Biology subjects

Le Vern, Y.

Publications and source records attributed to Le Vern, Y..

8 recordsLinked to original sources

bioRxiv2026

Environmental history shapes host-associated dynamics of sporulating and non-sporulating bacterial subpopulations during infection

Host-associated environments represent ecological contexts that can structure microbial population dynamics, yet their effects on sporulating pathogens remain poorly understood. We investigated how passage through a natural insect host shapes population-level traits in the entomopathogen Bacillus thuringiensis. Using Galleria mellonella larvae, we compared the characteristics of bacterial populations extracted from insect cadavers with those maintained under in vitro conditions. Passage through the host generated a distinct population structure, characterized by the stable coexistence of sporulating and non-sporulating bacteria and a larger non-sporulating fraction than in in vitro cultures. Host-extracted bacteria exhibited a different morphology and higher virulence than in vitro-grown populations, the latter being largely due to the non-sporulating fraction of the population, as shown by reinfection experiments with each subpopulation isolated via fluorescence-activated cell sorting. On the other hand, all subpopulations persisted similarly in the host and completed the infection cycle. Host-extracted subpopulations also showed increased tolerance to oxidative stress, consistent with an adaptation to conditions encountered within insect cadavers. Furthermore, competition assays revealed that non-sporulating bacteria from insect cadavers outcompeted sporulating cells, whereas the opposite was observed for in vitro-grown bacteria. In addition, spores produced in the host displayed reduced heat resistance but germinated more efficiently than laboratory-derived spores, highlighting environment-dependent properties which may affect transmission potential. Together, these results demonstrate that the host-associated ecological context drives functional differentiation within bacterial populations and modulates key traits linked to survival, competition, stress tolerance and persistence, emphasizing the importance of host-associated environments in structuring ecological properties of sporulating pathogens.

microbiology↗

bioRxiv2026

Functional divergence of regulatory and conventional bovine neutrophils following Mycobacterium bovis infection

Bovine tuberculosis (bTB), due to Mycobacterium bovis (Mb) infection, is a chronic cattle disease and neglected cause of zoonotic tuberculosis. The role of neutrophils in bTB is overlooked. We recently identified a new neutrophil subset in cattle and mice with a similar morphology to conventional inflammatory neutrophils (Nconv). However, unlike Nconv, these regulatory neutrophils (Nreg) express MHC-II at their surface and can suppress lymphocyte proliferation. In this study, we compared the responses of bovine Nconv and Nreg to infection with a virulent Mb strain circulating in France and the attenuated Mb BCG vaccine. Nreg and Nconv had different transcriptional profiles and were differentially activated by Mb infection. Both Nreg and Nconv efficiently killed Mb, but Nreg had higher levels of phagocytosis activity and ROS production. Nreg had higher levels of mitochondrial activity and an ultrastructural organization different from that of Nconv. Our results provide the first insight into the functional characterization of bovine neutrophil subsets during Mb infection and highlight a new layer of complexity in their functional diversity that must be taken into account to improve our understanding of bTB pathophysiology, which is urgently required to improve the management of this costly disease.

immunology↗

bioRxiv2025

Gene expression profiling of bovine raw milk is linked to the inflammatory status of the udder

Inflammation of the mammary gland, or mastitis, is a common disease of dairy cows with important consequences on the economy of dairy farms, well-being of cows and antibiotic usage. Monitoring of the inflammatory status of mammary gland currently relies on milk somatic cell counting. In order to improve this monitoring, methods aiming at differentiating cell types among milk cells are being developed. The objective of the present study was to explore the use of gene expression profiling from raw milk samples to define the inflammatory status of udder quarters. A pilot study allowed us to select 37 genes differentially expressed between three milk cell types, i.e. neutrophils, macrophages or T lymphocytes. Based on expression data measured by RT-qPCR for these genes in RNA extracted from quarter milk samples, we were able to identify four different types of milk samples, each with specific properties. One cluster was characterized by increased expression of genes typifying neutrophils, a second one was identified by increased expression of genes typifying macrophages while the two others were distinguished based on the expression of genes associated with T lymphocytes. Clustering of samples based on gene expression was shown to be comparable to that obtained by flow cytometry analysis. Our results highlight the potential of profiling of milk samples based on gene expression for the analysis of the inflammatory status of udders.

pathology↗

bioRxiv2025

Flagellin nebulization enhances respiratory immune responses in the porcine model

Respiratory delivery of the Toll-like receptor 5 agonist FLAMOD, a recombinant flagellin, offers a promising approach for treating bacterial pneumonia. FLAMOD stimulates the airway epithelium, mobilizing and activating immune cells and effectors to combat infections. While previous evidences were obtained in mouse models, this study represents the first comprehensive assessment of FLAMOD delivered by nebulization in pigs. Our results demonstrate that a single nebulization of FLAMOD did not cause any adverse effects on clinical parameters. Histological analysis supported that FLAMOD treatment led to immune cell infiltration in the lung tissue, indicative of an active immune response. Flow cytometry confirmed granulocyte recruitment in conducting airways. RNA sequencing established immune activation across the respiratory tract, from the nose, trachea, bronchi to the lungs, highlighting innate immunity, bacterial defense, cytokine and chemokine signaling, and granulocyte chemotaxis as key biological pathways. These findings demonstrated the capacity of FLAMOD to induce a robust and common immune response throughout the porcine respiratory system as well as specific compartmentalized immune signatures. This study establishes FLAMOD as a potent activator of innate immunity, providing a proof-of-concept for inhalation-based therapeutic strategies to combat bacterial pneumonia in the clinical setting.

immunology↗

bioRxiv2025

NOD2 stimulation reduces Cryptosporidium parvum level of infection in neonates by promoting intestinal epithelial production of antimicrobial peptides and cell renewing

At birth, the mucosal immune system of neonates is not fully developed, making them more susceptible to respiratory and intestinal diseases. Previously described host-directed therapies using TLR activation-based strategies have proven effective in controlling neonatal diseases, including cryptosporidiosis. In this study, we investigated the effect of NOD receptor stimulation on the control of enteric infection by the protozoan Cryptosporidium parvum in neonatal mice. NOD2 stimulation by intraperitoneal injection of MDP resulted in a rapid reduction in the parasite burden. The protective effect was associated with increased proinflammatory cytokine and antimicrobial peptide gene expression and a rapid influx of neutrophils to the site of infection, whereas NOD1 stimulation did not show a protective effect. The protective mechanism did not involve microbiota participation but involved IFN-{gamma} and IL-22 cytokines and was associated with increased intestinal epithelium renewal in infected neonates. Our findings, demonstrated in neonatal mice, elucidate how the stimulation of NOD2 with the bacterial ligand MDP actively contributes to the non-specific clearance of a parasitic infection within the intestinal epithelial cells. Author SummaryNewborns are particularly vulnerable to intestinal infections due to their immature immune systems. Developing strategies to enhance their ability to fight infections is crucial for improving neonatal health. In this study, we investigated how stimulation of a specific immune receptor, NOD2, can help neonatal mice control an intestinal infection caused by the protozoan Cryptosporidium parvum. We found that intraperitoneally administration of a bacterial molecule called MDP, which activates the NOD2 receptor, led to a rapid reduction in the parasite burden. This protection was associated with increased production of inflammatory molecules, antimicrobial peptides, and a significant influx of neutrophils to the site of infection. Importantly, the protective effect did not depend on the gut microbiota but involved specific immune signals, such as IFN-{gamma} and IL-22, and enhanced the renewal of intestinal epithelial cells. These findings highlight how targeting NOD2 can boost neonatal innate immunity, offering a potential host-directed strategy to combat severe intestinal infections, limit long-term intestinal damage and reduce the risk of fatal outcomes.

immunology↗

bioRxiv2023

Neutrophil subsets play dual roles in tuberculosis by producing inflammasome dependent-IL-1β or suppressing T-cells via PD-L1

Neutrophils can be beneficial or deleterious during tuberculosis (TB). Based on the expression of MHC-II and programmed death ligand 1 (PD-L1), we distinguished two functionally and transcriptionally distinct neutrophil subsets in the lungs of mice infected with mycobacteria. Inflammatory [MHC-II-, PD-L1lo] neutrophils produced inflammasome-dependent IL-1{beta} in the lungs in response to virulent mycobacteria and "accelerated" deleterious inflammation, which was highly exacerbated in IFN-{gamma}R-/- mice. Regulatory [MHC-II+, PD-L1hi] neutrophils "brake" inflammation by suppressing T-cell proliferation and IFN-{gamma} production. Such beneficial regulation, which depends on PD-L1, is controlled by IFN-{gamma}R signaling in neutrophils. The hypervirulent HN878 strain from the Beijing genotype curbed PD-L1 expression by regulatory neutrophils, abolishing the braking function and driving deleterious hyper-inflammation in the lungs. These findings add a layer of complexity to the roles played by neutrophils in TB and may explain the reactivation of this disease observed in cancer patients treated with anti-PD-L1. One Sentence SummaryRegulatory and inflammatory neutrophil subsets play inverse roles in tuberculosis.

immunology↗

bioRxiv2020

A large panel of chicken cells are invaded in vivo by Salmonella Typhimurium even when depleted of all known invasion factors

Poultry are the main source of human infection by Salmonella. As infected poultry are asymptomatic, the identification of infected poultry farms is difficult. Controlling animal infections is thus of primary importance. As cell tropism is known to govern disease, our aim was therefore to identify the infected host-cell types in chicks and the role of the three known invasion factors in this process (T3SS-1, Rck and PagN). Chicks were inoculated with wild-type or isogenic fluorescent Salmonella Typhimurium mutants via the intraperitoneal route. Our results show that liver, spleen, gall bladder and aortic vessels could be foci of infection and that phagocytic and non-phagocytic cells, including immune, epithelial and endothelial cells, are invaded in vivo in each organ. Moreover, a mutant defective for the T3SS-1, Rck and PagN remained able to colonize organs as the wild-type strain and invaded non-phagocytic cells in each organ studied. As the infection of gall bladder was not really described in chicks, invasion of gall bladder cells was confirmed by immunohistochemistry and infection was shown to last several weeks after inoculation of chicks. All together, these findings provide new insights into the dynamics of Salmonella spread in vivo in chicks at the organ and cellular levels.

microbiology↗

bioRxiv2020

Neutrophils encompass a regulatory subset suppressing T cells in apparently healthy cattle and mice

Neutrophils that reside in the bone marrow are switly recruited from circulating blood to fight infections. For a long time, these first line defenders were considered as microbe killers. However their role is far more complex as cross talk with T cells or dendritic cells have been described for human or mouse neutrophils. In cattle, these new roles are not documented yet. We identified a new subset of regulatory neutrophils that is present in the mouse bone marrow or circulate in cattle blood under steady state conditions. These regulatory neutrophils that display MHC-II on the surface are morphologically indistinguishable from classical MHC-IIneg neutrophils. However MHC-IIpos and MHC-IIneg neutrophils display distinct transcriptomic profiles. While MHC-IIneg and MHC-IIpos neutrophils display similar bacterial phagocytosis or killing activity, MHC-IIpos only are able to suppress T cell proliferation under contact-dependent mechanisms. Regulatory neutrophils are highly enriched in lymphoid organs as compared to their MHC-IIneg counterparts and in the mouse they express PDL-1, an immune checkpoint involved in T-cell blockade. Our results emphasize neutrophils as true partners of the adaptive immune response, including in domestic species. They open the way for discovery of new biomarkers and therapeutic interventions to better control cattle diseases.

immunology↗