Biology subjects

Ashwin, H.

Publications and source records attributed to Ashwin, H..

6 recordsLinked to original sources

bioRxiv2025

Bi-directional highways and super-seeder tissues underpin parasite dissemination in experimental visceral leishmaniasis.

Visceral leishmaniasis (VL) is a life-threatening parasitic disease caused by Leishmania donovani and L. infantum. Although VL is characterised by organ-specific immunopathology and parasitism of the spleen, liver and bone marrow, other tissues may harbour parasites without overt pathology. The mechanisms governing patterns of within-host dissemination and tissue tropism are largely unknown. We used a barcoded library of isogenic L. donovani and an ecological analysis framework to evaluate parasite population diversity across tissues and to map parasite dissemination in a murine infection model. We reveal an unexpected high degree of inter-connectivity between parasite populations demonstrating: i) continual bi-directional dissemination between viscera and skin; ii) the existence of "super-seeder" sites that act as hubs fuelling systemic spread; and iii) rerouting of dissemination "highways" following immune perturbation. These findings change our understanding of L. donovani pathogenesis, providing critical insights into infection dynamics with direct implications for relapse, treatment failure and transmission.

microbiology↗

bioRxiv2023

Integrated histopathology, spatial and single cell transcriptomics resolve cellular drivers of early and late alveolar damage in COVID-19

The most common cause of death due to COVID-19 remains respiratory failure. Yet, our understanding of the precise cellular and molecular changes underlying lung alveolar damage is limited. Here, we integrate single cell transcriptomic data of COVID-19 donor lungs with spatial transcriptomic data stratifying histopathological stages of diffuse alveolar damage (DAD). We identify changes in cellular composition across progressive DAD, including waves of molecularly distinct macrophages and depleted epithelial and endothelial populations throughout different types of tissue damage. Predicted markers of pathological states identify immunoregulatory signatures, including IFN-alpha and metallothionein signatures in early DAD, and fibrosis-related collagens in organised DAD. Furthermore, we predict a fibrinolytic shutdown via endothelial upregulation of SERPINE1/PAI-1. Cell-cell interaction analysis revealed macrophage-derived SPP1/osteopontin signalling as a key regulator during early DAD. These results provide the first comprehensive, spatially resolved atlas of DAD stages, highlighting the cellular mechanisms underlying pro-inflammatory and pro-fibrotic pathways across alveolar damage progression.

pathology↗

bioRxiv2023

UVB modifies skin immune-stroma cross-talk and promotes effector T cell recruitment during cryptic Leishmania donovani infection

Many parasites of significant public health importance assume skin residency without causing overt pathlogy. How immune and stromal cells respond to such "cryptic" infections and how exposure to UVB alters such responses in poorly understood. We combined scRNA-seq, spatial transcriptomics and inferential network analysis to address these questions in a model of cryptic skin infection by Leishmania donovani. In infected C57BL/6 mice, p-selectin and CXCL12 interactions dominate intercellular communication between leucocytes, fibroblast and endothelial cells, but effector T cell function remains muted. Following UVB exposure, increased numbers of IFN{gamma}+ CD4+ Th1 cells and NK cells enter the skin, communicating with stromal cells via CCL5-CCR5 and LFA-1-ICAM1/2. However, spatial mapping indicated that Th1 cells and macrophages occupied distinct niches after UVB exposure, likely limiting effector function. Our data provide the first holistic view of the immune landscape during cryptic L. donovani infection and demonstrate how UVB exposure fundamentally reshapes this response. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/526940v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@1238cbaorg.highwire.dtl.DTLVardef@ec350eorg.highwire.dtl.DTLVardef@18f412corg.highwire.dtl.DTLVardef@1ffd468_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2021

Spatial point pattern analysis identifies mechanisms shaping the skin parasite landscape in Leishmania donovani infection

Increasing evidence suggests that infectiousness of hosts carrying parasites of the Leishmania donovani complex, the causative agents of visceral leishmaniasis, is linked to parasite repositories in the host skin. However, a detailed understanding of the dispersal and dispersion of these obligatory-intracellular parasites and their host phagocytes in the skin is lacking. Using endogenously fluorescent parasites as a proxy, we apply image analysis combined with spatial point pattern models borrowed from ecology to characterize dispersion of parasitized myeloid cells (including ManR+ and CD11c+ cells) and predict dispersal mechanisms in a previously described immunodeficient model of L. donovani infection. Our results suggest that after initial seeding of infection in the skin, heavily parasite-infected myeloid cells are found in patches that resemble innate granulomas. Spread of parasites from these initial patches subsequently occurs through infection of recruited myeloid cells, ultimately leading to self-propagating networks of patch clusters. This combination of imaging and ecological pattern analysis to identify mechanisms driving the skin parasite landscape offers new perspectives on myeloid cell behavior following parasitism by L. donovani and may also be applicable to elucidating the behavior of other intracellular tissue-resident pathogens and their host cells.

microbiology↗

bioRxiv2021

Interferon-γ-producing CD4+ T cells drive monocyte activation in the bone marrow during experimental Leishmania donovani infection.

Ly6Chi inflammatory monocytes develop in the bone marrow and migrate to the site of infection during inflammation. Upon recruitment, Ly6Chi monocytes can differentiate into dendritic cells or macrophages. According to the tissue environment they can also acquire different functions. Several studies have described pre-activation of Ly6Chi monocytes in the bone marrow during parasitic infection, but whether this process occurs during experimental visceral leishmaniasis and, if so, the mechanisms contributing to their activation are yet to be established. In wild type C57BL/6 (B6) mice infected with Leishmania donovani, the number of bone marrow Ly6Chi monocytes increased over time. Ly6Chi monocytes displayed a highly activated phenotype from 28 days to 5 months post infection (p.i), with >90% expressing MHCII and >20% expressing iNOS. In comparison, in B6.Rag2-/- mice <10% of bone marrow monocytes were MHCII+ at day 28 p.i., an activation deficiency that was reversed by adoptive transfer of CD4+ T cells. Depletion of CD4+ T cells in B6 mice and the use of mixed bone marrow chimeras further indicated that monocyte activation was driven by IFN-{gamma} produced by CD4+ T cells. In B6.Il10-/- mice, L. donovani infection induced a faster but transient activation of bone marrow monocytes, which correlated with the magnitude of CD4+ T cell production of IFN-{gamma} and resolution of the infection. Under all of the above conditions, monocyte activation was associated with greater control of parasite load in the bone marrow. Through reinfection studies in B6.Il10-/- mice and drug (AmBisome) treatment of B6 mice, we also show the dependence of monocyte activation on parasite load. In summary, these data demonstrate that during L. donovani infection, Ly6Chi monocytes are primed in the bone marrow in a process driven by CD4+ T cells and whereby IFN-{gamma} promotes and IL-10 limits monocyte activation and that the presence of parasites/parasite antigen plays a crucial role in maintaining bone marrow monocyte activation.

immunology↗

bioRxiv2020

Characterization of a new Leishmania major isolate for use in a controlled human infection model

Leishmaniasis is widely regarded as a vaccine-preventable disease, but the costs required to reach pivotal Phase 3 studies and uncertainty about which candidate vaccines should be progressed into human studies significantly limits progress in vaccine development for this neglected tropical disease. Controlled human infection models (CHIM) provide a pathway for accelerating vaccine development and to more fully understand disease pathogenesis and correlates of protection. Here, we describe the isolation, characterization and GMP manufacture of a new clinical isolate of Leishmania major. Two fresh isolates of L. major from Israel were initially compared by genome sequencing, in vivo infectivity and drug sensitivity in mice, and development and transmission competence in sand flies, allowing one (L. major_MRC-02) to be selected for GMP production. This study addresses a major roadblock in the development of vaccines for leishmaniasis, providing a key resource for CHIM studies of sand fly transmitted cutaneous leishmaniasis.

microbiology↗