior to vaccination, the timing to resume treatment while maintaining subsequent vaccine responses remains undetermined. Here, we characterized SARS-CoV-2 S-directed antibody and B cell responses throughout three BNT162b2 mRNA vaccine doses in RTX-treated MS patients, with the first two doses given during treatment interruption. We examined B-cell mediated immune responses in blood samples from patients with RTX-treated MS throughout three BNT162b2 vaccine doses, compared to an age- and sex-matched healthy control group. The first vaccine dose was given 1.3 years (median) after the last RTX infusion, the second dose one month after the first, and the third dose four weeks after treatment re-initiation. We analyzed SARS-CoV-2 S-directed antibody levels using enzyme-linked immunosorbent assay (ELISA), and the neutralization capacity of patient serum against SARS-CoV-2 S-pseudotyped lentivirus using luciferase reporter assay. In addition, we assessed switched memory (CD19+CD20+CD27+IgD-), unswitched memory (CD19+CD20+CD27+IgD+), naïve (CD19+CD20+CD27-IgD+), and double negative (DN, CD19+CD20+CD27-IgD-) B cell frequencies, as well as their SARS-CoV-2 S-specific (CoV+) and Decay Accelerating Factor-negative (DAF-) subpopulations, using flow cytometry. After two vaccine doses, S-binding antibody levels and neutralization capacity in SARS-CoV-2-naïve MS patients were comparable to vaccinated healthy controls, albeit with greater variation. Higher antibody response levels and CoV+-DN B cell frequencies after the second vaccine dose were predictive of a boost effect after the third dose, even after re-initiation of rituximab treatment. MS patients also exhibited lower frequencies of DAF- memory B cells, a suggested proxy for germinal centre activity, than control individuals. S-binding antibody levels in RTX-treated MS patients after two vaccine doses could help determine which individuals would need to move up their next vaccine booster dose or postpone their next RTX infusion. Our findings also offer first indications on the potential importance of antigenic stimulation of DN B cells and long-term impairment of germinal centre activity in rituximab-treated MS patients