ß-1,3-Glucan recognition by Acanthamoeba castellanii as a putative mechanism of amoeba-fungal interactions.

In this study, we conducted an in-depth analysis to characterize potential Acanthamoeba castellanii (Ac) proteins capable of recognizing fungal ß-1,3-glucans. Ac specifically anchors curdlan or laminarin, indicating the presence of surface ß-1,3-glucan-binding molecules. Using optical tweezers, strong adhesion of laminarin- or curdlan-coated beads to Ac was observed, highlighting their adhesive properties compared to controls (characteristic time τ of 46.9 and 43.9 s, respectively). Furthermore, Histoplasma capsulatum (Hc) G217B, possessing a ß-1,3-glucan outer layer, showed significant adhesion to Ac compared to a Hc G186 strain with an α-1,3-glucan outer layer (τ of 5.3 s vs τ 83.6 s). The addition of soluble ß-1,3-glucan substantially inhibited this adhesion, indicating the involvement of ß-1,3-glucan recognition. Biotinylated ß-1,3-glucan-binding proteins from Ac exhibited higher binding to Hc G217B, suggesting distinct recognition mechanisms for laminarin and curdlan, akin to macrophages. These observations hinted at the ß-1,3-glucan recognition pathway's role in fungal entrance and survival within phagocytes, supported by decreased fungal viability upon laminarin or curdlan addition in both phagocytes. Proteomic analysis identified several Ac proteins capable of binding ß-1,3-glucans, including those with lectin/glucanase superfamily domains, carbohydrate-binding domains, and glycosyl transferase and glycosyl hydrolase domains. Notably, some identified proteins were overexpressed upon curdlan/laminarin challenge and also demonstrated high affinity to ß-1,3-glucans. These findings underscore the complexity of binding via ß-1,3-glucan and suggest the existence of alternative fungal recognition pathways in Ac.IMPORTANCEAcanthamoeba castellanii (Ac) and macrophages both exhibit the remarkable ability to phagocytose various extracellular microorganisms in their respective environments. While substantial knowledge exists on this phenomenon for macrophages, the understanding of Ac's phagocytic mechanisms remains elusive. Recently, our group identified mannose-binding receptors on the surface of Ac that exhibit the capacity to bind/recognize fungi. However, the process was not entirely inhibited by soluble mannose, suggesting the possibility of other interactions. Herein, we describe the mechanism of ß-1,3-glucan binding by A. castellanii and its role in fungal phagocytosis and survival within trophozoites, also using macrophages as a model for comparison, as they possess a well-established mechanism involving the Dectin-1 receptor for ß-1,3-glucan recognition. These shed light on a potential parallel evolution of pathways involved in the recognition of fungal surface polysaccharides.

Antibody Isolation in C. neoformans.

The importance of humoral immunity to fungal infections remains to be elucidated. In cryptococcosis, patients that fail to generate antibodies against antigens of the fungus Cryptococcus neoformans are more susceptible to the disease, demonstrating the importance of these molecules to the antifungal immune response. Historically, antibodies against C. neoformans have been applied in diagnosis, therapeutics, and as important research tools to elucidate fungal biology. Throughout the process of generating monoclonal antibodies (mAbs) from a single B-cell clone and targeting a single epitope, several immunization steps might be required for the detection of responsive antibodies to the antigen of interest in the serum. This complex mixture of antibodies comprises the polyclonal antibodies. To obtain mAbs, B-lymphocytes are harvested (from spleen or peripheral blood) and fused with tumor myeloma cells, to generate hybridomas that are individually cloned and specifically screened for mAb production. In this chapter, we describe all the necessary steps, from the immunization to polyclonal antibody harvesting, hybridoma generation, and mAb production and purification. Additionally, we discuss new cutting-edge approaches for generating interspecies mAbs, such as humanized mAbs, or for similar species in distinct host backgrounds.

Comprehensive characterization of extracellular vesicles produced by environmental (Neff) and clinical (T4) strains of Acanthamoeba castellanii.

We conducted a comprehensive comparative analysis of extracellular vesicles (EVs) from two Acanthamoeba castellanii strains, Neff (environmental) and T4 (clinical). Morphological analysis via transmission electron microscopy revealed slightly larger Neff EVs (average = 194.5 nm) compared to more polydisperse T4 EVs (average = 168.4 nm). Nanoparticle tracking analysis (NTA) and dynamic light scattering validated these differences. Proteomic analysis of the EVs identified 1,352 proteins, with 1,107 common, 161 exclusive in Neff, and 84 exclusively in T4 EVs. Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) mapping revealed distinct molecular functions and biological processes and notably, the T4 EVs enrichment in serine proteases, aligned with its pathogenicity. Lipidomic analysis revealed a prevalence of unsaturated lipid species in Neff EVs, particularly triacylglycerols, phosphatidylethanolamines (PEs), and phosphatidylserine, while T4 EVs were enriched in diacylglycerols and diacylglyceryl trimethylhomoserine, phosphatidylcholine and less unsaturated PEs, suggesting differences in lipid metabolism and membrane permeability. Metabolomic analysis indicated Neff EVs enrichment in glycerolipid metabolism, glycolysis, and nucleotide synthesis, while T4 EVs, methionine metabolism. Furthermore, RNA-seq of EVs revealed differential transcript between the strains, with Neff EVs enriched in transcripts related to gluconeogenesis and translation, suggesting gene regulation and metabolic shift, while in the T4 EVs transcripts were associated with signal transduction and protein kinase activity, indicating rapid responses to environmental changes. In this novel study, data integration highlighted the differences in enzyme profiles, metabolic processes, and potential origins of EVs in the two strains shedding light on the diversity and complexity of A. castellanii EVs and having implications for understanding host-pathogen interactions and developing targeted interventions for Acanthamoeba-related diseases.IMPORTANCEA comprehensive and fully comparative analysis of extracellular vesicles (EVs) from two Acanthamoeba castellanii strains of distinct virulence, a Neff (environmental) and T4 (clinical), revealed striking differences in their morphology and protein, lipid, metabolites, and transcripts levels. Data integration highlighted the differences in enzyme profiles, metabolic processes, and potential distinct origin of EVs from both strains, shedding light on the diversity and complexity of A. castellanii EVs, with direct implications for understanding host-pathogen interactions, disease mechanisms, and developing new therapies for the clinical intervention of Acanthamoeba-related diseases.

Recognition of Cell Wall Mannosylated Components as a Conserved Feature for Fungal Entrance, Adaptation and Survival Within Trophozoites of Acanthamoeba castellanii and Murine Macrophages.

Acanthamoeba castellanii (Ac) is a species of free-living amoebae (FLAs) that has been widely applied as a model for the study of host-parasite interactions and characterization of environmental symbionts. The sharing of niches between Ac and potential pathogens, such as fungi, favors associations between these organisms. Through predatory behavior, Ac enhances fungal survival, dissemination, and virulence in their intracellular milieu, training these pathogens and granting subsequent success in events of infections to more evolved hosts. In recent studies, our group characterized the amoeboid mannose binding proteins (MBPs) as one of the main fungal recognition pathways. Similarly, mannose-binding lectins play a key role in activating antifungal responses by immune cells. Even in the face of similarities, the distinct impacts and degrees of affinity of fungal recognition for mannose receptors in amoeboid and animal hosts are poorly understood. In this work, we have identified high-affinity ligands for mannosylated fungal cell wall residues expressed on the surface of amoebas and macrophages and determined the relative importance of these pathways in the antifungal responses comparing both phagocytic models. Mannose-purified surface proteins (MPPs) from both phagocytes showed binding to isolated mannose/mannans and mannosylated fungal cell wall targets. Although macrophage MPPs had more intense binding when compared to the amoeba receptors, the inhibition of this pathway affects fungal internalization and survival in both phagocytes. Mass spectrometry identified several MPPs in both models, and in silico alignment showed highly conserved regions between spotted amoeboid receptors (MBP and MBP1) and immune receptors (Mrc1 and Mrc2) and potential molecular mimicry, pointing to a possible convergent evolution of pathogen recognition mechanisms.

Complex and Controversial Roles of Eicosanoids in Fungal Pathogenesis.

The prevalence of fungal infections has increased in immunocompromised patients, leading to millions of deaths annually. Arachidonic acid (AA) metabolites, such as eicosanoids, play important roles in regulating innate and adaptative immune function, particularly since they can function as virulence factors enhancing fungal colonization and are produced by mammalian and lower eukaryotes, such as yeasts and other fungi (Candida albicans, Histoplasma capsulatum and Cryptococcus neoformans). C. albicans produces prostaglandins (PG), Leukotrienes (LT) and Resolvins (Rvs), whereas the first two have been well documented in Cryptococcus sp. and H. capsulatum. In this review, we cover the eicosanoids produced by the host and fungi during fungal infections. These fungal-derived PGs have immunomodulatory functions analogous to their mammalian counterparts. Prostaglandin E2 (PGE2) protects C. albicans and C. parapsilosis cells from the phagocytic and killing activity of macrophages. H. capsulatum PGs augment the fungal burden and host mortality rates in histoplasmosis. However, PGD2 potentiates the effects and production of LTB4, which is a very potent neutrophil chemoattractant that enhances host responses. Altogether, these data suggest that eicosanoids, mainly PGE2, may serve as a new potential target to combat diverse fungal infections.

Análise proteômica para a identificação de receptores fagocíticos de alta afinidade contra resíduos manosilados da parede celular fúngica

As micoses têm emergido nas últimas décadas dentre as principais causas de enfermidades humanas, particularmente em indivíduos sob risco constante de infecção. Devido à ausência de especificidade para um determinado hospedeiro, os fungos são capazes de causar doenças em múltiplas espécies animais. Estes microrganismos são capazes de interagir com hospedeiros ambientais, como a espécie de ameba de vida livre Acanthamoeba castellanii e macrófagos de diversas espécies, encontrando no interior destes, um ambiente propício para proteção, sobrevivência e disseminação. Nosso grupo descreveu a importância do receptor de manose (MR), identificado na superfície amebóide, como uma das principais vias de ligação fúngica. Na literatura, o receptor de manose também é descrito por sua participação na interação entre fungos e macrófagos. Assim, é possível estabelecer uma relação de similaridade entre amebas e macrófagos, não apenas por compartilharem propriedades de estrutura celular, motilidade, fisiologia e captura por emissão de pseudópodos e fagocitose, mas também pelo semelhante mecanismo de interação com microrganismos, apontando para possível evolução convergente dos receptores envolvidos. Diante disso, investigamos as proteínas de superfície, presentes em A. castellanii e macrófagos murinos, afim de encontrar possíveis candidatos à receptores de alta afinidade contra manoproteínas e mananas de parede celular fúngica. Inicialmente, após biotinilação das superfícies de ambas as células, processamos extratos contendo as proteínas de superfície de A. castellanii e macrófagos, que apresentaram um perfil proteico variando entre 10-250 KDa. Determinamos a ligação dessas proteínas aos fungos patogênicos Candida albicans, Cryptococcus neoformans e Histoplasma capsulatum. Confirmamos que os extratos de macrófagos apresentaram maior intensidade de ligação quando comparados aos extratos de amebas, apontando para a maior complexidade proteica de macrófagos em relação à superfície amebóide no mecanismo de interação com microrganismos. A partir disso, buscamos investigar as proteínas, presentes nesses extratos, que apresentavam afinidade por manose. Realizamos a purificação dos extratos protéicos de A. castellanii e dos macrófagos (RAW 264.7) por cromatografia de afinidade, em coluna de manose, além da confirmação por Western blot da presença desta lectina no extrato. Observamos afinidade dos extratos por ambos manose e mananas. Assim, direcionamos a nossa procura realizando o enriquecimento dos extratos de A. castellanii e macrófagos com manose. Analisamos os extratos enriquecidos por Western Blot, onde identificamos nos extratos de A. castellanii proteínas de, aproximadamente, 150 kDa, 75 kDa, 55 kDa e 35 KDa. Já nos extratos enriquecidos de macrófagos foram identificadas proteínas entre 50 e 170 KDa, além de bandas de menores pesos moleculares. Os extratos enriquecidos foram incubados com os fungos, para caracterizar as proteínas com capacidade de reconhecimento fúngico e os coprecipitados foram avaliados por espectometria de massas. Para determinar a importância desta lectina ligadora de manose na interação, realizamos ensaios de fagocitose, na presença e ausência de manose, caracterizando a importância deste receptor. Porém encontramos baixas porcentagens de inibição nos experimentos com macrófagos, concluindo que provavelmente, diferentemente das amebas, diversos outros receptores podem participar do mecanismo de interação, de forma compensatória, destacando a importância deste tipo de interação para cada espécie de hospedeiro e a possível diversidade. Os dados sugerem que, provavelmente, ocorre a evolução e o surgimento de outras vias de interação em hospedeiros superiores. Futuramente, após obtenção dos dados de caracterização de proteínas com alta afinidade por manose em ambos os organismos por espectrometria de massas, pretendemos realizar a construção, produção e caracterização de lectinas-Fc, utilizando sequências da lectinas identificadas na fusão com a porção Fc efetora de imunoglobulinas murinas. Como manoproteínas e mananas estão presentes universalmente na parede celular fúngica, estas proteínas quiméricas permitiriam o reconhecimento dos fungos por receptores Fc (FcR) presentes na superfície dos fagócitos, promovendo mecanismos de imunidade (inata e celular) e de ação antifúngica.