Biology subjects

Bielska, E.

Publications and source records attributed to Bielska, E..

4 recordsLinked to original sources

bioRxiv2018

Redistribution of a glucuronoxylomannan epitope towards the capsule surface coincides with Titanisation in the human fungal pathogen Cryptococcus neoformans

Disseminated infections with the fungal species Cryptococcus neoformans or, less frequently, C. gattii, are a leading cause of mortality in immunocompromised individuals. Central to the virulence of both species is an elaborate polysaccharide capsule that consists predominantly of glucuronoxylomannan (GXM). Due to its abundance, GXM is an ideal target for host antibodies, and several monoclonal antibodies (mAbs) have previously been derived using purified GXM or whole capsular preparations as antigen. In addition to their application in the diagnosis of cryptococcosis, anti-GXM mAbs are invaluable tools for studying capsule structure. In this study, we report the production and characterisation of a novel anti-GXM mAb, Crp127, that unexpectedly reveals a role for GXM remodelling during the process of fungal Titanisation. We show that Crp127 recognises a GXM epitope in an O-acetylation dependent, but xylosylation-independent, manner. The epitope is differentially expressed by the four main serotypes of Cryptococcus neoformans and gattii, is heterogeneously expressed within clonal populations of C. gattii serotype B strains and is typically confined to the central region of the enlarged capsule. Uniquely, however, this epitope redistributes to the capsular surface in Titan cells, a recently recognised subset of giant fungal cells that are produced in the host lung and are critical for successful infection. Crp127 therefore highlights hitherto unexpected features of cryptococcal morphological change and may hold significant therapeutic potential in differentially identifying cryptococcal strains and subtypes.\n\nImportanceCryptococcus neoformans and Cryptococcus gattii are the etiological agents of cryptococcosis, an invasive fungal infection responsible for approximately 200,000 deaths each year and 15% of AIDS-related deaths annually. Whilst the main virulence factor for both species is a highly variable polysaccharide capsule, formation of Titan cells also underlies the pathogenesis of C. neoformans. Previous studies have shown that capsule composition differs between yeast and Titan cells, however no clear distinctions in the expression or localisation of specific capsular epitopes have been made. In this study, we characterise a novel monoclonal antibody (mAb) specific to a capsular epitope that is differentially distributed throughout the capsules produced by yeast and Titan cells. Whilst this epitope is found within the midzone of yeast capsules, the presentation of this epitope on the surface of Titan cell capsules may represent a way in which these cell types are perceived differently by the immune system.

microbiology↗

bioRxiv2017

Mycophenolate mofetil increases susceptibility toopportunistic fungal infection independent of lymphocytes

Anti-proliferative agents that target lymphoid cells are common immunosuppressive agents used in the treatment of diverse autoimmune, graft versus host and inflammatory diseases. Mycophenolate mofetil (MMF) is an anti-proliferative agent that targets lymphoid dependence on inosine monophosphate dehydrogenase for the de novo purine synthesis of deoxyguanosine triphosphate (dGTP) for DNA replication. Here we show that MMF has a distinct and specific in vivo effect on macrophages, in the absence of lymphoid cells. This results in increased macrophage cell death that is dependent on the depletion of cellular GTP, independent of DNA synthesis. Furthermore, the macrophage specific effect of MMF treatment causes an increase in susceptibility to the opportunistic fungal infection Cryptococcus neoformans by reducing phagocytosis and increasing the release of intracellular pathogens via macrophage lysis. Our study demonstrates the need for a better mechanistic understanding of immunosuppressive treatments used in clinical practice and of the specific infection risks associated with certain treatment regimens.

immunology↗

bioRxiv2017

Fungal derived 15-keto-prostaglandin E2 and host proliferator-activated receptor gamma (PPAR-γ) promote C. neoformans growth during infection.

Cryptococcus neoformans is one of the leading causes of invasive fungal infection in humans worldwide. C. neoformans uses macrophages as a proliferative niche to increase infective burden and avoid immune surveillance. However, the specific mechanisms by which C. neoformans manipulates host immunity to promote its growth during infection remain ill-defined. Here we demonstrate that eicosanoid lipid mediators manipulated and/or produced by C. neoformans play a key role in regulating pathogenesis. C. neoformans is known to secrete several eicosanoids that are highly similar to those found in vertebrate hosts. Using eicosanoid deficient cryptococcal mutants{Delta} plb1 and{Delta} lac1, we demonstrate that prostaglandin E2 is required by C. neoformans for proliferation within macrophages and in vivo during infection. Genetic and pharmacological disruption of host PGE2 synthesis is not required for promotion of cryptococcal growth by eicosanoid production. We find that PGE2 must be dehydrogenated into 15-keto-PGE2 to promote fungal growth, a finding that implicated the host nuclear receptor PPAR-{gamma}. C. neoformans infection of macrophages activates host PPAR-{gamma} and its inhibition is sufficient to abrogate the effect of 15-keto-PGE2 in promoting fungal growth during infection. Thus, we describe the first mechanism of reliance on pathogen-derived eicosanoids in fungal pathogenesis and the specific role of 15-keto-PGE2 and host PPAR-{gamma} in cryptococcosis. Author SummaryCryptococcus neoformans is an opportunistic fungal pathogen that is responsible for significant numbers of deaths in the immunocompromised population worldwide. Here we address whether eicosanoids produced by C. neoformans manipulate host innate immune cells during infection. Cryptococcus neoformans produces several eicosanoids that are notable for their similarity to vertebrate eicosanoids, it is therefore possible that fungal-derived eicosanoids may provoke physiological effects in the host. Using a combination of in vitro and in vivo infection models we identify a specific eicosanoid species - prostaglandin E2 - that is required by C. neoformans for growth during infection. We subsequently show that prostaglandin E2 must be converted to 15-keto-prostaglandin E2 within the host before it has these effects. Furthermore, we find that prostaglandin E2/15-keto-prostaglandin E2 mediated virulence is via activation of host PPAR-{gamma} - an intracellular eicosanoid receptor known to interact with 15-keto-PGE2.

microbiology↗

bioRxiv2016

Lipopolysaccharide composition determines the preferred route and entry kinetics of bacterial outer membrane vesicles into host cells

Outer membrane vesicles are microvesicles shed by Gram-negative bacteria and play important roles in immune priming and disease pathogenesis. However, our current mechanistic understanding of vesicle - host cell interactions is limited by a lack of methods to study the kinetics of vesicle entry and cargo delivery to host cells in real-time. Here, we describe a highly sensitive method to study the kinetics of vesicle entry into host cells in real-time using a genetically encoded probe targeted to vesicles. We found that route of vesicular uptake, and thus entry kinetics and efficiency of cargo release, are determined by the chemical composition of the bacterial lipopolysaccharide. The presence of O-antigen facilitates receptor-independent entry, which enhances both rate and efficiency of cargo uptake by host cells. Collectively, our findings highlight the chemical composition of the bacterial cell wall as a major determinant of secretion-independent delivery of virulence factors during Gram-negative infections.

microbiology↗