Biology subjects

Hobbs, A.

Publications and source records attributed to Hobbs, A..

8 recordsLinked to original sources

bioRxiv2026

Clonal dynamics of germinal center refueling by secondary immunization

Many vaccine regimens involve delivery of multiple doses to the same anatomical site, such that booster doses frequently encounter germinal centers (GCs) still active from prior immunization. The consequences of this "GC refueling" to B cell clonality have not been systematically investigated. Using mouse models of mRNA-LNP vaccination combined with multicolor fate-mapping, longitudinal GC imaging, and immunoglobulin sequencing, we show that refueling triggers clonal burst-type expansion of GC-resident B cells, rather than recruiting local memory, resulting in marked focusing of GCs on the descendants of individual B cells. Refueling with a drifted antigen led to limited but detectable retraining of primary-cohort clones, although most variant-specific responses in this setting arose from newly recruited naive B cells. These findings identify GC refueling as a distinct mode of vaccine response with implications for sequential immunization strategies against rapidly evolving pathogens.

immunology↗

bioRxiv2025

Antibody-mediated feedback modulates interclonal competition in the germinal center

Serum antibodies from prior immune responses regulate B cell activation and germinal center (GC) access upon recall immunization. However, how antibodies produced by an ongoing immune response influence the outcomes of contemporaneous GCs is less clear. To explore this, we developed mouse models enabling the targeted ablation of plasma cells and antibodies produced by an immune response of interest, without affecting those produced homeostatically or by prior antigen encounters. Our findings show that, whereas antibody-mediated feedback is not required for affinity maturation, it can influence competition between B cells with different epitope specificities, specifically by reducing the abundance of clones that recognize the same epitopes as circulating antibodies. This modality of feedback represents a mechanism by which antibody responses can influence epitope specificity in ongoing GCs. These findings may therefore have implications for vaccination strategies aimed at steering clonal selection towards desired epitopes on complex antigens.

immunology↗

bioRxiv2024

Soil microbiome perturbation impedes growth of Bouteloua curtipendula and increases relative abundance of soil microbial pathogens

AbstractBouteloua curtipendula (sideoats grama) is a valuable prairie grass for livestock forage, supporting food webs of herbivorous insects, reducing soil erosion, and limiting weed infiltration in urban grasslands. Efficient establishment of B. curtipendula in prairie restorations and urban plantings could drastically improve long-term functionality of the space. Soil microbial communities have been linked to plant germination, growth, and drought tolerance in many plant species, however little is known about the factors contributing to B. curtipendula germination and early growth. In this study, we used sterilized soil to examine the impact of soil microbes on B. curtipendula growth under greenhouse conditions. We found Bouteloua curtipendula emergence and growth to be impaired in sterilized soil compared to non-sterilized soil. Using high throughput sequencing of the soil, we found that B. curtipendula grown in sterilized soil induced a greater proportion of plant pathogens and fewer nitrifying bacteria when grown in non- sterilized soil. For example, there was a significantly higher proportion of Acidovorax, Cellvibrio, and Xanthomonas which are known to contain plant pathogens, while plant- growth promoting bacteria, like Rhodopseudomonas, were significantly higher in the non-sterile conditions. We found that soil sterilization and growth of B. curtipendula changed the relative abundance of metabolic subsystem genes in the soil, however, by seven weeks after seeding, B. curtipendula transformed the bacterial community of sterile soil such that it was indiscernible from non-sterile soil. In contrast, fungal communities in sterilized soil were still different from non-sterilized soil seven weeks post-seeding. It appears that the bacteria are involved in the initial establishment of beneficial conditions that set the stage for a robust fungal and plant seedling development.

microbiology↗

bioRxiv2024

Accurate evaluation of live-virus microneutralisation for SARS-CoV-2 variant JN.1

Emerging SARS-CoV-2 variants require rapid assessments of pathogenicity and evasion of existing immunity to inform policy. A crucial component of these assessments is accurate estimation of serum neutralising antibody titres using cultured live virus isolates. Here, we report our updated culture methods for Omicron sub-variant JN.1 using Caco-2 cells and the subsequent evaluation of neutralising antibody titres (nAbTs) in recipients of BNT162b2-XBB.1.5 monovalent and the Ancestral/BA.5 containing bivalent vaccines. We compared culture of JN.1 in either Vero V1 cells or Caco-2 cells, finding culture in Vero V1 either resulted in low-titre stocks or induced crucial mutations at the Spike furin cleavage site. Using the sequence-clean culture stocks generated in Caco-2 cells, we assessed serum samples from 71 healthy adults eligible for a COVID-19 vaccination given as a 5th dose booster: all participants had detectable nAbs against JN.1 prior to vaccination, with baseline/pre-existing nAbTs between both vaccine groups comparable (p = 0.240). However, nAbTs against JN.1 post-vaccination were 2.6-fold higher for recipients of the monovalent XBB1.5 vaccine than the BA.4/5 bivalent vaccine (p<0.001). Regular re-appraisal of methods involved in the evaluation of new variants is required to ensure robust data are used to underpin crucial severity assessments as variants arise and vaccine strain selection decisions.

microbiology↗

bioRxiv2023

Opposing effects of pre-existing antibody and memory T cell help on the dynamics of recall germinal centers

Re-exposure to an antigen generates serum antibody responses that greatly exceed in magnitude those elicited by primary antigen encounter, while simultaneously driving the formation of recall germinal centers (GCs). Although recall GCs in mice are composed almost entirely of naive B cells, recall antibody titers derive overwhelmingly from memory B cells, suggesting a division between cellular and serum compartments. Here, we show that this schism is at least partly explained by a marked decrease in the ability of recall GC B cells to detectably bind antigen. Variant priming and plasmablast ablation experiments show that this decrease is largely due to suppression by pre-existing antibody, whereas hapten-carrier experiments reveal a role for memory T cell help in allowing B cells with undetectable antigen binding to access GCs. We propose a model in which antibody-mediated feedback steers recall GC B cells away from previously targeted epitopes, thus enabling specific targeting of variant epitopes.

immunology↗

bioRxiv2023

Dichotomy of neutralizing antibody, B cell and T cell responses to SARS-CoV-2 vaccination and protection in healthy adults

Heterogeneity in SARS-CoV-2 vaccine responses is not understood. Here, we identify four patterns of live-virus neutralizing antibody responses: individuals with hybrid immunity (with confirmed prior infection); rare individuals with low responses (paucity of S1-binding antibodies); and surprisingly, two further groups with distinct serological repertoires. One group - broad responders - neutralize a range of SARS-CoV-2 variants, whereas the other - narrow responders - neutralize fewer, less divergent variants. This heterogeneity does not correlate with Ancestral S1-binding antibody, rather the quality of the serological response. Furthermore, IgDlowCD27-CD137+ B cells and CCR6+ CD4+ T cells are enriched in broad responders before dose 3. Notably, broad responders have significantly longer infection-free time after their third dose. Understanding the control and persistence of these serological profiles could allow personalized approaches to enhance serological breadth after vaccination.

immunology↗

bioRxiv2022

Astrocyte mitochondria produce nitric oxide from nitrite to modulate cerebral blood flow during brain hypoxia

In low oxygen conditions, increases in cerebral blood flow maintain brain oxygen delivery but the mechanisms underlying hypoxia-induced dilations of cerebral vasculature are incompletely understood. Here we show that astrocytes accumulate nitrite and in response to hypoxia produce nitric oxide via mitochondrial reduction of nitrite by a molybdenum-containing enzyme sulfite oxidase. These data suggest that astrocytes can modulate cerebral blood flow in accord with brain tissue oxygenation via mitochondrial production of nitric oxide.

neuroscience↗

bioRxiv2021

VPS29 exerts opposing effects on endocytic viral entry

Emerging zoonotic viral pathogens threaten global health and there is an urgent need to discover host and viral determinants influencing infection. We performed a loss-of-function genome-wide CRISPR screen in a human lung cell line using HCoV-OC43, a human betacoronavirus. One candidate gene, VPS29, was required for infection by HCoV-OC43, SARS-CoV-2, other endemic and pandemic threat coronaviruses as well as ebolavirus. However, VPS29 deficiency had no effect on certain other viruses that enter cells via endosomes and had an opposing, enhancing effect on influenza A virus infection. VPS29 deficiency caused changes endosome morphology, and acidity and attenuated the activity of endosomal proteases. These changes in endosome properties caused incoming coronavirus, but not influenza virus particles, to become entrapped therein. Overall, these data show how host regulation of endosome characteristics can influence viral susceptibility and identify a host pathway that could serve as a pharmaceutical target for intervention in zoonotic viral diseases.

microbiology↗