Biology subjects

Dambuza, I. M.

Publications and source records attributed to Dambuza, I. M..

10 recordsLinked to original sources

bioRxiv2026

Using the Collaborative Cross to Dissect Immunological Mechanisms Governing Latent Infection, Granuloma Formation, and Neuroinvasive Disease Following Repeated Very Low-Dose Inhalation Exposure to Cryptococcus

BackgroundDecades of cryptococcal research have relied on a small number of hypervirulent laboratory strains, principally H99 and its derivatives, which cause rapid and lethal central nervous system infection and bypass the latent pulmonary phase that defines the natural history of human disease. As a result, the immune mechanisms that govern durable fungal containment in the lung, the reasons these mechanisms fail in genetically susceptible hosts, and whether the pulmonary immune response can engage the brain before any fungal cell reaches the central nervous system remain poorly understood. We address these gaps using a physiologically relevant repeated low-dose inhalation model in members of the Collaborative Cross and the BXD mouse panels. MethodsA repeated low-dose intranasal exposure model, consisting of four doses of 50 C. neoformans UgCl223 cells over 18 days, was compared with a single primary challenge in C57BL/6J mice. Six Collaborative Cross founder strains (A/J, C57BL/6J, 129S1/SvImJ, NOD/ShiLtJ, NZO/H1LtJ, CAST/EiJ) and one BXD founder (DBA/2J) were assessed for fungal burden, granuloma architecture, and CD4 T cell polarisation. The neuroimmune axis was interrogated by exposing BV2 microglia to serum from infected mice with confirmed lung-restricted infection or disseminated disease. ResultsRepeated low-dose exposure, in contrast to single-dose primary challenge, was linked with enhanced fungal containment, elevated frequency of CD44+ CD4 T cells, expansion of regulatory T cells, and organised granuloma formation. Across seven genetically diverse strains, host genetic background determined disease outcome, spanning four orders of magnitude in lung fungal burden, from near-sterilising control in NZO mice to overt central nervous system dissemination with brain lesions in CAST mice. Granuloma architecture varied markedly across backgrounds in a pattern that mirrors human granuloma heterogeneity. The Th17 and regulatory T cell axis, rather than Th1 or Th2 polarisation, distinguished progressors from controllers. Critically, serum from mice with confirmed lung-restricted infection induced morphological microglial activation in a strain-dependent pattern associated with the disease spectrum, providing initial evidence supporting the existence of a lung-brain immune axis in cryptococcal disease. ConclusionsThese data demonstrate that the immune dynamics of latent cryptococcal infection are fundamentally distinct from those characterised in primary high-dose models. Host genetic background influences not only pulmonary containment of Cryptococcus but may also impact the magnitude of distal brain immune responses, potentially through mechanisms that extend beyond direct fungal dissemination to the central nervous system. These findings suggest that early pulmonary immune events may shape subsequent neuroimmune outcomes and identify a previously underappreciated lung-brain axis in cryptococcosis that warrants in vivo validation.

immunology↗

bioRxiv2026

Cryptococcus gattii responds to mycobacterial exposure through coordinated remodelling of population dynamics and cell surface architecture, enhancing pulmonary persistence in a co-infection model

Cryptococcus neoformans and Cryptococcus gattii are major causes of fungal pneumonia and meningitis, frequently co-occurring with Mycobacterium tuberculosis in endemic regions, where co-infection is associated with increased mortality. Yet, how Cryptococcus adapts to mycobacterial co-presence within the lung remains poorly understood. Here, we show that mycobacterial cues trigger a conserved adaptive programme in C. gattii, mirroring responses previously observed in C. neoformans. Increasing exposure to mycobacteria drives cell and capsule enlargement and promotes titan cell formation, accompanied by dose-dependent remodelling of chitin and chitosan. Importantly, in vivo exposure to heat-killed mycobacteria increases C. gattii pulmonary burden, linking structural remodelling to enhanced persistence. These findings identify mycobacterial co-presence as a driver of fungal phenotypic plasticity and reveal pathogen-pathogen interactions as critical regulators of disease outcome, highlighting a previously unrecognised axis of co-infection relevant to C. gattii pathogenesis and therapeutic strategy.

microbiology↗

bioRxiv2026

Dectin-2-dependent adaptive immunity governs intestinal clearance of systemic Candida albicans

Effective immunity to Candida albicans requires coordination between innate recognition and induction of adaptive CD4 T cell responses. While the C-type lectin receptor Clec4n (Dectin-2) is known to drive Th17 polarization, its role in shaping tissue-specific adaptive responses remains incompletely understood. Here, we used an OT-II antigen-specific CD4 T cell transfer model combined with OVA-expressing Candida albicans to dissect the function of Dectin-2 during systemic infection. We found that Dectin-2 is dispensable for antigen presentation and CD4 T cell priming in gut-draining lymph nodes. Moreover, we show that Dectin-2-deficient mice fail to control fungal growth in the intestinal mucosa, despite elevated local production of IL-17A and GM-CSF. The increased susceptibility of the Dectin-2-deficient mice was associated with impaired neutrophil activation in the intestinal mucosa. These findings identify a tissue-specific checkpoint role for Dectin-2, linking balanced adaptive Th17 cytokine responses to granulocyte function, and revealing a previously unappreciated mechanism required for anti-fungal immune regulation at intestinal mucosal surface.

immunology↗

bioRxiv2025

Clec7a-mediated regulation of Killer-like Lectin Receptor expression controls T cell immunity

Clec7a is a C-type lectin receptor (CLR) originally defined for its non-redundant role in anti-fungal immunity. Subsequent work has broadened this view, implicating Clec7a in host defense against diverse pathogens and in the pathogenesis of cancer, autoimmunity, neuroinflammation, and developmental disorders. How a single innate receptor orchestrates such wide-ranging outcomes remains unresolved. We previously demonstrated that dendritic cell (DC)-expressed Clec7a is required for protective anti-fungal immunity in the gastrointestinal tract through regulation of fungus-specific CD4 T cell responses. Here, we show that Clec7a controls the expression of multiple C-type lectins in DCs, including a cluster of killer lectin-like receptors (KLRs). Notably, we reveal that these KLRs directly regulate DC function and control CD4 T cell responses. These findings define a novel Clec7a-KLR axis that integrates innate and adaptive immunity, highlighting a regulatory pathway with broad relevance for immune homeostasis, inflammation, and host defense.

immunology↗

bioRxiv2025

KLRE1 shapes antifungal immunity by tuning dendritic cell and T cell activation through distinct heterodimeric partners

Dendritic cells (DCs) instruct adaptive immunity by integrating inflammatory cues to regulate co-signalling molecules and T cell activation. We recently discovered that the pattern recognition receptor Dectin-1 (Clec7a) controls expression of a network of killer lectin-like receptors (KLRs), including KLRI1 and KLRI2, which regulate adaptive immune responses. Here, we identify KLRE1 as a key regulator of DC phenotype and function, acting through distinct heterodimeric interactions with KLRI1 and KLRI2. KLRE1 is expressed by tissue-resident and bone marrow-derived DCs and is dynamically regulated by inflammatory signals, including fungal stimuli. Mechanistically, KLRE1:KLRI1 heterodimers promote DC activation, increasing CD40, CD80, CD86, and MHC-II, whereas KLRE1:KLRI2 heterodimers restrain activation. Differential regulation of KLRI1 and KLRI2 by inflammatory signals shapes heterodimer availability and immune outcomes under distinct conditions. Functionally, KLRE1 deficiency enhances DC activation and T cell responses in vitro and in vivo during Candida albicans infection. Strikingly, KLRI1- and KLRI2-deficient mice showed opposite survival outcomes during systemic candidiasis, despite similar fungal burdens, implicating KLRE1 heterodimers in disease tolerance rather than pathogen clearance. Protection in KLRI1-deficient mice was associated with a more balanced T cell response, whereas susceptibility to infection associated with KLRI2 deficiency resulted from increased T cell activation and migratory potential, leading to systemic inflammation and renal dysfunction. Thus, KLRE1 heterodimers fine-tune DC-driven T cell immunity, balancing protection and immunopathology during fungal infection.

immunology↗

bioRxiv2025

Cryptococcus neoformans responds to presence of mycobacterium by diversifying its morphologies and remodelling its capsular material

Cryptococcus neoformans and Mycobacterium tuberculosis are opportunistic pathogens that share overlapping geographical distributions and physiological niches within the human body. Both are recognised by the World Health Organization as high-priority pathogens. Although clinical reports of co-infections with cryptococcosis and tuberculosis are increasing, experimental studies exploring their interactions remain scarce. Here, we demonstrate that C. neoformans can grow in physiologically relevant human plasma-like medium in the presence of either heat-killed M. tuberculosis antigen or the live vaccine strain, M. bovis BCG. In response to presence of mycobacteria, C. neoformans increased in number and exhibited enhanced virulence-associated traits, including titan cell formation, capsule enlargement and increased survival from phagocytosis. This work provides proof-of-principle for a dynamic, inter-pathogen interaction that may contribute to exacerbation disease outcomes in settings of a co-infection.

microbiology↗

bioRxiv2023

Human Plasma-Like Medium (HPLM) induces Cryptococcus neoformans in vivo cell morphologies

The fungal pathogen Cryptococcus neoformans (C. neoformans) forms yeast cells of different sizes and morphological characteristics during infection. These features are usually not seen in standard laboratory in vitro conditions. Here, we describe in vivo cell morphologies when C. neoformans is grown in human plasma-like medium at 37{degrees}C-5% CO2. We observed mixed-size populations of cells less than 1 m up to 16.8 m cell diameter, increased capsule size, high chitin and DNA content in larger cells. Our findings show serum is not required for HPLM-induced C. neoformans cellular heterogeneity. Thus, this new method offers an opportunity to investigate factors of C. neoformans that mediate pathogenesis or host-pathogen interactions in a physiologically relevant setting. IMPORTANCEDescription of new in vitro culture condition using the human plasma-like medium that supports the formation of the full range of in vivo cell morphologies of C. neoformans.

microbiology↗

bioRxiv2021

Host-derived Reactive Nitrogen Species mediate the Cryptococcus neoformans yeast-to-titan switch via fungal-derived superoxide

In the host lung, the human fungal pathogen Cryptococcus neoformans undergoes a morphological switch from small haploid yeast to large polyploid titan cell, contributing to C. neoformans virulence. Titan cells are less readily phagocytosed and can survive host nitrosative and oxidative stresses. We and others previously showed that titanization is triggered by host-relevant signals including CO2 and lung-resident bacteria, and addition of these factor is sufficient to induce titan cells in vitro. Here we investigate the molecular mechanisms that drive this transition and demonstrate that host-derived immune signals can increase the degree and frequency of titanization. Specifically, host-relevant reactive nitrogen species increase the accumulation of endogenous superoxide within cryptococcal cells, particularly within nuclei, where it can cause genotoxic stress. Consistent with this, we observe the accumulation of Rad51 protein, a marker of the double strand break repair pathway, in titanizing cultures. Blocking superoxide accumulation inhibits titanization, yet titanization also requires superoxide detoxification through Superoxide Dismutase (SOD) activity. Loss of mitochondrial Sod2 activity locks cells in the yeast phase, while Sod1 is required for the production of viable titan daughter cells. We hypothesize that the redox responsive transcription factor Yap1 in part mediates this response by regulating SOD2/SOD1. In addition, we show that Sod1 translocates to the nucleus, where it is likely involved in the detoxification of genotoxic superoxide. Together, these findings reveal a major new regulatory mechanism for the yeast-to-titan transition. Author SummaryDuring fungal infection, host phagocytes produce reactive oxygen and nitrogen species (ROS/RNS), major determinants of infection outcome. Fungal pathogens have developed numerous strategies to neutralize and detoxify ROS, but RNS remain important effectors for infection control. In the lung, the human fungal pathogen Cryptococcus neoformans can undergo a morphological switch from small haploid yeast to large highly polyploid titan cells with increased ROS/RNS stress resistance, and the capacity to produce haploid or aneuploid daughters. Here, we report that RNS are a major signal driving the frequency and degree of titanization and act by increasing endogenous ROS within the fungus. We show that the accumulation of endogenous ROS is required for the yeast-to-titan transition, and is associated with increased genotoxic stress leading to polyploidy. Yet, failure to detoxify this ROS, either in mutants defective in Superoxide Dismutase activity or the oxidative stress response protein Yap1, impairs titan cell budding and reduces progeny viability. Therefore, the interface of exogenous RNS and endogenous ROS regulation during host-pathogen interaction represents an Achilles heel for this major human fungal pathogen.

microbiology↗

bioRxiv2020

Characteristics of Titan cell formation vary across clinical isolates of Cryptococcus neoformans

Fungal morphology significantly impacts the host response. Filamentation and tissue penetration by Candida and Aspergillus species are essential for virulence, while growth as a yeast allows the thermal dimorphic fungi Coccidiodes, Histoplasma, and Talaromyces to reside inside phagocytes and disseminate. The basidiomycete Cryptococcus neoformans exhibits an unusual yeast-to-titan transition thought to enhance pathogenicity by increasing fungal survival in the host lung and dissemination to the central nervous system. In a common laboratory strain (H99), in vitro and in vivo titan induction yields a heterogenous population including >10 m titan cells, 5-7 m yeast cells and 2-4 m titanides. Previous reports have shown that titan cells are associated with enhanced virulence and the generation of aneuploid cells that facilitate stress adaptation and drug resistance, while small (>10 m) cells are associated with increased dissemination. However, the relationship between titan cells, small cells, and titanides remains unclear. Here, we characterize titanides and small cells in H99 and three clinical isolates and show that titanides share the lipid membrane order of their titan mothers and the G0 quiescent-like DNA staining of mating spores. In addition, we show that both titanizing and non-titanizing isolates exhibit altered capsule structure and PAMP exposure over time during in vitro culture, and generate aneuploidy in vivo. Author summaryThe human fungal pathogen Cryptococcus neoformans causes 200,000 HIV-associated deaths each year. In the lung, Cryptococcus makes an unusual yeast-to-titan morphological switch that contributes to disease development by altering immune polarization and introducing aneuploidy underlying host stress and drug resistance. Specifically, a proportion of 5 um haploid yeast endoreduplicate and swell, converting to large (> 10 um) polyploid titan cells that can then produce genetically distinct daughter cells. We recently developed an in vitro protocol for inducing large titan cells and additionally observed a novel small "titanide" cell type. Here we investigate the nature and origin of these small cells, demonstrating that they emerge during both in vitro and in vivo mouse-passaged titan induction in the well characterised lab strain H99 and are also apparent in a titanizing clinical isolate, Zc8. We show that these titanide cells share features with titan mothers (lipid order) and with spores produced during heterothalic mating. Finally, we show that the capacity of clinical isolates to produce both titan and titanide cells impacts aneuploidy and the emergence of drug resistance in vivo.

microbiology↗

bioRxiv2017

The Cryptococcus neoformans Titan cell is an inducible and regulated morphotype underlying pathogenesis

Fungi undergo changes in cell shape in response to environmental stimuli that drive pathogenesis and niche adaptation, such as the yeast-to-hyphal transition of dimorphic fungi in response to changing temperature. The basidiomycete Cryptococcus neoformans undergoes an unusual morphogenetic transition in the host lung from haploid yeast to large, highly polyploid cells termed Titan cells. Titan cells influence fungal interaction with host cells, including through increased drug resistance, altered cell size, and altered Pathogen Associated Molecular Pattern exposure. Despite the important role these cells play in pathogenesis, understanding the environmental stimuli that drive the morphological transition, and the molecular mechanisms underlying their unique biology, has been hampered by the lack of a reproducible in vitro induction system. Here we demonstrate reproducible in vitro Titan cell induction in response to environmental stimuli consistent with the host lung. In vitro Titan cells exhibit all the properties of in vivo generated Titan cells, the current gold standard, including altered capsule, cell wall, size, high mother cell ploidy, and aneuploid progeny. We identify bacterial peptidoglycan as a serum compound associated with shift in cell size and ploidy, and demonstrate the capacity of bronchial lavage fluid and E. coli co-culture to induce Titanisation. Additionally, we demonstrate the capacity of our assay to identify established and previously undescribed regulators of Titanisation in vitro and investigate the Titanisation capacity of clinical isolates and their impact on disease outcome. Together, these findings provide new insight into the environmental stimuli and molecular mechanisms underlying the yeast-to-titan transition and establish an essential in vitro model for the future characterization of this important morphotype.\n\nAuthor SummaryChanges in cell shape underlie fungal pathogenesis by allowing immune evasion and dissemination. Aspergillus and Candida albicans hyphae drive tissue penetration. Histoplasma capsulatum and C. albicans yeast growth allows evasion and dissemination. As major virulence determinates, morphogenic transitions are extensively studied in animal models and in vitro. The pathogenic fungus Cryptococcus neoformans is a budding yeast that, in the host lung, switches to an unusual morphotype termed the Titan cell. Titans are large, polyploid, have altered cell wall and capsule, and produce haploid daughters. Their size prevents engulfment by phagocytes, yet they are linked to dissemination and altered immune response. Despite their important influence on disease, replicating the yeast-to-Titan switch in vitro has proved challenging. Here we show that Titans are induced by host-relevant stimuli, including serum and bronchio-alveolar lavage fluid. We identify bacterial peptidoglycan as a relevant inducing compound and predict an in vivo Titan defect for a clinical isolate. Genes regulating in vivo Titanisation also influence in vitro formation. Titanisation is a conserved morphogenic switch across the C. neoformans species complex. Together, we show that Titan cells are a regulated morphotype analogous to the yeast-to-hyphal transition and establish new ways to study Titans outside the host lung.

microbiology↗